Projecting the impact of climate change on the effectiveness of Controlled Drainage in the U.S. Corn Belt

Abstract:

Subsurface tile drainage systems are used to create arable conditions for agriculture in low-gradient regions with poorly drained soils, such as the U.S. Corn Belt. Traditionally these systems allow excess water to continually drain from the landscape until the water table underlying the field drops below the depth of the tile drain. These ‘free draining’ systems increase the volume of subsurface water, and thus increase the amount of nutrients, leaving fields. Controlled Drainage (CD) is a water conservation practice that allows farmers to decrease the volume of water leaving their field by using a control structure to manually raise the resting water table above the tile drains. In order to better understand the potential impacts of climate change on agricultural drainage in the Corn Belt, this study focuses on evaluating differences in the simulated effectiveness of CD under different climate change scenarios. The Variable Infiltration Capacity (VIC) macroscale hydrology model, with a subsurface drainage algorithm, was calibrated to nine sites across the Midwest with drainflow records from 1987 to 2012. It is used to simulate drainflow from 1980-2010 and 2035-2064 using projections for the A1B, A2 and B1 emissions scenarios from the GFDL, PCM and HadCM3 models to represent variation in the severity of projected climate change. Simulated drainflow volume, timing, and variability for both freely-drained and controlled scenarios is used to quantify projected changes in drainflow and calculate metrics of CD effectiveness in mitigating negative water quality impacts, spatially under different climate scenarios. Assessing potential changes in effectiveness of CD due to climate change is necessary to investigate potential long-term benefits and drawbacks of this best management practice.