Impact of Tile Drainage on Evapotranspiration (ET) using Long-Term Daily High Resolution ET Estimated with Multi-Satellite Data Fusion Method

Subsurface tile drainage is a widely used agricultural practice in Midwestern USA, especially the Corn Belt, to remove excess water to improve crop yield. Research shows an increasing trend in baseflow and streamflow in the Midwest over the last 60 years which may be related to this artificial drainage activity. The influence of tile drainage on streamflow, nutrient load and crop yield has been studied using in situ measurements and models. However, how evapotranspiration (ET), as an important component of hydrologic cycle, is impacted by tile drainage is not well documented. In this study, we applied an energy balance based multi-sensor (GOES, MODIS and Landsat) data fusion method to estimate  daily 30 m ET over an intensively drained area in South Dakota, USA from 2005 to 2013 to explore the spatial and temporal ET patterns and their relationship to tile drainage system installation. Results suggest that tile drainage slightly decreases annual cumulative ET, particularly during the early growing season. During peak growing season, drained fields appear to have higher leaf area index (LAI) than undrained fields on average.  This positive biophysical feedback due to crop water use in mid-season suppresses the extent of the decrease of annual cumulative ET that might be anticipated from wide-spread drainage. Water balance analysis using Parameter elevation Regressions on Independent Slopes Model (PRISM) precipitation data, USGS gauge station observed streamflow, ET and Gravity Recovery and Climate Experiment (GRACE) soil storage change data demonstrates good balance, with the average residual from 2005 to 2012 as low as -3 mm.  As an independent check of simulated ET, the water balance analysis lends additional confidence to the study. The results of this study can improve our understanding of the influence of agricultural drainage practices on the regional hydrology, and inform future decision making regarding tile drain installation.