Dry season clouds and rainfall in northern Central America: Implications for the Mesoamerican Biological Corridor

The proposed Mesoamerican Biological Corridor (MBC) is an ambitious effort to stem the erosion of biodiversity in one of the world's biologically richest regions. The intent is to connect large existing parks and reserves with new protected areas by means of an extensive network of biological corridors within Mesoamerica/Central America to create an environment which provides better prospects for the long-term survival of native species while also addressing the region's socioeconomic needs. While the forest types in northern Central America generally receive some dry season rainfall, in the proposed protected regions, however, it is unclear whether current rainfall has been altered by regional land-use change. Based upon climatological rainfall records at 266 stations in Guatemala and adjacent areas, dry season rainfall in March is markedly lower in deforested areas than in forested areas of the same life zone for each of the widespread life zones. In general, dry season deforested habitats have higher daytime temperatures, are less cloudy, have lower estimated soil moisture and lower values of normalized difference vegetation index (NDVI) than do forested habitats in the same life zone. The result is hotter and drier air over deforested regions, with lower values of cloud formation and precipitation. Rainfall is predicted from the correlation of raingauge measurements and observed cloud cover; moreover, March rainfall deficiencies > 25 mm are found for several Holdridge life zones. The data suggest that deforestation is locally intensifying the dry season, increasing the risk of fire, especially for the long corridor connecting regions. In addition, forest regeneration in some parts of the MBC may not result in second-growth forest that is characteristic of that life zone but rather in forest regeneration more typical of drier conditions. The extent to which this would influence the conservation utility of any given corridor depends upon the ecological requirements of the organisms concerned.