A spatiotemporal analysis of irrigation water requirements in French croplands over the past decades

France is the first agricultural producer and the third most irrigated country in terms of surface area in the European Union. Agriculture weighs heavily on French water resources dynamics as it features the highest water consumptive use (i.e., most of the water applied on irrigated areas is evaporated and unavailable downstream). Water withdrawals for irrigated agriculture are usually quantified through modelling at catchment scale because direct measurements are incomplete. Models can conceptualise water withdrawals as a modulation of crop irrigation requirements (i.e., water added to rainfall to compensate crop evapotranspiration and alleviate water stress) by water availability and irrigation management constraints (e.g., yield objective, irrigation technology efficiency). Establishing these models over a large sample of catchments is challenging because this requires a large range of data at different spatial scales (plot, farm, catchment).

As a first step towards assessing water withdrawals, this study investigates the spatiotemporal dynamics of monthly irrigation water requirements at catchment scale over the past decades in France. It also evaluates the contribution of climate variability (e.g., precipitation, temperature) and changes in cropland characteristics (e.g., area, crop type) to irrigation water requirement trends. Using the soil-crop water balance models CROPWAT and Optirrig (Cheviron et al. 2020), we compute irrigation water requirements over irrigated area and total cropland to approximate the agricultural water usage and quantify the crop water deficit. We build gridded yearly maps of irrigated and cropland area in France by combining statistics at the district (“département”) level and remote sensing derived products like land cover maps. Using different models and parameter values (e.g., sowing dates, crop coefficients) enables structural and parametric uncertainty quantification. Our results show that, in spite of uncertainties, the increase and the distribution of irrigation water requirements follow the rise and expansion of irrigated area in France, while crop water deficit is highly driven by climate variability.

References:
Cheviron, Bruno, Claire Serra-Wittling, Magalie Delmas, Gilles Belaud, Bruno Molle, et Juan-David Dominguez-Bohorquez. 2020. « Irrigation Efficiency and Optimization: The Optirrig Model ». doi:10.5194/egusphere-egu2020-20547.