In the general context of global climate changes, the agricultural sector seems to be one of the most severely affected. The vast majority of previously developed studies indicated important impacts of climate changes on different crops, especially in developing countries [1
]. Under these changing conditions, the geographical position and local factors of an area are expected to have a crucial impact on agriculture, based on the current climatic characteristics, soil properties, resources of the area, existing infrastructure, and direction of change [5
One of the main elements for ensuring sustainable agriculture is agricultural land suitability analysis for various crops’ production. At the international level, some studies specifically focused on land suitability analysis for agriculture and on the impact of climate change on future land suitability [1
]. Agricultural land is facing enormous pressure from global environmental changes including climate change [7
], land degradation, and rapid urbanization [8
], as well as population growth [9
]. Among the processes of land use planning, land suitability analysis is a crucial factor [11
] and is a precondition to achieve optimal land use resource exploitation [12
Over the last decades, a significant decline in global wheat (−4.9%) and maize (−3.1%) production was attributed to temperature increases in cropping regions and during growing seasons in most countries [13
]. The extreme variations of temperatures during the growing season, induced by climate change, have an important impact on the global production of maize, wheat, and barley, placing additional stress on crops [14
]. Understanding all aspects related to the impact of climate change on land use and identifying suitable agro-ecological zones are factors essential to improving production [16
Suitable areas for some important crop cultivation will shift as a direct result of climate change [6
]. Agro-climatic suitability is a subsection of land suitability analysis that uses various agricultural indicators to assess the most appropriate land use for a specific location. Usually, this approach includes temperature and precipitation as base parameters from which many other indicators can be derived to assess the agro-climatic suitability of a given crop [20
Depending on the crops considered, the commonly used climatic factors for land suitability analysis are: potential and actual evapotranspiration [21
], aridity index [17
], diurnal temperatures [22
], growing degree days [17
], length of the growing season [25
], length of the different phenological stages [28
], relative humidity [29
], solar radiation [28
], sunshine hours [31
], temperature/precipitation [24
], and winds [32
Under present and future climate change conditions, at the European level, in the Post-2020 Common Agriculture Policy, three out of the nine policy’s specific objectives concern the environment and climate, and one aims to contribute to climate change mitigation and adaptation [34
]. In addition, the Common Agricultural Policy and EU Adaptation Strategy suggest for each member state to delineate the suitability for crop growth. Investigating this issue, we did not identify any online report made available by the member states. The only service freely available was that developed by the Joint Research Centre: Agri4Cast Resources Portal (https://agri4cast.jrc.ec.europa.eu/DataPortal
). The indices calculated have been derived from weather stations’ meteorological parameters interpolated on a daily basis from 1975 to the last calendar year completed.
In Romania, previous studies approached the subject of changes and trends in maize production [37
], as well as the impact of climate change on agricultural crops and several cultivar adaptations, using a limited number of factors [38
]. A good practices resource book in the climate change context [39
] and an official catalog of crop cultivars [40
] were also released as a part of the national agriculture development strategy. Simulation models of the climatic factors variations were used for Cluj County [41
], in which a good correlation between climate change and maize yields based on point data analysis for Romania was recently detected [42
A paper focused on the impact of climate change in winter wheat phenology in Romania [43
] revealed earlier occurrences of anthesis and maturity for several regions of the country. The effect of temperature changes on winter wheat phenology was determined using a phenology simulation performed with the model from the Decision Support System for Agrotechnology Transfer v. 188.8.131.52 Platform. The study was developed by using climatic observation data recorded in 10 points randomly distributed across Romania. Some other studies focused on extreme temperature and precipitation events, including those with impacts on agriculture, as well as on aridity indices and reference evapotranspiration [44
]. All previous studies were developed based on point observation and most of them revealed important changes in the analyzed indices over the historical period or in the near future. None of them considered gridded data.
The main aim of this paper was to detect changes in temperature requirements based on two agro-climatic indices (growing season length—GSL and growing degree days—GDDgrow), as well as in the area of different agro-climatic suitability conditions for the maize crop in a complex topographic region, based on gridded data, by comparing the results derived from two databases with different spatial resolution. We aimed to redefine the thermal agro-climatic suitability areas for maize, under present climate change conditions, based on a better spatial resolution compared to the existing one at the European level and made freely available by the Joint Research Centre: Agri4Cast Resources Portal (https://agri4cast.jrc.ec.europa.eu/DataPortal
). The products provided by the JRC platform were derived from meteorological parameters from weather stations interpolated on a 25 × 25 km grid, which in our opinion can be questionable for regions with complex topography characterized by important changes in temperature conditions due to elevation and exposure over short distances. Under these circumstances, we developed a comparative study between the suitability zones based on the gridded data available at the European level and those available for Romania (ROCADA database) [50
], which is about 5 times more sensitive in terms of spatial resolution. This is the first agro-climatic study developed for a European region based on gridded data at a better spatial resolution than 25 km × 25 km.
We chose for this study the maize (Zea mays
L.) crop since it is one of the main crops in the considered region and covers 35.52% of the agricultural area of the county [51
]. The methodology proposed by our study can be replicated for any other crop and for any region in Europe or worldwide.
Previous studies [77
] have documented the agro-climatic regions in Romania using traditional methods involving general information (classical mapping techniques derived from direct terrain observation data) and applied to natural features (climate, topography, and hydrology) with limitations in terms of ground spatial resolution and accuracy. The methodology proposed in the present study provided an accurate and rapid solution, assessing the thermal conditions of the arable land based on geospatial analyses.
In the general context of global climate change, research-based decisions of the authorities and stakeholders in agriculture are very important, since switching to an early maturity hybrid before the switching window will most likely not be beneficial, and may even reduce profitability. Persevering with a full season or mid-maturity hybrid after the switching window will most likely result in reduced profitability, too [79
]. As we demonstrated, employing a coarse spatial resolution in regions with complex topography would cause big errors in agro-climatic conditions identification by overestimating better conditions, which could lead to significant losses. Under these circumstances, when using agro-ecological conditions derived from low-resolution data, especially in regions with complex topography, the stakeholders should be very cautious. This study, in its present form, could become an important tool for local farmers in order to adopt the most appropriate measures to increase their profitability by choosing hybrids according to the switching window for suitable conditions, following examples from other regions of the world (e.g., USA) [79
Even more importantly, this study could serve as a good starting point for a model developed for much larger regions affected by climate change as part of their adaptation strategy towards a smarter and more sustainable agriculture [80
]. As expert-knowledge analysis was identified as the major limitation of the models [83
], we consider that our results could greatly contribute to adapting an existing agro-climatic suitability model or to developing a new one at a better spatial resolution, especially for other regions with complex topography, by including a large variety of climatic (precipitation, evapotranspiration) and non-climatic (soil type, slope gradient and aspect) parameters (overlapping more layers), in order to avoid growing season constraints and to determine phenophase-specific climate sensitivities [28
], as well as to achieve realistic site-specific results and a higher efficiency of resource use in agricultural ecosystems [88
Since our focus area covered a large variety of topography used for agriculture, ranging from low to high altitude, the results could be of interest to agriculture scientists and stakeholders in other regions of Europe or from other continents characterized by complex topography. This paper aimed not only to reassess the suitability zones under the impact of climate change, particularly temperature-based indices on maize crops from a new perspective, but also to prove that increasing accuracy, by using a much better spatial resolution compared to that existing at a European level, leads to a better evaluation of the agro-climatic conditions, especially in regions with complex topography. Furthermore, the results can be employed to forecast and reassemble the suitability areas that are extremely important for agriculture and the economy. For all the stakeholders involved in crop production, the potential yield of maize is directly connected to the length of the growing season (GSL) and to the accumulated temperature during GSL (GDDgrow). It is of major economic importance that a scientific argument based on agro-climatic indicators must be the main starting point for repositioning the suitability areas.
The main purpose of the work was to justify scientifically that, at a regional level, using a better spatial resolution for identification of agro-climatic conditions for maize crops could be of crucial importance. Using a coarse spatial resolution in regions with complex topography could dramatically influence the quality of the results on agro-climatic conditions (overestimation for up to 16% of the total area considered, included in a better suitability zone), leading to important damage derived from a decrease in productivity as a result of choosing inappropriate hybrids. The proposed methodology, focused on the improvement of the spatial resolution, which can be replicated for any other region in Europe or worldwide (but especially in an area with complex topography), could be extremely important in order to get high-quality results in the general context of sustainable, smart-oriented, and scientifically-based agriculture.
Secondly, our results indicated that, despite the almost general impact of climate change on agriculture reported so far, for some regions (like Cluj County) it led to a switch towards better suitability conditions for maize crops. Even though no important changes were identified in the GSL, the conditions for maize crops became more suitable due to the significant increase of GDDgrow, which was detected for the entire arable land area of the county. Thus, suitability zone I, which did not exist until 1990 (based on mean decadal values), became dominant during the sub-period 2001–2013. Our study proves that due to climate change, the areas of suitability considerably changed and current climatic conditions allow for temperate regions to support all the range of maize hybrids. Under these changing conditions, in approximately the same number of days, a higher temperature is cumulated and can be used by crops, allowing us to conclude that a switch of hybrids can be made in the focus area. Moreover, our model allowed identification of the thermal requirements for maize crops for each hybrid type at a spatial resolution of 11 km x 11 km, which is also good enough to produce a high sensitivity model for future development of forecasting.
Based on the results of this research and to meet the stakeholders’ needs, especially those of the maize growers, we can conclude that further analysis is needed to investigate this topic in more detail. This should focus on:
Extending the study to larger regions such as Romania as a whole or the entire PannEx region [90
] in order to re-assess the agro-thermal conditions by including the requirements for each pheno-phase;
Developing the model by including other types of data (e.g., precipitation and soil) over the same historical period, as well as over the coming decades (2021–2050) based on Regional Climate Models output data.
Since critical hybrid switching decisions should be based on long-term research covering a wide range of climatic conditions [79
], we consider that the results of this study could become an extremely important tool for stakeholders in the agriculture field (agriculture scientists, farmers, seed sellers, etc.) and for the public authorities in Cluj County in order to improve the productivity of the maize crops, primarily, and to design a new development strategy for a smart and sustainable climate change-oriented agriculture.