Using field scale ET estimated with high spatiotemporal resolution remote sensing data to study impact of tile drainage on evapotranspiration

To remove excess water and improve crop yield, subsurface tile drainage is widely used in the U.S. Corn Belt The impact of subsurface tile drainage on streamflow, nutrient load and crop yield has been studied using in situ measurements and models. Some studies found that the increasing trend in streamflow in the Midwest over the last 60 years may be related to this artificial drainage activity. However, as an important component of hydrologic cycle, evapotranspiration (ET) changes due to tile drainage have not been adequately evaluated, especially at the field scale. In this study, we explored the spatial and temporal ET patterns and the impact of tile drainage over a drained area in South Dakota, USA. We estimated 30 m daily ET over the study site from 2005 to 2013 using an energy balance based multi-sensor data fusion method. ET on MODIS and Landsat overpass days was retrieved and then fused using Spatial-Temporal Adaptive Reflectance Fusion Model (STARFM) to estimate daily ET at 30 m resolution. Results demonstrated slight decrease of annual cumulative ET for the drained site, especially during the early growing season. The water balance of the watershed encompassing the study site was evaluated. Parameter elevation Regressions on Independent Slopes Model (PRISM) precipitation data, USGS gauge station streamflow, Gravity Recovery and Climate Experiment (GRACE) soil storage change data and the estimated ET were used for estimating the water balance. The average residual error from 2005 to 2012 was -3 mm, which indicates the water balance method is robust. The results of this study provide information about the impact of tile drainage on ET and demonstrate the value of using estimated ET for watershed-scale water balance estimation.