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 bridge 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?

In 2019, the DRBC established the Advisory Committee on Climate Change to provide 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. 

Through modeling, research, and analytical studies, the DRBC is examining the impacts of sea level rise and climate-induced changes to atmospheric temperature, precipitation and hydrology on water security and resiliency to ensure an adequate and equitable supply of suitable quality water for Basin water users and the environment.

Ongoing efforts include:

  • Establishing assumptions and scenarios to define a range of potential impacts due to sea level rise

  • Incorporating methods to evaluate sea level rise into screening-level flow management models

  • Evaluating historical trends for precipitation, temperature and flow and other water resource indicators from climate change

  • Obtaining and analyzing downscaled global circulation model output for use in trend analysis and hydrologic models

  • Using hydrologic models to develop flows for a range of scenarios to evaluate the Basin’s vulnerability to future hydrologic conditions including drought

  • Evaluating alternative flow management programs and outcomes

  • Evaluating groundwater and surface water availability considering the effects of climate change

  • Identifing additional freshwater storage and other adaptation measures to meet future water availability, climate adaptation, drought management and flow management needs

  • Developing tools to evaluate the effects of climate change and sea level rise on aquatic habitat in tidal and non-tidal portions of the Delaware River

  • Developing a framework for evaluating the impacts of climate change on water quality and emerging contaminants

  • Providing technical analysis for Commission planning endeavors

  • Performing a literature review and other assessments related to flooding to incorporate into a comprehensive climate change and sea level rise impact assessment

DRBC Reports/Presentations:
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