Evapotranspiration Climatology of Indiana, USA Using In-Situ and Remotely Sensed Products

Abstract

An inter-comparison of multi-resolution evapotranspiration (ET) datasets with reference to ground-based measurements for the development of regional reference (ETref) and actual (ETa) evapotranspiration maps over Indiana, USA, is presented. A representative ETref equation for the is identified by comparing against ten years of in-situ measurements (2009-2019). A statewide ETref climatology is developed using the ETref equation and high-resolution, surface meteorological data from gridMET. For ETa analyses, MODIS, SSEBop, GLEAM (3.3a and 3.3b versions), and NLDAS (Noah and VIC) datasets are evaluated using AmeriFlux data. Thirty years of rainfall data from CHIRPS is used with the ET datasets to develop effective precipitation fields. Results show that the standardized Penman-Monteith equation performs as the best ETref equation with median symmetric accuracy (MSA) of 0.37, Taylor’s skill score (TSC) of 0.89, and r2=0.83. The analysis shows that the gridMET dataset overestimates wind-speed and requires adjustment before a series of statewide ETref climatology maps are generated (1990-2020). For ETa, the MODIS and GLEAM (3.3b) datasets outperform the rest with MSA=0.5, TSC=0.8, and r2=0.8. The state ETa dataset is generated using all MODIS data from 2003 and blending the MODIS data with GLEAM (3.3b) to cover data unavailability. Using the top-performing datasets annual ETref for Indiana is computed as 1110 mm, ETa as 708 mm, and precipitation as 1091 mm. A marginal increasing climatological trend is found for Indiana’s ETref (0.013 mm/year) while ETa is found relatively stable. The state’s water availability, defined as rainfall minus ETa, has remained positive and stable at 0.99 mm/day (annual magnitude of +3820 mm).