Increasing temperatures and a lack of precipitation are the two primary components of a drought. Warmer air absorbs more moisture from the atmosphere in wetter areas, and drier air evaporates more moisture from arid regions. Additionally, climate change alters the patterns of large-scale atmospheric circulation, which can shift storm tracks away from typical paths and magnify weather extremes. While climate models predict continued drier weather across the U.S. Southwest, the Mediterranean, and Australia, these changes may result in a longer duration of droughts.
The mechanisms that produce precipitation vary greatly from one location to another. In areas where rainfall is below normal, the convective processes are most important. The convective process produces heavy rainfall within an hour, while stratiform processes generate less intense precipitation for longer periods. These water events are classified into different types, depending on their properties. In addition, precipitation can be divided into different types, such as ice. Regardless of the mechanism, droughts affect agriculture and all other sectors of society.
Although the cause of droughts remains unknown, climate change is changing the timing of water availability. In the Northern Hemisphere, warmer winter temperatures mean less precipitation falls as snow, which negatively affects ecosystems and water management systems. The melting snowpack also serves as a source of cold water for certain species, including salmon. However, this decrease in snow cover increases surface temperatures, further exacerbating the effects of drought.