Longest Stretch of Dry Days

Longest Annual Stretch of Dry Days

This tool is excerpted from Mid-Atlantic Regional Climate Impacts Summary and Outlook: Fall 2022.

Tool Background

While the focus of water management in the Mid-Atlantic is often on extreme high precipitation, drought can and does occur. In the late 1990s, for example, drought across the region led to major crop losses and declarations of emergency for 11 localities in Virginia. States also imposed restrictions on water users as water supplies lowered.1 Other past droughts in the region, such as in 2002, have also produced losses in crop production, and some have co-occurred with heat waves, resulting in impacts to human health and fatalities.

As of December 1, parts of central Virginia are designated as abnormally dry. In fact, most states in the Mid-Atlantic regularly experience abnormally dry conditions. Since 2005, Pennsylvania, Virginia and Maryland have all seen abnormal dryness for at least part of the year.2 The number of consecutive days without precipitation can show when drought may be forming or if an area may experience abnormal dryness into the future. Even short duration periods of dryness could exacerbate drought conditions. Severe and extreme drought conditions in the region can last as short as days or weeks and up to months, though very rarely years.

The following data tool presents an analysis of historical and projected consecutive dry days. The key findings from this tool are presented below.

Key Findings

  • The Mid-Atlantic region is projected to experience a similar number of consecutive dry days in the future under the low emissions scenario.
  • Under the high emissions scenario, a few areas will experience small increases in the number of consecutive dry days, particularly northern Maryland and southern Pennsylvania.
  • By the end of the century, the Mid-Atlantic region could see 22.9 days of less than 0.1 inches of precipitation in a row per year in a high emissions future, compared to an historical average of 21.6.

Figure 1. Longest Annual Stretch of Dry Days

How to Use the Tool

Selecting Temperature Thresholds, Time Periods and Future Emissions
UUse the filters to the right of the maps to adjust the temperature threshold used to calculate the longest stretch of dry days and the 30-year time period. Users can also select the future emissions scenario (Low or High Emissions).

Viewing Data for a State or County
Use the State and County filters to the right of the table to have the plot show data for a particular location of interest.

Technical Notes

Localized Constructed Analogs (LOCA) is a downscaled climate data product available at 1/16-degree (6-km) resolution over the continental United States. LOCA data sets3 include the 32 climate models available in the Coupled Model Intercomparison Project 5 (CMIP5) archive, for two future greenhouse gas concentration trajectories: a low emissions future, Representative Concentration Pathway (RCP) 4.5;4 and a high-emissions future, RCP 8.5.5 For this study, we used LOCA data over the Chesapeake Bay watershed from 1950–2100 (or 2099 for some models) for calculations of the baseline periods and the percent differences from those baselines. Access LOCA datasets and learn more about the methodology.