Validation of seven global remotely sensed ET products across Thailand using water balance measurements and land use classifications

Study region: Annual and monthly ET values from seven global remote sensing products (ALEXI, CMRSET, ETMonitor, GLEAM V3.3b, MOD16A2, SEBS V3 and SSEBop) were validated for 172 sub-basins in Thailand. Study focus: This study describes a generalised validation procedure that uses rainfall (P), streamflow (Q) and storage change data (from the Gravity Recovery and Climate Experiment - TWSCGRACE) and land use information. For each sub-basin, bulk ET was computed using the water balance framework and compared to estimates by ET products. Inverse water balance computations were applied to infer the storage change estimates from each product (ΔS = P – Q - ETRS), which were compared to TWSCGRACE to assess their monthly scale performances. New hydrological insights for the region under study: All products performed very well on the annual basis (mean NSE > 0.96) and satisfactorily on the monthly scale (mean NSE > 0.65). Land use classifications from the Land Development Department were used to examine the ability of four candidates (CMRSET, MOD16A2, GLEAM V3.3b and ETMonitor) to provide ET estimates with correspondence to physical land use conditions. By also considering product resolutions and data accessibility, MOD16A2 was consensually shown to be the most promising product to be used for water resources management in Thailand. In addition to local applications, the outcomes emanate the potential for utilisation on the global scale which should be further investigated.