Mesoscale Evapotranspiration from In Situ and Satellite Observations

Land-atmosphere interactions play an important role in influencing weather and climate at both local and regional scales in the Southern Great Plains of the United States and quantifying the variability of evapotranspiration (ET) would contribute to increased understanding of surface-atmosphere exchange that impact processes such as drought development and precipitation recycling. This study developed a methodology to estimate ET from satellite observations via the Moderate Resolution Imaging Spectrometer (MODIS) along with in situ observations of soil and atmospheric variables at Oklahoma Mesonet sites: the Mesonet Evapotranspiration MOdel (MEMO). The daily values of ET computed by MEMO were validated with independent observations from eddy correlation flux towers with linear correlations (R2) exceeding 0.75. Given the results, ET was computed across Oklahoma from 2000 to 2013. Climatological analyses of ET as well as the anomaly analyses were conducted for each of the 9 climate divisions of Oklahoma and for the whole state at temporal periods spanning daily, monthly, seasonally, and annually. In particular, the mesoscale variability was determined as well as the annual cycle which consists of four distinct phases. Correlation and coupling strength between ET and other environmental variables such as air temperature, precipitation, and soil moisture were also analyzed. Finally, the dynamics of ET during flash drought in 2012 as well as long-term drought development (e.g., 206 and 2011) was quantified. In the end, the development of MEMO sheds improved understanding of the water cycle in the region and serves as a critical tool for monitoring water resources.