PNNL

Abstract

As climate change shifts crop exposure to dry and wet extremes, a better understanding of factors that govern crop response is needed. Recent studies have identified shallow groundwater – groundwater with sufficiently high water tables to interact with the crop rooting zone – as a key factor, although existing evidence is largely based on theoretical crop model simulations, indirect or static groundwater data, or small-scale field studies. Here, we use observational satellite yield data and dynamic water table simulations from 1999-2018 to provide field-scale evidence for shallow groundwater effects on maize yields across the United States Corn Belt. We identify three lines of evidence supporting groundwater influence: 1) crop model simulations better match observed yields after improvements in groundwater representation; 2) machine learning analysis of observed yields and modeled groundwater levels reveals a subsidy zone from water table depths between 1.1 and 2.5 m, with yield penalties at shallower depths and no effect at deeper depths; and 3) locations with groundwater levels typically in the subsidy zone display higher yield stability across time. We estimate an average 4% yield increase when groundwater levels are at 1.5m depth (compared to below 2.5m), with benefits roughly doubled in dry conditions. Groundwater yield subsidies occur ~35% of years on average, with 75% of the region benefitting in at least 10% of years. This study provides empirical evidence for large-scale groundwater yield impacts and further underlines the need for better quantification of groundwater levels and their dynamic responses to short- and long-term weather conditions.