Impact of Land Use and Land Cover Changes on U.S. Climate: A CMIP6 LUMIP Analysis

Land use and land cover change (LULCC) significantly influences climate systems, yet its integration into climate projections remains uncertain. This study utilizes data from the CMIP6 Land Use Model Intercomparison Project (LUMIP) to explore the historical and projected impacts of LULCC on the climate of the contiguous United States. We analyzed the impacts of historical LULCC by comparing simulations with LULC fixed at 1850 levels against simulations with observed historical LULC variations. Additionally, future scenarios were assessed by comparing SSP370 with SSP370 modified by SSP126 LULCC, and SSP126 with SSP126 modified by SSP370 LULCC, allowing us to isolate the effects of LULCC from different socioeconomic pathways. Historical analysis indicates that LULCC, particularly the expansion of cropland and grazing land, has led to cooling effects in the Midwest and northern Great Plains. This cooling is associated with increased latent heat flux in summer, altering temperature, and changes in surface albedo and wind speed influencing winter conditions. In terms of precipitation, historical LULCC has impacted precipitation through its effects on large-scale atmospheric circulation, resulting in decreased winter precipitation in the Midwest and Northeast due to reduced latent heat. Future projections under varying socio-economic scenarios suggest that deforestation could lead to warming along the East Coast in summer due to reduced latent heat, while continued agricultural expansion in the Midwest might counteract warming through increased moisture. Winter precipitation changes show decreases in the southern Midwest linked to forest cover reduction and increases along the Gulf Coast, potentially driven by both regional land-atmosphere feedbacks and broader circulation effects. This study shows the critical role of LULCC in shaping regional climate variability across the U.S and emphasizes the importance of region-specific analyses to fully comprehend these diverse impacts