NOAA National Centers for Environmental Information | State Climate Summaries 149-NC | May 2019 Revision

NORTH CAROLINA Key Messages Mean annual temperature has increased by almost 1°F since the beginning of the 20th century. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century. The number of landfalling hurricanes in North Carolina is highly variable from year to year. Hurricane- associated storm intensity and rainfall rates are projected to increase as the climate warms. A large portion of North Carolina’s coastline is extremely vulnerable to projected sea level rise due to its low elevation and subsidence of land in the northern part of the Coastal Plain. By the end of the 21st century, global sea level is projected to rise 1–8 feet, with a likely range of 1–4 feet.

North Carolina has a humid climate with very warm summers and moderately cold winters. The climate exhibits substantial regional variation due to the state’s diverse geographic elements, which include the Appalachian Mountains in the west, the Piedmont Plateau in the central region, and the Coastal Plain to the east. Elevations in the state range from sea level along the Atlantic Coast to over 6,000 feet in the western mountains (the largest elevation range of any state east of the Mississippi River). Average annual temperatures in the state vary more than 20°F from the highest elevations to the lowest points on the coast. Winter temperatures are moderated somewhat by the Appalachian Mountains which partially block cold air coming from the Midwest.

Observed and Projected Temperature Change

Figure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for North Carolina. Observed data are for 1900–2018. Projected changes for 2006–2100 are from global climate models for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions)1. Temperatures in North Carolina (orange line) have risen almost 1°F since the beginning of the 20th century. Shading indicates the range of annual temperatures from the set of models. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Historically unprecedented warming is projected during the 21st century. Less warming is expected under a lower emissions future (the coldest years being about as warm as the hottest year in the historical record; green shading) and more warming under a higher emissions future (the hottest years being about 10°F warmer than the hottest year in the historical record; red shading). Source: CICS-NC and NOAA NCEI.

1Technical details on models and projections are provided in an appendix, available online at https://statesummaries.ncics.org/pdfs/TechInfo.pdf. NOAA National Centers for Environmental Information | State Climate Summaries

Mean annual temperature has increased by almost 1°F the wettest was 2014–2018, with an average of 55.1 in North Carolina since 1900, less than in northern and inches per year. There is no overall trend in annual western portions of the United States. North Carolina is precipitation. Precipitation totals are generally highest part of a larger region of the southeastern U.S. that has in the summer, with a peak in July. Southwestern North exhibited little overall warming in surface temperatures Carolina is one of the wettest locations in the Southeast, over the 20th century. During the first half of the 20th receiving more than 90 inches of precipitation annually century, many years were warmer than the long-term in a few locations. The number of heavy rain events average, followed by a cool period in the 1960s and (days with rainfall of 3 inches or more) was highest in 1970s. Since that time, temperatures have steadily the last four-year period (2015–2018; Figure 3c). There increased, with temperatures being consistently above is no overall trend. The state averages around 5 inches normal since the late 1990s (Figure 1). Average winter of snowfall annually, although the higher elevations temperatures have been above average since 1990, with of the Appalachian Mountains can receive up to 100 the last four-year period (2015–2018) as warm as the inches. Snow and ice storms have the potential to early 1930s and early 1950s (Figure 2a). Average summer cause significant damage. Some of these storms are the temperatures have been the warmest on record over result of “cold air damming,” which occurs when cold air the last 14 years (Figure 2b). Although North Carolina becomes trapped against the Appalachian Mountains has not experienced an increase in the frequency of very by a layer of less dense warm air above it. A strong cold hot days (days with maximum temperature at or above air damming event took place on February 12–13, 2014, 95°F; Figure 3a), the last nine years (2010–2018) have causing a severe winter storm. Large portions of the seen the largest number of very warm nights (days with state received between 5 and 10 inches of snow and minimum temperature at or above 75°F) in the historical some areas received as much as half an inch of freezing record (Figure 4). rain.

Statewide average annual precipitation has ranged The “Bermuda High,” a semi-permanent high pressure from a low of 34.74 inches in 2007 to a high of 68.4 system off the Atlantic Coast, plays an important inches in 2018. The driest multiyear periods were in role in the summer climate of the state. Typically, the early 1930s and early 1950s, and the wettest in the Bermuda High draws moisture northward or the late 1900s and late 2010s (Figure 3b). The driest westward from the Atlantic Ocean and Gulf of Mexico, consecutive 5-year interval was 1930–1934, with causing warm and moist summers with frequent an average annual precipitation of 44.4 inches, and thundershowers in the afternoons and evenings. Daily

a) Observed Winter Temperature b) Observed Summer Temperature

Figure 2: The observed winter and summer temperatures across North Carolina for 1895–2018, averaged over 5-year periods (bars; last bar represents 4-year average). Filled circles connected by black line segments show annual values. The horizontal black lines show the long-term averages for 1895–2018 are 41.3°F for winter and 75.6°F for summer. These values are from NCEI’s version 2 climate division data set. The 1930s and 1950s were some of the warmest periods in North Carolina’s history, while the 1960s–70s was a cool period for the state. Over the past fourteen years, winter and summer temperatures have once again increased. Source: CICS-NC and NOAA NCEI.

NORTH CAROLINA | 2 NOAA National Centers for Environmental Information | State Climate Summaries a) Observed Number of Very Hot Days b) Observed Annual Precipitation

c) Observed Number d) Total Hurricane Events in North Carolina of Extreme Precipitation Events

Figure 3: The observed (a) number of very hot days (days with maximum temperature at or above 95°F; 1900–2018), (b) annual precipitation (1895–2018), and (c) extreme precipitation events (annual number of days with precipitation of 3 inches or more; 1900–2018), averaged over 5-year periods (bars; last bar represents 4-year average). Filled circles connected by black line segments show annual values. Horizontal black lines show the long-term averages. Graph (d) shows the total number of hurricane events (wind speeds reaching hurricane strength somewhere in the state) for 1900–2018, totaled over 5-year periods (last bar represents a 4-year total). Figures 3a and 3c are averages from all available long-term reporting stations (19 for temperature and 24 for precipitation). Figure 3b is from NCEI’s version 2 climate division dataset. In North Carolina, the frequency of very hot days has declined compared to the mid 20th century. The higher frequencies of such days during the 1930s through 1950s correspond to periods of exceptionally dry weather. Annual precipitation and the number of 3-inch days have been well above normal over the last 5 years (2014–2018). Hurricanes reach the North Carolina coast with hurricane force winds about once every three years. Source: CICS-NC and NOAA NCEI. and weekly variations in the positioning of the Bermuda North Carolina’s location along the Atlantic Coast High can have a strong influence on precipitation makes the state vulnerable to tropical storms and patterns. When the Bermuda High extends westward hurricanes. A storm reaches the state at hurricane into the southeastern United States, warmer and drier intensity about once every three years (Figure 3d). than normal weather occurs, which can culminate However, storms that reach the state at less than in heat waves and drought. In 2007, as the result hurricane intensity can also have major impacts. The of a strong Bermuda High over the Southeast and a late 1990s and early 2000s were a notably active period strengthening La Niña, the state experienced its driest of storms reaching the state at hurricane intensity year in history. By the end of August, most of the state (Figure 3d). In addition to damaging winds and coastal was in severe drought. flooding from storm surges,extreme precipitation from these storms is a great hazard to the state. In 1999, Hurricane Floyd dropped 15–20 inches of rain in

NORTH CAROLINA | 3 NOAA National Centers for Environmental Information | State Climate Summaries the eastern part of the state, which was still recovering Observed Number of Very Warm Nights from flooding caused by Hurricane Dennis several weeks earlier. Beginning on September 6, 2004, the remnants of Hurricane Frances dropped 6–10 inches of rain across much of western North Carolina over a three-day period. Less than two weeks later, the remnants of Hurricane Ivan struck the same area, dropping 10 inches of rain and causing hundreds of landslides in the mountains. During October 7–9, 2016, Hurricane Matthew dumped torrential rain in eastern North Carolina with many locations receiving more than 10 inches and a few locations in excess of 18 inches, causing major flooding. In September 2018, the most intense rainfall event on record occurred as Hurricane Figure 4: The observed number of very warm nights (annual Florence dropped 20–36 inches in eastern North number of days with minimum temperature at or above 75°F) for Carolina, causing widespread destruction with losses 1900–2018, averaged over 5-year periods (bars; last bar represents 4-year average). Filled circles connected by black line segments in excess of $22 billion (in 2019 dollars), more than the show annual values. The horizontal black line shows the long-term combined losses from Floyd and Matthew. In addition average for 1900–2018 is 4.6 nights per year. These values are to damage from high winds and flooding, hurricane averages from 19 long-term reporting stations. The second half of the 20th century was a cool period for North Carolina, with the strikes can produce tornadoes. Rainbands associated frequency of very warm nights well below the long-term average. with Hurricane Frances spawned multiple tornadoes in The 2010–2014 5-year period saw the largest number of very warm the central and eastern portions of the state. nights in the historical record—almost double the long-term average. Source: CICS-NC and NOAA NCEI.

Severe thunderstorms are another hazard commonly experienced within the state. These occasionally spawn Projected Change in Annual Precipitation tornadoes. The largest such outbreak occurred on April 16, 2011, with 30 confirmed tornadoes and 24 deaths.

Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, average annual temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records (Figure 1). Future heat waves are likely to be more intense, but cold wave intensity is projected to Figure 5: Projected change in annual precipitation (%) for the middle decrease. of the 21st century relative to the late 20th century under a higher emissions pathway. Hatching represents portions of the state where Although there is no historical trend, annual the majority of climate models indicate a statistically significant change. North Carolina is on the southern end of a large area of precipitation is projected to increase in North Carolina projected increases in annual precipitation over the northeastern (Figure 5), primarily in the winter and spring. Naturally U.S. Source: CICS-NC, NOAA NCEI, and NEMAC. occurring droughts are projected to be more intense because higher temperatures will increase the rate of hurricane-associated storm intensity and rainfall rates loss of soil moisture during dry periods. Additionally, are projected to increase as the climate warms.

NORTH CAROLINA | 4 NOAA National Centers for Environmental Information | State Climate Summaries

elevation and to geological factors that are causing Increasing temperatures raise concerns regarding sea sinking of the land in the northern part of the state. level rise in coastal areas. Since 1900, global average sea Sea level rise will present major challenges to North level has risen by about 7–8 inches. It is projected to rise Carolina’s existing coastal water management system another 1–8 feet, with a likely range of 1–4 feet, by 2100 and may cause extensive economic damage through as a result of both past and future emissions from human losses in property, tourism, and agriculture. activities (Figure 6). Sea level rise has caused an increase in tidal floods associated with nuisance-level impacts. Observed and Projected Change in Global Sea Level Nuisance floods are events in which water levels exceed the local threshold (set by NOAA’s National Weather Service) for minor impacts. These events can damage infrastructure, cause road closures, and overwhelm storm drains. As sea level has risen along the North Carolina coastline, the number of tidal flood days (all days exceeding the nuisance level threshold) has also increased, with the greatest number occurring in 2016 and 2018 at Wilmington (Figure 7). Large increases in Figure 6: Global mean sea level (GMSL) change from 1800 to 2100. Projections include the six U.S. Interagency Sea Level Rise nuisance flooding at Wilmington are projected (Figure Task Force GMSL scenarios (navy blue, royal blue, cyan, green, 7). A large portion of North Carolina’s coastline is orange, and red curves) relative to historical geological, tide gauge extremely vulnerable to sea level rise due to its low and satellite altimeter GMSL reconstructions from 1800–2015 (black and magenta lines) and the very likely ranges in 2100 under both lower and higher emissions futures (teal and dark red boxes). Global sea level rise projections range from 1 to 8 feet by 2100, with a likely range of 1 to 4 feet. Source: Adapted from Sweet et al. 2017.

Observed and Projected Annual Number of Tidal Floods for Wilmington, NC

Figure 7: Number of tidal flood days per year for the observed record (orange bars; 1936–2018) and projections for two possible futures: lower emissions (light blue) and higher emissions (dark blue) per calendar year (2000–2100) for Wilmington, NC. Sea level rise has caused an increase in tidal floods associated with nuisance-level impacts. Nuisance floods are events in which water levels exceed the local threshold (set by NOAA’s National Weather Service) for minor impacts, such as road closures and overwhelmed storm drains. The greatest number of tidal flood days (all days exceeding the nuisance level threshold) occurred in 2016 and 2018 at Wilmington. Projected increases are large even under a lower emissions pathway. Near the end of the century, under the higher emissions pathway, some models project tidal flooding every day of the year. To see these and other projections under additional emissions pathways, please see the supplemental material at https://statesummaries. ncics.org/pdfs/TidalFloods.pdf. Source: CICS-NC and NOAA NOS.

WWW.NCEI.NOAA.GOV | HTTPS://STATESUMMARIES.NCICS.ORG/NC | LEAD AUTHORS: REBEKAH FRANKSON, KENNETH KUNKEL | CONTRIBUTORS: LAURA STEVENS, DAVID EASTERLING, RYAN BOYLES, ADRIENNE WOOTTEN, HEATHER ALDRIDGE, WILLIAM SWEET NORTH CAROLINA | 5