Land Cover / Climate Interaction at Global and Regional Scales

Thursday, 18 December 2014: 10:54 AM
Yongkang Xue, University of California Los Angeles, Department of Atmospheric and Oceanic Sciences, Los Angeles, CA, United States
Land cover and climate interact at regional and global scales through biophysical, biogeochemical, and ecological processes. Land cover change (LCC) affects regional climate through impacts on surface albedo and surface net radiation, on the partitioning of available energy between sensible and latent heat fluxes, on the atmospheric heating, moisture flux convergence and circulation, and the partitioning of rainfall between evaporation and runoff. Meanwhile, the climate variability and change also affect the LCC.

Based on historical anthropogenic land cover change data from 1948-2005, numerical experiments that were designed to test its impact using general circulation models indicate that the LCC enhances the global warming in past half century. This is because after land degradation, reduction of evaporation is dominant, leading to surface warming. The reduction of net radiation due to high surface albedo plays a secondary role. Meanwhile, its impact on the regional monsoon is significant. The produced monsoon rainfall anomaly is not only limited within the land degradation area but extend to much large area through its interaction with the atmospheric circulations.

The warming climate and climate variability also affect the vegetation distribution. For instance, with a coupled biophysical and dynamic vegetation model forced by the observed meteorological data, the North America leaf area index (LAI) shows an increasing trend after the 1970s in responding to warming. Meanwhile, the effects of the severe drought during 1987-1992 and the last decade in the southwestern U.S. on vegetation are also evident from the simulated and satellite-derived LAIs. The land covers in some parts of North America also show substantial changes. Evaluations of these simulations using satellite data are crucial. The critical issues in applying satellite data for LCC studies are also discussed.