2021 Weather In Review: Delaware Water Gap National Recreation Area

Visitors and park staff gather at the observation area along the Dingmans Falls Boardwalk

NPS photo

In order to better understand ecosystem health in national parks, the Eastern Rivers and Mountains Network measures ecosystem "vital signs" in select national parks in West Virginia, Pennsylvania, New Jersey, and New York. One of those vital signs is weather and climate. Below is a summary of 2021 weather conditions at Delaware Water Gap National Recreation Area.

This brief provides county-scale weather data averaged from all of the counties surrounding the park, including data from 1895–2021 (i.e. period of record). These counties include Monroe, Northampton, and Pike counties, Pennsylvania and Sussex and Warren counties, New Jersey. Data and analyses herein are courtesy of the National Oceanic and Atmospheric Administration's (NOAA) Climate at a Glance Program.

Weather vs. Climate

First of all, what is the difference between weather and climate? Weather consists of the short-term (minutes to months) changes in the atmosphere. Weather is what is happening outside at this very moment, be it rain, snow, or just a warm sunny day. Climate is what you expect to see based on long-term patterns of over 30 years or more. An easy way to remember the difference is that climate is what you might expect, like a hot summer, and weather is what you get, like a warm rainy day.

The following information includes a discussion of 2021 weather placed in the context of long-term climate (i.e. how did 2021 compare to a "normal" year?).

2021 Summary

In all, 2021 was extremely warm and moderately wet. The year ended as the 7^th warmest and 26^th wettest on record. Data indicate that over the long term, annual average temperature and annual total precipitation have both increased (+0.27 °F per decade and +0.39 inches per decade, respectively).

Temperature

In total, 2021 was the 7^th warmest year ever recorded at the park with all seasons being very warm (Figure 1). Eleven months had higher than normal temperatures with January, March, August, October, and December all being at least 3.5 °F above long-term averages (Table 1).

Figure 1. Seasonal and annual temperature rankings for counties surrounding the park. An arrow at the top of the figure would represent the warmest year/season on record (since 1895); at the bottom, the coldest year/season on record.

_{Table 1. Monthly and annual average temperature and departure from long-term averages. Departures from average show how different 2021 was compared to relevant averages from 1895-2020.}

Month/Year	Average temperature (°F)	Departure from long-term average (°F)
January	28.3	+3.8
February	26.6	+0.8
March	39.2	+4.3
April	48.7	+2.3
May	56.7	-0.4
June	67.2	+1.7
July	70.9	+0.7
August	71.6	+3.5
September	64.0	+2.8
October	56.6	+6.4
November	39.3	+0.1
December	36.4	+7.8
2021	50.5	+2.8

Precipitation

In total, it was moderately wet year for counties surrounding the park, but it was highly variable across seasons with the summer being very wet and the spring being relatively dry (Figure 2). The year ended as the 26^th wettest ever recorded. In all, 52.56 inches of precipitation fell, almost 6 inches more than the long-term average (Table 2).

Figure 2. Seasonal and annual precipitation rankings for counties surrounding the park. An arrow at the top of the figure would represent the wettest year/season on record (since 1895); at the bottom, the driest year/season on record.

_{Table 2. Monthly and annual total precipitation and departure from long-term averages. Departures from average show how different 2021 was compared to relevant averages from 1895-2020.}

Month/Year	Total precipitation (in.)	Departure from long-term average (in.)
January	1.71	-1.59
February	4.04	+1.05
March	3.27	-0.40
April	1.68	-2.22
May	4.71	+0.65
June	2.96	-1.33
July	6.56	+1.90
August	8.31	+3.84
September	9.73	+5.58
October	6.27	+2.47
November	1.81	-1.80
December	1.50	-2.21
2021	52.56	+5.94

Temperature and Precipitation Trends
(1895-2021)

Data for counties surrounding the park indicate that annual average temperature has increased approximately +0.27 °F per decade and annual total precipitation has increased approximately +0.39 inches since 1895 (Figure 3).

National Park Service scientists have forecast future changes in climate too. Models estimate that by 2100, annual average temperature at the park will increase by 3.2–9.4 °F (from a best-case to worst-case scenario, respectively). Annual total precipitation is expected to increase by 8–15% (see Gonzalez et al., 2018 for details).

Figure 3. Annual average temperature (°F) and annual total precipitation (in.) from 1895–2021 for counties surrounding the park. Dashed lines represent linear estimates of change.

Climate Change

Today's rapid climate change challenges national parks in ways we've never seen before. Wildlife migrations are altered, increasingly destructive storms threaten cultural resources and park facilities, habitat is disrupted—the list goes on. Go to the NPS Climate Change site to discover how climate change is affecting our nation's treasures, what the National Park Service is doing about it, and how you can help.

For more information, contact Mid-Atlantic Network Biologist, Jeb Wofford or Eastern Rivers and Mountains Network Program Manager, Matt Marshall.