Climate Change
Introduction

Climate change refers to fluctuations in the Earth's climate over a long period of time. Defined as the average of global or of a locale's weather patterns over an extended period of time, climate is different from normal variations in weather, which can change on a regional scale, hour to hour, day to day, season to season. 

Changes in atmospheric temperature, precipitation and sea level, as well as their associated impacts to water availability, may create new challenges to meeting water quality, supply and water resource management goals. 

To plan how best to address these challenges, water resource managers look at observed conditions, typically the most critical that has been experienced in a region.

In the Delaware River Basin, both the flood of record and the drought of record occurred more than 50 years ago, in 1955 and 1962-1967, respectively.

The Easton-Phillipsburg Bridge collapsed during the 1955 Flood. Photo courtesy of LehighValleyLive.com.   A view of the Delaware River at Trenton, N.J. during the 1965 drought. Photo from the DRBC archives. 
The Delaware River Basin's flood of record was August
1955. This photo shows the b
ridge between Easton,
Pa. and Phillipsburg, N.J. wiped out during that flood.
Photo courtesy of lehighvalleylive.com.
The Delaware River Basin's drought of record occurred in
the 1960s. This photo shows the
Delaware River at
Trenton, N.J. in July 1965.

Photo from DRBC's archives. 
Climate Change & the Delaware River Basin

Observed historic data were used to evaluate trends and changes in air temperature, precipitation, streamflow and sea level in the Delaware River Basin.

Temperature:

Average annual air temperature data from 1960 through 2019 at five weather stations inside the Basin and two nearby locations outside of the Basin (used due to lack of data within the upper Basin) suggest an increasing trend in temperature.

Temperatures in the upper Basin (Poughkeepsie, N.Y. and Binghamton, N.Y.) and lower Basin (Wilmington, Del. and Philadelphia, Pa.) have increased by more than 2°F. Temperatures mid-basin (Trenton, N.J.; Reading, Pa.; Allentown, Pa.) have increased by approximately 1°F.

Graph of temperature increases in/near the Delaware River Basin. Graphic by the DRBC.

Precipitation:

The DRBC looked at precipitation data annually and seasonally from 360 weather stations in the Basin. On an average annual basis, precipitation has increased in almost all areas. However, when looked at seasonally, there was not a single trend. Precipitation increases generally occurred in the summer (June, July and August) and fall (September, October and November).  Winter precipitation (December, January, and February) showed a slight decrease in many areas of the upper Basin and a slight increase in most areas of the lower Basin. Spring precipitation (March, April, May) has decreased slightly in the middle Basin and mostly increased in the lower Basin.

Change in Average Annual Precipitation between 1950-1984 v 1985 – 2019. Graphic by the DRBC.

Streamflow:

Streamflows are affected by many factors; temperature, precipitation, evapotranspiration and land use can all alter the volume and timing of flow. 

A trend analysis was performed with streamflow data from 20 representative USGS monitoring stations (with periods of record of 30-40 years) on tributaries to the Delaware River. As you can see from the figure below, there is great variation seasonally and across the Basin, and trends (increasing and decreasing) were weak. 

Trends in Average Total Streamflow and Average Seasonal Streamflow in the Delaware River Basin. Graphic by the DRBC.Sea Level Rise:

Sea levels are rising from storm and tidal flooding and also from salinity intrusion. A change in sea level affects the overall volume of water in the Delaware Estuary and Bay, which can affect the movement of the salt front, increasing salinity in the upper portion of the estuary. This is a concern to human and aquatic life.

Below is a time-series of measured sea level at Lewes, Del., and Philadelphia, Pa., which show rates of SLR of 3.61 mm/yr and 3.06 mm/year, respectively. Since 1960, the sea level has risen by 8.7 inches at Lewes and 7.3 inches at Philadelphia. 

Rates in Sea Level Rise at Lewes, Del. and Philadelphia, Pa. Data: NOAA; Graphic: DRBC.

Future Impacts:

Local climate change impacts for the Delaware River Basin include increased temperature, changes in precipitation patterns and sea level rise, all of which affect water supply and water quality.

  • Increased temperatures will affect evapotranspiration rates; more evaporation means less water available for streamflow. Increased temperatures will also affect stream water quality; turbidity levels will likely increase, and dissolved oxygen levels decrease.

  • Precipitation is predicted to occur in the form of fewer, more intense storms occurring in the winter months. This means a potential increase in flood events coupled with extended drought cycles. 

  • The seasonality of flows may also change, for example, less snowpack in the winter may cause lower flows in the spring.

  • Sea level rise may require increased releases from reservoir storage to augment freshwater flows to repel salinity and/or costly modifications by public water suppliers to treat increases in dissolved solids and protect drinking water. Other water users south of Philadelphia may be impacted if increased salinity makes water resources unsuitable for conventional treatment.  

  • Changes in estuary salinity will also affect habitat for fish and shellfish, as well as impact wetlands and marshes.

  • Climate change could also affect instream flow and temperature conditions for aquatic biota. 

What is the DRBC Doing?

  • Advisory Committee on Climate Change: created in 2019, the Advisory Committee on Climate Change provides the DRBC and the basin community with scientifically based information for identifying and prioritizing these threats to the basin's water resources, as well as recommendations for mitigation, adaptation and improved resiliency.

  • Including climate change impacts in its planning for future water supply availability

  • Re-examining whether new drought or flow management programs are needed in the DRB

  • Modeling and other analyses to further define the range of risks due to climate change and evaluate future water demands

Once this work has been completed, different adaptation and mitigation measures will be needed to develop robust plans and resources to increase our resiliency and address the risks posed by climate change.

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