Drought is a driver of forest disturbance that impacts various forest ecosystem processes and increases forest susceptibility to other disturbance agents. Quantified as the cumulative lack of precipitation in a given area, drought indices can be used to quantify the direct effects of moisture stress on forests as well as related and interacting forest disturbances. As temperatures are anticipated to increase and precipitation is anticipated to become less consistent across the region, the impacts of drought may become more severe in the Northeast. We used 20 years of data from the US Drought Monitor (USDM), categorized into the four of the USDM drought severity categories found in the region: D0 - Abnormally Dry, D1 - Moderate Drought, D2 - Severe Drought and D3 - Extreme Drought. ¹

Analysis

• Frequency
• Extent
• Severity
• Location

Disturbance Trend Summary

The data indicate that while the number of weeks in moderate to extreme drought is relatively stable over the study period, the number of weeks with abnormally dry conditions has increase slightly.

The same pattern exists for the percent of the region experiencing drought in any given year, with stable trends for moderate to severe drought but slight increases in the percent of the region experiencing abnormally dry conditions.

Highlights

• 2002 was abnormally dry, with drought conditions reported somewhere in the region for every week of the year, and extreme drought reported for 39 weeks.
• 2016 was also particularly dry, with drought conditions reported across almost 60% of the region. It is notable as being one of the primary causes of the extensive Lymantria dispar outbreaks in southern New England (see Pests and Pathogens - Established Invasives)
• Trend data indicates that drought conditions are becoming more common and widespread but the high year to year variability prevents any of these trends from being statistically significant.