Assessing the adaptive capacity of durum wheat cultivars to future climate

The perspective of climate change requires an analysis of the adaptation possibilities of species currently cultivated. A powerful tool for adaptation is the relevant intra-specific biodiversity of crops. The knowledge, for different crop cultivars, of the responses to different environmental conditions (e.g. yield response functions to water regime) can be a tool to identify adaptation options to future climate. Moreover climate scenario needs to be downscaled to the spatial scale relevant to crop and farm management. Distributed models of crop response to environmental forcing might be used for this purpose, but severely constrained by the very scarce knowledge on variety-specific values of model parameters, thus limiting the potential exploitation of intra-specific biodiversity towards adaptation. We have developed an approach towards this objective that relies on two complementary elements: A) database on climatic requirements of durum wheat varieties: the yield response functions to water availability were determined from scientific literature. These functions were applied to describe the behaviour of the cultivars with respect to the soil water availability; B) the simulation performed by the agro-hydrological model SWAP (soil-water-plant and atmosphere), to determine the future soil water regime at landscape scale. The case-study presented here shows how the yield response of durum wheat cultivars to soil water availability can be defined by means of variety-specific threshold values of soil water (or evapotranspiration) deficit. The soil water regime calculated by the distributed model is compared with the threshold values to identify varieties compatible with expected climate. The operation is repeated for a set of realizations of each climate scenario. This analysis is performed in a distributed manner, i.e. using the time series for each model grid to assess possible variations in the extent and spatial distribution of cultivated area of durum wheat cultivars. The selected study area is a hilly region of about 40,000 ha in Southern Italy (Fortore Beneventano, Campania Region), characterized by a complex geomorphology including clayey and marl flysch hills and highlands, narrow alluvial planes, and small sandstone relieves. Future climate scenarios in the area were generated within the Italian National Project AGROSCENARI. Climate scenarios at low spatial resolution generated with general circulation models (AOGCM) were down-scaled by means of a statistical model (Tomozeiu et al., 2007). The downscaled climate scenario includes 50 realizations of daily minimum, maximum temperature and precipitation data, on a regular grid with a spatial resolution of 35 km, for the 2021-2050 period. The downscaled climate scenario was further refined by using the distributed model which describes the soil water regime in four soil systems units. Spatial pattern of soil water and evapotranspiration deficit was determined for the 50 realizations of the daily time series, taking into account the four soil systems, and was compared with threshold values to evaluate cultivars' adaptation options to the foreseen future climate. The case study shows how, in the future climate scenario, the intra-specific variability will allow to maintain current crop production system.