Impacts of meteorological forcings on simulated soil moisture stress for rainfed crops at a US Corn Belt site

Temperature and precipitation change can increase crop water stress leading to declines in crop yield. In the US Corn Belt, previous studies have found that the topsoil is drying. But crops, even in systems with restrictive soil layers, access water from beneath the topsoil and it is poorly understood how weather variability will affect water availability throughout the entire root zone. To investigate these impacts, I built an integrated surface water–groundwater model of a field in the Central Mississippi River Basin. Using stochastically downscaled precipitation forcings, I found that in the topsoil (top 30 cm), less frequent precipitation leads to soil water more frequently dropping below the stress point. Increased precipitation during the spring did not impact the simulated soil moisture because soil was already near saturation at that time, meaning that additional precipitation primarily increased runoff. The shallow groundwater and soil layers beneath the topsoil did not experience drying, though unquantified recharge pathways limit the interpretation of groundwater results. Overall, this study showed that less frequent, more intense precipitation increases topsoil moisture stress. But the moisture in the critical zone below the topsoil is not likely to be affected, meaning it can be an important water source to sustain crop yields in places with unreliable precipitation. Thus, improvements to genetics and management that facilitate deep root growth should be investigated to sustain agricultural production in the future.