Using a single column model with ground-based, aircraft, and satellite data sets we assess the combined role of smoke and dust aerosols, land degradation/aridization (LDA), and their impact on the planetary boundary layer (PBL) in influencing near-surface air temperature over the Sahel. Our study is unique because it assesses the combined role of smoke and dust aerosols on PBL evolution and near-surface air temperatures during both day and nighttime. More importantly, using a theoretical framework, we provide a careful explanation of the geophysical processes responsible for the changes in PBL and near-surface air temperature. Our results indicate that during northern hemisphere winter months, dust, and smoke over Sahel radiatively combine to impact the PBL. We show that aerosol mixtures dominated by dust modify PBL height in a manner that minimizes/maximizes surface layer cooling/warming at times when daytime maximum/nocturnal minimum temperatures occur. Furthermore, we find that increasing smoke contribution to total column aerosol optical extinction counteracts nighttime warming through daytime cooling. When smoke constitutes half or more of to the total column aerosol optical extinction, the ratio of longwave to shortwave radiative forcing is less than 10%, and nighttime cooling ensues. Minimum temperature is most sensitive to changes in mid-visible aerosol optical depth (AOD) values <1 and doubling of dust AOD within this range during the 1950-1980 Sahelian LDA event is estimated to have a nocturnal warming potential of 0.6 degrees C.

The area of desertified land has increased by 27.3% from 1987 to 2000 in Maduo County, northeastern Qinghai-Tibet Plateau. Driving forces of land degradation has been extensively studied in the region. Using Factor Analysis (FA), we evaluate contribution of human activity and natural environmental change to land degradation. Four common factors were extracted in this study. The result shows that climate related other than human-related factors, are the major inducing factors of land degradation in Maduo County. Climate change and consequent change of permafrost account for 70% to the land degradation. Increasing evaporation and declining precipitation in the beginning of the growing season hamper seedling establishment. Decreasing frozen days and rising active layer lower bound make surface soil loose and less soil moisture available for plant.