Assessing the sensitivity of lower atmospheric characteristics to agricultural land use classification over the Lower Mississippi River Alluvial Valley

Abstract

The Lower Mississippi River Alluvial Valley (LMRAV) is a key agricultural area within the USA, and although it receives a substantial level of annual rainfall, irrigation remains a requirement to sustain high productivity. Since a large percentage of irrigation comes from limited groundwater sources, predictions of surface and lower atmospheric characteristics associated with convective rainfall processes are critical for planning and managing water resources. While numerical weather models are a key tool in this prediction effort, there is considerable error in the models associated with the correct categorization of regional land use. This is especially true for the LMRAV, where most agricultural land is defined as dry cropland despite the extensive use of irrigation. To improve the accuracy of regional model simulations over the LMRAV, this study investigates the sensitivity of changing the dominate land use category from dry to irrigated cropland within a high-resolution Weather Research and Forecasting (WRF) model simulation. Based on a 5-month simulation (May–Sept. 2016) over the LMRAV, results of the study show that replacing dry cropland with irrigated cropland leads to substantial variations in the low-level thermal and moisture balances. In general, the northern LMRAV was shown to have the greatest increase (decrease) in latent (sensible) heat flux in August and September, with a corresponding increase in 2-m dew point temperature where latent heat flux increased. Additionally, boundary layer heights were shown to decrease over the northern LMRAV over the simulation, likely a result of decreased temperatures resulting from a dampened sensible heat flux.