Drought in Delaware

Highlights:

• The recent wet trend continues, with most of Delaware receiving 2 to 3 inches of rain since last week.
• Stream conditions are improving and chloride levels in the Christina River continue to stay well below any level of concern as a result.
• Groundwater conditions are improving statewide, with wells in New Castle County getting closer and closer to normal.
• Delaware is likely to see above normal temperatures through June, while precipitation departures are less predictable at this time.

Statewide Drought Discussion

Our weather during the first full week of April continued the wet trend we have been seeing recently.  Since last week, most locations in Delaware received 2 to 3 inches of rain, with southern New Castle and northern Kent counties receiving slightly less than 2 inches of rain (Figure 1). 

While the recent rainfall has certainly been helpful to alleviating the drought, we’re still playing “catch up” in some areas.  Looking at our long-term climate stations, since January 1st, Georgetown is 2.10 inches above normal, while Wilmington is 1.09 inches below normal according to data managed by the National Weather Service.  These spatial differences in precipitation departures show up in statewide soil moisture data as well, where northern Delaware is in the normal range in the top meter of soil, while southern Delaware is above normal (Figure 2).

Looking at stream conditions in northern Delaware, the flow on White Clay Creek at Newark, the combined flow of the Red Clay Creek near Stanton and the White Clay Creek near Newark (combined flow at Veolia’s filter plant), and the flow on the Brandywine Creek at Wilmington improved significantly compared to last week (March 31).  All of the streams reported in this update are flowing just below the median flows for this time of year.  Continued weekly precipitation will be needed to bring the streamflows up to or above the median flows for this time of year. 

Chloride concentrations in the Christina River near Newport remain well below the first threshold of concern (250 ppm) at 8.96 ppm.  The last time the chloride concentration was above 250 ppm was about a month ago during the first week of March (263.2 ppm).  In general, chloride conditions have improved throughout the first week of April as precipitation conditions have improved.

We continued to see improvement in groundwater conditions statewide.  The water level in well Db24-18 (located just south of Newark) has increased to 14.8 ft below land surface (Table 1). It is slowly starting to recharge, and is now out of drought warning and moved into drought watch.  The water level in this well typically ranges between 9.7 and 13.3 ft below land surface during April.  Elsewhere in New Castle County, well Hb12-05 (SW New Castle County) has shown significant improvement in groundwater conditions over the last month and half, particularly the last few weeks (Figure 3).  Its depth to water value now sits about one foot below the median well level for this time of year.  Groundwater conditions in Kent and Sussex counties are still improving, as well.       

Weather and Climate Outlook:

The short-term weather pattern remains fairly active over the next week or two.  This should continue the wet trend we’ve been experiencing and continue to help with getting our water conditions closer to normal.  April is well on track to being at least a normal precipitation month. 

Looking toward the spring and summer, we should see a return to ENSO (El Nino-Southern Oscillation) neutral conditions in the global climate regime.  This factor combined with the recent trend has NOAA’s Climate Prediction Center (CPC) predicting a 40-50% greater chance of the next three months (April – June) being above normal for Delaware and the surrounding region.  Precipitation is less predictable in this type of seasonal climate regime, so the CPC’s forecast is “equal chances” for our region, which means precipitation could just as easily be below normal as above normal for the next three months (Figures 4 and 5).

We’ll need to monitor the temperature trends just as closely as the precipitation trends in the coming months, since temperature is a critical factor in how quickly we lose water from the soil to the atmosphere through evaporation and transpiration.  If we see above normal temperatures over the next three months, we would expect to “lose” more water than normal from the ground to the atmosphere.