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  • J.D. Solomon

The Way One State Evaluates Climate Change


A white and brown pointer on the other side of flooded waters. Communicate with FINESSE.
A dog is cutoff from his home during a recent extreme weather event.

South Carolina appears in many evaluations as one of the top ten states that are susceptible to climate change. One climate change source cites, “When it comes to extreme weather, South Carolina is among the states that get hit hardest. It averages about 26 tornadoes per year and is regularly in the path of hurricanes along the Atlantic coast. Heat and coastal flooding are also issues.”


Well, according to most local weather experts, tornados are not that big of an issue. Tropical cyclones, heat, and flooding are part of the natural weather realities. There is a twenty-year upward trend in temperatures and flooding.


Only warming overnight temperatures are statistically significant when we get inside the numbers. As always, we get a better feel for the trends and statistics when we look at the data instead of the narratives.


NOAA National Centers for Environmental Information

The three summary points for South Carolina from the NOAA State Climate Summaries 2022 are the following:


1. Temperatures in South Carolina have risen more than 1°F since the beginning of the 20th century. The state warmed during the early part of the 20th century and then cooled substantially during the middle of the century. Warming has occurred since then, but only recently have temperatures reached the levels of the 1930s.


2. Total annual precipitation has been below average during most years since 2000 but was above average during the 2015–2020 period. There has been no overall trend in annual precipitation since the beginning of the 20th century; however, a few recent years (notably 2015, 2018, and 2020) have been very wet.


3. Since 1921, sea level at Charleston has risen by 1.3 inches per decade, nearly double the global sea level rise of 0.7 inches per decade. Sea level rise is an important concern in South Carolina due to the state’s extensive coastline, which includes an abundance of salt marshes and estuaries, as well as natural seaports such as Georgetown and Charleston.


South Carolina’s Climate

South Carolina’s position on the east coast makes the state susceptible to cold air masses moving in from the northwest. The state's mild winters are a product of the Appalachian Mountains, which tend to block most cold air outbreaks. However, cold air damming events occur mainly from October to May when cool air masses flow from the northeast and are funneled along the Appalachians' windward side.


The Atlantic Ocean and its Gulf Stream flowing northward off the coast is important since land and water heat and cool at different rates. The position of the Bermuda High dominates South Carolina's weather during the warm season, which provides a persistent flow of warm, moist air into the region.


The statewide surface elevation ranges from sea level to elevation 3560 at Sassafras Mountain in Pickens County. More than 90% of the state is at an elevation of less than 1,000 feet. These changes in elevation impact the temperature and precipitation trends observed across the Lowcountry, Midlands, Pee Dee, and Upstate regions of South Carolina.


SC Climate Office Responsibilities

Tracking specific climate information changed from the federal level to the state level in 1976. South Carolina’s Climate Office was formally created in 1981, around the same time as most other US States. The duties of the SC Climate Office include the following:

  1. Coordinate and collect weather observations for the purpose of climate monitoring

  2. Summarize and disseminate weather and climate information

  3. Perform climate and weather impact assessments

  4. Demonstrate the value of climate information in the decision-making process

  5. Conduct applied climate research

In other words, the State Climate office is the source of climate change (variability) data.


Temperature

South Carolina’s annual average temperatures range from just below 57 degrees to just above 65 degrees (F). The annual average temperature naturally increases as you move from upper to lower elevations.


In the South Carolina Pee Dee River Basin, which begins in the north-central part of the state and terminates in the east-central, temperatures range from 61 degrees to just above 65 degrees (F). For context, it takes a drop of water a little over a week to travel this distance.



Since the late-1800s, the statewide annual average temperatures have gone through multiple periods of above and below-normal temperatures. A warmer period occurred from approximately 1910 to 1960, followed by a cooler period until 1990. The overall pattern of average temperatures across South Carolina has increased since the mid-1970s.


A substantial rise in minimum (overnight) temperatures have driven this increase.


While there is no statistical trend in temperature change in South Carolina, the increase in the number of overnight events over 75 degrees Fahrenheit is statistically significant.

The warmest year on record for the state is 2017, with an average temperature of 65.1 degrees, and seven of the top ten warmest years have occurred since 2010.




Precipitation

Annual Average Precipitation ranges from below 46 inches to above 56 inches. The statewide annual rainfall average from 1895 to 2021 is 47.80 inches. The precipitation data is skewed by the number of years with rainfall above the average (South Carolina is susceptible to tropical storms).


The geography of the state has an impact on the observed precipitation. Higher precipitation is experienced near the NC mountains and along the coast. Lower amounts of rainfall are experienced in the piedmont and sandhills.


South Carolina’s driest year was 1954, with a statewide average rainfall of 31.72 inches. Many locations in the Midlands and Pee Dee regions recorded less than 30 inches during that year.

A decade later, the state reported the wettest year on record, with an annual average of 69.32 inches in 1964.


Of the last 21 years in South Carolina, 15 have been characterized by warm-season drought conditions.





Extreme Rain

The amount of precipitation that tropical cyclones contribute is often lost when analyzing trends across the entire state. Since 1956, numerous storms have dropped more than a foot of rain over multiple days within the Palmetto State.


The highest 24-hour rainfall total for the state is 14.80 inches measured in Myrtle Beach due to the passage of Hurricane Floyd in September 1999.

Before the historic flooding in the Pee Dee region caused by Hurricane Matthew (2016) and Tropical Storm Florence (2018), the remnants of the Lake Okeechobee Hurricane (1928) and the Homestead Hurricane (1945) produced the highest crests on record at many river gauges across the watershed. During Matthew and again with Florence, many stations across the South Carolina Midlands and Pee Dee set new multi-day precipitation records.


Tropical Cyclones

Tropical storms are part of South Carolina’s climatology and history.

Impacts are not limited to the coast. Inland portions of the state have been affected by:

• Heavy rains

• Flooding

• High winds

• Tornadoes


From 1851 to 2021, forty-four (44) tropical cyclones made direct landfall along the South Carolina coastline. Of these, only four made landfall as major (Category 3 or higher) hurricanes; the October 1893 Hurricane, Hurricane Hazel (1954), Hurricane Gracie (1959), and Hurricane Hugo (1989). There is no record of a Category 5 hurricane making landfall in South Carolina.



Sources:

Climatology of South Carolina, Hope Mizzell & Elliot Wickham, South Carolina State Climatology Office of the SC Department of Natural Resources, Presentation on September 27th, 2022.


Overview of South Carolina’s Climate and Hazards, SCNDR State Climatology Office, Spring 2022.


NOAA National Centers for Environmental Information, State Climate Summaries 2022, South Carolina - State Climate Summaries 2022 (ncics.org), accessed October 2022.


 

JD Solomon Inc provides program development, asset management, and facilitation at the nexus of facilities, infrastructure, and the environment.



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