Drought is an often-misunderstood natural disaster, characterized by extended periods of low rainfall that result in water shortages and other impacts. It’s the most common cause of natural disasters, and accounts for between 80-90% of all disasters globally. It’s also one of the most important global challenges, affecting people, communities, food production, and our ecosystems.
Drought can occur anywhere, and is caused by many different factors. Climate change is making the world drier, and rising temperatures speed up evaporation in dry regions. Other contributing factors include changes in ocean surface temperature, the jet stream, and local landscapes.
When people think of drought, they most often envision the 1930s Dust Bowl or images of depleted ponds and dying crops. While these are the most well-known types of drought, there are actually five main kinds of drought: meteorological, hydrologic, agricultural, socioeconomic, and ecological (see below).
Meteorological drought occurs when an area is experiencing a lack of precipitation over a long period of time. This is the type of drought most commonly monitored and reported by the National Weather Service, using the Palmer Drought Severity Index (PDSI). This index is complex to develop and monitor, but it does a good job of predicting long-term drought.
The most severe form of drought is what’s called an “aridification drought.” An aridification drought is characterized by a persistently low water supply, and can be exacerbated by other factors like fire, over-allocated groundwater, or changing climate patterns.