Assessing irrigated crops' adaptability under future climate: the interplay of water management and cultivars' responses

The effect of climate evolution on the sustainability of irrigated agricultural systems willbe site-specific depending on: (i) resource availability, (ii) crops' water requirements, (iii)soil hydrological behavior and (iv) irrigation management strategies.In an irrigated district of Southern Italy, for two field crops (maize and tomato), we haveevaluated various irrigation scheduling options in different climate scenarios, and wehave assessed the adaptability of many cultivars.We have first estimated the yield response to water of several maize and tomatocultivars. Next, to identify options for adaptation, we have evaluated the compatibility ofsuch responses with indicators of soil water availability, with different irrigationstrategies, for a reference (current) and future climate. This compatibility assessmentwas done for each soil unit within the study area. The derived spatial and temporalvariations of soil water regime and adaptability were studied.Two climate scenarios were considered: reference (1961-90) and future (2021-2050)climate, the former from climatic statistics, and the latter from statistical downscaling ofgeneral circulation models (AOGCM). Climatic data consist of daily time series ofmaximum and minimum temperature, and daily rainfall on a grid with a spatialresolution of 35 km.The work was carried out in the Destra Sele irrigation scheme (22.000 ha). Twenty-fivesoil units were identified and their hydrological properties were determined (measuredor estimated from HYPRES pedo-transfer functions). Upper boundary conditions werederived from the two climate scenarios. Maize and tomato crops (in the rotations typicalof the area) were considered.A mechanistic model of water flow in the soil-plant-atmosphere system (SWAP) wasused to describe the hydrological conditions in response to climate and irrigation. Themodel was calibrated and validated in the same area for many different crops. Cropspecificinput data and model parameters were estimated on the basis of localexperiments and of scientific literature and assumed to be generically representative ofthe species.Simulations were performed for reference and future climate, and for different irrigationscheduling options. In all soil units, a set of irrigation scheduling volumes was applied:from full to no irrigation, through different levels of deficit irrigation. From simulationruns, indicators of soil water availability were calculated; moreover the marginalincreases of transpiration per unit of irrigation volume (?T/I) were computed, in bothclimate scenarios. Indicators and marginal increases were used to evaluate crops'adaptability to future climate.To this purpose, for several maize hybrids and tomato cultivars, yield responsefunctions to soil water availability were determined (data from scientific literature andexperiments). Cultivars' response functions were evaluated, in all soil units, against theindicators' values, for irrigation levels with different ?T/I.Less water intensive cultivars and irrigation volumes that optimize transpiration (andyield) could thus be identified in both climate scenarios, and irrigation managementscenarios were determined taking into account soils' hydrological properties, cropbiodiversity, and efficient use of water resource.The results have shown the spatial patterns of soil water regime, that were stronglyinfluenced by soils' characteristics. Moreover the case study has shown how, in thefuture climate scenario, with limited water resources, the intra-specific biodiversity willallow to maintain current crop production system.