The Chesapeake Bay is one of the most vulnerable regions in the nation experiencing the impacts of climate change. As part of the Chesapeake Bay Program’s work toward this outcome, the partnership has adopted five indicators to track the impact that changing climatic conditions are having on the physical environment. Patterns and trends observed in these indicators—which include air temperature, stream temperature, precipitation, river floods, and sea level rise—will inform our understanding of the environmental conditions that could influence our ability to protect and restore the Bay. Water temperature, for instance, can impact the abundance and distribution of underwater grasses and the stream habitat available to brook trout.
According to data from the National Oceanic and Atmospheric Administration (NOAA), air temperature across the Chesapeake Bay watershed has increased over the last 100 years. Of the 33 climate divisions located within the watershed, 32 have experienced statistically significant long-term increases in air temperature. Average increases in air temperature have ranged from 0.4 degrees Fahrenheit per century in southern West Virginia to more than 2.5 degrees Fahrenheit per century in Delaware. Regions closer to the mainstem of the Bay have warmed more than regions farther upstream.
In some parts of the country, climate change is causing more frequent “high temperature extremes.” While there is more than one way to define a high temperature extreme, the Chesapeake Bay Program considers an unusually hot day to be one on which the maximum temperature observed at a particular weather station is among the top five percent of daily highs observed at that weather station across all years of measurement. In our watershed, only one weather station has experienced a statistically significant increase in high temperature extremes since 1948.
In contrast, a “tropical nights” analysis—which examines trends in nighttime lows rather than daytime highs—does show a clear warming trend in the region. High nighttime temperatures are often linked to a heat wave’s more serious impacts on human health.
According to data from the U.S. Geological Survey (USGS), average annual stream temperature in the Chesapeake Bay watershed has increased by 1.1 degrees Fahrenheit over the past six decades.
Seventy-nine percent of the 72 stream sites monitored between 1960 and 2014 experienced an increase in water temperature. Of these increases, more than half are considered statistically significant trends. At these sites, stream temperature has increased by an average of 2.1 degrees Fahrenheit.
In general, the largest increases in stream temperature have occurred in the southern part of the watershed.
According to data from NOAA, annual precipitation totals in some parts of the Chesapeake Bay watershed have increased over the last 100 years. Of the 33 climate divisions located within our watershed, 32 experienced an increase in total annual precipitation between 1901 and 2017. Seven of these divisions—four of which are located in New York—experienced increases that can be considered statistically significant.
As climate change alters air circulation patterns across the region and around the world, annual precipitation rates will rise in some areas and fall in others. In our watershed, annual precipitation rates have increased most notably in New York and slightly in Maryland, Pennsylvania, West Virginia and Washington, D.C. In contrast, annual precipitation rates have experienced very little change in western Virginia.
According to data from USGS, river flooding in the Chesapeake Bay watershed has grown larger and more frequent over the past 50 years. Between 1965 and 2015, 72 percent of 47 stream sites in Delaware, Maryland, Pennsylvania, Virginia and West Virginia experienced an increase in the size of river floods. Seventy-one percent of stream sites experienced an increase in the frequency of river floods. Because most of these stream sites experienced variation in flood size and frequency from year to year, experts do not consider these trends to be statistically significant.
While flood size and frequency can be impacted by site-specific and regional factors, climate change has been linked to more extreme precipitation events. Experts anticipate more frequent and more extreme precipitation events to generate larger and more frequent upstream floods.
Sea Level Rise
According to data from NOAA, relative sea level has risen at each of the seven long-term tide gauge stations on the Chesapeake Bay and its tributaries. Between 1960 and 2017, sea level has increased between one-eighth of an inch and approximately one-sixth of an inch each year.
Total increases in sea level at these seven tide gauge stations range from seven inches in Baltimore to more than 10 inches in Norfolk, Virginia. (This is taller than the height of the average pencil.) Regionally, relative sea level rise is compounded by the natural sinking of the land’s surface. Locally, it can be exacerbated by the human extraction of groundwater.
The Chesapeake Bay Program is considering developing or adopting additional indicators to track the environmental, ecological, and social impacts of climate change. Additional indicators of climate change related to the physical environment may include:
- Changes in the surface water temperature of the Bay;
- Changes in the acidity of the Bay and its tidal tributaries; and
- Extreme precipitation events.
Additional indicators of the ecological conditions responding to climate change may include:
- The abundance of harmful algal blooms;
- The spatial extent and ability of wetlands to act as a physical buffer;
- The spatial distribution of select, climate-sensitive bird species;
- The spatial distribution of select, climate-sensitive fish species; and
- The community composition of underwater grasses in the Chesapeake Bay.
Additional indicators of the social conditions affected by climate conditions may include:
- The frequency of tidal flooding in four coastal cities; and
- The extent of developed land located within a floodplain or storm surge risk zone and the estimated property damage caused by flooding and storm events.
In 2018, Eastern Research Group, Inc., (ERG) worked with the Chesapeake Bay Program to develop an implementation strategy that defines and describes the steps and resources needed to create these climate-related indicators. (This strategy also describes nine indicators that could be used to track our progress toward building climate resiliency.) As partnership priorities evolve and new sources and methods of analyzing data emerge, the Chesapeake Bay Program may choose to change its course or implement certain indicators from this suite. Further development of these indicators will depend on the quality of supporting data, the added value of the indicators in question and the priorities and resources of the Climate Resiliency Workgroup.