A remote sensing approach to estimating crop water needs in Mediterranean basins with data scarcity issues

Irrigated agriculture is a major contributor to global groundwater use, and can sometimes lead to the overexploitation of aquifers. The Requena-Utiel, Campina de Faro and Ain Timguenay aquifers in Spain, Portugal and Morocco, respectively, are facing such a situation, with excessive pumping raising concerns about the aquifer's water levels and the long-term health of the groundwater body. Accurate estimation and remote monitoring of crop water needs are crucial for effectively managing the limited water resources in the region by providing farmers with accurate recommendations on water use.

The eGROUNDWATER project aims to address this issue by applying a water balance method based on Vegetation Index data of croplands. The method uses the Fractional Vegetation Cover (FVC) to estimate bare soil evaporation and vegetation transpiration, agro-climatic data and optical data (CopernicusESA/EROS-USGS). Potential evapotranspiration was calculated using the FAO method. The result of this process was a model for determining the irrigation water needs of crops within the region that allows researchers to differentiate stressed and over-irrigated areas with a high degree of precision.

The model was developed for the Spanish case study and was successfully applied to the Moroccan and Portuguese cases, where data scarcity at the local scale is also an issue. Remote sensing allows for more accurate detection of crop water needs, enabling the alignment of water requirements and agricultural demands. Although evapotranspiration estimates based on remote sensing may be subject to bias, these biases can be identified and corrected using reliable ground data. If daily images are not available, it is possible to upscale daily evapotranspiration estimates to seasonal or annual estimates. At the end, annual crop water needs can be modeled using a yearly map of irrigated areas, which is helpful for planning and managing water resources at the plot scale.

In conclusion, this research has shown that remote sensing can be a valuable tool for accurately estimating and monitoring crop water needs and for improving water resource management in three Mediterranean regions. By using the described methods, it is possible to align water use with agricultural demands more effectively and to ensure sustainable use of the aquifer's limited resources.

Acknowledgements:

This study has received funding from the eGROUNDWATER project (GA n. 1921) a project from the PRIMA programme, supported by Horizon 2020, the European Union's Framework Programme for Research and Innovation.