Long vs Short Term Impacts

Drylands are particularly vulnerable to climate variability, of which precipitation is the most important component. For example, a slight shift in seasonal precipitation and/or frequency of extreme rain events could potentially lead to overexploitation of the meager resources of drylands and contribute to further degradation of the very resource base on which human populations are so dependent. Preliminary studies with general circulation models (GCMs) projected that a doubling of atmospheric carbon dioxide (due to the rapidly expanding human population and associated activities) would result in lower precipitation, as well as shifts in the timing and frequency of rains, in the interior of large continents.10 Recent GCM studies also predict increases in rainfall intensity and longer dry periods in many dryland regions of the globe.11

Since nearly all drylands are characterized by extreme year-to-year weather fluctuations, it is often difficult to distinguish between short-term variability and long-term changes in ecosystem appearance, as well as between temporary and permanent changes (Fig. 6.2).12 Short term variability tends to affect the range and frequency of "shocks," whereas long term change alters the resource in vegetation may or may not be reversible, depending on the interactions of numerous climatic, edaphic, and biological factors. In the long run, however, global climate change may further exacerbate the already high natural variability of drylands, leading to permanent degradation of their productive potential, particularly since there is a lack of "buffering" by large reserves of organic matter in the soils or in woody vegetation.1

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