Droughts, prolonged periods of dryness, have always challenged ecosystems and human societies. Unlike traditional droughts that develop gradually over months or years, “flash droughts” emerge rapidly. These events escalate quickly, impacting regions before preparation can occur. Understanding this accelerated drought type is increasingly relevant in a changing climate.
Defining Flash Droughts
Flash droughts differ from conventional droughts by their rapid onset and intensification, often within weeks. Unlike traditional droughts, which result from long-term precipitation deficits, flash droughts are driven by atmospheric factors that quickly deplete moisture. Indicators include rapidly declining soil moisture, rising temperatures, and increased atmospheric demand for water (evaporative demand). This rapid drying can turn green landscapes brown in as little as two weeks. Their rapid development leaves ecosystems and human systems minimal time to adapt.
The Rapid Onset Mechanism
Flash droughts are triggered by specific meteorological conditions. High temperatures, strong winds, and low humidity create high evaporative demand, pulling moisture from the land. This process, evapotranspiration, rapidly transfers water from soil and plants into the atmosphere. Even with recent rainfall, these conditions quickly deplete soil moisture, causing rapid vegetation stress. Atmospheric blocking patterns can intensify drying by leading to prolonged clear skies and stagnant air.
Widespread Consequences
Flash droughts have widespread consequences across various sectors. Agriculture is particularly vulnerable, experiencing immediate impacts like crop failure, reduced yields, and livestock stress, as rapid onset leaves little time for adaptation. For example, a 2012 flash drought in the central U.S. caused an estimated $30 billion in damages. Water resources are quickly strained, leading to rapid declines in streamflow and reservoir levels, and increased irrigation demand. Ecosystems face increased wildfire risks from drying vegetation, and wildlife struggles to adjust to sudden moisture loss.
Identifying and Tracking Flash Droughts
Identifying and tracking flash droughts requires different approaches than traditional drought monitoring, which relies on long-term precipitation deficits. Scientists use real-time data from various sources to detect these rapid events. Weather stations and satellite observations provide information on soil moisture, vegetation health, and evaporative stress. Several indices and tools help monitor rapid environmental changes and vegetation health:
Evaporative Stress Index (ESI): Highlights areas with high water loss by describing anomalies in evapotranspiration.
Quick Drought Response Index (QuickDRI)
Vegetation Condition Index (VCI)
Normalized Difference Vegetation Index (NDVI)