Drought in Delaware

Highlights:

• Summertime precipitation patterns have led to highly variable precipitation totals across Delaware since June 1st
• Stream conditions are a mixed bag, with some locations near their medium flows for this time of year, while others are below their median flow levels
• Groundwater conditions continue to improve on the heels of a wet May
• Short-term conditions don’t look particularly wet, while the rest of June is likely to be warmer than normal

Statewide Drought Discussion

Rainfall has been highly variable across Delaware so far in June.  Figure 1 shows month-to-date precipitation totals for the DEOS network for June 2025. 

New Castle County saw limited precipitation overall, as the thunderstorms mostly missed that area.  Meanwhile Dover has seen over two inches of precipitation, including 1.83 inches on June 7th.  Otherwise, only western and southern portions of Sussex County has seen precipitation totals greater than an inch.   Now that we’re well into June, it’s critical to not just focus on how much precipitation we receive, but also how much water we lose from the surface in the form of evapotranspiration.  June is typically one of our highest months in terms of evapotranspiration with warm temperatures and high solar radiation values driving the process.  Figure 2 shows a map of precipitation minus evapotranspiration (P – RefET). 

Despite western and southern Sussex County receiving over an inch of rain since June 1st, many locations still saw a deficit, or negative P-RefET value.  This indicates that more water was “lost” than “gained” so far this month in that area, as well as in most of the rest of Delaware.  This balance between precipitation and evapotranspiration will require close monitoring as we go through the summer when drought can develop rapidly.  

Across northern Delaware, water conditions are slowly improving from recent drought conditions. For the past week, the streamflows in the northern part of the state are very close to their respective medians for this time of year; however, more precipitation will be needed to keep flows at this level as temperatures begin to rise, and evapotranspiration kicks into high gear. Flows on streams in Kent and Sussex Counties are a mixed bag – some streamflows are at their respective medians and some streamflows are much below the median value. 

Chloride concentrations in the Christina River near Newport remain well below the first threshold of concern (250 ppm) at approximately 5.32 ppm. The last time the chloride concentration was above 250 ppm was during the first week of March (263.2 ppm).  In general, chloride conditions continued to remain low so far in June. Chlorides on the Delaware River have been well below the 250 ppm threshold since at least mid-February, which along with precipitation,  helps contribute to the low chloride concentrations on the Christina River.

Groundwater conditions in the unconfined aquifer (i.e., surficial aquifer) continued to recharge slightly over the past week.  One long-term monitoring well that continues its slow recovery is  DGS well Db24-18 (located just south of Newark).  The groundwater level in this well is at 12.5 ft below land surface (Table 1), which is about 0.4 feet above the below normal level for this time of year. The water level in this well typically ranges between 9.4 and 12.9 feet below land surface during June. Meanwhile, well levels at USGS well Hb12-05, located in southern New Castle County, continue to remain in good shape, as the current level is between the 75th and 90th percentile (Figure 3).

Weather and Climate Outlook: 

Precipitation over the next seven days is fairly limited.  The National Weather Service’s Weather Prediction Center’s 7-day quantitative precipitation forecast (QPF) has most of the Delmarva Peninsula with 0.5” of precipitation or less through June 18th (Figure 4).  

However, like most summertime weather scenarios in Delaware, large spatial variability in precipitation is possible, so some locations could see quite a bit more, while other locations see quite a bit less than 0.5 inches. 

Looking beyond the next week or so, weather conditions are expected to be well above normal, which means we’ll likely see higher evapotranspiration rates during the latter half of June.  This will mean that we’ll need more rainfall than normal to keep soil moisture conditions stable and streamflow and groundwater levels throughout Delaware improving.