Handbook of drought indicators and indices

Why is it important to monitor droughts? Droughts are a normal part of the climate, and they can occur in any climate regime around the world, even deserts and rainforests. Droughts are one of the more costly natural hazards on a year-to-year basis; their impacts are significant and widespread, affecting many economic sectors and people at any one time. The hazard footprints of (areas affected by) droughts are typically larger than those for other hazards, which are usually constrained to floodplains, coastal regions, storm tracks, or fault zones. Perhaps no other hazard lends itself quite so well to monitoring, 156because the slow onset of droughts allows time to observe changes in precipitation, temperature, and the overall status of surface water and groundwater supplies in a region. Drought indicators, or indices, are often used to help track droughts and these tools can vary depending on the region and the season.