Actual Evapotranspiration Estimates from In Situ Oklahoma Mesonet Observations and MODIS Satellite Data

Evapotranspiration (ET) is an important variable in the hydrologic cycle and land-atmosphere interactions, and quantifying ET is important in understanding energy and moisture transfer between the land surface and the atmosphere. The Oklahoma Mesonet is an automated network of 120 environmental monitoring sites across Oklahoma, which collects in situ observations of soil and atmospheric variables. This study was designed to utilize the in situ data to estimate actual ET at Oklahoma Mesonet sites via a modeling framework developed by Senay (2008). Specifically, potential evapotranspiration and fractional water index values from the Oklahoma Mesonet were integrated with normalized difference vegetation index (NDVI) values from the MODIS sensor aboard the Terra and Aqua satellites to calculate actual ET for the 2012 warm-season (April-October) at the Marena Oklahoma Mesonet site (MARE). The estimated ET values were subsequently compared to (1) ET data collected from an eddy correlation flux tower located approximately 400 m west of MARE and (2) estimates from the Senay (2008) methodology. The overall results demonstrated that incorporating the in situ observations significantly improved the actual ET estimates at the MARE location. In particular, incorporating soil moisture observations from 5-60 cm led to the more realistic and accurate representation of ET trends during flash drought development from July-August 2012.