Review of Green Water Systems for Urban Flood Resilience: Literature and Codes

Abstract

Achieving Urban Flood Resilience (UFR) is essential for modern societies, requiring the implementation of effective practices in different countries to mitigate hydrological events. Green Water Systems (GWSs) emerge as a promising alternative to achieve UFR, but they are still poorly explored and present varied definitions. This article aims to define GWSs within the framework of sustainable practices and propose a regulation that promotes UFR. Through a systematic review of existing definitions and an analysis of international regulations on sustainable urban drainage systems (SuDSs), this study uncovers the varied perceptions and applications of GWSs and their role in Blue–Green Infrastructure (BGI). Furthermore, the research puts forth a standardized definition of GWSs and emphasizes the implementation of SuDSs in Peru. This approach aims to address the existing knowledge gap and contribute to the advancement of sustainable urban infrastructure.

1. Introduction

Urban Drainage Systems (UDSs) are essential for stormwater management, as they contribute to urban development by addressing the increasing incidence of floods caused by intense storms, which are often linked to climate change. This leads to an increase in surface runoff and saturation of drainage networks, causing damage to property, infrastructure, and the environment [1]. In particular, urban flooding occurs due to the insufficient capacity of traditional drainage systems based on Gray Infrastructure (GrI), for example van Oorschot et al. [2] refer to them as urban elements constructed by humans that impact the local environment. This generates growing concern due to urban densification, population growth, and increased impervious surfaces. UDSs (Urban Drainage Systems) are generally not designed to handle runoff from extreme storms, which limits their effectiveness as a tool for combating urban flooding. This limitation is related to the type of UDS as well as the spatial characteristics and variations within a city [3]. In Europe, these systems are designed for rainfall events with specific return periods. However, there is a significant gap between the expected protection and the actual risk of extreme flooding, as these events can occur anywhere in a city. This highlights the need for a thorough analysis of hazards and risks that includes both natural factors and the built environment [4]. In other parts of the world, such as North America and Latin America, population growth, vulnerability, and a lack of understanding of sustainable urban infrastructure exacerbate urban flood risks. Based on this, Arosio et al. [5] argue that urban flood management is compromised by the lack of accurate data and appropriate models, which impairs the provision of essential services during and after extreme events. Also, Rodríguez-Rojas et al. [6] emphasize the need to close the gap in sustainable drainage systems by integrating SuDSs that replicate the natural hydrological cycle, including infiltration, retention, and reuse of water. The incorporation of these systems into regulations and laws is often developed in a general manner and lacks specific regulatory measures. Consequently, it is crucial to improve urban drainage infrastructure and adopt effective flood management strategies to enhance urban resilience and mitigate adverse impacts, especially in Latin America.

The research focuses on presenting the context and problem statement in Section 2. Additionally, Section 3 outlines the methodology employed in the study. Section 4 details the systematic search conducted using two databases (Scopus and Web of Science), with a focus on defining Green Water Systems (GWSs). This section analyzes the obtained results accompanied by graphs and tables to aid understanding, and it also integrates the concept into the flow chart on urban flood management. Additionally, it addresses the existing regulatory framework on SuDS design worldwide, providing an explanatory and dynamic approach to clarify the concepts developed and related to the article, since it performs a systematic search to obtain results on definitions for GWSs and Design Codes for SuDSs. Section 5 aims to assess the social and economic aspects of applicability regarding the proposed Design Code in Peru, as well as to substantiate the GWS concept.

2. Background

According to the data available in EM-DAT, based on the impact that floods have on the world, Figure 1 shows the number of people affected by floods on each continent, proving the vulnerability they suffer [7].

Meanwhile, Figure 2 presents the number of deaths due to floods on each continent [7].

Based on the graph, Asia had the highest number of affected people (deaths and victims), which gives an idea of how flood management has not been implemented effectively in several countries on the continent, while continents such as Europe and Oceania have considerably lower figures. This pattern suggests that the impact of natural disasters varies significantly at a global level, influenced by various factors. The main causes of this disparity are the density and distribution of the population, the geographic location (rural or urban areas), the predominant type of meteorological event, the socioeconomic conditions, and the magnitude of the exposed population, among others.

Transferring these data to a national scale, according to EM-DAT, Peru has recently experienced hydrological phenomena that had a serious impact on its citizens. Figure 3 illustrates the number of victims and Figure 4 the number of deaths in recent years.

According to the data presented, the current context of traditional urban drainage systems in Peru is interpreted, with particular emphasis on extreme weather events associated with the El Niño phenomenon (ENSO). Years 2017 and 2023 recorded the highest figures for deaths and affected people, coinciding with intense rainfall linked to these phenomena. Following this, Espinoza Vigil and Booker [8] highlight that during the period of 2016–2017, ENSO had a devastating impact in Peru, with torrential rains that caused damage to infrastructure and affected about 2 million people. Similarly, Thielen et al. [9] note that in 2023, there was an intensification of ENSO, driven by a significant increase in the surface sea temperature, which generated extreme and widespread rainfall in various regions of the country. These events underline the vulnerability of traditional drainage systems, based on gray infrastructure, which have not been able to efficiently manage the volume and intensity of precipitation associated with El Niño. Given this panorama, the need arises for a transition towards more resilient drainage systems supported by green infrastructure or solutions based on nature, which can more effectively reduce the number of deaths and victims in the future impacts of extreme climate phenomena.

According to Barreto et al. [10], UDSs can be optimized in terms of system capacity, pollution reduction, and reduction of damage to urban infrastructure, in addition to promoting proper environmental management. However, there is a permanent gap facing extreme rainfall events in Peru. Currently, the comprehensive management of rainwater in urban environments is linked to restoring water cycles, that is, reusing water from rainfall through collection and storage infrastructures. In addition, this comprehensive management aims to make cities more habitable, based on an approach based on water management, the use of existing infrastructure, and natural alternatives, proposing a real solution to the deteriorated infrastructure, urbanization, the need for sustainable tools, and the climate crisis [11]. In this regard, the International Water Association (IWA) promotes an intelligent society in water use and a wise behavior in water use, highlighting the advancement of digital technologies and the integration of hybrid solutions combining natural infrastructure with conventional methods. Furthermore, a cross-disciplinary collaboration between stakeholders is crucial to identify and resolve conflicts and to develop adaptation strategies that will drive the transition towards sustainable and resilient urban drainage systems [12].

One of the pillars proposed in this GWS research is based on Green Infrastructure (GI), for example; [13,14] define this term as a set of natural and sustainable solutions designed to manage rainwater effectively in urban environments. It is also linked to the concept of “Nature-based Solutions” (NBSs), and these integrate the water cycle in built areas, adapting to different denominations such as Sustainable Drainage Systems (SuDSs), which replicate natural hydrological responses to reduce flow and store water, mitigate urban flooding, and consequently improve local quality of life and promote water security.

Based on this, the integration of GI with traditional gray infrastructure in urban flood management provides effective solutions, social benefits, and improved ecosystem services for human well-being and economic development [15]. Meanwhile, [16] highlight the integration of blue infrastructure (BI), which comprises the components of the natural environment related to water, such as rivers, lakes, and wetlands. This approach proposes the use of water resources in a sustainable way. Considering the above, [17] mention the importance of achieving a green–gray–blue infrastructure (BGGrI) mix, as they highlight this approach as a comprehensive and sustainable alternative to traditional green–gray infrastructure in urban stormwater management. In accordance with this vision, BGGrI proposes a strategy that combines centralized measures to effectively adapt the impacts of urban development and extreme weather events, and that is because integration with BI elements such as rivers and wetlands strengthens the path to more resilient cities by providing natural flood defenses and other climate adaptation benefits, but they require careful coordination to avoid negative impacts.

In Peru, some potential challenges to achieving a balance between GI and NBS-based tools in accordance with existing gray infrastructure in developing urban areas are the lack of implementation spaces since dense urban areas are occupied by gray infrastructure. One solution proposed by Griffiths et al. [18] is to reuse underused spaces, such as industrial areas or riverbanks, and implement green roofs and vertical gardens. Furthermore, integrating NBS with gray infrastructure requires a hybrid approach, such as bioretention zones and permeable pavements, to reduce the load on traditional systems. The cost of NBS is another challenge, as indicated by Shkaruba et al. [19], since its benefits are long-term. However, mixed financing and international climate funds can be used. The lack of clear regulations also limits its adoption, which underlines the need to develop policies that promote the transition to hybrid systems. Added to it, resistance to change can be overcome with education, awareness raising, and pilot projects that demonstrate its effectiveness and benefits, such as improving water quality and increasing green areas.

However, this research focuses on the implementation of green and gray infrastructure (GGrI) in an urban context, as it reduces Combined Sewer Overflows (CSOs), which are events where urban sewer systems such as those designed to carry both waste and stormwater cannot handle the volume of water during heavy rains. This is why the implementation of GGrI proposes an improvement in urban water quality and offers a real long-term solution by optimizing the use of existing infrastructure and integrating real-time control techniques, which maximize the efficiency of the system to manage rainfall events and reduce CSOs effectively [20]. In addition, Alves, Vojinovic, Kapelan, Sanchez, and Gersonius [20] enhanced the integration of GI, as it manages urban flood runoff with nature-based solutions (NBSs), reducing pressure on drainage systems during heavy rains and, therefore, improving urban resilience in combination with traditional gray infrastructure and more robust and efficient water management. Figure 5 details the idea of continuity integration of terms related to this research in order to control urban flooding. From the figure, urban flooding caused by high rainfall is traditionally managed through GrI, such as sewers and storm drains. However, its limited capacity to manage storm run-off has led to the adoption of hybrid approaches, integrating green and gray infrastructure (gardens, parks, green areas), forming the integrated green-gray infrastructure (GGrI). In addition, the incorporation of blue infrastructure (BI), which leverages natural water resources such as rivers, lakes, and wetlands, refines this model into a blue, green, and gray infrastructure (BGGrI). Sustainable urban drainage systems (SuDSs) complement this strategy in parallel, focusing on resilient groundwater management and run-off infiltration through systems that promote biodiversity, amenity, and both water quantity and quality, providing a holistic and sustainable solution for urban flood management.

Now, with the concepts and definitions developed in Figure 5, where does the term GWS fit? This term is currently not included in neither papers nor literature reviews; however, its interpretation focuses on the tools implemented by green infrastructure to combat the phenomenon of flooding. Ortega Sandoval et al. [21] interpreted this term as part of an integrated urban stormwater management approach that incorporates green infrastructure techniques, where they sought to mitigate the adverse effects of rapid urbanization, including increased run-off volume and peak flow, as well as problems of rainfall flooding and waterlogging. Liquete et al. [22] also understand it as part of the NBS, which seeks to address social, environmental, and economic challenges through the use of natural ecosystems or nature-inspired solutions. In the European context, the use of green infrastructure is promoted as a smart strategy to achieve multiple political objectives, including those related to climate change, natural risk management, and water policy. It is also important to mention that the countries of the European Union have made various commitments to achieve resilient cities, which are highlighted in the framework of the Smart Mature Resilience project (2017), focusing on the improvement of the capacity of cities to adapt and recover from environmental, social, and economic threats, such as natural disasters, climate change, and socio-economic crises [23]. This underlines the importance of implementing such measures in Latin American countries such as Peru, adjusting them to the specific vulnerability that each nation faces to natural phenomena.

Meanwhile, Rusman et al. [24] refer to GWSs as an aquaculture system that uses dense populations of microalgae present in ponds or other water sources, fed with agricultural and domestic waste, sometimes supplemented with chemical fertilizers. This approach allows for the improved management and quality control of water, as well as facilitating the system’s rainwater transport. In addition, Zanardo et al. [25] define it as systems used in aquaculture, especially in shrimp production, that use water from ponds where different species of fish are grown.

Therefore, due to the ambiguity of the term in question, this study carried out a literature review to understand the various definitions of GWSs. The literature exploration aimed to answer the following sustainability-based questions (QBSs):

• How are GWSs developed as a sustainable tool to mitigate urban flooding defined?
• Are GWSs a viable alternative to combat pluvial flooding in Peru? Are they the best tool available?

Additionally, and based on the responses of the QBS, a definition of GWSs is given in this article from an approach based on NBSs, resulting in a typology of SuDSs. However, it is relevant to consider the definitions of SuDSs by some authors, such as Abellán García et al. [26] who conceptualize it to manage runoff in cities more sustainably and provide other benefits such as mitigation and adaptation to climate change. Also, Ortega Sandoval, Sörensen, Rodríguez, and Bharati [21] define it as urban green infrastructure designed for stormwater control, which promotes more sustainable management of runoff in cities and additionally replicates natural drainage conditions prior to urban development and highlights that SuDS research and implementation vary geographically and typologically, depending on local climates and urban conditions.

SuDSs undoubtedly play a fundamental role in this research, since they provide a solution to flooding in an urban context. However, for the viability of these, there are “Regulations” or “Design Codes” that provide the criteria, parameters, and considerations depending on the type of GWS to be designed. For instance, the SuDS Manual C753 CIRIA [27] is a British guide that provides a comprehensive and detailed framework for the design, implementation, and maintenance of SuDS and offers a variety of SuDS typologies, including bioretention zones, green roofs, permeable pavements, and infiltration ditches. This regulation promotes the sustainability and multifunctionality of SuDSs based on a holistic approach, considering both water management and social and environmental benefits. Meanwhile, the NS-166 “Criterios para Diseño y Construcción de Sistemas Urbanos de Drenaje Sostenible” EEAB [28] is a Colombian regulation focused on adapting SuDSs to the particular conditions of the city of Bogotá. This regulation considers the climatic, topographic, and urban characteristics of the city, providing precise criteria and guidelines for the design and construction of SuDSs suitable for these conditions, and it also includes the use of local materials and proper construction techniques for the urban environment of the city. Although it also promotes sustainability, its focus is mainly on efficient water management and flood risk reduction, prioritizing hydraulic efficiency and adaptability to local conditions. Now, according to these generalized approaches around the globe, we carried out a literature review to understand the various regulations and guidelines that regulate the design, criteria, parameters, and considerations for the construction of SuDSs in an urban context in Peru. This exploration of the literature aimed to answer the following questions based on design codes (QBCs):

• What are the design parameters and characteristics of a GWS with applicability to Peru?
• Is it feasible to develop a “Design Code” proposal for SuDSs for an urban context in Peru?

3. Materials and Methods

The methodological development is presented below in Figure 6.

Scopus and Web of Science (WoS) are considered two of the most rigorous databases in the world, as stated by Zhu and Liu [29], and this is because they attract different countries, disciplines, and researchers to publish their research. Also, according to Martín-Martín et al. [30], Scopus and WoS are notable because of the correct coverage of indexing and reliable information search. In this article, both search engines were selected since they offer different results to be analyzed. Although the information retrieved from Scopus was relevant and varied, the aim was to understand how multiple authors describe GWSs, as this allows for a broader perspective and a more complete approach to the subject. Meanwhile, WoS offered search results aligned with the goal of achieving UFR, as it contained papers addressing topics such as sustainable urban water management, green and blue infrastructure, sustainable development, green space construction, green technology, water security, and green water infrastructure systems. However, there is no precise definition of what GWSs are, which required a detailed analysis of how the authors interpreted and defined these systems. Furthermore, a comparative analysis of international regulations on sustainable urban drainage systems (SuDSs) was conducted with the aim of adapting these guidelines to the Peruvian context. Design codes from various countries with different climates and economies were examined, with a focus on bioretention areas as part of Green Water Systems (GWSs). Based on this analysis, specific design parameters are proposed for Peru, tailored to its climatic and geographical conditions, with the goal of enhancing sustainability and urban water management.

4. Results

4.1. Literature Review

The literature review was carried out using specific search operators offered by search engines, with the aim of finding papers related to “Green Water Systems” (GWSs). The following consultation was used in the first place: “Green Water Systems” OR “Green Water System”, retrieving 38 papers for analysis. Subsequently, an expanded search was conducted using the combination Green AND Water AND Systems OR System, which yielded 32,431 results. These results were filtered by topics of interest or keywords such as (urban, flood, drainage), the area of study (environmental science, engineering), and the type of document, selecting only scientific papers. As a result of this filtering process, 99 papers were obtained and considered for analysis. It should be noted that both search chains cover a period of results from 1999 to 2024. This process is illustrated in Figure 7.

Of the 38 papers selected for analysis, which focus exclusively on the main topic of “Green Water Systems” (GWSs), majority were related to sustainable tools for combating urban flooding. A significant percentage of these studies address topics in aquaculture and marine sciences, while a smaller number focus on areas such as agriculture and chemical ecology. This distribution reflects the various applications and approaches within the field of GWSs, highlighting the importance of this concept across different scientific and geographical contexts.

Table 1. Distribution of papers in countries that have at least one GWS-related article.

Country	Documents
Australia	2
Brazil	5
Egypt	1
Spain	1
E.E.U.U.	6
Philippines	2
Greece	1
India	9
Iran	3
Malaysia	3
Peru	2
Sweden	1
Thailand	1
Vietnam	1
Total	38

shows the distribution of the analyzed papers according to their country of origin, which allows for identifying the regions of the world where research on GWSs is most active and how it is oriented towards different areas of study.

Table 2. Journals consulted and their categorization by indicators.

Scientific Journal	ID	Quartile
Aquaculture International	R1	Q2
Algal Research	R2	Q1
Applied Biochemistry and Biotechnology	R3	Q2
Aquaculture	R4	Q1
Aquaculture International	R5	Q2
Aquaculture Nutrition	R6	Q1
Aquaculture Reports	R7	Q1
Aquaculture Research	R8	Q2
Comparative Biochemistry and Physiology—Part A: Molecular and Integrative Physiology	R9	Q1
Developmental and Comparative Immunology	R10	Q3
Environmental Science: Water Research and Technology	R11	Q1
Fisheries Science	R12	Q3
Food Security	R13	Q1
Indian Journal of Fisheries	R14	Q4
International Journal of Agriculture and Biology	R15	Q3
Israeli Journal of Aquaculture—Bamidgeh	R16	Q3
Journal of Green Building	R17	Q2
Journal of Sustainability Science and Management	R18	Q3
Journal of the World Aquaculture Society	R19	Q3
Scientific Reports	R20	Q1
Journal of Fish Diseases	R21	Q1

shows the journals in which GWS-related papers were published, presenting results regarding the line of research on aquaculture, marine sciences, chemical ecology, agrotechnology, pharmacy, and environmental sustainability, in addition to adding an indicator for the development of

Table 3. The distribution of the 38 analyzed papers according to their study areas reveals a significant percentage in the fields of aquaculture and marine sciences. This predominance highlights the relevance of these disciplines in research on Green Water Systems (GWSs), demonstrating their application and importance in these sectors.

ID	Aquaculture	Agriculture	Agrotechnology	Marine Science	Chemical Ecology	Pharmacy	Environmental Sustainability	Total
R1	2							2
R2					1			1
R3	1							1
R4	3			3	1			6
R5	1			2				3
R6	1	1						2
R7		1						1
R8	3		1	1				5
R9				1				1
R10				1				1
R11							1	1
R12				1				1
R13							1	1
R14	1			1				2
R15				1				1
R16	1							1
R17	1						1	1
R18				1				1
R19	1			1				2
R20						1		1
R21	1							1
Total	16	2	1	13	2	1	3	38

.

It is important to highlight that each of the analyzed journals was within the relative importance indicators related to the research line (aquaculture, marine sciences, agrotechnology, chemical ecology, pharmacy, and environmental sustainability), with 43% of journals in Q1, 23% in Q2, 28% in Q3, and 5% in Q4. Thus, Table 3 presents, based on the analyzed journals, the research line that develops the concept of GWSs.

From Table 3, it is evident that the aquaculture and marine science lines predominate with 76.3% in relation to the others, and that is because the closest definition of what a GWS is lies within these study areas. From the point of view of aquaculture in relation to larval farming, GWSs are an aquaculture method using green water, which consists of microalgae or phytoplankton in order to improve the environment and nutrition of larvae of different marine families, such as various species of fish [32,33,34,35,36,37,38,39], octopus [40], crabs [41,42], and lobsters [43,44,45]. Also, different authors pay attention to the breeding of shrimps from natural feeding strategies produced endogenously [46,47,48,49,50,51,52,53,54,55,56,57,58,59,60]. The breeding of sea horses with microalgae paste replacing a clear water system [61]. Aly et al. [62] argue that GWSs use microalgae such as “Chlorella” to improve water quality and aquatic animal health, increasing their growth and survival, and this system is activated to provide an abundant source of natural food. Ref. [63] refers to it as an ecological method for synthesizing an adsorbent nanocompound used in the removal of heavy metals from water. Finally, from the science of environmental sustainability, Keys and Falkenmark [64] emphasize GWSs based on green water management, which covers evaporation and precipitation used mainly in agriculture. Rhoads et al. [65] frame Green Water Systems in sustainable buildings because they can have unexpected consequences for public health and aesthetics. Also, Brazeau and Edwards [66] refer to GWSs as instantaneous hot water systems that promise energy and water savings.

On the other hand, when placing GWSs with Boolean operators, that is, Green AND Water AND Systems OR System, the search engine returned 99 relevant results. The papers retrieved from the search were selected, disregarding certain filters such as geographic, contextual, temporal, and interdisciplinary criteria. However, since the search focused on urban flooding and drainage, articles related to urban resilience, sustainable urban drainage systems, the need for sustainable tools, stormwater management, green technology in hydrology, sponge cities, NBS, and emerging related concepts were prioritized. Figure 8 shows the number of documents per country assigned to this search.

The figure shows that China has a significant impact on GWS-related studies, accounting for 25.3% of published papers. However, the UK with 15.2% and the US with 7.1% also maintain a strong presence in this field of research. Upon reviewing the papers from China, it was observed that they focus on sustainable water management in urban environments. The titles highlight concepts such as “sponge cities”, green and gray infrastructure, stormwater management, and resilience strategies. These studies address key challenges such as climate change adaptation, optimizing water use, and integrating sustainable technologies into urban planning. For example, Molnar-Tanaka and Surminski [67] addressed flood management in Asia in the light of intensified extreme weather events such as monsoon rains, starting with the restoration of ecosystems such as mangroves and wetlands in Indonesia and the Philippines, a nature-based construction approach to reduce coastal erosion and flooding in Indonesia, the implementation of SuDSs (green roofs and permeable pavements) in cities such as Tokyo and Jakarta, and, of course, community participation and the inclusion of local communities in the maintenance of projects as a key component of success. However, the integration of these lessons into the Peruvian context requires adaptations to the country’s specific hydrological conditions. Asia is facing complex conditions due to a combination of geographic and climatic factors as it faces challenges such as extreme monsoon rains, river overflows, subsidence terrain, and accelerated urbanization. The influence of “El Niño” in Peru as a climatic phenomenon is devastating on the north coast of the country due to torrential rains and floods, a scenario without a direct equivalent in the above-mentioned Asian regions. However, a flexible adaptation strategy is proposed in Section 5, which allows for the integration of strategies used in Asia into the Peruvian context.

Figure 9 presents an analysis of the field of research based on the number of papers retrieved through the search “Green AND Water AND Systems OR System”. The results obtained show a significantly different picture compared to a specific search for “Green Water Systems”. Based on this, disciplines such as aquaculture and marine sciences are virtually excluded from the agenda, suggesting that these areas have less relevance or impact in the context of green systems and water management in urban or sustainable environments. This contrast underlines the importance of a proper selection of search terms to obtain a more accurate view of the field of study.

Environmental sciences and water resources are highlighted as the predominant areas in the analysis, together representing 71% of the evaluated fields of study. This strong presence reflects the interconnection and relevance of both disciplines in the current research, emphasizing their crucial role in developing sustainable solutions for water management and environmental preservation. Undoubtedly, the review revealed high-quality information related to urban flood mitigation. However, it is important to highlight that the specific concept or definition of GWSs is not explicitly mentioned in any of the analyzed papers. Instead, this concept can be inferred or interpreted implicitly through the content of the studies. This suggests that, although the topic is addressed, the lack of a clear and direct definition might limit the uniform understanding and consistent application of the term in research on sustainability and water management in urban environments.

This hypothesis is demonstrated, based on Refs. [68,69,70,71], which indicate that the tools and systems needed to mitigate urban challenges related to flooding, water scarcity, and climate change are the “Sponge Cities” through the incorporation of green systems. They focus on rainwater collection and reuse, offering a sustainable and efficient solution to manage water resources in vulnerable environments. Centralized stormwater management, proposed by a large body of the literature [72,73,74,75,76,77,78,79,80,81], through the implementation of systems that control runoff, minimize erosion and pollution and promote water reuse. Adapting existing an infrastructure to improve resilience to climate change, plus [82,83,84,85,86] implementing models and assessments, such as the Storm Water Management (SWMM) and Real Time Control (RTC), allow for the design and improvement of a drainage infrastructure, adapting it to future needs and local characteristics even though these models have not reached the expected range. On the other hand, references [87,88] denote systems that include vegetation, which not only improve the urban aesthetic but also increase resilience to flooding by naturally absorbing water (NBS). The various proposed strategies such as the integration of BGI, GIS tools, and SuDS seek to maximize environmental, social, and economic benefits while minimizing environmental impact [20,81,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103]; additionally there is need for policy and strategic frameworks to emphasize effective water resource management, including green water valuation and technologies adapting to new concepts for water monitoring and conservation in vulnerable areas [71,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120]. A concept that is highlighted among papers [13,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139] is urban resilience, which is achieved through the integration of green, blue, and gray infrastructures from a proactive and innovative approach. In addition to this, [140,141] support the sustainability criterion in urban ecosystem management, which not only controls floods but also provides vital ecosystem services such as habitat provision and water quality regulation. In parallel to these ideas, SuDSs stand out as a stronger foundation due to their multifunctional approach, which includes systems such as green roofs, vegetated ditches, and permeable pavements, among others, which strengthen and encourage a reduction in the load of traditional drainage infrastructure and the improvement of water efficiency [142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157]. Finally, [158,159] play a crucial role in urban flood mitigation by providing advanced tools to model and assess water behavior in urban environments through the use of hybrid frameworks that combine hydrological and hydraulic modeling.

Based on the approach outlined in the definitions of the first search model, “Green Water Systems” is understood as a sustainable aquaculture approach that uses phytoplankton or microalgae to improve water quality and the health of aquatic organisms. This system aims to optimize the aquatic environment to enhance the growth and survival of various species, either in recirculating Green Water Systems or in microalgae-enriched tanks. Although definitions related to UFR in the environmental sustainability field are limited, these are not closely linked to urban flood mitigation. However, the second search model, which combines the terms “Green AND Water AND Systems OR System”, focuses on sustainable tool approaches based on the integration of traditional infrastructure with green elements and the need to implement them in a real context such as SuDSs, highlighting an important role in water management, hydrological technology, and innovate concepts, all in order to mitigate urban flooding and promote sustainable practices in water management.

4.2. Design Codes of SuDS

Since various countries already have guidelines or standards for SuDS design in their territories, these will serve as a basis for developing a GWS proposal using SuDSs. In this study, the countries considered in the comparison were selected because they represent a wide range of climates and economies.

Table 4. Distribution of SuDS types designed in the guides or regulations of each studied country.

Country	Climate [160]	Economy [161]
United Kingdom	Maritime	Developed
Canada	Continental	Developed
Colombia	Tropical	Developing
El Salvador	Tropical	Developing
Malaysia	Tropical	Developing
Spain	Mediterranean	Developed

displays the comparison of climatic and economic classification for each country shown for the review of parameters.

Within these climatic and economic classification criteria, Peru would be categorized as a tropical climate country with a developing economy. Below are the regulations and guidelines used in this article:

• United Kingdom: The SuDS Manual (C753) [27].
• Colombia: EAAB—Norma Técnica de criterios para diseño y construcción de sistemas urbanos de drenaje sostenible (NS-166) [28].
• El Salvador: Guía Técnica para el diseño de SuDS [162].
• Canada: Guide de Gestion des eaux pluviales [163].
• Malaysia: Urban Stormwater Management Manual [164].
• Spain: Guía Básica para el Diseño de Sistemas Urbanos de Drenaje Sostenible [165].

4.3. Proposed GWS Definition

Based on the systematic approach developed in Section 3, it is concluded that there is no clear and concise definition of GWSs within the fields of urban flood management, resilience, sustainability, environmental sciences, and water resources. However, a more established definition exists in the context of aquaculture and marine sciences, which diverges towards a different approach that is unrelated to the concept of resilience against urban floods. The main gap identified in the definition of GWSs lies in the ambiguity of the concept and the lack of a clear and standardized definition. It is observed that using the same keywords, different approaches in the literature search yield divergent results, highlighting a significant gap in the literature. While in the field of aquaculture the concept is well-defined and focused on water quality improvement, its relationship with resilience to urban flooding is limited. Meanwhile, a second approach is centered on the integration of green infrastructure for water management in urban settings, which is crucial for addressing floods. Therefore, it is essential to define GWSs not only in terms of their use but also in relation to their capacity to improve urban water management in order to effectively integrate both approaches. Accordingly,

Table 5. Key Pillars and Components of Green Water Systems (GWS) for Urban Flood Mitigation and Sustainable Water Management.

ID	Pillar	Description	Relevance
1	Urban Resilience	Enhances the ability of cities to resist and recover from flood events.	Green infrastructure, such as floodable parks, green roofs, and rain gardens, absorbs and retains rainwater.
2	Water Cycle	Efficient management of the urban water cycle through the capture, filtration, and reuse of rainwater, complemented by the evapotranspiration of plants.	Plants in green infrastructure help regulate the water cycle through evapotranspiration, while also promoting water infiltration.
3	Water Filtrations Systems	Natural and mechanical systems that treat water before it is discharged or reused.	Vegetation, artificial wetlands, and permeable soils act as natural filters in urban areas.
4	Nature-based solutions (NBSs)	Nature-based solutions that use ecological processes to manage water and mitigate flooding.	NBSs, such as wetland restoration and green space creation, control water flow and enhance resilience.
5	Stormwater Management	Control of runoff and stormwater flow during heavy rainfall events.	Infrastructure such as green swales, biofilters, and retention tanks mitigate the risk of flooding.
6	Sustainability	Promotes sustainability by reducing the demand for gray infrastructure, using local and renewable resources in water management.	Green infrastructure minimizes ecological impact, fostering local and sustainable water management solutions.
7	SuDS	Sustainable urban drainage systems that control runoff and promote natural water infiltration.	Infiltration trenches, permeable pavements, and biofiltration systems are key examples of green infrastructure within SuDSs.

presents the key pillars and components necessary for developing a standardized definition of GWSs in the context of integrating infrastructures that can be used as tools to mitigate urban floods.

Taking this into account, formulating a definition for GWSs requires a definition of “Green Water”; refs. [107,166] define it as water derived from precipitation that is stored in the soil and subsequently absorbed by plants through processes such as evapotranspiration. This type of water is part of a natural cycle and differs from blue water (surface or groundwater) or gray water (contaminated water). However, based on the systematic search analysis, important variables emerge that researchers highlight in their studies. Figure 10 brings together those key terms that are fundamental for a concrete and clear definition of what a GWS is.

Based on this, a Green Water System can be defined as follows: A Green Water System is an approach to sustainable water management in urban environments that considers the natural water cycle and combines nature-based solutions, such as integrated green water collection and filtration systems, with sustainable urban drainage systems. These elements work together to improve stormwater management, promote sustainable tools, and enhance urban resilience to flooding, ensuring a balance between gray, green, and blue infrastructure. This method considers specific parameters of green water to ultimately reuse the captured water for specific purposes.

This definition helps clarify a key term in urban flood management. By integrating concepts of Sustainable urban drainage systems (SuDS), water collection, and transport systems, it provides a clearer, more direct, and comprehensive approach to developing resilient infrastructure in an urban context. This helps to bridge the knowledge gap in the study of sustainable tools, promoting a robust and applicable conceptual framework for water management and the water cycle.

Moreover, the climatic and geographical contrast of Peru, as one of the countries with the highest megadiversity, presents a significant challenge for the implementation of Green Water Systems (GWSs). The diverse regions, which include arid coastal zones, tropical rainforests, mountains, and high-altitude cities, along with fragmented infrastructure and economic limitations, hinder their applicability. However, this same diversity makes the country particularly vulnerable to the uncertainties of climate change, necessitating immediate mitigation and adaptation actions. The lack of adequate adaptation to the local context may limit the direct applicability of solutions implemented in other countries. Furthermore, excessive specialization in geographical and conceptual approaches has restricted the diversity of perspectives, potentially leading to generalized and less relevant results. Therefore, this research emphasizes the importance of conducting localized studies to avoid inadequate or ineffective solutions and to ensure that the proposed solutions can be replicated in other countries with similar vulnerability contexts.

There is an urgent need to adapt GWSs to Latin American contexts, which face diverse climatic and social challenges. The lack of studies on GWSs in urban areas with tropical, subtropical, and semi-arid climates limits their effective implementation. The region’s climatic diversity presents an opportunity to investigate the performance of these systems in areas with high environmental variability. Additionally, it is crucial to explore their applicability in middle-income cities with informal growth, and to develop governance mechanisms that promote community participation and long-term sustainability. Research should also focus on the adaptation of GWSs in mountainous and Amazonian regions, where unique topographical and climatic conditions pose significant challenges. Furthermore, the effects of extreme climate phenomena such as El Niño and La Niña must be analyzed, as well as how variations in rainfall and droughts impact the performance of these systems. Finally, there is a gap in comparative studies on the transfer and scalability of GWS technologies in Latin America, representing a promising field for future research.

4.4. International Review of SuDS Regulations

Table 6. The distribution of SuDS types designed in the guides and/or regulations of each studied country.

Types of SuDS	United Kingdom	Colombia	El Salvador	Canada	Malaysia	Spain
Green roofs	X		X	X
Soakaways	X
Water butts	X
Rainwater tank	X	X	X		X
Filter strips	X		X
Trenches	X	X	X	X		X
Swales	X	X	X		X	X
Bioretention	X	X	X	X	X	X
Pervious pavement	X	X	X	X	X	X
Geocellular/modular systems	X
Sand filters	X			X
Infiltration basins	X	X		X
Detention basins	X			X
Ponds	X		X		X	X
Stormwater wetlands	X		X	X	X	X
Reduced lot grading
Rear year ponding
Pervious pipes				X	X
Oil/grit separators				X
Filter drains	X			X		X
Trees	X	X				X

analyzes the various types of SuDSs in the mentioned countries in Section 3.

However, it is worth noting that despite having a variety of SuDSs, the focus is on one particular type: bioretention areas. According to CIRIA [27], these areas are vegetated zones that help filter runoff, and they consist of layers of materials such as gravel and sand that assist in filtering and treating water. They offer benefits such as reduced runoff, improved water quality, and decreased drainage infrastructure. And based on the research conducted by [166], these areas can store captured water in an underground reservoir for future reuse. In summary, these bioretention areas are also a type of Green Water System due to their ability to treat and manage rainwater for reuse. Therefore, this type of SuDSs meets the definition of GWSs proposed in Section 4.3. As a result, they are considered in the review of parameters shown in

Table 7. Review of the design parameters for bioretention areas in countries that include them.

Design Parameters	Units	Country
		United Kingdom	El Salvador	Canada	Colombia	Malaysia	Spain
Area	ha			1 or less		1 or less
Impervious Surface Area	%	5 to 10	5 to 10	5 to 10
Slope	%		<10	<5	<10	<5
Distance to the water table	m	1	3	1.2	>1.8	>0.6	1
Composted organic material	%		5 to 10
Time for adequate capacity	h	24
Water Depth	m	<0.15
System Depth	m				<0.3		<0.3
Width	m						>0.6
Conductivity	mm/h			25 or more	>7	>13	100–300
Planting density	plants/m2						6 to 10
Velocity	m/s					<0.5

.

The variation in values in the previous table is evident, which is due to the different hydraulic characteristics of the area being addressed.

4.5. Application in Peruvian Context

Currently, Peru has a stormwater drainage regulation, CE.040 Saneamiento [167]; yet, this document does not consider sustainable systems, and it mentions traditional drainage systems as the only alternative. Among these systems are infiltration galleries, which aim to filter water similarly to bioretention areas. Unfortunately, it only provides the maximum flow velocity within this system as the sole parameter.

Based on the above, comparing the design parameters for bioretention areas in Section 4.4 the following values in

Table 8. Proposed design parameters.

Design Parameters	Units	Proposal
Area	ha	1 or less
Impervious Surface Area	%	5 to 10
Distance to the water table	m	>0.6
Composted organic material	%	5 to 10
Time for adequate capacity	h	24
Water Depth	m	<0.15
System Depth	m	<0.3
Width	m	>0.6
Planting density	plants/m2	6 to 10
Velocity	m/s	<0.5

are recommended as part of the proposed regulations.

All the recommended parameters from each regulation and guide were considered.

The selection of parameters was carried out following the common values of the countries studied, while, for conductivity and slope, an analysis was performed for the characteristics they must have to meet the demand of each region. In this way,

Table 9. Features for each studied country.

Features	Units	Country
		United Kingdom	El Salvador	Canada	Colombia	Malaysia	Spain
Precipitations	mm/h	Moderate (30–80)	Intense (80–150)	Moderate (30–80)	Moderate to intense (40–100)	Intense (100–200)	Moderate (30–80)
Soils	-	Clayey and loamy	Volcanic and clayey	Glacial and clayey	Clayey and loamy	Lateritic and clayey	Calcareous and clayey
Conductivity	mm/h	Moderate (120–600)	Low (12–120)	Low (12–120)	Moderate (60–300)	Low (12–120)	Moderate to high (600–1200)

provides the characteristics of each area of the country in which the standard/design guide for bioretention areas was developed, which provides an idea of the reasons for the choice of those parameters, because the rainfall patterns and soil type are different across regions.

However, taking into account the natural regions of Peru, with their respective rainfall and soil patterns, indicated in

Table 10. Features and recommended values for each natural region.

Features	Units	Peru’s Natural Regions
		Coast	Andean Highlands	Amazon Rainforest
Precipitations	mm/year	Low (10–50)	Moderate (500–1500)	Intense (1500–3000)
Soils	-	Sandy and loamy	Clayey and loamy	Lateritic and clayey
Recommended conductivity	mm/h	Low to moderate (12–120)	Moderate (120–600)	High (600–1200)
Recommended slope	%	<5	<20	<5

, the following conductivity and slope values are recommended based on their characteristics, remembering that in areas with greater precipitation (e.g., Amazon rainforest), a high conductivity must be available so that the system does not fail, as well as a low slope, which reduces the risk of erosion. At the other extreme, we have the Peruvian coast, whose precipitation is usually low; therefore, the conductivity does not have to be so high, allowing for low to moderate values.

According to Andrés-Doménech et al. [168] who carried out a study on how SuDSs are being implemented in Spain, the barriers used in their diagnosis can provide an idea of what prevents the implementation of the recommended parameters. These barriers are divided into three dimensions (social and governance, regulatory framework, technical), where the following barriers applicable to this context were found: insufficient resources, a lack of monitoring and evaluation, an uncoordinated institutional framework, and a lack of political and public will.

Another factor to consider is the seismicity of Peru, since it is located in the Pacific Ring of Fire [169], making it a highly seismic area. Regarding the feasibility of replicating the standards from Malaysia to Peru, since it is a bioretention area, it can be performed with alternative materials from the area if those used in Malaysia are not found. However, profitability will depend on the area in which it is to be applied due to the price assigned in that area.

Additionally, since it involves a GWS and aims to reuse green water, it will need to use a storage tank using the Daily Water Balance method. The following expressions developed by García-Colin, Díaz-Delgado, Salinas Tapia, Fonseca Ortiz, Esteller Alberich, Bâ, and García Pulido [166] can be used to design the tank, taking into account precipitation and evapotranspiration in the system. The efficiency of supply over a period j (${EF}_j$) is represented by a split between daily accumulated deficit and demand as shown in Equation (1).

$${EF}_j=1-\frac{\sum {Def}_i}{\sum R_i}$$

(1)

where $\sum {Def}_i$ is the cumulative deficit and $\sum R_i$ is the sum of the irrigation depth, which may be considered with or without leaching as appropriate. In turn, the amount of water in the tank is calculated using Equations (2) and (3).

$${Def}_i=\{\begin{array}{cc}\hfill 0,& {SG}_i+{SG}_{i-1}\ge R_i\hfill \\ \hfill R_i-{SG}_i-{SG}_{i-1},& {SG}_i+{SG}_{i-1}<R_i\hfill \end{array}$$

(2)

$${SG}_i=\{\begin{array}{cc}\hfill 0,& {Gp}_i+{SG}_{i-1}\le R_i\hfill \\ \hfill {SG}_i+{SG}_{i-1}-R_i,& {SG}_i+{SG}_{i-1}>R_i\hfill \\ \hfill S,& {SG}_i+{SG}_{i-1}-R_i\ge S\hfill \end{array}$$

(3)

where ${SG}_i$ is the percolation (offer), and $R_i$ is the daily irrigation depth (demand), both in units of mm; ${SG}_{i-1}$ is the daily amount of water, and $S$ is the proposed height, both measured in mm. With this procedure, we can determine the efficiency of each proposed reservoir’s height, allowing for us to verify whether the system will be capable of storing water and releasing it at the desired time.

To ensure the effectiveness of GWSs throughout the year, it is essential that the daily water balance method is implemented in combination with proper GWS planning. This approach allows for systems to be flexible and adapt to changing conditions, avoiding overloading in the rainy season and ensuring that stored water is available during droughts.

As the daily water balance method takes into account the inputs and outputs of water in the system, a detailed analysis of the climatic and seasonal differences in precipitation can be performed, which will allow for its adaptability to the climatology throughout the year. In this way, in the rainy season, the GWS can manage large volumes of water, ensuring that flooding does not occur and that the water is retained or infiltrated in a controlled manner, while, in the dry season, the stored water can be used to maintain system operation, allowing for the GWS to remain effective and sustainable throughout the year.

5. Discussion

The discussion in this article is related on the research questions (QBS and QBC), and based on the methods used and the results obtained, we address each of the formulated questions.

• How are GWS developed as a sustainable tool to mitigate urban flooding defined?

Green Water Systems (GWSs) encompass a comprehensive approach to the collection and management of green water in urban environments. These systems employ nature-based solutions and sustainable urban drainage practices. This method considers green water parameters to optimize water capture and reuse. The primary goal of GWSs is to mitigate urban flooding. To achieve this, they efficiently integrate existing infrastructure (gray infrastructure) with green and blue infrastructure elements. This integration not only improves stormwater management and reduces flood risk, but also contributes to overall environmental sustainability by promoting a more balanced and resilient urban environment (UFR).

• Are GWS a viable alternative to combat pluvial flooding in Peru? Are they the best tool available?

Peru presents a great climatic and geographic diversity. Coastal and urban areas, such as Lima, Arequipa, Cusco, and other regions of Peru, can benefit from GWSs due to their capacity to manage rainwater/precipitation and reduce flood risk in areas with limited gray infrastructure. However, in regions with intense rainfall or mountainous terrain, implementing or integrating GWSs may require technical adjustments to adapt to local conditions. Additionally, GWSs promote environmental sustainability by integrating vegetation (green areas) with existing urban infrastructure, improving water quality and fostering biodiversity. They highlight their connection to SuDSs as fundamental design pillars, encouraging the creation of green spaces that enhance quality of life in urban areas without the need to completely replace existing systems, such as stormwater drainage and sewer systems. Nature-based solutions (NBSs) align with GWS principles by offering a more integrated approach that combines green, gray, and blue infrastructure with water management systems. Figure 11 highlights how GWSs fit into the proposed continuity line for urban flood management.

Compared to the strategies implemented in Asia, hydrological conditions in Peru are significantly different from those of the Asian continent. This is why a different approach should be developed in the construction of flexible infrastructures capable of controlling the variability of extreme weather events, such as drainage systems that mitigate intense rainfall in short periods. In the case of Peru, these systems must adjust to the cyclical and uncertain nature of the “El Niño” phenomenon, integrating forecasts based on regional climate behavior, which would strengthen the capacity to adapt to climate change and improve resilience to natural disasters. Given the economic context and urban fragmentation of the country, a progressive implementation of these systems is proposed, prioritizing the most vulnerable areas to flooding caused by “El Niño”, especially in coastal cities. One of the most important lessons from Asia is the development of advanced monitoring and early warning systems, which have been effective in predicting extreme rainfall and coordinating rain management, preventing disasters. In Peru, the integration of these systems would be key to mitigating the impact of floods and significantly improving emergency response capacity. In addition, China has implemented the concept of “Sponge Cities”, which take advantage of natural areas to capture and store water. In Peru, the promotion of green spaces in cities is essential, since their scarcity increases vulnerability to extreme events. These solutions would not only relieve pressure on drainage infrastructure, but would also generate important social benefits, improving the quality of urban life.

This article explores the conceptual and practical differences in the application of GWSs within two distinct contexts: aquaculture and urban flood management. In aquaculture, GWSs are linked to water quality management systems, whereas in the context of urban flooding, they are integrated with NBSs and sustainable flood management tools. Despite these differences, both approaches share a common link: the use of natural processes for water management. For instance, the natural filtration, retention, and purification processes used in aquaculture could be applied in urban water management. An example is the construction of wetlands and water retention systems, which capture and filter rainwater before it reaches drainage systems. Moreover, certain aquaculture technologies, such as water recirculation systems with biofilters and sedimentation units, could be adapted for rainwater recycling in urban bioretention systems. These systems could filter and reuse rainwater collected from rooftops or pavements for non-potable purposes, such as garden irrigation and cleaning. Lastly, biofiltration systems in aquaculture, which use beneficial bacteria to break down contaminants and maintain water quality, could be applied in urban bioretention systems. Here, vegetation would act as a natural biofilter, improving the quality of water entering the system.

It can be concluded that GWSs can be a valuable tool for combating urban flooding in Peru, especially when adapted to local conditions and integrated with existing infrastructure. According to Espinoza Vigil and Carhart [170], the need for and the challenge of implementing sustainable and resilient infrastructure in a Peruvian context will depend on a holistic management and approach to prevent them from operating in isolation and adapting to the changing needs of the population in Peru. Added to this, the effectiveness of GWSs will depend on proper planning and design, as well as their integration with other water management strategies.

• What are the design parameters and characteristics of a GWS type with applicability to Peru?

As seen in Section 4.4 of the Results, the most important parameters to consider are area, impervious surface area, slope, distance to the water table, composted organic material, time for adequate capacity, water depth, system depth, width, conductivity, planting density, and velocity. Each of these design criteria has been developed using the International System of Units (SI) in each of the countries studied, so the proposal for Peru will also follow these units. However, if another region wishes to use this research to develop its own regulations and uses a different system of units, the values are easily convertible. It is also noted that the proposal is pending field validation for future implementation.

• Is it feasible to develop a “Design Code” proposal for SuDSs in an urban context in Peru?

Although this research standardizes GWSs through the use of bioretention areas, which is a type of SuDSs, it does not overlook the opportunity to utilize the design parameters of this system to develop SuDS regulations in Peru. It is important to note that Peru already has stormwater drainage regulations; however, they lack parameters regulating SuDSs or GWSs. Therefore, this article can be used to expand the current regulatory framework.

Regarding SuDS design regulations, it should be noted that there are more documents worldwide that regulate their design. In some of the countries mentioned in Section 3, there are various guides for each region within the country. For example, in Spain, this study used the document from Valencia. However, there is another guide from Madrid, which was not included in this study because the parameters examined are similar regardless of the city.

Peru currently does not have regulations governing SuDSs or GWSs. However, OS.010 [171] of its National Building Regulation has “Filter Gallaries” that have a similar use to the bioretention zones. However, they do not have the defined parameters seen in this investigation.

The primary barrier to implementation lies in integration, policy, and resistance to change. The lack of political coordination across government levels, absence of regulations for green and blue infrastructure (GBI) or nature-based solutions (NBSs), and an entrenched culture favoring traditional solutions—perpetuated even at the university education level, which promotes gray infrastructure over green—may hinder the adoption of bioretention systems. Furthermore, the preference for quick fixes and cost perceptions may also diminish the implementation of this innovative approach. To overcome these challenges, developing clear regulations, capacity-building for professionals and the public, and demonstrating the effectiveness of GBI/NBS through strategic pilot projects will be crucial. Additionally, public education and promoting long-term benefits will be key to ensuring the successful adoption of GBI/NBS in major cities nationwide.

6. Conclusions

Flood resilience in urban areas can be significantly improved with the proposed definition of Green Water Systems (GWSs), as they offer a comprehensive approach to managing green water in urban environments. GWSs utilize nature-based solutions and sustainable drainage practices, optimizing water capture and reuse by considering important parameters such as evapotranspiration. In Peru, GWSs are a viable option for mitigating floods in urban areas, adapting to specific local conditions, and enhancing stormwater management. Additionally, they promote sustainability by integrating vegetation with existing urban infrastructure, improving water quality and fostering biodiversity. However, the effectiveness of GWSs will depend on proper planning and their integration with other water management strategies. Although they do not completely replace traditional drainage systems, their combination with gray infrastructure and alignment with nature-based solutions (NBSs) offers a sustainable solution to urban flooding. Therefore, GWSs can be a valuable tool within a comprehensive strategy to enhance flood resilience.

These conclusions open a broad and necessary field of research, as there exists a significant gap in the research on this topic. In particular, the adaptation of Green Water Systems (GWSs) to arid climates and high mountain areas, such as those found in Peru, represents a critical and underexplored area due to climate variability and water availability. It is essential to design bioretention systems and other GWS elements that are effective in these contexts. Furthermore, there is a need to investigate the integration of gray infrastructure with green infrastructure, exploring how to achieve this transition effectively and with minimal implementation costs. This also highlights the lack of interdisciplinary research that includes economists, sociologists, and ecologists, who can provide a comprehensive perspective to overcome social and economic barriers in Peru and Latin America, facilitating a more appropriate and sustainable implementation of these systems.