Quantifying the Relative Roles of Land Use Change and Remote Forcing on the 1930s Dust Bowl Drough

The 1930s Dust-Bowl drought in the U.S. Great Plains had devastating environmental and societal impacts. Understanding the causes of this persistent severe drought can help us to predict similar droughts and mitigate their effects. In this work, the Weather Research and Forecasting (WRF3.6) model, coupled with the Community Land Model (CLM4.0), was used to examine how land-cover change during the 1930s affected regional atmospheric circulation and resulted in a severe drought, and how this effect persisted in three different large-scale circulation (remote-forcing) conditions. Model simulation results show considerable decrease of the net surface radiation and subsequent reduction in the atmospheric radiation when using the 1930s land cover, compared to using the pre-settlement and present-day land cover. A compensating subsidence (warming) in the atmosphere causes an increase in pressure in the lower troposphere and near the surface. In the meantime, this process competes with the reduction of pressure stemming from a decrease in evaporative cooling. During the Dust Bowl, the changes in pressure in the U.S. Great Plains weakened the zonal pressure gradient force (PGF) over the Great Plains. Weakened PGF results in the collapse of the Great Plains low-level jet via the Coriolis' effect and thereby reduces the transport of moisture to the Great Plains from the Gulf of Mexico. This reduction in moisture transport results in a decrease of 0.9mm/day of precipitation in the Great Plains, intensifying and sustaining the drought. Similar results have also been found in simulations using various large-scale circulations. They show the important role regional-scale land-cover change plays in sensitive areas of the development of severe drought relative to remote forcing.