Land use and local climate: A case study near Santa Cruz, Bolivia

The Tierras Bajas regions of eastern Santa Cruz, Bolivia have undergone among the most rapid rates of concentrated deforestation during the 1980s and 1990s. We investigate the sensitivity of local climate to these land cover changes as observed from Landsat images acquired between 1975 and 1999. The Simple Biosphere model (SiB2) is used to assess the effects of both morphological and physiological changes in vegetation and the implications for fluxes of water, energy and carbon between the vegetation and the atmosphere during the rainy season. Conversion from tropical forest to cropland implicates morphological changes in vegetation as the primary drivers for a daily maximum warming of about 2degreesC and a slight nighttime cooling, suggesting that clearing of tropical forests for agricultural use may increase the diurnal temperature range, mainly by increasing the maximum temperature. On the other hand, the conversion of wooded grassland to cropland resulted in a similar daily warming and drying but exclusively due to vegetation physiological activity. The area-averaged monthly mean response for each conversion type resulted in a warming of about 0.6degreesC for the conversion of broadleaf evergreen and 1.2degreesC for conversion of wooded grassland. These temperature differences represent an augmentation in the local heat source associated with a reduction in evapotranspiration due to land cover conversion and do not reflect variations forced by changes in atmospheric circulation. When averaged over the entire domain, the effect of landscape conversion results in a reduction of the latent heat flux and an increase in sensible heat flux, producing a large-scale apparent heat source of 0.5degreesC during January. This warming is in line with an increasing trend observed in monthly mean temperature in Santa Cruz, Bolivia during the same period.