Assessment of Soil Moisture, Evapotranspiration and CO2 Levels Under Different Landcovers and Environments.

The soil moisture and ET are key components of hydrologic cycle and are closely linked to ecosystem productivity. Investigating the relationships between key components of the hydrologic cycle such as evapotranspiration (ET) and soil moisture in one hand and carbon dioxide (CO2) flux in the other hand is important to understand their spatial and temporal variations under future changing climate scenarios in humid and semiarid environments. Several remote sensing satellites have been monitoring soil moisture (e.g. AMSR-E, SMOS, SMAP), ET (e.g., MODIS), and CO2 (e.g., MODIS, SMAP) at different temporal and spatial scales with different levels of measurement accuracies. The main goal of this study is to investigate the relationships between ET, soil moisture and CO2 in humid and semiarid environments across Texas and Oklahoma using different remote sensing products (as listed above). First, soil moisture data from AMSR-E (2003-2011, Res= 25km), SMOS (2009-present, Res=35–50 km) and SMAP (2015-present, Res=36 km) were used to develop a daily soil moisture database for 2003-2016; these data were then compared with observed soil moisture data from 109 and 116 Mesonet and USDA-NRCS Scan stations covering the study area, respectively. MODIS ET (MOD16A2, Res=1 km) and SMAP Carbon Net Ecosystem Exchange data (SMAP L4_C, Res=9 km) were compared with observed ET and CO2 flux data from 11 eddy covariance flux towers covering the study area. Preliminary results show a strong positive correlation between soil moisture and ET whereas there is a negative correlation between ET and CO2. Overall, across-site analysis indicates that the soil moisture, ET and CO2 all respond differently to various landcovers, and environments (humid vs semiarid) due to differences in water availability, root distribution and soil properties.