Projection of irrigation water demand based on the simulation of synthetic crop coefficients and climate change

Abstract. In a context of major changes (climate, demography, economy, etc.), the Southern Mediterranean area faces serious challenges with intrinsically low, irregular and continuously decreasing water resources. In some regions, the proper dynamic of irrigated areas is very important so that it is needed to include it in future scenarios. A method for estimating the future evolution of irrigation water requirements is proposed and tested in the Tensift watershed, Morocco. Monthly synthetic crop coefficients (K_c) of the different irrigated areas were obtained from a time series of remote sensing observations. An empirical model using the synthetic K_c and rainfall was developed and fitted to the actual data. The model appears to be reliable with an average r² of 0.69 for the observation period (2000–2016). The sub sampling tests suggested that a loss of performance (r² = 0.45) is to be expected for two time periods after the observations (2050). This flexible system of equations has been used to reinterpret a local water management plan and to incorporate two downscaled climate change scenarios (RCP4.5 and RCP8.5). The examination of irrigation water requirements until 2050 revealed that the difference between the two climate scenarios was very small (< 2 %), while the two agricultural scenarios were strongly contrasted both spatially and in terms of their impact on water resources. The approach is generic and can be refined by incorporating irrigation efficiencies.