The Biogeophysical Impacts of Land Use/Land Cover Change in the Southeastern U.S.

Abstract:

This presentation explores the biogeophysical impacts of land use/land cover (LULC) in the Southeastern U.S. over the past century. A reconstructed LULC change dataset was constructed from a series of existing LULC datasets. Land surface and satellite observations were analyzed to estimate the net radiative forcing due to LULC change. Albedo and latent energy were specifically addressed for the dominant land use change of agriculture to evergreen forests. The results show that in the Southeastern U.S. for the period of 1920 to 1992 the change in sensible (as a result of albedo) and latent energies are in direct competition with each other. In the spring and early summer months, the croplands are in peak production and the latent energy associated with their ET is comparable to that of the forested areas, so the change in radiation due to albedo dominates the signal. However, during the late summer and fall months most major crops have matured (or been harvested) thus reducing their transpiration rate while forests (particularly evergreens) maintain their foliage; and with their deep roots, are able to continue to transpire as long as atmospheric conditions are favorable. This later influence of latent energy appears to more than offset the increased radiative forcing from the spring and early summer. Overall, the mean annual net radiative forcing as a result of the LULC change from cropland and forests is estimated to be -1.06 w/m². This result supports a probable contribution to the ‘warming hole’ over the Southeast during the majority of the 20th century.