The Current Status of Irrigated Agriculture in Cape Verde and Its Link to Water Scarcity

Abstract

In arid regions with low precipitation, like most of the Cape Verde islands, irrigation is essential for maintaining agricultural production and food security. However, due to significant investment needs, it is critical to improve irrigation efficiency and reduce water losses. The aim of this study is to evaluate irrigated agriculture in Cape Verde and its relationship with water scarcity through the calculation of key indicators and the analysis of statistical and remote sensing data. Crop production data were collected from the Ministry of Agriculture and Environment, and climatic data from the National Institute of Meteorology and Geophysics of Cape Verde (INMG) and FAO’s WaPOR platform. The aridity index was calculated using the UNEP method based on data from INMG. The island of Sal showed the lowest aridity index value (0.07), while Cachaço (São Nicolau island) had the highest (0.41). Sugarcane is currently the dominant irrigated crop, covering over 3000 hectares, about 62% of irrigated land, despite its high water demands. The expansion of sugarcane threatens long-term water sustainability and food production. Promoting crops with higher water productivity and technical training are key actions to ensure the sustainability of irrigated agriculture in Cape Verde. Findings point to the urgent need to improve irrigation infrastructure, maintenance, and system design.

1. Introduction

As the world’s population continues to grow, the demand for food also increases. Agricultural production can be increased by expanding cultivated areas and/or increasing productivity [1]. One strategy to boost crop productivity is irrigation, which not only increases production but also enables year-round farming and regularizes crop yield, helping to reduce poverty and hunger [2]. However, these decisions require significant investments that must be profitable. Therefore, it is crucial to ensure sustainable management of available water and minimize various losses that may occur during irrigation operations [3]. In Cape Verde, irrigated agriculture plays an extremely important role in securing agricultural production and food sovereignty, as demonstrated by Silva [4] and Monteiro [5]. The problem of limited water resources in Cape Verde has long been a major challenge for the country [6,7]. Cape Verde has been affected by severe and prolonged droughts over the last few decades [8]. Additionally, the small area available for agriculture and topographical features such as mountain peaks and steep slopes limit the cultivation area in this archipelago [9]. Although successive governments have made significant investments in water mobilization [10,11], further efforts are needed to improve water management in various sectors, particularly agriculture. This problem is exacerbated by climate change, as extreme precipitation and temperature phenomena are increasing in intensity and frequency [12].

According to the African Development Bank [13], despite its historical importance, agriculture in Cabo Verde has experienced a steady decline in both economic relevance and employment share over the past two decades. The sector’s contribution to GDP dropped from 9.7% in 2000 to 7.8% in 2021, while its share in total employment fell sharply from 23% to 10.6% over the same period. In fact, the government policies implemented in Cape Verde to mitigate the effects of water scarcity in the agricultural sector have primarily centered on constructing dams [11] and enhancing irrigation efficiency via programs that support and encourage drip irrigation [14]. The exploitation of alternative water sources, such as treated wastewater and desalination, has also been suggested as a possible solution. Despite the measures and strategies adopted, its effectiveness has been limited due to a number of factors, including economic, technical, and capacity building, to properly manage these investments.

In regions with water scarcity, due to the low availability of this resource, it is crucial to ensure water use efficiency, increasing water productivity and minimizing water losses or inappropriate use. The efficiency of an irrigation system can be defined as the ratio between the amount of water supplied by a particular subsystem and the amount of water withdrawn by that subsystem [15,16]. Water productivity can be defined as the ratio between plant biomass or grain production and the amount of water used by the plant, including rainfall and irrigation water [17,18]. According to Pereira et al. [19], water scarcity is not only limited to arid and drought-prone regions but can also affect areas with abundant rainfall. This issue concerns both the availability and quality of water resources, as degraded water sources may no longer meet more stringent requirements. In regions with water scarcity, the development of measures to reduce losses is essential, but this requires the losses to be identified and quantified. In this study, we adopt the definition of water loss from [3], in which water “losses” is simply water that is not being used by the intended crops as evapotranspiration. This definition ignores alternative uses of irrigation water, such as moistening the soil to support tillage for planting or harvesting, cooling, frost protection, or fertilizer application. Nevertheless, this definition fits the Cape Verdean context since practically all these water applications are not relevant, given the agricultural practices adopted. There are many technologies and management practices that can be used to improve water management in arid and semi-arid regions, with the aim of increasing their sustainability. These include drip irrigation (which is already widely used in Cape Verde, although application efficiencies remain low), subsurface drip irrigation, and deficit irrigation [20,21,22]. Conversely, as Fereres and Soriano [23] illustrate, deficit irrigation, with the application of reduced volumes of water during the less sensitive phases of crop growth, can sustain productivity and enhance water use efficiency. Similarly, the modernization of irrigation and energy systems has been demonstrated to engender significant benefits, as evidenced by Berbel et al. [24], specifically the utilization of solar energy for water pumping. While these technologies have been proven to increase irrigation efficiency, implementing them in Cape Verde presents significant challenges, including establishing technical support networks, providing training and knowledge on their use, and creating market conditions that will generate a return on investment.

The aim of this study is to diagnose the current status of the irrigation sector in Cape Verde, including the water demand for agriculture, examining its production and irrigation systems characteristics, the availability of water resources, and climate limitations induced by aridity. The specific objectives are to calculate indicators and perform data analysis, exploring the various data sources available to support the development of measures to improve water use in this sector in the context of water scarcity.

2. Materials and Methods

2.1. Studied Area

The Cape Verde Archipelago is located on the east coast of the Mid-Atlantic Ocean, between latitudes 14°48′ N and 17°12′ N and the longitudes 22°44′ W and 25°22′ W, about 500 km from the westernmost point of the African continent, the Senegalese coast [25]. As Semedo [25] notes, Cape Verde lies within the vast Sahel region, which stretches from the Atlantic coast to the Red Sea. Cape Verde is an African country consisting of ten volcanic islands of different sizes and distribution, as shown in Figure 1, occupying a total area of 4033 km² and with an exclusive economic zone (EEZ) of approximately 700 km² [26]. The islands are divided into three groups: (i) the northern group Santo Antão, São Vicente, Santa Luzia (is not inhabited), and São Nicolau; (ii) the southern group Santiago, Fogo, and Brava; and (iii) the eastern group Sal, Boavista, and Maio.

2.2. Data Collection

This study is based on five complementary sources: (1) agricultural data available in the country from the Ministry of Agriculture and Environment and the National Institute of Statistics (INE); (2) meteorological data from the National Institute of Meteorology and Geophysics; (3) the grey literature, mainly documents related to the agricultural sector in Cape Verde; (4) the scientific literature on the subject; and (5) data taken from FAOSTAT, WAPOR, and AQUASTAT on the six main agricultural products in terms of production (tons) and harvested area (ha).

The first step of this work consisted of compiling the scattered information on irrigated agricultural areas at the level of each island and at the national level, where the evolution of the irrigated areas, the main irrigated crops, and the production and productivity of these crops are to be studied using data from the Ministry of Agriculture and Environment, the National Institute of Statistics, and the FAO. The second step was to assess the evolution of precipitation over the years and how this relates to the production and productivity of the main crops. The third step was to characterize irrigated agriculture in Cape Verde and what measures have been taken to mitigate water scarcity and the impact of perceived climate change.

2.3. Climate Data

The Cape Verde islands have a semi-arid tropical climate, classified as BWh according to the Köppen–Geiger climate classification [27], characterized by high temperatures and low rainfall throughout the year. Even in the coldest months January and February, minimum temperatures range between 19 °C and 25 °C. For this study, the meteorological stations used for climatic characterization are presented in

Table 1. Location of the meteorological stations used in this study [28].

Latitude (°)	Longitude (°)	Elevation (m)	Localities	Island
17.02	−25.08	22	Porto Novo	Santo Antão
16.62	−24.33	715	Cachaço	São Nicolau
15.13	−23.13	482	Assomada	Santiago
15.04	−23.47	73	São Domingos	Santiago
15.02	−24.31	81	Mosteiros	Fogo
14.88	−24.48	174	São Filipe	Fogo
16.72	−22.94	53.8	Sal	Sal
14.95	−23.48	94.5	Praia	Santiago
16.53	−24.59	32	Mindelo	São Vicente

.

Aridity Index

The aridity index, which compares precipitation to potential evapotranspiration, is a useful measure for climate classification. For this study, the index was calculated according to the methodology of the United Nations Environment Program [29].

$$\mathrm{A}\mathrm{I}\mathrm{u}={\displaystyle \frac{\mathrm{P}}{\mathrm{P}\mathrm{E}\mathrm{T}}}$$

(1)

where AIu is the aridity index, P is the average annual precipitation, and PET is the potential evapotranspiration. To ensure consistency, both P and PET must be expressed in the same units, such as millimeters. See Table 2 for aridity index classification. For this research, was used the Hargreaves–Samani (H-S) equation [30,31] to calculate evapotranspiration. The equation can be represented as follows [30,31].

$$\mathrm{E}\mathrm{T}\mathrm{o}=0.0135\times \mathrm{K}\mathrm{r}\mathrm{s}\sqrt{(\mathrm{T}\mathrm{m}\mathrm{a}\mathrm{x}-\mathrm{T}\mathrm{m}\mathrm{i}\mathrm{n})}\times \mathrm{R}\mathrm{a}\times (({\displaystyle \frac{\mathrm{T}\mathrm{m}\mathrm{i}\mathrm{n}+\mathrm{T}\mathrm{m}\mathrm{a}\mathrm{x}}{2}})+17.8)$$

(2)

where ETo is the reference evapotranspiration (mm/day), Ra is the radiation at the top of the atmosphere (mm/day), Tmax is the maximum temperature (°C), and Tmin is the minimum temperature (°C). Krs is the radiation adjustment coefficient, which varies from 0.19 in coastal areas to 0.16 in inland areas.

Typically, the H-S equation uses a Krs value of 0.17 [32]. This equation was calibrated to the Cape Verde conditions by [33], comparing the estimated values against the FAO Penman–Monteith equation, which is considered the most accurate method for computing ETo [32]. As a result of this study, ref. [33] proposed the following linear regression equation: y = 1.4615x − 0.7662, with R² = 0.99, where y is the corrected ETo value, and x is the result obtained using the Hargreaves–Samani method (Krs = 0.17).

Table 2. Climate classification using the aridity index (AIu) [34].

Classification	Aridity Index
Humid	AIu ≥ 1.00
Sub-humid	0.65 < AIu < 1.00
Dry sub-humid	0.50 < AIu < 0.65
Semi-arid	0.20 < AIu < 0.50
Arid	0.05 < AIu < 0.20
Hyper-arid	AIu ≤ 0.50

Table 2. Climate classification using the aridity index (AIu) [34].

Classification	Aridity Index
Humid	AIu ≥ 1.00
Sub-humid	0.65 < AIu < 1.00
Dry sub-humid	0.50 < AIu < 0.65
Semi-arid	0.20 < AIu < 0.50
Arid	0.05 < AIu < 0.20
Hyper-arid	AIu ≤ 0.50

2.4. Water Use

For the analysis of water use in Cape Verde’s agricultural sector, six indicators were selected based on their relevance for assessing availability, efficiency, sustainability, and pressure on water resources, considering the specific challenges faced by small island states with limited water resources. The selected indicators include the following:

(i)

Water withdrawal for agriculture as a percentage of total renewable water resources (%);

(ii)

Water use efficiency in irrigated agriculture, which is calculated as the agricultural value added per agricultural water use (USD/m³);

(iii)

Contribution of the agricultural sector to water stress, which is calculated as the proportion of agricultural sectoral withdrawals over total freshwater withdrawals (%);

(iv)

Percentage of the area equipped for irrigation using groundwater (%);

(v)

Percentage of the area equipped for irrigation using surface water (%);

(vi)

Water productivity per agricultural crop (kg/m³) [35], calculated using the following equation:

$$\mathbf{W}\mathbf{P}=\mathbf{c}\mathbf{r}\mathbf{o}\mathbf{p} \mathbf{y}\mathbf{i}\mathbf{e}\mathbf{l}\mathbf{d} \left(\mathbf{k}\mathbf{g}\right)/\mathbf{i}\mathbf{r}\mathbf{r}\mathbf{i}\mathbf{g}\mathbf{a}\mathbf{t}\mathbf{i}\mathbf{o}\mathbf{n} \mathbf{w}\mathbf{a}\mathbf{t}\mathbf{e}\mathbf{r} \mathbf{a}\mathbf{p}\mathbf{p}\mathbf{l}\mathbf{i}\mathbf{e}\mathbf{d} \left({\mathbf{m}}^3\right)$$

(3)

The first five indicators were obtained from AQUASTAT—FAO’s Global Information System on Water and Agriculture. The selected indicators address key dimensions of water management, including the intensity of water abstraction for agriculture in relation to renewable water availability, the economic efficiency of water use in irrigated areas, the degree of contribution of the agricultural sector to the overall national water stress, dependence on groundwater and surface water sources for irrigation, and water productivity at the crop level. This integrated approach allows for a more comprehensive assessment of the agricultural sector’s water performance and supports the planning of policies for efficient water use.

2.5. Crop Evolution and Production

To analyze the evolution of crop area and production, data on area, production, and productivity were obtained from both national statistics and FAOSTAT. The processed and analyzed data were then used to identify trends and patterns over time. The results obtained are presented in graphs that allow the evolution of the different crops over time to be visualized.

3. Results and Discussion

3.1. Climate Characterization

As shown in Figure 2, there are around 5 °C differences in average temperature between Cachaço (Sao Nicolau) and Praia (Santiago). The differences in temperature throughout the year have the same trend for all the islands.

Precipitation varies greatly, both spatially and temporally. The annual average rainfall variation on the primarily agricultural islands of Cape Verde from 1993 to 2022 is presented in Figure 3. It is clear that rainfall varies significantly annually; particularly, low rainfall values have been observed on the island of São Nicolau over the last six years of the period considered (2017–2022).

The aridity index and its classification for several locations on the main agricultural islands are shown in

Table 3. Average annual maximum temperature (Tmax), minimum temperature (Tmin), precipitation (P), potential evapotranspiration (PET), aridity index (AIu), and climatic classification based on data from 1993 to 2022 for some localities in Cape Verde [28].

Localities	Island	Tmax (°C)	Tmin (°C)	PET (mm)	P (mm)	AIu	Classification
Porto Novo	Santo Antão	29	21	1425	263	0.18	Arid
Cachaço	São Nicolau	23	17	1069	448	0.41	Semi-arid
Assomada	Santiago	25	19	1223	282	0.23	Semi-arid
São Domingos	Santiago	26	22	973	227	0.23	Semi-arid
Mosteiros	Fogo	28	23	1146	366	0.32	Semi-arid
São Filipe	Fogo	29	22	1363	154	0.11	Arid
Sal	Sal	27	22	1194	80	0.07	Arid
Praia	Santiago	29	22	1375	185	0.13	Arid
Mindelo	São Vicente	27	23	1009	134	0.13	Arid

. It is obvious that there are differences in the index between different places. Cachaço locality in Sao Nicolau Island is characterized by an aridity index of 0.41. Among the analyzed locations, Sal Island had the lowest drought index of 0.07. As expected, reduced precipitation correlates with a reduced aridity index, indicating a drier climate and lower biomass production (see Figure 4).

The relation between the aridity index and biomass production is noteworthy when aridity indices AIu (Table 2) are compared to gross biomass water productivity (Figure 4). It is important to note that gross biomass water productivity (seasonal) measures total biomass production compared to total water consumption (actual evapotranspiration) during the vegetation growth cycle. FAO’s Wapor database provides information on the spatial distribution of gross biomass water productivity in the Cape Verde islands and identifies the areas where biomass growth relative to water use is the greatest (FAO, 2023). The Assomada and São Domingos weather stations on the islands of Santiago (AIu = 0.23), Cachaço weather station in São Nicolau (AIu = 0.41), and Mosteiros weather station in Fogo island (AIu = 0.32) present the highest aridity index values, which indicates the areas with the highest water availability, overlapping the areas with the highest biomass production in Cape Verde, indicated by values more than 3 kg/m³ (green areas), as shown in Figure 4, which shows the gross biomass water productivity (seasonal) for the Cape Verde islands in 2019. It is worth noting that this year was one of the driest years (Figure 3) in the Cape Verde archipelago.

The actual evapotranspiration and interception (ETIa) is defined by [36] as the sum of soil evaporation, crop canopy transpiration, and rainfall interception by the crops. The annual values of ETIa, expressed in millimeters per year (mm/year), estimated for the main islands of Cape Verde between 2018 and 2024 are shown in

Table 4. Actual evapotranspiration and interception (annual) for the Cape Verde islands [36].

	Islands
Year	Santiago	Fogo	Brava	Boavista	Maio	Sal	São Vicente	São Nicolau	Santo Antão
2018	232	104	362	137	96	146	169	310	98
2019	200	102	302	136	72	137	161	279	80
2020	287	150	384	140	129	144	195	317	127
2021	270	95	293	130	128	137	162	277	88
2022	328	153	421	171	109	141	173	328	117
2023	351	196	499	125	131	137	171	302	130
2024	411	220	494	133	150	137	175	326	136

[36]. The analysis of the ETIa values between 2018 and 2024 on the Cape Verde islands shows a general upward trend, with significant differences between the islands. The island of Brava has the highest value throughout the period, reaching 498.75 mm/year in 2023. On the other hand, Fogo, Maio, and Santo Antão recorded the lowest values, with minimum values of 95.21 mm/year (Fogo/2021), 72.31 mm/year (Maio/2019), and 79.97 mm/year (Santo Antão/2019). The island of Santiago shows a significant increase from 232.48 mm/year in 2018 to 411.03 mm/year in 2024. Islands with a more arid climate, such as Sal and Boavista, maintained lower and relatively stable values, varying between 136.45 mm/year and 143.95 mm/year for Boavista and between 136.51 mm/year and 146.38 mm/year for Sal.

Table 5. Number of droughts by meteorological station from 1962 to 2013 obtained from [37].

Localities	Island	Moderate Drought	Severe Drought	Extreme Drought	Total
Porto Novo	Santo Antão	n.a.	n.a.	n.a.	n.a.
Cachaço	São Nicolau	n.a.	n.a.	n.a.	n.a.
Assomada	Santiago	1	1	2	4
São Domingos	Santiago	3	2	2	7
Mosteiros	Fogo	5	3	1	9
São Filipe	Fogo	n.a.	n.a.	n.a.	n.a.
Sal	Sal	5	2	2	9
Praia	Santiago	6	2	2	10
Mindelo	São Vicente	4	3	1	8

n.a.—not available.

was constructed using data from a study of droughts in Cape Verde [37]. Table 5 contains the meteorological stations that were previously used to calculate AIu. Analysis of the table shows that arid and semi-arid climate conditions are accompanied by a high frequency of droughts, including severe and extreme ones. Therefore, Cape Verde is highly vulnerable to water scarcity due to its frequent experience of abnormally low rainfall in addition to normal conditions of lack of precipitation.

3.2. Characterization of Irrigated Agriculture in Cape Verde

The agricultural area in Cape Verde in 2017 was 36,456 hectares, of which 87% are rainfed and 10.7% are irrigated. The remaining 2.3% were used for mixed agricultural practices with rainfed and irrigated crops (see

Table 6. Distribution of the areas dedicated to agriculture, irrigated, rainfed, and mixed by island, obtained from the general agricultural census [38].

Islands	Total Agriculture (ha)	Irrigated (ha)	Rainfed (ha)	Mixed Agricultural—Irrigated and Rainfed (ha)
São Antão	5246	1268	3770	207
São Vicente	942	302	597	44
São Nicolau	1030	146	854	30
Sal	74	2	72	0
Boavista	276	242	34	0
Maio	466	73	316	77
Santiago	21,076	1747	18,880	443
Fogo	6827	90	6694	43
Brava	520	43	476	1
Cape Verde	36,456	3913	31,692	845

). Agricultural areas in 2015, according to the RGA (General Agricultural Census), accounted for around 9% of the country’s area, a slight decrease of only 1% compared to the 2004 RGA (General Agricultural Census) data. Of the total area of the agricultural plots, 82.5% was cultivated, and the remaining areas were used for fallow land, permanent pastures, rotating pastures, forest land, and other uses [38]. Comparing the values in Table 6 and the gross biomass water productivity (Figure 4), it is easy to see that the islands with the largest irrigated areas have higher gross biomass water productivity values. For example, Santiago and Santo Antão, the islands with the largest areas dedicated to irrigated agriculture (1747 and 1268 ha, respectively), have biomass water productivity values from 1 kg/m³ upwards.

Irrigated agriculture is practiced on a smaller scale in Cape Verde compared to rainfed agriculture. According to the General Agricultural Census [38], the irrigated area increased by 22.2% between 2004 and 2015, attributed to significant investments in water mobilization and the creation of irrigated perimeters [38]. In Cabo Verde, the potential irrigable land area, located mainly on the islands of Santo Antão and Santiago, is between 2500 and 3000 ha [11]. Nevertheless, the same authors suggest that this area could expand to up to 5000 hectares, according to the [39] study. The islands of Santiago and Santo Antão account for about 90% of the irrigated land.

The irrigated plots are located at the bottom of the valleys, in the lower part of the slopes, and on small plateaus [40]. According to the 2015 Census of Agriculture data, the total area of irrigated land at the national level was 3913 hectares in 2015. About 83% of this is cultivated, which corresponds to 3248 hectares (see Figure 5). Considering these data and the previous forecasts, there is still a margin for an increase in the irrigated area by 1000 hectares. However, this increase will largely depend on water availability. It should be considered that the cultivated area may change over the years, depending on the fluctuations in water availability.

The two municipalities with the largest agricultural area, Ribeira Grande and Santa Cruz, are located on the islands of Santo Antão and Santiago, respectively. Ribeira Grande has an agricultural area of about 562 hectares, while Santa Cruz has about 516 hectares, as shown in Figure 5. It is noteworthy that Sal Island has the smallest irrigated agricultural area of 2 hectares as can be seen in the Table 6. Since this area is significantly smaller compared to other municipalities, it is represented in Figure 5.

A comparison was made between the aridity index and the percentage of irrigated land in a given municipality where information was available [38]. Figure 6a shows that there is no direct relationship between the aridity index AIu and the percentage of irrigated land. To complement this analysis, we compared the number of years of drought between 1962 and 2013 [37] with the percentage of the irrigated area (Figure 6b) and found that there is also no relationship between the number of years of drought and the extent of irrigation. Thus, it is evident that the adoption of irrigation by the farmers depends on various factors, particularly economic and social ones, and that water scarcity alone, whether induced by aridity or drought, cannot explain the distribution and intensity of irrigation in the Cape Verde islands.

Between 2020 and 2022, there was a slight reduction in water withdrawals for irrigation, from 37.73% to 34.41% of renewable water resources, suggesting a possible optimization in water use [41]. Irrigation efficiency gradually increased from USD 0.071/m³ in 2020 to USD 0.076/m³ in 2022, indicating greater economic productivity per unit of water (

Table 7. Indicators of agricultural water use and efficiency (2020–2022) [41].

Year	Agricultural Water Withdrawal as % of Total Renewable Water Resources (%)	Irrigated Agriculture Water Use Efficiency (USD/m3)	Agricultural Sector Contribution to Water Stress (%)	% of Area Equipped for Irrigation by Groundwater	% of Area Equipped for Irrigation by Surface Water
2020	37.73	0.071	26.64	10.35	63.26
2021	36.42	0.075	24.32	10.35	63.26
2022	34.41	0.076	23.27	10.35	63.26

). The agricultural sector’s contribution to water stress, which is defined as the ratio of total freshwater withdrawn to the total renewable freshwater resources within a specific region, after considering environmental flow requirements [42], has also decreased, from 26.64% to 23.27%, reflecting improvements in water resource management. Finally, surface water irrigation predominates (63.26%) compared to groundwater irrigation (10.35%).

Irrigated agriculture is limited by water availability.

Table 8. Distribution of water resources by islands and sources in millions of m³/year [7].

Island	Surface Water (Average Period)	Groundwater
		Gross (Average Period)	Explorable (Average Period)	Explorable (Dry Period)
Santo Antão	27.0	28.6	21.3	14.3
São Vicente	2.3	0.6	0.4	0.2
São Nicolau	5.9	4.2	2.5	1.5
Sal	0.7	0.4	0.1	0.05
Boa Vista	2.5	1.6	0.7	0.3
Maio	4.7	2.1	0.9	0.5
Santiago	56.6	42.4	26.0	16.5
Fogo	79	42	12.0	9.3
Brava	2.3	1.9	1.6	1

shows the availability of surface and groundwater on the Cape Verde islands. In general, the islands with the lowest water availability have the smallest areas dedicated to irrigated agriculture, except for Fogo Island, which ranks second in terms of surface water availability (79 million m³/year) and third in terms of groundwater availability (gross 42 million m³/year for the average period and explorable 12 and 9.3 million m³/year for the average period and dry period, respectively).

Of all the CV islands with the greatest agricultural aptitude (Santo Antão, São Nicolau, Santiago, and Fogo), Fogo Island has a very small area of irrigated agriculture (90 hectares), which contrasts with its greatest availability of surface water (Fogo = 79, Santiago = 56.6, Santo Antão = 27, and Sao Nicolau = 5.9 million m³/year). This may be due to the price of water for irrigation, which is very high compared to the other islands. The island of Santiago shows the highest value of groundwater availability, with 26 and 16.5 million m³/year explorable for the average and dry periods, respectively, which is in line with the island’s larger irrigated area, as shown in Table 6.

When analyzing the production of crop groups (Figure 7) such as roots and tubers, fruit crops, vegetables, and sugarcane in Cape Verde based on FAOSTAT data [43], a significant increase in production has been observed since 1999, particularly for vegetables and sugarcane. Since 1989, the production of certain crops, especially vegetables, has declined. Roots, tubers, and fruit crops have become the most produced product types nationally. Sugarcane production has remained relatively stable (see Figure 5). Based on data from the Statistical Yearbook of the National Statistics Institute [44], vegetable production decreased by about 24% between 2013 and 2017, with production ranging from 52,444 to 38,953 tons. It should be noted that in 2014, production was 52,444 tons. Production of roots and tubers fell by about 46%, from 27,163 tons in 2013 to 14,661 tons in 2015. In contrast, fruit production only fell by 5%, ranging between 16,639 and 15,730 tons. The reasons for this decline are unclear. The decline in rainfall (Figure 2), particularly in 2014 and 2017, and the decline in cultivated areas in 2014, 2015 and 2016 (as shown in Figure 8) may have contributed to the decline in production of certain crops (Figure 7). These results contradict the expected outcomes of investments in irrigated agriculture, including increased water availability and widespread use of drip irrigation.

Upon analysis of data on precipitation variation (Figure 2) and production variation (Figure 6 and Figure 8) of the main agricultural products, it becomes evident that there is a direct correlation between precipitation levels and agricultural production. In years with higher precipitation values, there was a corresponding increase in agricultural production, particularly for vegetables and sugarcane. This relationship can be easily discerned, as evidenced by the 1999 case, where prior to that year, there were years of minimal rainfall and low production. The islands of Santiago, Fogo, São Nicolau, and Santo Antão exhibited a notable increase in production this year, a trend that aligns with the precipitation pattern.

As precipitation levels rose, so did production, while a decline in precipitation led to a corresponding decline in production. However, a decline in production was observed beginning in 2015. Various factors may be attributed, including social and economic; for example, the RGA 2015 indicates that the number of individuals engaged in agricultural activities declined by 17.9% between 2004 and 2015, while the total area devoted to agricultural production decreased by 1% over the same period. Another potential factor contributing to this reduction may have been the impact of the global pandemic. In fact, ref. [45] concluded that small family farmers on the islands of Santo Antão and Fogo indicated that mobility restrictions during the quarantine period made it difficult to send products to the country’s largest cities.

In 2000, the area dedicated to irrigated agriculture grew significantly, so this year, the area exceeds 4000 hectares, where there has been an increase in the production of crops such as sugarcane and vegetables. In 2011, the irrigated area exceeded the projected attainable potential of 5000 hectares and has remained at around 5000 hectares in recent years. Based on the RGA 2015 data, it is estimated that the average area of irrigated plots is around 0.5 ha. There has been an expansion in the production areas of sugarcane, which currently occupies the largest irrigated area in Cape Verde, with an area of more than 3000 ha (Figure 8). Since 2000, the production area for tomatoes has increased significantly to over 1000 hectares. However, this area has decreased since 2015 and currently stands at around 550 ha. This situation is worrying, as the decline in tomato cultivation has led to an increase in sugarcane cultivation, as shown in Figure 8. Sugarcane is a non-food crop primarily used to produce spirits.

Regarding the productivity of the main crops grown in irrigated agriculture in Cape Verde, bananas presented the highest productivity, with 18 to 30 t/ha (Figure 9). This productivity has remained relatively constant over the years until 2017, when a decline began to be observed, likely due to the country’s drought years (Figure 2). Between 2017 and 2019, cassava was one of the least productive crops, with a productivity range of around 8 to 12 tons/ha. In contrast, sugarcane and tomato were the two highest-yielding crops, with productivity ranging from about 7 to 22 tons/ha and 9 to 26 tons/ha, respectively, over the period 1987 to 2022 (Figure 9).

Studies depicting the productivity of irrigated crops, for example, ref. [46], determined the average productivity of different crops in two irrigation systems: drip and surface furrow irrigation. In the hot season, the average crop productivity was 1.8 kg/m² in the drip system and 1.2 kg/m² in the conventional system, respectively. The author reports that in the cool season, the average carrot productivity was 1.7 kg/m² in the drip system and 1.0 kg/m² in the traditional system. For tomato crops, the productivity in the drip system was 2.1 kg/m² in the cool season and 2.4 kg/m² in the hot season, while in the traditional system, it was 2.3 kg/m² in the cool season and 2.4 kg/m² in the hot season. It was not possible to identify a plausible justification for the increase in watermelon productivity; perhaps the increase to 60 t/ha in 2019 was due to a data gap, which is why we chose not to include it in Figure 9.

Between 1987 and 2018, carrots remained one of the most productive crops in terms of water use, while lettuce has once again reached high levels in recent years (Figure 10). Banana water productivity was relatively stable, with a slight drop, and cabbage maintained moderate values. Sugarcane showed a sharp reduction in water productivity, unlike tomatoes, which showed significant growth. These data reflect differences in water management between crops over time (Figure 10).

3.3. Characterization of Irrigation Systems

Cape Verde farmers mainly use two irrigation systems: surface furrow irrigation and drip irrigation, as indicated on the Ministry of Agriculture and Environment website [14]. The current adoption rate of drip irrigation is 45%. The objective was to increase this rate to 55% by 2024 [14]. However, so far, there are no statistical data that would allow us to know whether this objective has been achieved. In Cape Verde, traditional surface irrigation is mainly practiced using small, blocked furrows with lengths ranging from 3 to 12 m. Additionally, small basins with an area of 4 to 20 square meters are employed for vegetable and fruit plants, respectively. As the sources of water are springs, wells, and boreholes, in many cases, the water must traverse a considerable distance to reach the plots. It is conveyed in concrete channels, which have recently been substituted by pipelines. There is no study that refers to the flow rate used in this irrigation system in Cape Verde, but based on the data already collected in the field by the authors, it has not yet found a flow rate that exceeds 3 L/s. Due to the slope of the land, terraces need to be built (Figure 11). The furrows and basins are constructed on the terraces, and in many cases, two crops are planted, one at the top of the bed or furrow and the other at the bottom of the basin or furrow (see Figure 10).

Due to its efficiency, drip irrigation is the preferred process for growing vegetables. Because the country has steep slopes and small plots of land, water is typically obtained from boreholes or wells and stored in tanks. The construction of terraces is necessary, but it increases installation costs due to the creation of subunits and the need to purchase additional equipment such as irrigation accessories (e.g., elbows), self-compensation drippers, pressure regulators, and sand filters. However, the topography of the islands can be advantageous, especially for pressure generation in the irrigation system, when the height of the reservoir exceeds the height of the plots.

Drip irrigation has become popular due to its ability to increase water efficiency and water saving; nevertheless, there are significant deficiencies in the operation, maintenance, and management of drip irrigation systems. These problems are due to inadequate hydraulic design and lack of timely maintenance. Ref. [47] found low values for the uniformity coefficient, with only two of the eight subsectors examined being within the 80–90% range recommended for drip irrigation. Irrigation management is empirical, which results in significant water losses. In addition, on Santiago Island, the same author found losses for percolation between 125 and 255 mm/year due to problems in the sizing, management, and maintenance of the irrigation system. The author also reported that in the locality of Achada da Baleia in São Domingos Municipality, about 30 m³ ha⁻¹ d⁻¹ of groundwater is used for drip irrigation, while about 50 m³ ha⁻¹ d⁻¹ is required for surface irrigation. In fact, drip irrigation systems, when well designed and maintained, make it possible to meet crop irrigation requirements with less water consumption by reducing losses through soil evaporation and deep percolation when compared to traditional furrow irrigation systems. Thus, in the context of water scarcity, drip irrigation increases the resilience of irrigated agricultural systems, as it allows for an increase in available water by reducing the losses associated with low application efficiency. Many drip irrigation systems in Cape Verde do not have adequate filtration systems, resulting in poor performance. Previous studies, such as those carried out by [48], have shown high chloride (>2000 mg/L), sodium (>1300 mg/L), and bicarbonate ions, as well as a significant increase in pH (>8.0), highlighting the need for a good filtration system [11]. It is also worth noting that zones of saline intrusion have already been discovered on islands, where water bodies in coastal areas have high levels of chloride and sodium [48]. This is a crucial consideration, as investments in treated wastewater could potentially worsen existing problems in these systems. Regarding research on treated wastewater in Cape Verde, the use of alternative water sources for irrigation is an important new line of research in a region with many limitations in terms of available water resources. In this context, ref. [49] investigated the relationship between various water quality factors and the nutritional value and chemical composition of sorghum. Analysis of the treated water from the Santa Cruz wastewater treatment plant showed pH values of approximately 7.5 and an electrical conductivity of approximately 2970 µs/cm.

According to [46], the cost of water in traditional irrigation systems is 50% higher than in drip systems. However, these costs do not have a significant impact on the overall production costs since the cost of water per cubic meter on the island of Santiago is negligible. This discrepancy is because the cost of water for traditional irrigation is higher than for drip irrigation as a measure to encourage the use of drip irrigation. According to [50], water consumption, in general, represents a residual weight (<5%) in the cost structure of agricultural production. In his study, analyzing the financial profitability of horticultural crops (tomatoes, peppers, and carrots) under drip and surface irrigation systems in the municipality of Santa Cruz in Santiago Islands, ref. [10] concludes that the drip irrigation system resulted in higher production, profitability, and profit for all the three crops. However, to achieve these goals, certain prerequisites are required, such as sufficiently large systems, regular maintenance, and well-managed irrigation. Unfortunately, farmers often overlook these aspects. According to [46], it is not easy to determine whether vegetable yields under the drip irrigation system are superior to those under the traditional irrigation system in Cape Verde growing conditions.

3.4. Challenges in Water Management in Cape Verde and Strategies Adopted to Increase Water Availability and Efficient Water Use

Cape Verde faces serious challenges in managing its water resources due to its arid location and erratic climate. The country has invested in building dams, exploring alternative sources such as desalination, and improving irrigation. However, the effectiveness of these strategies has been limited by several factors. The measures and strategies adopted can be classified into three principal categories: water mobilization, particularly the construction of dams; the pursuit of alternative water sources, notably desalination and treated wastewater; and irrigation management, including the introduction of drip irrigation.

(a)

Mobilization of Water

Cape Verde has invested heavily in irrigation infrastructures, with the prospect of mobilizing 75 million cubic meters of water by 2017, and the previous government set a target of building 17 dams [11]. Currently, the country has nine dams, seven of which are located on the island of Santiago, one on São Nicolau, and another on the island of Santo Antão. Some studies point to water quality problems in dams; for example, ref. [51] concluded that cyanobacteria were the dominant species within the phytoplankton community and that they posed a significant risk, particularly given that the identified taxa have the potential to produce a range of toxins in five dams on the island of Santiago, while [52] observed, in general, in the reservoirs of five dams located on the island of Santiago high pH values (7.4–9.36), sodium (43–131 mg/L Na), chlorides (39.6–169.4 mg/L Cl), and carbonates (121.2–193.2 mg/L CaCO₃). Therefore, this indicates a deficiency in the management of water resources with regard to both quantity and quality.

The main problems have to do with their construction in valleys, usually the best agricultural areas. Given the irregular rainfall, when it does occur, it quickly fills up with solid material transported from higher ground, which drastically reduces the usable capacity of the dams. Ref. [53] carried out a bathymetric survey of the Poilão dam reservoir in March 2013, which pointed to an annual sedimentation rate of close to 90,000 m³/year, meaning that in just seven years, the reservoir’s storage capacity has almost halved. The dam was subject to an intervention in 2019 to partially remove the solid material, restoring part of the exploitable storage volume. Nonetheless, infrastructures for erosion protection would have to be built upstream to help retain this solid material, which is economically unsustainable.

(b)

Alternative Water Sources

The impact of water resource scarcity on the country’s economic development requires the exploration of alternative water sources to reduce the heavy dependence on groundwater and improve its management. Ref. [7] highlights that despite its limitations, water is a crucial factor in Cape Verde’s socio-economic progress. Alternative sources of water, such as the use of treated wastewater and desalination, have been pointed out as an option, especially in recent years, but still, in practical terms, few experiments are using these technologies. Except for desalinated water, water sources depend on rainfall, surface water, and groundwater [54]. In addition to traditional sources of water, alternative water sources such as wastewater and desalination can be utilized to enhance water availability for agriculture. Regarding desalination of water for agriculture, there are experiences in other regions, such as the Canary Islands, where there is a robust commitment to desalination, particularly with reverse osmosis technology, which accounts for 69% of the desalinated water produced [55]. Cape Verde has extensive experience in water desalination for human consumption. Investing in the desalination of water for agriculture using photovoltaic solar energy could be an interesting solution for some areas in Cape Verde.

(c)

Irrigation Management

The challenges of efficient water management will escalate due to climate change, according to the NAP 2021 [56]. As a Small Island Developing State (SIDS), Cape Verde is extremely vulnerable to negative impacts and unpredictable climate. The country has long faced a hostile climate, with climate change exacerbating weather phenomena such as drought and violent coastal storms. The potential impacts of climate change on agricultural production are primarily due to rising temperatures and precipitation reduction. Projections for the region indicate a trend towards higher temperatures (estimated at approximately 0.4 °C from 1990 to 2020) [57], altered precipitation patterns characterized by an overall reduction in rainfall (around 20 to 30%), and an increased frequency of extreme drought events.

Cyclical droughts have been a persistent challenge throughout the country’s history [58,59], with a significant impact on agriculture. Traditional irrigation practices, which are often inefficient, exacerbate these problems. To address this issue, the state has invested heavily in water mobilization and expansion of drip irrigation [46]. Drip irrigation was first introduced in the early 1980s, as noted by Mendes [46]. However, farmers faced obstacles in using this system due to high installation costs and lack of technical support. In addition, the traditional irrigation calendar is not suitable for the drip irrigation system, which would only be possible if small reservoirs were built on farmers’ properties to store water and allow farmers to irrigate more frequently. This increases investment costs, which, according to information collected on the field, has been one of the barriers for some farmers. To overcome this obstacle, a program to support drip irrigation was launched by the government, which finances 50% of the costs of installation, to promote the transfer from surface to localized irrigation [14].

3.5. Foreign Experiences That Can Be Adopted in Cape Verde

To improve water use efficiency (WUE), several practical techniques can be employed, including sustainable irrigation practices, crop-specific agronomic strategies, and innovative technological solutions. These methods enable farmers to enhance water management efficiency, reduce crop vulnerability to water stress, and ultimately, increase agricultural sustainability [60].

For instance, arid and semi-arid regions have adopted more efficient irrigation techniques to enhance water utilization efficiency and boost agricultural productivity. In Mexico, the implementation of modern irrigation methods, such as drip irrigation systems and soil water balance models, has led to more efficient water management and increased agricultural productivity [20]. In Spain, the transition to pressurized irrigation systems, including drip and sprinkler systems, has resulted in a notable improvement in water use efficiency [21]. In the Canary Islands in Spain, implementing subsurface drip irrigation with reclaimed water has enhanced ruminant production sustainability and forage yield, making it profitable for fodder production in the region [22]. Additionally, combining desalinated seawater with other water sources like groundwater and reclaimed water can ensure water and food security, especially in arid regions, by providing crops with adequate mineral nutrients without causing salt ion injuries or toxicity, as demonstrated in banana crop experiments in the Canary Islands [61]. In the semi-arid region of Brazil, innovative approaches, such as the Capillary Underground Irrigation System for Family Farming (SISCAFI), have shown promise in providing sustainable and cost-effective irrigation solutions using recycled materials such as PET bottles and textile waste, contributing to environmental preservation and rural development [62]. In addition, the use of other technologies, such as biodegradable superhydrophobic sand (SHS) as a soil cover, has led to significant reductions in evaporation, increased soil moisture, and better crop yields, as stated by [63].

Adopting similar techniques in Cape Verde could help mitigate water scarcity and increase agricultural sustainability. While the adoption of new irrigation practices and technologies may require additional investments compared to conventional techniques, the resulting water or energy savings and increased crop yields can compensate for the higher initial costs [51]. This underscores the importance of adapting technologies and methods to local conditions and the training and qualification for its use.

3.6. Crop Irrigation Requirements and Water Management

Irrigation requirements depend heavily on annual rainfall. Research has been conducted in Cape Verde to determine irrigation requirements for horticultural crops [47], which estimated net irrigation requirements (NIRs) for the period 1984 to 2008 during extreme and severe drought periods for Santiago Island (see

Table 9. Net irrigation requirements for the main crops produced in Cape Verde under extreme and severe drought conditions [47].

Crops	Climate Demand	Precipitation (mm)	ETP (mm)	NIR (mm)
Carrot	Severe	17.1	365	383
	Extreme	1.9	375	420
Onion	Severe	7.1	829	824
	Extreme	4.3	706	883
Tomato	Severe	7.1	584	564
	Extreme	1.9	544	630
Cassava	Severe	340.0	1048	840
	Extreme	111.0	1057	907
Sweet potato	Severe	156.1	459	380
	Extreme	55.6	523	442
Corn	Severe	0.0	754	728
	Extreme	0.0	757	731
Banana	Severe	524.7	1525	1366
	Extreme	348.0	1440	1500
Peppers	Severe	7.1	521	509
	Extreme	1.9	487	560
Sugarcane	Severe	342.5	1512	1421
	Extreme	304.2	1626	1638

ETP—potential evapotranspiration.

). Moreno [47] defined severe climate demand as corresponding to an 80% probability of seasonal irrigation requirements not being exceeded, while extreme climate demand corresponds to a 95% probability of not being exceeded. Ref. [32] estimated NIR for three precipitation scenarios (scenario 1 = dry year, scenario 2 = average year, and scenario 3 = rainy year) for the island of São Nicolau (

Table 10. Net irrigation requirements for the main horticultural crops in São Nicolau [32].

Crops	Climate Scenarios	NIR (mm)
Banana	Dry year	950
	Average year	1045
	Rainy year	1061
Onion	Dry year	678
	Average year	660
	Rainy year	678
Cabbage	Dry year	391
	Average year	410
	Rainy year	380
Potato	Dry year	518
	Average year	528
	Rainy year	488
Carrot	Dry year	440
	Average year	406
	Rainy year	335
Tomato	Dry year	517
	Average year	420
	Rainy year	312
Lettuce	Dry year	225
	Average year	207
	Rainy year	208
Sweet potato	Dry year	655
	Average year	605
	Rainy year	595

).

These studies estimate the amount that needs to be supplied to different crops depending on the availability of precipitation. Years with higher rainfall are years with lower water demand for irrigation and vice versa, which poses a challenge for irrigation management because the years with the highest irrigation demand are also the years with the lowest water availability (Table 9 and Table 10).

Due to their longer development cycles, bananas and sugarcane require more water compared to other crops, especially vegetables. In fact, sugarcane has a higher NIR than horticultural crops, as shown in Table 9. In severe drought, the NIR of the sugarcane is approximately 1400 mm, while in extreme drought, it is approximately 1600 mm. This raises concerns about the sustainability of irrigation areas during periods of low rainfall. On the other hand, sugarcane raises food sovereignty concerns as it is a non-food crop, and the country has limited water and land resources. However, sugarcane has proven to be a lucrative crop for farmers.

From the perspective of sustainable water resources management in agriculture, it is evident that the option of increasing the area dedicated to sugarcane cultivation has been a visible trend in recent years. This is illustrated by Figure 8, which depicts the evolution of the irrigated agriculture area dedicated to sugarcane cultivation, which reached approximately 62% in 2022.

4. Conclusions

It has been confirmed by this study that irrigated agriculture plays a fundamental role in sustaining agricultural production and food security in Cape Verde. The cultivation of vegetables and sugarcane would not be viable under rainfed conditions, given the country’s prevailing arid and semi-arid climate.

However, several significant challenges persist, notably water scarcity, the increasing variability of climatic conditions, and the low operational efficiency of irrigation systems. Available evidence indicates that surface irrigation methods consume approximately 20 m³/ha/day more water than drip irrigation. While drip systems are theoretically more efficient, their performance in Cape Verde is undermined by design flaws, lack of regular maintenance, and limited technical capacity among users.

The analysis of irrigation systems—namely furrow and drip irrigation—highlights the need for investment in infrastructure and the strengthening of irrigation management. Improvements in design, operation, and maintenance must be supported by farmer training programs and institutional technical assistance to ensure efficient water use and reduce operational losses.

The crop-based analysis further emphasizes the importance of irrigation planning and crop selection, especially during dry years. A noteworthy concern is the growing dominance of sugarcane cultivation, which accounted for 62% of irrigated land in 2022. Although economically motivated by its use in traditional beverage production (grogue), sugarcane requires between 1400 and 1600 mm of water annually, significantly more than horticultural crops. This trend raises concerns regarding the long-term sustainability of water use and its implications for national food security.

In addition, there has been insufficient investment in dam desilting, water distribution infrastructure, and overall water system modernization. While successive governments have prioritized water mobilization through the construction of dams and boreholes, these initiatives must now be complemented by sustained investment, improved governance, and technical capacity development to address both current inefficiencies and future climatic risks.

To enhance the sustainability of irrigated agriculture in Cape Verde, namely to optimize water use, improve agricultural performance, and secure food systems under increasing water constraints, it is essential to (i) promote technically sound and well-maintained irrigation systems, (ii) prioritize crops with high water productivity and strategic food security value, (iii) expand access to training and capacity building for farmers and irrigation managers, and (iv) integrate irrigation management with climate adaptation strategies, especially in arid and semi-arid agroclimatic zones.