Annual evapotranspiration retrieved solely from satellites' vegetation indices for the Eastern Mediterranean

Abstract

We present a simple model to retrieve actual evapotranspiration (ET) solely from satellites (PaVI-E). The model is based on empirical relationships between vegetation indices (NDVI and EVI from MODIS) and total annual ET (ET Annual) from 16 FLUXNET sites representing a wide range of plant functional types and ET Annual. The model was applied separately for (a) annual vegetation systems (i.e., croplands and grasslands) and (b) systems with combined annual and perennial vegetation (i.e., woodlands, forests, savannah and shrublands). It explained most of the variance in ET Annual in those systems (71% for annuals, and 88% for combined annuals and perennials systems) while multiple regression and modified Temperature and Greenness models using also land surface temperature did not improve its performance ( p 0.1). PaVI-E was used to retrieve ET Annual at 250 m spatial resolution for the Eastern Mediterranean from 2000 to 2014. Models' estimates were highly correlated ( R = 0.92, p < 0.01) with ET Annual calculated from water catchments balances along rainfall gradient in the Eastern Mediterranean. They were also comparable to the coarser resolution ET products of MSG (LSA-SAF MSG ETa, 3.1 km) and MODIS (MOD16, 1 km) at 148 Eastern Mediterranean basins with correlation coefficients ( R) of 0.75 and 0.77 and relative bias of 5.2 and −5.2%, respectively ( p < 0.001 for both). The proposed model is expected to contribute to hydrological study in the Eastern Mediterranean assisting in water resource management, which is one of the most valuable resources of this region.