Hydrological impacts of enhanced irrigation under drought conditions in Europe

Anthropogenic climate change is expected to pose significant challenges for European agriculture. Rising temperatures, altered precipitation patterns, and increasing frequency and intensity of extreme weather events, including prolonged and intensified droughts, are projected to substantially increase irrigation water demands. To date, a large fraction of European croplands relies solely on rainfed cultivation. Consequently, the projected increase in drought conditions will likely require an expansion of irrigated areas to mitigate climate-induced yield losses.

This study examines the hydrological impacts of enhanced irrigation across Europe with a particular focus on river discharge, using the Community Water Model (CWatM) at 5′ resolution. CWatM is a large-scale water resources model that simulates precipitation–runoff processes with river routing, capturing both natural hydrological processes and anthropogenic water demands. Its integrated approach provides a unique opportunity to investigate not only impacts of climate change but also impacts arising from the expected increase in irrigation water demand.

The model was calibrated and validated against GRDC discharge data using a regionalized calibration approach. Six irrigation scenarios, representing a stepwise transition from rainfed to irrigated cropland, were implemented in CWatM and simulated for the exceptionally hot and dry summers of 2003 and 2018, which may be considered representative of future summer conditions under climate change.

Simulation results indicate that even a moderate expansion of irrigated areas (converting 10 % of currently rainfed cropland to irrigated cropland) could lead to a substantial increase in unmet water demands and a significant reduction in summer river flows. Rivers in Central and Eastern Europe (e.g., Loire, Rhine, Elbe, Oder, Danube) with agriculturally dominated river basins are particularly affected. For the years 2003 and 2018, summer discharges of these rivers are already below the interquartile range of the 30-year average (1990-2019) under the default scenario (i.e., without additional irrigation); and decline even markedly further under irrigation expansion scenarios. These severely reduced summer low flows pose significant risks to river ecosystems and long-term river resilience. Simulations further revealed that reductions in river discharge are largely independent of the source of water abstraction (groundwater or surface waters), which is likely related to the fact that baseflow from groundwater reservoirs is one of the most important sources of river water during dry periods.

The results highlight the importance of effective water management adaptation strategies in intensively farmed regions of Central and Eastern Europe to prevent future water scarcity and to reduce the ecological risks associated with increasingly severe and prolonged low-flow periods.