Climate change in Guadiana river basin and its impacts on crop water demand

This study evaluates climate change tendencies over several climatic parameters observed in the Guadiana river basin, south Portugal and its potential impacts on crop water and irrigation requirements. Parameters analyzed were annual rainfall and its seasonal distribution, temperature and evapotranspiration, collected from available regional meteorological data from a 46-year period (1963-2009). The impacts of climate change in Guadiana basin’s irrigated crops was studied running long-term soil water balance simulations to evaluate the trend of irrigation water requirements considering maximum potential yield. The simulations were focused on a set of locally representative crops including wheat, maize, olive trees, vineyards and citrus. Climate data analysis showed an increase in average annual air temperature, and declining annual rainfall, with an increasing irregularity in monthly rainfall distribution. As a consequence of climate change, estimated crop irrigation requirements simulated in the considered period illustrate a rising tendency pattern, although different statistical significance was found amongst crops. Out of the studied crops, those with a typical high water demand, such as maize, and crops depending more directly on soil water content accumulated from rainfall during the winter season, such as wheat, both show a more significant tendency to increase their irrigation demands, while crops well adapted to the Mediterranean climate, such as olive trees, remained more conservative in their future irrigation water demands