Fish & Water
Drought is defined as a prolonged deficiency in precipitation, affecting agriculture and the environment. Understanding its types and management strategies is crucial for mitigating its effects.
What do you think of when you hear the term drought? Some may think of the 1930s Dust Bowl, a period of four severe drought episodes that exacerbated the conditions of the Great Depression. Others may think of a lack of rain, depleted lakes, or dying crop fields. It may surprise you that there is no universal definition for drought.
What is Drought?
The general definition of drought is a deficiency in precipitation over an extended period that leads to a water shortage. However, drought is more accurately defined by its impacts. For example, agricultural drought refers to rain shortages that negatively impact agriculture. This could be anything from reduced soil moisture that hinders crop growth to low pond levels that leave livestock without drinking water. There are five main types of drought: meteorological, hydrologic, agricultural, socioeconomic, and ecological (table 1).
Table 1. Types of Drought
| Type of Drought | Description | Impact |
|---|---|---|
| Meteorological Drought | Defined by how dry a region is compared to the average year or simply by how long it has been dry. Meteorological drought is region specific. | Dry weather patterns dominate an area (e.g., 1930s Dust Bowl) |
| Hydrologic Drought | Defined by the impacts of decreased precipitation on surface and subsurface water supplies. The frequency and severity of hydrologic drought is defined on a watershed or river basin scale. | Low water levels in streams, reservoirs, and groundwater |
| Agricultural Drought | Defined by agricultural impacts from rain shortages, decreased evapotranspiration, soil water deficits, and reduced water supplies. The severity of agricultural drought depends on crop types and growth stage. | Low crop yield or impacted livestock health |
| Socioeconomic Drought | Defined by decreased precipitation impacts on the supply and demand of economic goods like drinking water or water for industrial use. | Reduced hydroelectric power production, tourism, public health, infrastructure, etc. |
| Ecological Drought | Defined as a prolonged and widespread deficit in naturally available water supplies that create multiple stresses across ecosystems (communities of organisms that live and interact in a common environment like a pond). | Decline in plant growth, local species, ecosystem health, and water availability for freshwater ecosystems |
Drought Management
Drought is expensive—impacts from exceptional drought can cost billions of dollars! They also create environmental, societal, and agricultural damage. Managing drought to reduce its effects is important so communities can recover. Drought management has four parts: planning, response, recovery, and mitigation. Unlike most disaster management strategies, drought management involves prolonged response and recovery phases that start while the drought is ongoing. The response phase of drought is longer than most disasters because an area can experience abnormally dry conditions a long time before a drought is officially declared. The damages from drought do not occur as quickly as tornadoes or floods. The recovery phase is mostly natural. While proper planning can mitigate drought impacts, it simply must rain.
The other two management phases, planning and mitigation, are similar to the management phases of most natural disasters. Planning helps prepare for future droughts, and mitigation entails finding ways to increase resilience to drought. In agriculture, that could include breeding drought-resistant crop varieties or helping operators build irrigation infrastructure when applicable. Drought indicators and triggers also serve as management tools to respond to and communicate drought conditions.
Drought Indicators
Drought indicators are variables or parameters used to describe drought conditions, and they play a significant role in monitoring and communicating drought. Examples of drought indicators include precipitation, evapotranspiration rates, lake and groundwater levels, soil moisture, streamflow, and drought indices. Physically based indicators, such as groundwater levels and soil moisture depth, can be directly measured and are easily observable. Drought indices, on the other hand, play a different role. Indices are computed numerical representations of drought intensity. Unlike physical indicators, they are not directly measured. Instead, physical indicators are used to build drought indices and those indices become a form of drought indicator. For example, the Standardized Precipitation Index takes precipitation data and creates an index indicating abnormal dryness and wetness. Drought indices serve many purposes and are helpful to compare current physical indicators with historical trends (figure 1).
Figure 1. Purposes of drought indices
Drought Triggers
Drought triggers are the thresholds of indicators and indices that initiate and terminate drought management actions. They are most often used to create actionable responses to various drought conditions.
Some of these actionable responses are used to conserve resources during drought, thereby reducing overall drought impacts. Others are used to transition back to normal conditions following a drought. Like drought indicators, there are physically derived triggers and index-derived triggers. Physical triggers include lake and groundwater levels. Like physical indicators, physical triggers are easy to measure, monitor, and set thresholds. They are also highly effective for communicating drought impacts to the public because they are easily seen and impacted by changes in water supply. For example, residents of waterfront neighborhoods quickly realize when their lake is losing water, and families who rely on well water are directly impacted when groundwater supplies run low. Physical triggers can initiate quicker responses to drought because they are easy to measure and communicate with the public.
Alabama Drought Management Plan
Droughts may not look as scary as other natural disasters when they are occurring, but they are just as damaging. This is why our state has the Alabama Drought Management Plan in place. The plan implements actions mandated by state legislation regarding water resources and drought planning and response. The plan defines specific processes to address drought and drought-related activities. It also provides additional details on how the planning process identifies ways to prepare for drought, areas most impacted by drought, the associated risks, and ways to mitigate impacts during drought emergencies. The plan is revised every 5 years by the Alabama Department of Economic and Community Affairs (ADECA) Office of Water Resources. The newest Drought Management Plan was released in November 2024 and is available on the ADECA website.
This article is a written product of Alabama Drought Reach.
Brianne Minton, former Alabama Drought Reach Coordinator, and Jessica Curl, Administrator III, Instructional Outreach Programs, Crop, Soil and Environmental Sciences, Auburn University
New May 2025, What is Drought? Understanding the Basics, ANR-3146