Midwest Regional Hydrology Impacts of Improved Crop and Soil Management.

Climate change and growing rainfall variability necessitate agricultural management that promotes water storage and there is growing interest to determine how this can be done through a focus on soil water storage or greenwater use efficiency. Global analyses have found that there are tremendous production and environmental benefits from water savings strategies that improve water infiltration and reduce soil evaporation, but there is a need to better understand specific crop and soil management strategies facilitate water savings on a regional level. In this analysis we sought to understand how improvements to the soil through crop diversification would impact hydrology on a landscape scale using a case study of the Midwestern state of Iowa, reflective of the broader corn-soybean crop rotations throughout the Corn Belt of the United States. We calibrated the Basin Characterization Model, a regional hydrology platform, for performance across 17 watersheds covering the majority of the state including several urban areas. We then created hypothetical scenarios for crop and soil improvements that converted approximately one-fourth of the most erodible or least profitable lands currently used for agriculture to perennials and another one-fourth to corn or soybeans grown in combination with a cover crop, assuming approximately a 10% improvement in soil water storage based on prior research for these practices. These scenarios led to an average decrease in runoff of 28-32 percent as well as a 23-26 percent greater plant water use. We also found that these crop and soil management changes led to reduced flood frequency up to 39%. Our analysis also included an evaluation of several future climate scenarios and we found that improved crop and soil management led to similarly successful savings of water runoff and increased water available for crop use by the end of the 21st century. Overall these results demonstrate that a focus on soil health and water storage can improve regional hydrology outcomes with future climate change.