*Information From Climate And Droughts
Figure 1. Propagation of precipitation defecits through other components of the hydrologic cycle. (Modified from Changnon, 1987). |
Changnon (1987) illustrates how the definitions of a drought are related to specific components of the hydrologic cycle and how precipitation deficits are related to drought (fig. 1). Figure 1 shows how the effects of two hypothetical precipitation deficits are propagated over time through the surface-runoff, soil-moisture, streamflow, and ground-water components of the hydrologic cycle. From this perspective, precipitation can be considered to be the carrier of the drought signal, and streamflow and ground-water levels can be considered to be the last indicators of the occurrence of a drought (Hare, 1987; Klemes, 1987).
If precipitation is the carrier of the drought signal, then climate describes the long-term characteristics of this signal. The climatic factors associated with drought, including a description of the local climate in areas that have precipitation deficits, are described in the following section. These factors are then related to atmospheric circulations that extend well beyond the local area. Finally, possible causes of drought-related atmospheric circulations and the relation of these causes to nonatmospheric factors are described.