Drought in Delaware

Note:  The next drought report will be on October 8th, 2025

Highlights:

• Precipitation was well below normal in August, leading to large water balance deficits across the state
• Soil moisture conditions have regressed significantly over the last few weeks, particularly in southern Delaware and northern Delaware north of I-95
• Streamflow conditions have taken a downward turn across the state due to the lack of rain and seasonable evapotranspiration rates
• Groundwater in the surface aquifer remains fairly stable across Delaware
• Short-term precipitation gains are possible over the next week, but the forecast is less certain throughout the remainder of September

Statewide Drought Discussion

Delaware is not currently experiencing drought conditions, however a dry August has led to abnormally dry conditions in some parts of the state. 

Precipitation

Dry weather returned for most of Delaware in the month of August.  The mean precipitation for the DEOS Network last month was only 1.29 inches.  This is well over 3 inches below the 1991-2020 statewide average of 4.69 inches, according to NOAA. 

The prolonged dry conditions actually go back into July for some locations in Delaware, particularly Milford, Harrington, Ellendale, and Slaughter Beach.  Overall, the summer of 2025 is likely to go down as a below normal season in terms of precipitation despite a wet July.  Looking back at the last six months, which is an important timeframe for hydrologic impacts, statewide precipitation is slightly above normal.

Temperature/Evapotranspiration

Delaware has experienced very mild temperatures over the last couple of weeks along with relatively low humidity conditions.  The statewide average reference evapotranspiration for August was 4.44 inches, which means that for the month, Delaware saw a 3.15 inch deficit.  Figure 2 shows the August P-ET (precipitation minus reference evapotranspiration) conditions for the DEOS Network.  Note that these differences vary considerably across the state, with a statewide maximum of -4.22 inches (Townsend) and statewide minimum of -0.64 inches (Stockley).

Soil Moisture

The large P-ET differences over the last month have had a significant effect on soil moisture conditions, particularly in southern Delaware, where the sandier soils inherently have a lower water holding capacity.  Figure 3 shows percentiles for soil moisture in the top 1 meter of soil for the Mid-Atlantic region of the United States. 

Virtually every location south of Dover and north of I-95 are below the 20th percentile for this time of year.  Most of these soil moisture deficits have developed in the last couple of weeks.  If these conditions persist, a flash drought, or rapidly intensifying drought, could develop as we near the end of the growing season.

Streamflow

A dry August has taken a noticeable toll on Delaware’s streams. In northern New Castle County, streamflows have been running below normal for several weeks, reaching their lowest sustained levels since late winter. Without a stretch of wetter weather in September, flows are likely to stay low. The good news is that cooler late-summer temperatures have helped limit evapotranspiration, which would have made conditions worse during a hotter spell. Streams in Kent and Sussex Counties are also seeing very low flows, continuing a trend from the past few weeks.

Chlorides

Chloride levels in the Christina River near Newport have recently risen above the first threshold of concern (250 ppm), reaching 271.6 ppm. This is the highest level recorded since February. Without enough rainfall to bring in fresh water and dilute the river, chloride levels are likely to keep climbing. High chloride concentrations accelerate the corrosion of pipes, bridges, and other infrastructure, which can increase maintenance costs and potential failures. In addition, aquatic life in streams like the Christina River and White Clay Creek is sensitive to rising chlorides. Elevated concentrations can stress or harm fish, insects, and plants that rely on fresh water.

Chloride levels in the Delaware River are right where we’d expect them for this time of year. On August 28th, the salt front was measured near river mile 73.6, which is almost exactly where the salt front is located this time of year (river mile 74). This location is close to Delaware’s northern border with Pennsylvania.

Groundwater

Groundwater levels across Delaware have shown a range of conditions this summer. In northern New Castle County, levels in the unconfined (shallow) aquifer have remained steady, with a monitoring well just south of Newark (Db24-18) holding within its typical August range (11.0 to 13.4 feet below land surface).  Elsewhere around the state, groundwater levels remain a mixed bag. Water levels in well Hb12-05, located in southern New Castle County, is at its “average” depth for August. In contrast, well Mc51-01a located in southwestern Kent County, has been declining since May and is now below the 5th percentile, indicating much lower-than-normal conditions. Meanwhile, well Pf24-02 located in southeastern Sussex County, has consistently stayed within the normal range since May, with a brief rise into above-normal conditions in early August (Figure 4). Wells running lower than normal (like the one in Kent County) can stress water supplies and increase the risk of shortages during dry periods.

Weather and Climate Outlook

A couple of frontal boundaries will move through the region over the next week, bringing the potential for a general 0.5 to 1.5 inches of precipitation across the state based on current forecast model guidance from NOAA.  Higher amounts are more likely in northern Delaware than southern Delaware.  Going beyond the short-term, September shows “equal chances” of being above or below normal for Delaware for both precipitation and temperature according to NOAA’s Climate Prediction Center (Figures 5 and 6).  Equal chances means that there is not enough of a trend in any of the important climate indicators to recommend an above or below normal prediction.  In essence, the forecast is a toss up.  We are coming into the peak of the Atlantic hurricane season (i.e., second week of September historically), so there’s always a chance we could see some moisture from a tropical system over the next month or two.  Thus, we’ll continue to monitor the tropics from now through early November.