A new approach in monitoring regional water use efficiency in response to climate variability: a case study in Hungary

This study develops and evaluates a biomass soil moisture index (NWUESM) for determining water use efficiency (WUE) that is less expensive and simplier to compute than the standard regional WUE indicator (RWUEEC). The research uses a section of the Tisza-Körös valley irrigation system region (TIKEVIR) in northeastern Hungary as a case study site. NWUESM is computed as a ratio of Normalized Difference Vegetation Index (NDVI) to volumetric soil moisture content at 30cm and 60cm soil depths respectively and actual regional WUE (RWUEEC) as a ratio of Gross primary productivity (GPP) to actual evapotranspiration (ET). NWUESM (30 cm) and NWUESM (60 cm) showed consistent positive correlation and alignment with RWUEEC trends over time with however NWUESM (60 cm) demonstrating superior accuracy compared to NWUESM (30 cm) as a proxy for computing and predicting RWUEEC. Correlation between RWUEEC and predicted regional WUE (RWUEEC Pred) at 60cm yielded higher R 2 values of 0.9956 for 2018, 0.9486 for 2020, and 0.9452 for 2022 with lower RMSE of 0.038 for 2018, 0.0686 for 2020, and 0.0576 for 2022. In contrast, the correlation between RWUEEC Pred at 30cm and RWUEEC yielded R 2 values of 0.9817 for 2018, 0.9333 for 2020, and 0.761 for 2022, with RMSE values of 0.0777 for 2018, 0.0782 for 2020, and 0.2529 for 2022 respectively. Water productivity peaked around June and July in the test area reflecting optimal growing conditions for crops and thus water through irrigation should reach 60 cm depth due to soil moisture stability. • Newly developed index links biomass and soil data to assess water use efficiency • The index aligns closely with the actual water use efficiency seasonal fluctuations • The new index enables scalable monitoring of agricultural water use • Facilitates real-time crop water use monitoring for irrigation scheduling