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Description
This thesis research investigates the impacts of wildfires on the surface energy and water cycles of tropical South America. Burned area fractions derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) date of burning product were integrated into the SSiB2 land surface model for a series of six-year simulations, in which the land cover in burned areas was degraded based on the burned area data and on the survival rate of predominant vegetation types. In addition, based on a customized remote sensing investigation, surface darkening associated with ash and char deposition from fire activity was simulated by lowering ground albedo for 72 days after a fire. In general, the vegetation degradation associated with fire activity increased surface albedo over burned areas by exposing relatively bright bare ground causing an annual average decrease in surface net radiation of 4 W/m2 in savannas. The associated decrease in surface available energy caused drops in surface latent and sensible heat fluxes, which were most prominent in the six months after the fire season. Overall, postfire conditions of tropical South America yielded a more stable planetary boundary layer, indicated through reduced near-surface relative humidity and equivalent potential temperature. The areas most impacted were those most expansively burned within the savanna and rainforest biomes. The model results suggests wildfires can cause a weakening of boundary layer instability and consequently reduce convective precipitation activity. Furthermore, with air temperature predicted to increase and rainfall rates projected to decrease in the next decades due to global warming, wildfires are predicted to increase in frequency throughout the region. Our results suggest that under a warmer, drier climate, the land surface impacts associated wildfire activity may become more prominent and could lead to further reductions of surface net radiation and gross primary productivity in tropical South America.
