A Methodology for Estimating Actual Evapotranspiration at Oklahoma Mesonet sites with Applications to Drought Monitoring

Land-atmosphere interactions play an important role in influencing weather and climate on both local and regional scales. A critical link to land-atmosphere interactions is evapotranspiration (ET). Thus, quantifying the variability of ET during drought periods would contribute to a better understanding of drought development and alleviation. This study analyzed in situ data and normalized difference vegetation index (NDVI) values from MODIS sensors from Terra and Aqua satellites to estimate actual ET at Mesonet sites across Oklahoma from 2000 to 2013 via the Mesonet Evapotranspiration Model (MEMo). Climatological analysis of ET as well as the anomaly analyses were made for each of the 9 climate divisions of Oklahoma and for the whole state at temporal periods spanning months, seasons and the annual cycle. Statistical methodologies were utilized to acquire the spatial and temporal correlation, lag analysis and coupling strength between ET, soil moisture, vegetation, and atmospheric demand. Results and plots from the analysis demonstrated a 14-year climate of ET across Oklahoma and the statistical relationship between the key variables in the land-atmosphere interactions during drought periods in the studied years. Additionally, cases picked from this 14-year period were specifically studied to have a insightful view of significant droughts and flash droughts.