A Primer on Drought Hazard Levels

This primer is excerpted from Mid-Atlantic Regional Climate Impacts Summary and Outlook: Winter 2024–2025.

Introduction

Drought categories—such as Moderate, Severe, and Extreme Drought—are critical indicators for cities, planners, and resource managers in the Mid-Atlantic as they can guide water management, emergency planning, and economic decision-making. Because drought can have significant impacts, especially to the agricultural and water resources sectors, drought categories may trigger actions to mitigate the impacts of ongoing drought or to provide relief to those who may already be impacted. For example, the duration and intensity of a drought may lead to the implementation of regulations on regional water resources, the enactment of water conservation measures at the municipal level, or the provision of drought relief funding to individual farmers. Developing or worsening drought conditions can also heighten wildfire risks, prompting emergency responders to prepare for potential outbreaks. Tracking the development and intensification of drought conditions can assist multiple sectors in planning, preparedness, and response measures.

Given the significance of drought categories across multiple sectors, it is essential to understand how they are developed and what they represent to inform decision-making.

The U.S. Drought Monitor (USDM)

The U.S. Drought Monitor (USDM) is a weekly map depicting current drought conditions across the U.S. and its territories.¹ Released every Thursday, the color-coded map categorizes drought intensity from normal conditions (None) to Exceptional Drought. The most current USDM map as of writing is shown in Figure 1.

Source: U.S. Drought Monitor

Established in 1999, the USDM is widely used by state planners, policymakers, fire managers, and the agricultural community. It also plays a crucial role in triggering disaster declarations and relief programs for agencies such as the U.S. Department of Agriculture (USDA) Farm Service Agency and the Internal Revenue Service (IRS). The USDM website provides valuable resources, including historical archives, comparative change maps, time-series graphs, as shown in Figure 2, and regional data. Each weekly map includes a narrative explaining the reasoning behind the classifications and any observed changes.

Source: U.S. Drought Monitor

Colors in the bar chart represent drought conditions present in the Mid-Atlantic for each year from 2000 to 2025 (Abnormally Dry, Severe Drought, Moderate Drought, Extreme Drought, and Exceptional Drought).

Abnormally dry conditions are most common throughout the time series, with extreme drought occurring in 2002 and 2024. No drought conditions were present between 2003 and 2005.

How Drought Maps Are Created

The USDM is produced through a collaboration between the National Drought Mitigation Center (NDMC), National Oceanic and Atmospheric Administration (NOAA), and the USDA.²A rotating lead author synthesizes a range of data, as shown in Figure 3, including precipitation, soil moisture, evapotranspiration, vegetation health, streamflow, and groundwater levels. Local impacts, reported by federal and non-federal partners, help ground-truth the data. Importantly, USDM maps reflect current conditions only and do not incorporate forecasts.

Source: U.S. Drought Monitor

A flow chart depicting the factors contributing to Drought Maps: precipitation, snowpack, humidity, evapotranspiration, vegetation health, streamflow, and lake and reservoir levels.

Drought Categories

USDM categories include: Normal or wet Conditions (None), Abnormally Dry (D0), Moderate Drought (D1), Severe Drought (D2), Extreme Drought (D3), and Exceptional Drought (D4). Each category corresponds to a percentile range of indicators, as shown in Figure 4 below. For instance, D4 conditions typically occur once or twice in a century. The map also includes S (short-term drought, less than six months) and L (long-term drought, more than six months) designations.

Category	Description	Example Percentile Range for Most Indicators
None	Normal or wet conditions	30.01 or Above
D0	Abnormally Dry	20.01 to 30.00
D1	Moderate Drought	10.01 to 20.00
D2	Severe Drought	5.01 to 10.00
D3	Extreme Drought	2.01 to 5.00
D4	Exceptional Drought	0.00 to 2.00

Examples of Drought Impacts

As drought conditions intensify, impacts become more severe, and may include:

• D0 (Abnormally Dry): Lawns brown, streams decline slightly, early crop stress
• D1 (Moderate Drought): Increased irrigation, stunted crops, voluntary water conservation, restrictions on outdoor burning
• D2 (Severe Drought): Low streamflows, fish kills, rising hay prices, crop damage
• D3 (Extreme Drought): Dry wells, significant agricultural losses, wildlife disease outbreaks, water quality concerns
• D4 (Exceptional Drought): Critical water shortages, record-low groundwater levels and streamflow

Figure 4 illustrates additional potential effects of each drought level.

Source: Northeast Regional Climate Center

Drought Stage	Impacts
Drought Stage Zero: Abnormally Dry	Fire danger increases Crop growth is stunted Lawns start to brown Water levels decrease
Drought Stage One: Moderate	Honey production decreases Stressed trees and landscaping Suggested water consumption Irrigation use increases
Drought Stage Two: Severe	Warnings for outdoor burns High prices for hay Well water quantity and quality decline Many fish die off
Drought Stage Three: Extreme	Farmers struggle financially Widespread crop loss Wells run dry Wildlife disease outbreak

For example, during the summer of 2024, rolled corn leaves were observed in Adams County, PA (D0), as shown below in Figure 5.³

Source: CMOR

In fall 2019, Moderate Drought (D1) resulted in lower hay yields, requiring farmers to use their winter feed supplies earlier than expected. In July 2024, Severe Drought (D2) contributed to reduced flows in the Piney River, Virginia. A farm in Mineral County, West Virginia, experienced Extreme Drought (D3) during the summer of 2024 and had crispy pastures with nothing for their animals to graze, shown in Figure 6. Exceptional Drought (D4), while rare in the Mid-Atlantic, could lead to water scarcity and shortages.

Source: CMOR

The Condition Monitoring Observer Reports (CMOR) system allows individuals to report drought impacts, contributing to interactive maps used by the public and USDM authors.⁴ Continued monitoring and adaptation are essential as climate patterns shift and water availability challenges evolve.

State-Level Drought Monitoring

Several Mid-Atlantic states have independent drought monitoring, declaration and response systems. Table 2 shows the various drought categories used by states in the Mid-Atlantic, as well as the indicators used to categorize drought.

State	Drought Categories	Drought Indicators
New York	Normal Watch Warning Emergency	Precipitation Groundwater Stream flows Lake and reservoir levels
Pennsylvania	Normal Warning Emergency	Precipitation (PDSI, SPI, % of ave) Groundwater Stream flows
Maryland	Normal Watch Warning Emergency	Precipitation Groundwater Stream flows Reservoir storage
Delaware	Watch Warning Emergency	Six and 12 month precipitation Water table level Stream flows Reservoir storage Chloride concentration in water bodies
Virginia	Normal Watch Warning Emergency	Precipitation Groundwater Stream flows Reservoir storage
West Virginia	NA	NA

State drought declarations are often tied to response measures, e.g., water conservation or temporary restrictions on outdoor burning, that are laid out in state-level planning documents, such as hazard mitigation plans, water plans, or dedicated drought plans. For example, the Virginia Drought Monitoring Task Force designates three categories of drought—drought watch, drought warning, and drought emergency—for each of its 13 drought evaluation regions.⁵ These are shown below in Figure 7.

Sources: U.S. Drought Monitor and Virginia Department of Environmental Quality

During a drought watch they increase awareness of current conditions and distribute water conservation information, during a drought warning they begin voluntary water conservation, and in a drought emergency they begin mandatory water conservation. Other states have similar frameworks tied to hazard mitigation and water planning policies.⁶

Drought and Climate Change

Drought has impacted the Mid-Atlantic multiple times over the past century, with the drought of record occurring in the 1960s. This longer-term drought, which took place from 1962 to 1969, was one of the most severe and prolonged dry periods in the region's history, significantly impacting water resources, agriculture, and hydropower.

With climate change, the Mid-Atlantic has seen annual precipitation slightly increase, but when and how that precipitation falls is changing. Winters, in particular, have gotten wetter and more precipitation is falling in extreme events. As the atmosphere warms, it can hold more water, causing longer time between rainfall events. When precipitation does fall, it tends to be in intense downpours. Water can scour the land and is lost to runoff, rather than being absorbed in the soil. Figure 8 shows projections of dry days, indicating that the Mid-Atlantic may see increases in periods of dry days by the end of the century.