Climatic Consequences of a Large-Scale Desertification in Northeast Brazil: A GCM Simulation Study

Abstract

The climatic impacts of a large-scale desertification in northeast Brazil (NEB) are assessed by using the Center for Weather Forecasting and Climate Studies?Center for Ocean?Land?Atmosphere Studies (CPTEC?COLA) AGCM. Two numerical runs are performed. In the control run, NEB is covered by its natural vegetation (most of NEB is covered by a xeromorphic vegetation known as caatinga); in the desertification run, NEB vegetation is changed to desert (bare soil). Each run consists of five 1-yr numerical integrations. The results for NEB wet season (March?May) are analyzed. Desertification results in hydrological cycle weakening: precipitation, evapotranspiration, moisture convergence, and runoff decrease. Surface net radiation decreases and this reduction is almost evenly divided between sensible and latent heat flux. Atmospheric diabatic heating decreases and subsidence anomalies confined at lower atmospheric levels are found. The climatic impacts result from the cooperative action of feedback processes related to albedo increase, plant transpiration suppression, and roughness length decrease. On a larger scale, desertification leads to precipitation increase in the oceanic belt close to the northernmost part of NEB (NNEB). In the NEB?NNEB dipole, the anomalies of vertical motion and atmospheric circulation are confined to lower atmospheric levels, that is, 850?700 hPa. At these levels, circulation anomalies resemble the linear baroclinic response of a shallow atmospheric layer (850?700 hPa) to a tropical heat sink placed over NEB at the middle-layer level. Therefore, NEB climate does show sensitivity to a vegetation change to desert. The present work shows the possibility of significant and pronounced climate impacts, on both regional and large scales, if the environmental degradation in NEB continues unchecked.