Irrigation reduces land-atmosphere coupling strength in the Midwest and Northern Great Plains

Abstract:

Land-atmosphere coupling strength indicates the degree of feedbacks between soil moisture anomaly and precipitation, playing an important role in local and regional weather and climate. The U.S. Midwest and Great Plains are global hot spots with strong coupling strength reported by many climate models and some observations. However, few models used in these studies have included or analyzed effects from irrigation in these regions, where 10% of croplands are irrigated. Irrigation could substantially increase soil moisture and growing season crop leaf area index, thereby altering water and energy cycles and ultimately precipitation. In this study, we used a regional climate model that incorporated dynamic crop growth and precision irrigation (WRF3.3-CLM4crop) to investigate irrigation effects on land-atmosphere coupling strength. We quantify the coupling strength using two recently developed indices. Both indices showed a significant decline in coupling strength with irrigation in the Midwest and Northern Great Plains. Decreases were highly correlated with the degree of increase in soil moisture in irrigated cropland. For non-irrigated areas, the correlation between changes in soil moisture and coupling strength are nonlinear, with some areas increasing and some decreasing in coupling strength although they all have increased soil moisture on average. Our study suggests climate models that do not incorporate an irrigation scheme may overestimate the land-atmosphere coupling strength in irrigated regions.