9 Jun (CLIM) Williams, MS Defense – Heterogeneous Land Cover

Jaedyn Williams, GMU Climate Science MS Program 

Modeling the Intricacies of Climate Feedbacks on Homogeneous versus Heterogeneous Land Covers 

Tue, 9 Jun, 3:30pm, Exploratory Hall L003 

Advisor: Paul Dirmeyer

This goal of this study is to investigate how the shift toward increasing monocultures changes land-atmosphere (L-A) interactions via the water and energy cycles. This project focuses on land management practices at subgrid spatial scales in models. Growing season (May-Sept) simulations with the single-column Community Earth System Model (CESM), version 2, are used to examine the atmospheric response to midlatitude land use heterogeneity. Since the crop model is not active, different crop types are represented by C3 and C4 grasses, which behave similarly to C3 crops in the Southern Great Plains (SGP) region, such as wheat which is heavily prevalent. Different combinations of natural vegetation distributions, such as deciduous trees, evergreen trees, and bare ground, are also simulated to understand how land cover ratios affect and feed back on atmospheric processes, including convection. The main conclusions from this study show that different combinations of natural vegetation distribution do result in different feedbacks on atmospheric processes, particularly sensible heat fluxes, latent heat fluxes, and convection. When comparing convective variability between the homogeneous and heterogeneous cases, the differences are the greatest between the Atmospheric Radiation Measurement (ARM) SGP modeling simulation and the homogeneous case with only deciduous trees or the heterogeneous cases with a portion of trees. In addition, the results indicate that for the ARM SGP location, the inclusion of trees changes the boundary layer properties over a growing season as much as the interannual variability between wet and dry years, while combinations of grasses or bare ground do not. The differences found with tree coverage could be attributed to higher canopy heights and higher amounts of evapotranspiration. Overall, this study illustrates the sensitivity of the atmosphere to different combinations of land heterogeneity and homogeneity during wet or dry years.