Assessing the Suitability of Evapotranspiration Products and Surface Energy Balance Estimates in the Semi-Arid Gundar River Basin, South India

The semi-arid Gundar River Basin in South India is home to around two million people. Agriculture remains central to sustaining livelihoods in this region, and competition for water resources has intensified over the years owing to factors such as variability in monsoon precipitation, shifting agricultural practices, and migration to urban areas. The landscape is dotted with centuries old water storage tanks (reservoirs) built to collect runoff and recharge groundwater, and the hydrology of the region is further complicated by the widespread presence of Prosopis juliflora, a water consuming invasive species that increases competition for water. With evapotranspiration (ET) accounting for up to 60% of the water outflux in semi-arid regions, there is a pressing need to quantify ET in this region to support improved water and resource management.

The region lacks ET monitoring networks, is highly heterogeneous, and requires the use of satellite datasets and climate data products to understand catchment scale ET behaviour and its evolution over time. This study aims to intercompare ET derived from SEB methods: SEBAL (novel estimates generated using Landsat data) and METRIC (through the EEFlux product), both available at 30m resolution with global ET products such as MOD16 and GLEAM at the basin scale between 2010 and 2020. ET estimates will be aggregated to a common spatial scale, stratified using NDVI classes, and analyzed according to the study’s objectives: (1) examining consistency among datasets across different seasons, (2) investigating interannual variability using the correlation coefficient (r), root mean squared error (RMSE), anomaly assessment, and (3) assessing long term ET trends using the Mann–Kendall test and detecting breakpoints with Pettitt’s test given the basin’s recent history of frequent droughts. Physical consistency will be evaluated using reference ETo estimates, enabling an assessment of the utility of the various ET methods applied in this unique hydrological setting with significant implications for local livelihoods.