Influence of landuse on cumulus cloud climatology in Central America

There is growing evidence that landuse changes produce changes in regional climates. The Central American region is one area in which landscape type is being rapidly altered, with the second highest rate of tropical deforestation. However, to date there has been only indirect evidence of regional climate being impacted by landuse practices.

The nature of the underlying surface has a strong influence upon the formation of boundary layer cumulus cloudiness. The presence and type of vegetation alters the surface energy budget substantially. Thus, it can be expected that the nature of boundary layer cumulus over heavily vegetated areas will differ substantially over that in deforested areas. In this study a daytime boundary layer cumulus climatology for Central America is produced, and correlations are made with surface conditions.

Geostationary Environmental Operational Satellite (GOES) data is used to determine the frequency of occurrence of cumulus cloud fields over the Central American region during the dry season (January - May 1999). A structural thresholding method is applied to channel 1 imagery to automatically detect cumulus cloud fields in the region over land and ocean. For example, it is found that the frequency of occurrence of cumulus cloudiness is much higher in the less developed (forested) regions of Nicaragua than in the neighboring (deforested) regions of Costa Rica. The transition from high cumulus cloudiness over Nicaragua to low cumulus cloudiness regions in Costa Rica is very sharp and occurs along the border. Landsat data is utilized to examine these regions in greater detail. It is found that there are "holes" in the cumulus cloud field that are directly associated with regions that have been converted to banana plantations and other agricultural uses. Because cumulus cloudiness is so strongly associated with precipitation in the regional dry season, there is a tendency for the deforested regions to have lower precipitation rates. Ancillary surface data from Costa Rica will be discussed to support these conclusions.