Quantifying the Impacts of Tile Drainage on Cropland Evapotranspiration in The Midwest USA: Comparisons between Process-based and Satellite-based Modeling

With increasing demand for crop yield increments, tile drainage is widely installed underneath the soils across the US Corn Belt. The surface water cycle can be significantly affected by the artificial tile drainage system, since parts of water can be rapidly drained away before being evaporated into the atmosphere or being utilized by plants. However, the impacts of tile drainage on cropland evapotranspiration(ET) remains uncertain and the estimation divergency from various approaches is less explored. Here, we examined how the tile drainage intensity has affected the cropland ET and the ratio of transpiration(T) to total ET in the midwest USA from 2003 to 2017 with a process-based model(Dynamic Land Ecosystem Model(DLEM)) and a satellite-based model(Penman-Monteith-Leuning model(PML)). The modeling estimates shows that total ET in tile-drained cropland area accounts for about 45% and 36% of cropland total with DLEM and PML respectively. In cropland area, the ET/precipitation (PPT) ratios from DLEM in tile-drained area and none-tile drained area are inconsistent with the results from PML. Annual accumulated ET to annual total precipitation from DLEM and PML show different trend along the tile drainage intensity gradient. As for T to ET ratio, results from DLEM show a significant increasing trend with the increasing area percentage of tile drainage whereas those from PML show an opposite trend This study implies a need to consider belowground water management practices in estimating dynamics of ET and water balance component over space and time.