What Causes a Drought?

Droughts occur when evaporation and transpiration rates consistently exceed precipitation over an extended period of time. This prolonged imbalance results in water shortages, crop damage, and reduced streamflow. The primary causes of drought are insufficient rainfall or inadequate snowpack.

There are four main types of droughts: permanent, seasonal, unpredictable, and invisible. Permanent droughts are found in the world’s driest climates where agriculture is impossible without irrigation. Seasonal droughts occur in regions with distinct wet and dry seasons, requiring careful timing for planting crops. Unpredictable droughts can happen anywhere, but they are most characteristic of humid and subhumid climates. Although usually brief and localized, these droughts can occasionally be ongoing and widespread. Invisible droughts occur during hot summers when high evaporation rates outpace rainfall, gradually reducing water availability.