Land-Use and Land Cover Changes Strongly Modulate Warm-Season Precipitation over the Central United States

The Central United States is reported to be a “hotspot” of land-atmospheric coupling during the warm season and has witnessed major cropland expansion since the preindustrial period. Recent observational studies over the Midwest report cooling of summer temperatures and an increase in warm season precipitation, likely induced by historical land use and land cover changes (LULCC). Global and regional climate model simulations show consistent warm temperature and dry precipitation biases over this region which can be partly alleviated by increasing model resolution to capture mesoscale convection systems (MCSs). Coincidentally, changes in land cover and land management also occur on fine spatial scales that require modeling at finer resolutions to capture their spatial heterogeneity. While decadal simulations at uniform 10-30km resolutions globally remain computationally formidable, recent advances in Earth system models make it feasible to perform global simulations on variable resolution (VR) meshes.

In this study, we aim to test the hypothesis that LULCC strongly modulate simulated warm season surface climate over the Central US by conducting numerical experiments using the spectral element dynamical core of the Community Earth System Model version 2. These simulations were configured either on the standard 1^o grid or on a VR grid with static regional grid refinement to 1/8^o over the Contiguous United States for the historical period (1984-2010) with two alternative land use datasets corresponding to the preindustrial (year 1850) and present day (year 2000) conditions. Our results show that the skill in simulating precipitation (2m air temperature) over the Central US are primarily dependent on resolution (land use representation). A statistically-significant LULCC induced increase in precipitation over the Midwest occurs in May and June in high-resolution simulations while such influence is weaker in coarse-resolution simulations. This precipitation change comes from an increase in the number of MCS-like features because historical LULCC shifts the thermodynamic environment towards one that is more conducive to convection. Our study demonstrates the potential of using VR Earth system models for hydro-climate simulations in regions with significant LULCC.