Satellite-derived irrigation water requirement as a support tool for climate-resilient water management in the Alps

Water scarcity is increasingly emerging as a critical issue even in traditionally water-abundant regions such as the European Alps. The coexistence of multiple end users - often characterized by competing and sometimes conflicting demands, ranging from aquatic ecosystem conservation to hydropower generation - renders water management one of the most pressing socio-economic and environmental challenges in mountain catchments. Although irrigation represents the third-highest priority water use after drinking and sanitation, the volumes required and actually withdrawn for agricultural purposes remain poorly constrained in mountain environments. This knowledge gap stems from a combination of factors, including technical limitations, pronounced spatial fragmentation, and historically rooted governance. Improving the estimation of irrigation water requirements is therefore a key step toward a more informed, efficient, and climate-resilient management of water resources.

Here, we present an approach for estimating irrigation water requirements (IWR) based on Sentinel-2–derived NDVI, coupled with spatially explicit meteorological drivers, namely air temperature, precipitation, and potential evapotranspiration. Daily IWR maps at 20 m spatial resolution are produced for the Aosta Valley, an inner-Alpine valley of approximately 3,200 km² located in the western Italian Alps, covering the period 2018–2025. The analysis focuses in particular on dry years (e.g. 2022), for which anomalies are computed at multiple spatial and temporal scales in order to investigate the different dimensions of drought severity in a topographically complex setting.

A more detailed analysis is conducted for a ~81 km² sub-basin, where the coexistence of multiple surface-water uses frequently leads to substantial river depletion during the summer season. In this basin, a set of discharge measurements enables the quantification of water withdrawals for both irrigation and hydropower production, thereby allowing a quantitative assessment of the relationship between estimated water requirements and actual water use. We show that, through the optimization of water allocation strategies, the risk of water scarcity can be substantially mitigated even during exceptionally dry summers such as 2022.

Wall-to-wall products such as those presented here, characterized by adequate spatial and temporal resolution, further provide a valuable basis for planning the location, design, and sizing of multi-purpose water storage reservoirs in hydrologically critical areas.