A GARDENER’S LOOK AT THE CLIMATE IN NORTH CAROLINA BACKYARDS: HISTORY OF CLIMATE STUDIES AND PIEDMONT REGION CLIMATE — 2023 UPDATE
This is the annual update to the article, A GARDENER’S LOOK AT THE CLIMATE IN NORTH CAROLINA BACKYARDS: WAKE COUNTY, PIEDMONT REGION — 2020. The 2021 update can be found here and the 2022 update here. While the article’s background, history of climate change studies in North Carolina and how gardeners can themselves access online climate tools remain, climatic records and observations have been updated to include 2023 data.
The research-based conclusions remain the same: All published North Carolina climate change studies have not found significant, enduring and unprecedented changes in the state’s climate to date, even though the most recent one claims some climate change is taking place and predicts changes in the future (discussed in more detail below). The trend of no unusual increase in severe weather events continued, hurricanes continued their decades-old pattern of decreasing in frequency and intensity, and climatic factors important to gardeners such as average Spring and Fall freeze dates, soil temperature, humidity and growing seasons remain within a historically normal range.
Gardeners increasingly are being provided with information on climate change in North Carolina. However, a couple of additional perspectives are helpful: (1) input from average home gardeners about what climate and weather issues matter most to them and (2) an examination of the local climate and weather where we actually live. Presenters have warned gardeners of changes in the climate involving rising temperatures, extreme rains, more frequent and powerful hurricanes and the specter of drought. This has led to advice which at times is regressive such as not to use modern, scientifically developed fertilizers, to replace our lawns, stop using power tools, in addition to watching out for spiders with more powerful venom and new insects being attracted to warming soils.
This article is written for gardeners by a fellow home gardener and is meant to empower gardeners to assess and evaluate the climate in their own location. The following information will give gardeners the tools to look behind the figures if they wish to do so. These days, the information by which many observations and conclusions about the weather can be made is at our fingertips and there is no reason that gardeners cannot also be citizen scientists and figure a good number of things out for themselves.
For years I had been your average home gardener but then received intensive horticultural training and education through a state university program which emphasized making decisions, as well as giving and interpreting advice, grounded on research-based information. I was preparing a presentation on Fall gardening and managed to figure out the average first Fall and last Spring freeze dates in my hometown of Raleigh, Wake County, North Carolina. Through this process and interactions with representatives of various climate agencies, I had a peek into how climatological calculations and conclusions were made and learned that as gardeners we should always verify what we are being told by climate and weather authorities and support our decisions with our own research whenever possible.
When we are told that our climate has changed and that the change is (1) significant, (2) enduring and (3) unprecedented, we want to know if real, transparent facts exist where we actually live to support these conclusions. So, this article is an examination of whether there exists in Wake County, North Carolina, and the surrounding Piedmont region, significant, enduring and unprecedented climatological trends. It also examines some statewide issues such as drought and hurricanes, and also examines climate issues that are of particular interest to gardeners.
WAKE COUNTY
Wake County is in the middle of the state of North Carolina and is where the state capital of Raleigh sits.
North Carolina is known to be divided into three regions, the Mountains in the West, the Piedmont region in the middle and then the Coastal area to the East. Wake County is in the Piedmont region and the weather observations reported later will be applicable to many of the surrounding areas in the Piedmont, which generally has a similar topography and climate.
HISTORY OF CLIMATE CHANGE STUDIES IN NORTH CAROLINA
First, a brief history of climate change research in North Carolina to provide a background before drilling down to the conditions in Wake County. There have been three major climate change studies in the past couple of decades.
Two leaders of the State Climate Office of North Carolina (SCONC), published a 2002 paper in Environment International titled Analysis of Climate Trends in North Carolina (1949–1998).¹ This study started off by noting that North Carolina has one of the most complex climates in the country and that most of the climate trends found were local, not statewide. The study found on a statewide basis that while temperatures in the last 10 years of the study were warmer than usual, they were not warmer than the temperatures experienced in the 1950’s. They did find that the dates between last Spring freeze and first Fall freeze had become longer and that precipitation had increased during the study period for the Fall and Winter seasons but had decreased during the Summer and remained the same for Spring. Maximum temperatures had remained fairly constant and there was no widespread pattern showing increasing minimum temperatures across the state.
2015 Climate Change in North Carolina Report
This report, by the State Climate Office of North Carolina, looked at a much longer time period, investigating records back to the late 1800’s.² The report found no warming trend in the 113-year study period starting from 1895. While there was some warming since the mid-1970’s, it was found to be not unprecedented and similar to the warming observed from 1910–1950. The 2015 SCONC report stated that in North Carolina there is “no meaningful trend that is associated with global warming.”
Interestingly, while the report noted a rise in minimum temperatures, this was only in urban areas and was not found in rural areas. The report concluded that possibly this was due to urban development, but it was not due to global warming. The report also found no meaningful trends in precipitation and that there had not been more frequent or longer droughts in modern times.
The SCONC summed up its view on climate change in 2015 by pointing out that it also had analyzed dozens of other temperature data “(including seasonal patterns, days with extreme high and low temperatures, a variety of temperature thresholds, degree days, growing season data, frost data), and one common thread joined them all: “… the trends are generally flat …” The State Climate Office concluded that, “… local climate variability is so high in North Carolina that significant trends are difficult to deduce.”
This report likely remained on the State Climate Office of North Carolina website until 2016. While other content on this website goes back to 2012, the report can no longer be found and apparently was scrubbed from the site.
2020 Climate Study — North Carolina
This study was done in response to an order of the new Governor of North Carolina after his 2016 election and examined records through 2018.³ The above prior climate change studies were not mentioned in the study, nor is there any mention of the history of climate change studies in the state. The study addressed climate issues statewide, and also in the three main regions of the state, Western Mountains, the Piedmont and the Coastal Plain. The 2020 study’s conclusions as to climate trends for the entire state ambiguously included, as to average annual temperatures, that recent temperatures had increased statewide “about” 1° since 1895 (but nowhere in the report is the actual figure reported nor use of the adverb “about” defined). Further, it is not made clear whether this “about 1°” figure was compared to the existing average annual temperature in 1895 or compared to the average annual temperature for all the years since 1895.
Reference to the study’s charts and graphs does not assist with this issue because in a confounding twist, the 2020 study acknowledged that it used a different data set for all of its charts and graphics depicting temperatures and precipitation. Instead of using the data set from which it obtained its climate information (“NOAA’s National Centers for Environmental Information (NCEI) Climate Divisional Dataset (nClimDiv), version 2.”), it instead turned to a different data set for its charts and graphs, “NOAA NCEI’s Global Historical Climatology Network-Daily (GHCN-D), version 3.” The study did not explain how it used climate information from one dataset for its conclusions, but then used data from a different data set to illustrate these conclusions in its charts and graphs. As to the report’s use of the GHCN-D network for the content of its charts, however, NOAA acknowledges that two-thirds of the stations in this network record only precipitation. NOAA further states that anyone using this dataset should also cite a published article which found, according to NOAA, that, “In general, the stations providing daily observations were not managed to meet the desired standards for climate monitoring. Rather, the stations were deployed to meet the demands of agriculture, hydrology, weather forecasting, aviation, etc.”⁴ The 2020 study failed to cite this article.
In any event, given the specific scope of this article, that is, Wake County and the surrounding Piedmont area, reference will be made to the 2020 study’s conclusions regarding the Piedmont.
Of the 14 climate categories examined by this study related to the outdoor environment which could affect gardens, only two significant trends in the Piedmont were noted: (1) an increase in the average temperature from an undetermined time in the 1990s (while noting a similar increase in the 1930s — 1950s), and (2) days per year with minimum temperatures of 75° having increased since 2005 (while again noting a similar increase in the 1930s — 1950s).³
The study found very hot days (95° or higher) decreasing and the number of cold days (32° or lower) with no overall trend but increasing since 2014. The study found no long-term overall trends in the Piedmont in annual hottest temperatures, annual precipitation, extreme precipitation (days with 3 or more inches of rain), drought, and no overall historical trends in ice storms, tornadoes and thunderstorms. The study did reference an increase in annual coldest temperatures (based on an historical simulation method for an abbreviated period of 1970–2005) and decreasing snowfall but only as of 2007. The study did not address the history or future of hurricane impacts in the Piedmont region section of the report.
The 2020 study contains long range predictions which reach 60–80 years into the latter part of this century and therefore cannot be held to account by most of the existing population. The study projects significant changes in the Piedmont for each of the climate categories examined except for ice-storms and winter storms. However, the State Climate Office of North Carolina noted in its 2015 report that the climate models of the Intergovernmental Panel on Climate Change (“IPCC,” the lead United Nations body on climate change) had predicted warming over the past 50 years, but which had not occurred. The SCONC concluded that, “Unfortunately, the best global climate models we have do not do a good job of simulating the temperature and precipitation patterns over the southeastern US, and NC in particular.”²
2022 Average Temperature Study
Lastly, this author conducted a recent study involving the six geographically dispersed NOAA designated “Primary Local Climatological Data Stations” located in North Carolina, depicted in this graphic and which can be found here.⁵
The working hypothesis of this study was that the statements of scientific consensus of widespread global warming since the 1990’s would be reflected in unprecedented warming temperatures in these six Primary (meaning the highest quality and reliability) weather stations dispersed across the state. However, the results of the study revealed that in only three out of 18 instances, or 16%, were there rises in average temperatures that also did not have a corresponding rise in the average temperature being measured in a 30-year period starting in years prior to 1950. In other words, in 84% of the historical average temperatures at these weather stations, the temperatures were similar to those from the years pre-1950, meaning that generally any rise in average temperatures in the past 30 years is not unprecedented and is similar to the temperatures in the first few decades of the last century.
QUALITY AND RELIABILITY OF WEATHER STATIONS
The quality and reliability of the weather observation stations used when determining historical weather records in the 2020 climate change study should be examined so that the average gardener knows what kind of weather data is being relied upon. The 2020 study notes that it included and relied on the use of so-called “COOP” stations. There generally are three kinds of weather stations in descending order of quality, First Order (also known as Primary), Secondary and then COOP. First Order stations are those of the highest quality and reliability. They are monitored by professionals and reliably record hourly (and even sub-hourly) observations and are subject to additional and more rigorous quality checks than all other stations. As explained by a representative from the National Oceanic and Atmospheric Administration (“NOAA”): “When it comes to station quality, NOAA NCEI First Order stations are about as quality as it comes across the U.S. There are about 500 stations, mainly major airports, that are considered First Order sites, including KRDU (the Raleigh-Durham Airport). These sites often have more instrumentation and include more data when ordering official data from NCEI. Typically, these stations are a part of the Automated Surface Observation System (ASOS).” (“NCEI” = National Centers for Environmental Information).⁶
COOP stations (part of a Cooperative Observer Program), while more numerous, are monitored by volunteers (such as a homeowner with a station placed on his/her property) which can result in gaps in weather data records. While volunteer COOP observers can play an important role in providing weather information for forecasting and basic weather information, periods of missing weather recordings can preclude reliance on them in determining long term trends at a particular site.
While there exists a complex system of quality adjusting to take into consideration the vagaries of the COOP stations, nonetheless, none of the first three North Carolina climate change studies identified above discloses whether any minimum station quality qualifications and criteria were employed or whether any COOP stations were disqualified from use. There exists a First Order station in Wake County and the surrounding Piedmont area at the Raleigh Durham International Airport (RDU, also referred to in weather records as “KRDU”).
As gardeners, we like to get down to ground level, so let’s take an actual look at some local First Order and COOP stations in Wake County.
Here is an aerial shot of the installation that includes the First Order weather station at RDU (id #13722)⁷:
It has been in place since 1944 and is professionally managed and monitored, while recording hourly and sub-hourly observations. It has a 100% record of days recording and reporting the weather data discussed in this article. It presently records 95 weather parameters. Through NOAA’s ThreadEx program⁸, historical weather observations from 1887 by its predecessor station are included in the weather records provided.⁹ Examination of climatic records at weather stations in the ThreadEx program are an accepted, recognized method of assessing regional climate trends in the United States.¹⁰ Among all weather stations in the state, NOAA has designated RDU as one of only six “Primary Local Climatological Data Stations” for North Carolina.¹¹ These stations are regarded as “Primary” because of the extensive and manual quality control checks they are subject to, which other weather stations are not.¹¹
On the other hand, here is an image of a COOP weather station, (id #311535), located in Cary, North Carolina:
It is located in the front yard of a home in a residential neighborhood in Cary and with temperature observations beginning in just in 2001. It monitors three weather conditions, temperature, precipitation and snowfall. It is reported as missing 335 days of temperature observations.¹²
This is the Falls Lake Weather COOP station (id #312993). It is in the backyard of a home in a residential neighborhood.
A closer look reveals that it is a weather apparatus manufactured by the Davis instruments company which can be purchased online.
This station has been in use just since 2000 and is reported to have 505 missing days of temperature data in its average temperature reports.¹³
Here is the list of COOP stations in Wake County as provided by NOAA.¹⁴
Of the 14 COOP type weather stations listed in Wake County¹⁵, six have not been functional this century and two stopped functioning in 2010, 2012, one in 2022 and one in 2023. Of the remaining four stations, three stations have start dates since 2000 and one since 1993. So, for example, three stations with only 20 years of weather data, and missing hundreds of days of data, presumably were included in the 2020 climate change study to determine whether there have been climate changes since 1895. However, NOAA’s clear and unambiguous guidance is that when trying to determine what the climate is like during a period of time (what NOAA refers to as a “climate normal”) at least 30 years of weather observations should be used. Lastly, unlike the RDU First Order station in Wake County, none of these Wake County COOP stations have an uninterrupted report of complete climate records dating back to 1887.
NOAA’s use of at least 30 years of data is longstanding and based on the instructions of almost a century ago by the International Meteorological Organization to calculate climate normals by using 30-year periods. NOAA also relies on the general rule in statistics that at least 30 numbers are needed to obtain a reliable estimate of their mean or average.¹⁶ Additionally, the USDA has stated that at least 50–100 years of data of overall average temperatures are needed to assess changes in the climate.¹⁷
In other contexts, COOP stations only have been used if they meet minimum criteria. For example, in determining the annual minimum temperatures for their Plant Hardiness Zones, the United States Department of Agriculture (USDA) only used COOP stations if they had low temperature recordings at least 80% of the time in the cold months and for a minimum number of years.¹⁸
Using COOP stations with only a few recent years of incomplete observations, or even using older stations yet with significant incomplete records, dilutes the purity of the historical observations, particularly when examining a regional area such as the Piedmont and where higher quality, First Order weather stations with a long history of non-missing data exist.
While most studies and reports on weather and climate issues do not identify the individual weather stations involved, sometimes they are identified when reporting, for example, freeze dates in particular localities. If so, for the home gardener, the reporting history of any weather station can be searched at: http://xmacis.rcc-acis.org, which is supported by the NOAA Regional Climate Centers.¹⁹ Details of an individual station history such as maintenance, location and other items can be found by going to NOAA’s Historical Observing Metadata Repository at https://www.ncdc.noaa.gov/homr/# and entering the station id number or using the search function to find it.
EXAMINATION OF WEATHER DATA FROM FIRST ORDER WEATHER STATION RDU
The following will examine the historical weather data as reported and maintained by NOAA’s climate records for the weather station located at RDU and its NOAA selected predecessor station. Importantly, some of the categories are additional to those examined in prior climate change studies in order to be more directly relevant to gardeners, for example, humidity, average frost dates, growing season and soil temperature (using two stations other than RDU).
AVERAGE TEMPERATURE
The average temperature reported at RDU since 1887 is 60.15°.²⁰ This can be broken down by decade as follows:
1887–1893: 59.34°
1894–1903: 60.05°
1904–1913: 60.17°
1914–1923: 60.17°
1924–1933: 60.92°
1934–1943: 61.89°
1944–1953: 60.19°
1954–1963: 58.82°
1964–1973: 58.89°
1974–1983: 59.05°
1984–1993: 60.07°
1994–2003: 60.07°
2004–2013: 61.38°
2014–2023: 62.10°
A cool, warm, cool, warm trend through the decades can be seen by viewing these numbers and this chart:
The last three decades since 1994 the average temperature has been 61.18°, a 1.03° increase above the historical average. This can be compared to another warming period in the first half of the last century, namely the average temperature in the 30-year period from 1921–1950, which was 60.73° (.60° above the historical average), and which reflects just a .45° difference between these two 30-year periods. So, the average temperature for the past 30 years is not unprecedented in that a prior 30-year period from earlier last century also was more than half a degree warmer than the normal. The five warmest decades since 1887 have been (1) 2014–2023, (2) 2004–2013 (3) 1924–1933 (4) 1934–1943 and (5) 1944–1953.
Climate records from the 1950’s and before are deemed significant by the climatic research community as they occurred during a pre-industrial period reflective of natural (that is, non-manmade) climate conditions. As the lead author of the 2020 North Carolina Climate Study wrote, “Because industrial development was minimal until about midway through the 20th Century, the earlier record reflects mainly natural variability.”²¹
The 2020 North Carolina Climate Change study made references to this earlier warming period, but only compared the single 10-year time-period of 2009–2018 with another single decade, 1930–39. The report found a difference of “about 0.6°” but then moved on without further comparisons with other prior temperature phases in the 1800’s or 1900’s. However, as discussed above, NOAA requires that when comparing climate normals from periods of time to use at least 30-year, not 10-year, periods¹⁷, and it is the position of the lead author of the 2020 climate study that temperatures from the mid-20th century and before reflect non-manmade climate patterns to compare against more modern climate observations and patterns.²¹
AVERAGE MINIMUM TEMPERATURES
The average annual minimum temperature at RDU from 1887 to 2023 was 49.71°.²² The last 30 years since 1994 the average has been 50.36°. The average annual minimum temperature from 1913–1942 was 51.04°. The highest five decades of average annual minimum temperatures have been (1) 1933–1942, (2) 2014–2023 (3) 1923–1932 (4) 1913–1922 and (5) 1893–1902.
It is clear that the past 30 years of average minimum temperatures in in the Piedmont area are not unprecedented and are lower, or colder, than another 30-year period about century ago, from 1913–1942. Here is the chart reflecting these figures.
So, while minimum temperatures have been rising somewhat the past three decades, they were appreciably higher in the first few decades of the last century.
AVERAGE MAXIMUM TEMPERATURES
The average annual maximum temperature since 1887–2023 has been 70.59°.²³ The last 30 years since 1994 the average annual maximum temperature has been 72.01°, a 1.42° increase over the historical average. The average annual maximum temperature from 1928–1957 was 71.11°, a .55° increase over the average, thus again revealing that a 30-year period, or “climate normal,” from nearly 100 years ago also had higher than average maximum historical temperatures.
This is the related chart.
The above three averages show that for the last three decades, the average temperature has risen, but similar to a like period in the last century, the average minimum temperatures are almost a full degree colder than a similar period last century, while the average maximum temperatures have risen but a similar 30-year period in the mid-20th century also had average maximum temperatures higher than the historical average.
MINIMUM DAILY TEMPERATURES EQUAL TO OR ABOVE 75°
Before leaving the basic temperature observations, let’s take a look at the trend described by the 2020 climate change study of an increase in daily minimum temperatures equal to or greater than 75° since 2005, but with a well-above average spike in these types of days in the initial study period of 1900–1904. The study published a graph to illustrate this but notes that the figures used are from three sources, “NCICS (North Carolina Institute for Climate Studies), NOAA NCEI (National Centers for Environmental Education) and the State Climate Office of North Carolina” without explanation as to whose numbers were used, what numbers were used, whether they were combined, or in general how they were compiled.
In any event, the corresponding numbers from the First Order weather station in Wake County at RDU, shows that since 1887 there have been on average 2.96 days a year with the minimum temperature equal to or greater than 75°. There were 4.20 such days on average per year from 1914–1943 and 5.16 such days on average per year from 1994–2023.²⁴
As can be seen from the below graph, years with 10 or more days of 75° minimum temperatures (also referred by some presenters as “warm nights”) have been occurring for all of the weather reporting history, with a 30-year period pre-1950 of having an average of between four and five such days a year along with the last 30-years also having a similar, although slightly higher, average.
❗️
Before leaving this category, keep in mind that in 2015 the State Climate Office of North Carolina specifically found in its Climate Change in North Carolina report that while noting a trend of higher minimum temperatures (which it defined using the term “morning lows), this only was found in urban, not rural areas. The report concluded that this was a result of urbanization of North Carolina’s cities and “was not evidence of any impact from greenhouse gases and global warming to North Carolina’s climate.”² The 2020 study ignored this previously reported urban/rural issue involving a trend in higher minimum temperatures and did not address it.
RAIN
The average annual rainfall at RDU since 1887 is 44.66” a year.²⁵
The last 30 years have averaged 46.43” a year. The 30 years from 1887–1916 had an annual average of 46.66” a year. The year with highest amount of rainfall was 1936 with 64.22.”
Here is the corresponding chart.
The above shows that there has been no recent significant, enduring and unprecedented trend in average annual rainfall.
However, there have been claims about an increased incidence of “extreme’ rainfalls so let’s examine that issue.
“EXTREME” RAINFALL
Extreme rainfall is defined by the 2020 Climate Change report as when it rains three or more inches a day. This type of event could affect our gardens resulting in flooding, standing water, excessive moisture and plant trauma. Even though the 2020 report did not find any trends of significance involving extreme rainfall in the Piedmont region, let’s examine our rainfall patterns nonetheless.
1” RAINFALL EVENTS
The average number of days per year with 1 or more inches of rainfall since 1887 at RDU is 11.75.²⁶ In the last 30 years the average has been 11.93 days per year. From 1912–1941 the average was a similar 11.7 days with 22 days in 1936.
Here is the related chart.
2” RAINFALL EVENTS
The average number of days a year in which it rains 2” or more at RDU since 1887 is 2.21 days.²⁷ For the last 30 years the number is 2.53 days. The average for 1931–1960 was 2.56 days. So, no unprecedented extreme rainfalls of 2” or more per year in the last 30 years.
Here is the related chart.
3” OR MORE OF RAIN A DAY
It has been said that the number of days of “extreme” rain events of 3” or more a day had, and would, increase. Presenters referenced the heavy rainfall effects of Hurricane Matthew in 2016 (the effects of hurricanes to be discussed a bit later). While we all can recall the slow moving, swollen rivers after Matthew, according to the 2020 North Carolina Climate Change report³, no trend of an increasing number of extreme rain events has been found in the Piedmont. It can also be mentioned that the Matthew rainfall was the only extreme rainfall event in the Piedmont in 2016.
The average number of days a year since 1887 it has rained 3” or more is .54.²⁸ The past 30 years has seen an annual average of .80 such days. However, there was a 30-year period from 1931–1960 when the average was a similar .73 days. There have been only two such events the past five years. The 2020 NC Climate Change study found no trend in the Piedmont region relating to these types of extreme rains.
Here is the related chart.
SNOWFALL
The average annual snowfall reported at RDU since 1887 is 6.50”.²⁹ The average for the last 30 years is 5.08”. The average for the 30-year period from 1894–1923 was 5.65,” thus representing a previous 30-year period with below average annual snowfall.
NUMBER OF SNOW DAYS PER YEAR
The average number of days it snowed per year over recorded RDU history since 1887 is 3.61.³⁰ The average number of snow days per year for the past 30 years is 3.2.³⁰ The average number of snow days per year for the 30-year period of 1922–1951 was 3.33, thus reflecting a similar figure in an earlier time period in the last half of the 20th century.
Here is the related chart.
The above data reflects that no meaningful trends appear with respect to snow days.
HUMIDITY
Even though the State Climate Office of North Carolina predicts a more humid future for our state, a review of the relative humidity observations at RDU weather station reveals that there is no observable trend of increasing humidity. The average annual humidity readings in the past 30 years are in fact lower than the overall average. Climate change studies have not addressed whether humidity is increasing or not, perhaps because most weather stations in the COOP network do not report on humidity.
The average annual relative humidity at RDU since 1948 (the first-year reports on humidity are available) is 69.90. The average annual relative humidity in the past 30 years is 69.17.³¹
SOIL TEMPERATURE
None of the previous North Carolina climate studies looked at soil temperatures. However, a presenter at a gardening lecture conjectured that due to presumed warming temperatures a type of plant-parasitic worm (nematode) was migrating into warming soils in Wake County.
According to NOAA, there are two sources of soil temperature records in North Carolina, (1) the USDA Natural Resources Conservation Service, National Water and Climate Center and (2) the State Climate Office of North Carolina. However, the USDA source only has one station gathering soil temperature information and it is located in a far eastern part of the state in Plymouth, Washington County, and has only been reporting soil temperatures since 1994.
The State Climate Office of North Carolina, however, operates two weather stations in Wake County reporting on soil temperatures, the Lake Wheeler Road Field Lab and the Reedy Creek Field Lab. According to the SCONC these “ECONet” type stations are the only source of monitored and reported soil temperature recording data in the state.³² The Lake Wheeler station has been reporting soil temperatures since 1982 while the Reedy Creek Lab has been reporting them since 2001.
However, each station has had missing time periods and other irregularities in reports of its figures. First, there is some odd reporting of records for the Lake Wheeler station. Its soil temperature records from 1982–2022, when accessed on March 3, 2023, contained missing values for 12 years, or 1993–2003 and 2008. However, when these same records for 1982–2023 were accessed on February 4, 2024, the report listed only five years of missing values, or 1993–1997, with no explanation of how previously missing temperature values from over 20 years ago were now included. See, these two reports at endnote 33.
Further, when the Reedy Creek records were accessed on March 23, 2023, the report reflected that this station was missing (including obviously incorrect recordings such as -499.3°) seven different years of soil temperature recordings since it began taking readings in 2001. However, when accessed on February 4, 2024, without any explanation, each of the years had a figure in it. However, these figures remain suspect as while they all are around the approximate 60° mark and the reading for the year 2012 is only 35.7°. ³³ These significant missing periods of time and mysteriously changing reports (see endnote 33) prevent a clear and credible analysis of soil temperatures over a relevant and useful period of time.
However, since soil temperatures are so important to gardening, let’s at least take an informal, even if not scientifically reliable, look at the average annual soil temperatures at the Lake Wheeler station based on the most recent information available. Since the Reedy Creek station last year had only has 10 complete years of information since its installation in 2001 and this year still has suspect figures, a review of its readings is not warranted.
To the extent the Lake Wheeler Road station’s most recent average annual soil temperature records are from 1982 through 2023, but still missing five years from 1993–1997, the first 30 years averaged soil temperatures (again, not counting 1993–1997) of 63.10°. The most recent 30 years (also not counting 1993–1997) reflects average annual soil temperatures of 62.79°.³³
To the extent there is available soil temperature data, the Lake Wheeler station reflects somewhat cooler average annual soil temperatures in the past 30 years compared with its first 30 years starting in 1982, so no warming trend. In any event, due to the recent beginning dates of observations and the large amounts of missing and changing data, these stations cannot confidently be used to determine trends in soil temperatures in Wake County. Consequently, there is no long-term, reliable evidence to support an assertion that soil temperatures have experienced any significant, enduring warming in the Central Piedmont area of North Carolina, and the lack of recording history into the mid-20th century and beyond preclude any analysis of precedential temperature records.
DROUGHT
The 2015 Climate Change in North Carolina report did not find any long-term trends in either the Piedmont or the entire state with respect to droughts.² The 2020 NC Climate Change study concluded that droughts are a natural part of North Carolina’s climate and did not find any increase in droughts over history.³
Additionally, in the most recent North Carolina Department of Environmental Quality, Division of Water Resources, NC Drought Management Advisory Council Annual Report (2023), it was stated that no clear historical trend had been seen and summarized North Carolina’s history of droughts as follows:
“North Carolina experienced extreme drought conditions from 1925 through 1927 with PHDI values reaching -4.1 at one point. A very wet period followed and then an extreme 16 drought occurred in 1932–1933. This extreme drought period saw the lowest individual monthly PHDI value of -4.74. Occasional, Moderate Droughts occur in the 1940’s and 1950’s but it wasn’t until the late 1980’s that extreme drought returned. The PHDI reached a low of -4.6 in July 1986. Moderate to wet conditions returned in the 1990’s but two of the most extreme droughts in North Carolina’s recorded meteorological history occurred between 2000 and 2010. One of the wettest years also occurred during this period. Since 2010, conditions have been less extreme but highly variable swinging from moderately wet to moderately dry. … The North Carolina PHDI values for the report period averaged -1.76 (NOAA, 2023). These values reflect the very wet winter period and a moderately dry spring. Since the 2007 to 2008 drought, conditions had been trending wetter than normal. However, conditions over the last year swung back to below normal … .”³⁴
These conclusions came along with the following chart showing the occurrences and severity of droughts in the state since 1895 to 2021.
As for Wake County, NOAA’s National Integrated Drought Information System contains information in graphic format about the frequency and severity of droughts in specific counties.³⁵ Here is a chart of the drought history in Wake County from 1895 through 2023:
As can be seen, the dark, tall thicker red spikes reflect extreme drought conditions over time, with the last one in 2007 and not much since then and with apparent frequent and intense drought activity in the 1920s and 1930s.
The last drought of significance in memory that brought about water use restrictions to Wake County residents was in 2007. Even so, the State Climate Office of North Carolina in its 2015 report concluded that longer-term data “suggests drought periods in the past that may have been more severe than those witnessed in NC in modern times.”²
In short, from the beginning of drought-related measurements in the late 1800’s, North Carolina occasionally experiences extreme drought and annually experiences some periods of drought in different parts of the state and this pattern continues to the present.
Lastly, a word about a term that is appearing in more informal reports on this topic, that is, the phrase, “flash drought.” The above noted report by the NC Drought Management Advisory Council Annual, to its credit, focused on the serious subject matter of actual droughts and did not engage in the use of the non-serious term “flash drought.” Unfortunately, the State Climate Office of North Carolina has begun to use the term to describe what has historically been known as a “dry spell.”
The 2002, 2015 and 2020 North Carolina studies did not even consider the subject of a dry spell worthy of investigation or discussion and the term “flash drought” was never used. Lastly, if “flash droughts” were such a scientifically established phenomena, there would be an accepted definition of what they are. However, a group of scientists, including two from NOAA, tried to determine what a “flash drought” was and found that there are at least 29 different definitions in the scientific literature.³⁶ Accordingly, it is not a credible, established meteorological principle, and instead apparently a recent catchy phrase used by those who want to impart a sense of alarm, instead of focusing on the serious issue of real drought.
HURRICANES
Have extreme weather events such as hurricanes become more frequent and/or more powerful? Hurricanes in the past have significantly affected Wake County and the Piedmont and can cause a great deal of destruction, including, from a gardener’s perspective, the toppling of trees and washing out and blowing away of gardens.
Initially, though, from an on-the ground perspective, a recently retired manager of the City of Raleigh Urban Forestry Department commented that the only widespread destruction of trees in the area in recent memory has been from hurricanes Hazel in 1954 and Fran in 1996.³⁷
As far as the frequency of hurricanes affecting the state as a whole, a chart from the State Climate Office of North Carolina illustrates that the frequency of all storms affecting the state of North Carolina has declined in the last decade and had its peaks in the 1950s and 1970s.³⁸
The graph above shows the total number of all types of storms (however weak) affecting North Carolina by decade.
If the storms less powerful than tropical storms are removed from consideration, this is what the chart looks like for tropical storms and all hurricanes³⁸
The above charts clearly illustrate that the number of tropical storms and hurricanes affecting North Carolina has precipitously fallen off over the decades.
The State Climate Office of North Carolina removed these charts illustrating the decline in the number and intensity of hurricanes affecting North Carolina from its website since the publication of this author’s original article in 2021. However, SCONC reports no hurricanes affecting North Carolina in 2022 or 2023 so the information communicated by these charts remain the same.
Until 2022 the SCONC provided data as to the historical statewide number of storms greater than or equal to 25 miles per hour making direct landfall on North Carolina. This historical data, when compiled in a bar chart, reflects this information showing the number of such storms decreasing in the past several decades:
Storms of the same wind velocity “affecting North Carolina” according to the SCONC look like this, with a marked decrease in the past decade:
Examining the data from more of the center of the state, the following charts from the SCONC show the frequency and intensity of all storms categorized as “tropical storms” (40 miles per hour or more) since 1851 and within 100 miles of the original State Capital at 1 E. Edenton Street in Raleigh. This data contains reports of all storms with winds of 40 mph or more, so includes all tropical storms and hurricanes within 100 miles of the Wake County area through 2023.³⁸
The above charts reflect that since 1851 the frequency of tropical storms and hurricanes within 100 miles of the Original State Capital in Raleigh has been as follows:
1994–2023: 3 hurricanes, 10 tropical storms
1964–1993: 5 tropical storms
1934–1963: 8 tropical storms
1904–1933: 7 tropical storms
1874–1903: 3 hurricanes, 15 tropical storms
1851–1873: 1 hurricane, 7 tropical storms (only 23 years)
Notable is the year 1893 which had three tropical storms, including a Category 1 hurricane. There have been only four tropical storms and no hurricanes in the past 10 years.
The below chart illustrates the above information.
But some commentators have said that even if the hurricanes are less frequent, they have become more powerful. So, let’s look at the same history of tropical storms above, but set out and ranked by strength in terms of mile per hour winds (measured down to a maximum of 40 mph).
Placed in chart form, below is the above information through 2023 which reflects that storm intensity has been decreasing over the decades.
As shown above, for the past 173 years tropical storms and hurricanes in the Wake County area, and the state itself, have not been becoming more frequent nor more powerful in recent years. They were more frequent and stronger farther back in history.
SPRING AND FALL FREEZE DATES
All gardeners pay attention to freeze dates, especially the Spring freeze date (which in meteorological circles is referred to as the “last” freeze date and the Fall freeze date is the “first” freeze date). Gardeners’ Spring planting decisions revolve around the average last freeze date and impatient gardeners spend a great deal of money on early Spring plant purchases and make strategic decisions about moving plants from the inside, whether it be the house, garage or greenhouse, to the outdoors.
According to NOAA, the average Spring freeze date in Wake County and surrounding area, per the RDU station (1887–2023), is April 4th. The average Fall freeze date is November 4th.³⁹
The earliest last Spring freeze date is March 1st in 1935 and the latest last Spring freeze date is May 9 in 1956.
Here are charts depicting these dates over time, first for Spring through 2023 and then for Fall through 2023. To the extent that global warming advocates warn that the last Spring freeze date is, or will be, occurring earlier and earlier in an unprecedented manner as the growing season allegedly becomes longer, this is not borne out by the historical data which shows most of the earlier Spring freeze dates occurring in the first half of the last century.
Similarly, the “first” Fall freeze date has not been delayed in a significant, enduring and unprecedented manner as borne out by the following chart.
Gardeners should be in verify mode when presented with “average freeze date” calculations, primarily to ensure the information is the best available and applicable to their location. An example is a Wake County COOP type weather station which has been used to represent average freeze dates, the Falls Lake station, COOP id #312993, images and a description of which appear above in this article. While this station was first put into service in 2000, it is missing significant periods of data and has been situated in three different locations. The station did not start reporting data in years in which both the Spring and Fall freeze dates could be determined until 2009 and overall is missing over 35% of the first/last freeze dates for the period from 2000–2023. It also failed to report any first freeze date for the Fall of 2019.
By contrast, the RDU station information has yielded data for each year since 1887, as seen below:
For those gardeners interested in determining freeze dates in your vicinity, you can consult the weather station at the nearest Primary Local Climatological Data Stations (see endnote 11) or at your nearest and largest airport since these are likely to have more complete data than other stations. In any event, freeze date and growing season information is easily obtained for any station by going to the climate center designated by NOAA as the lead agency for determining freeze dates at locations across the country, the Midwestern Regional Climate Center (“MRCC”): https://mrcc.purdue.edu/CLIMATE/index.jsp and see further details and instructions at endnote 39.
PLANT HARDINESS ZONES
The developers of the plant hardiness zone maps have stated that these zones, or any change in the zones, should not be used as a proxy for whether climate change is occurring, primarily because they are based only on one low temperature reading a year. Even so, it is interesting to note that Wake County, and many other areas in the Piedmont area of North Carolina recently were reassigned to plant hardiness zone 8(a), which actually is where they were for many years from 1928–1990. See related article here.
GROWING SEASON
The length of time between the two average Spring and Fall freeze dates is referred to as the growing season and its current average length in the Wake County and surrounding Piedmont area is 213 days³⁹.
Here is a decade-by-decade numerical summary of the length of the growing season since 1887:
1888–1893: 218
1894–1903: 227.3
1904:1913: 219.4
1914–1923: 224.1
1924–1933: 235.6
1934–1943: 236.3
1944–1953: 206.4
1954–1963: 201.7
1964–1973: 195.7
1974–1983: 193.3
1984–1993: 204.1
1994–2003: 207.5
2004–2013: 214
2014–2023: 216.2
The average length of the growing season in the past 30 years (212.7 days) is shorter than the historical average of 213 days and markedly shorter than the time period in the late 1800’s and the first half of the last century (for example the 30-year time period from 1912–1941 the average length of the growing season was 232.20 days).³⁹ So, the recent growing season is significantly shorter than the average during periods in the first half of the last century.
Here are these figures in chart form through 2023.³⁹:
The chart illustrates that our recent growing season lengths are not unprecedented and are shorter than the majority of historical recorded periods.
CONCLUSIONS
The 2002 and 2015 reports on climate change in North Carolina conclude there are no significant, enduring and unprecedented statewide climatological trends that are associated with global warming. A third study in 2020 reported temperature trends in the Piedmont region reflective of global warming present in only some, but not most, temperature categories, with no increase in extreme weather events, and overall found only a less than 1 degree rise in average temperatures since 1895. A 2022 study found that there have been no unprecedented change in 84% of three average temperature categories from North Carolina’s six Primary Local Climatological Data Stations.
This article’s examination of average temperatures in the Wake County area in North Carolina’s Piedmont region found recent 30-year average temperatures rising, but in similar fashion of past periods, average minimum temperatures decreasing, and average maximum temperatures increasing, although periods of increase also occurring in the last century. While days with minimum temperatures of 75 degrees or more occurred more frequently than average in periods in both the 1900’s and this century, the only study to address the issue (the 2015 State Climate Office Climate Change Report) found that this only occurred in urban, nor rural, areas and was not related to global warming.
Looking at special categories of interest to gardeners (humidity, soil temperature, average freeze dates, growing season) reveals that there do not appear to be any abnormal and unprecedented trends occurring and if anything, seasonal coolness trends are indicated with shortening growing seasons in recent years compared to the last century. Extreme weather events such as 3” rains and hurricanes have not increased in frequency or intensity, with hurricane activity and intensity clearly decreasing locally and across the state over the past several decades. Drought has not been an issue for a long time and in any event is noted to appear periodically throughout history.
By Tom Packer, North Carolina State Extension Certified Master Gardener, President of the Gardeners of Wake County, Board Member of the North Carolina Cooperative Extension Agricultural Programs Foundation and longtime backyard farmer in North Carolina and Northern California. All this article’s content is that of Mr. Packer alone as an individual and not as a member of or on behalf of any organizations or groups with whom he is affiliated, including those identified above.
Other horticulturally related articles by Mr. Packer can be found at https://medium.com/@tpacker25.
ENDNOTES
[1] https://drive.google.com/file/d/1MI4vnDo9vrH-YRSbwpIQqjhYnB5PnHeS/view?usp=sharing
[2] https://web.archive.org/web/20150420025024/http://www.nc-climate.ncsu.edu/climate/climate_change and https://drive.google.com/file/d/1Y4YgPJ7L0-YW7b3k1vGGTggEXw8AOCFs/view?usp=sharing
Note: This report was found in a website archive search site. It was captured by the website archive service on April 20, 2015 and prior dates. This report no longer appears on the website of the State Climate Office of North Carolina.
Heating Degree and Cooling Degree Days, which are used to quantify the energy needed to heat or cool buildings and houses, were found to vary over time in concert with the area’s annual average temperature and are not addressed in this article.
[4] https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=gov.noaa.ncdc:C00861;view=iso; https://www.ncei.noaa.gov/metadata/geoportal/rest/metadata/item/gov.noaa.ncdc:C00861/html
See, “Publications citing this dataset should also cite the following article: Matthew J. Menne, Imke Durre, Russell S. Vose, Byron E. Gleason, and Tamara G. Houston, 2012: An Overview of the Global Historical Climatology Network-Daily Database. J. Atmos. Oceanic Technol., 29, 897–910. doi:10.1175/JTECH-D-11–00103.1.”
[6] Personal communication with author — July 20, 2020.
[7] While the RDU weather station is a First Order station, identification #13722, according to a NOAA representative all major airport weather stations are also assigned a COOP station number, here, RALEIGH AP #317069, even if they are not COOP-type stations. So, there is only one weather station at RDU, it is a First Order station, and there is not a separate COOP station at the site.
[8] See, https://threadex.rcc-acis.org/ re NOAA’s ThreadEx records (click on “About.”).
[9] APPENDIX B — Accessing NOAA Daily Temperature and Precipitation Extremes Based on Combined/Threaded Station Records, NATIONAL WEATHER SERVICE INSTRUCTION 10–1004, MAY 17, 2020, “This new ThreadEx data set provides a consistent basis for the reporting of daily extremes for the longest period of time meaningful. With the ThreadEx effort, maximized, consistent, updated daily extremes will be available for government, partner, and general public (especially media) use.” And see, Yuchuan Lai, David A. Dzombak, Use of Historical Data to Assess Regional Climate Change, Journal of Climate, 10.1175/JCLI-D-18–0630.1, 32, 14, (4299–4320), (2019), citing Kunkel, K. E., D. R. Easterling, K. Redmond, and K. Hubbard, 2003: Temporal variations of extreme precipitation events in the United States: 1895–2000. Geophys. Res. Lett., 30, 1900, “The availability of these pre‐1948 daily data affords an opportunity to perform studies with unprecedented detail, extending back to the late 1800s of trends in short duration extreme events.”
[10] Use of Historical Data to Assess Regional Climate Change, Yuchuan Lai and David A. Dzombak, Journal of Climate, American Meteorological Society, July 15, 2019, pages 4299–4320, https://doi.org/10.1175/JCLI-D-18-0630.1
[11] NATIONAL WEATHER SERVICE INSTRUCTION 10–1004, MAY 17, 2020, Operations and Services, Climate Services, NWSPD 10–10, Appendix C. The other five Primary Local Climatological Data Stations (PLCDs) in North Carolina are Asheville Regional Airport (AVL), Hatteras Billy Mitchell Airport (HSE), Charlotte Douglas International Airport (CLT), Greensboro Regional Airport (GSO) and Wilmington New Hanover Airport (ILM). These stations are regarded as “Primary” because of the extensive and manual quality control checks they are subject to, which other weather stations are not. (Per communication with NOAA representative on April 27, 2021).
[12] http://xmacis.rcc-acis.org/ — Seasonal Time Series / Avg temp / Mean / por -2023 / Annual / Average of Months / Daily Station Selection 311535; https://docs.google.com/document/d/1YhsD2XL28UzRj1UXhSwc_DidEvOhuxqd/edit?usp=sharing&ouid=115138207048984797333&rtpof=true&sd=true
[13] http://xmacis.rcc-acis.org/ — Seasonal Time Series / Avg temp / Mean / por -2023 / Annual / Average of Months / Daily Station Selection 312993; https://docs.google.com/document/d/1kgw9fY-NoMUXtzqEW1GOIlnuIzyXjaJG/edit?usp=sharing&ouid=115138207048984797333&rtpof=true&sd=true
[14] Communication from NOAA representative with author on January 21, 2021.
[15] The station identified as 317069 NSW COOP Raleigh AP is not included in this count of COOP stations as this is, per endnote 6, First Order station KRDU #13722.
[16] See: https://www.ncdc.noaa.gov/news/defining-climate-normals-new-ways
[17] See: https://drive.google.com/file/d/1MA7gw5GgsVCusiA8JwzZaUqvsFqRN6AV/view?usp=sharing and http://web.archive.org/web/20201114005450/https://planthardiness.ars.usda.gov/PHZMWeb/AboutWhatsNew.aspx
[18] Daly, C., M.P. Widrlechner, M.D. Halbleib, J.I. Smith, and W.P. Gibson. 2012. Development of a new USDA Plant Hardiness Zone Map for the United States. Journal of Applied Meteorology and Climatology, 51: 242–264 at 259.
[19] After entering the site at http://xmacis.rcc-acis.org/, for RDU historical records, enter Single Station, Seasonal Time Series, the weather record and time-period and select the station by entering its station, Raleigh area, and then RDU.
[20] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ av temp/mean/ por — 2023 / Station: Raleigh Area/ RDU
[21] Temporal Variations of Extreme Precipitation Events in the United States: 1895–2000, Kenneth E. Kunkel, David R. Easterling, Kelly Redmond, Kenneth Hubbard, American Geophysical Union (AGU), GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 17, 1900, September 09, 2003. https://doi.org/10.1029/2003GL018052
[22] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ min temp/mean/ por — 2023 / Station: Raleigh Area/ RDU
[23] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ max temp/mean/ por — 2023 / Station: Raleigh Area/ RDU
[24] http://xmacis.rcc-acis.org/ : single station/seasonal time series/min temp/number of days/Threshold: ≥ 75°/ por — 2023 / Station: Raleigh Area/ RDU
[25] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ precipitation/sum/ por — 2023 / Station: Raleigh Area/ RDU
[26] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ precipitation/number of day/ equal to or greater than 1 inch/ por — 2023 / Station: Raleigh Area/ RDU
[27] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ precipitation/number of day/ equal to or greater than 2 inches/ por — 2023 / Station: Raleigh Area/ RDU
[28] http://xmacis.rcc-acis.org/ : single station/seasonal time series/ precipitation/number of day/ equal to or greater than 3 inches/ por — 2023 / Station: Raleigh Area/ RDU
[29] http://xmacis.rcc-acis.org/: single station/seasonal time series/ snowfall/sum/ por — 2023 / Station: Raleigh Area/ RDU. Reported trace amounts were counted as .01 inches.
[30] http://xmacis.rcc-acis.org/: single station/seasonal time series/ snowfall/number of day/ ≥.1 inch/ por — 2023 / Station: Raleigh Area/ RDU
[31] This information formerly in 2021 was accessible at: https://climate.ncsu.edu/cronos/?station=KRDU&temporal=monthly%20Average%20Daily%20Relative%20Humidity/average/percent%20(%)/height%20%E2%80%93%202m . However, now it must be accessed after registration with the State Climate Office of North Carolina at: https://products.climate.ncsu.edu/cardinal/ The humidity readings obtained can be found at: https://docs.google.com/document/d/1pnNDqG8UINEi6lTTozeNC2bRkwSm3NbU/edit?usp=sharing&ouid=115138207048984797333&rtpof=true&sd=true
[32] Communication with author on July 27, 2020.
[33] This information formerly was available at:https://climate.ncsu.edu/cronos/?station=LAKE&temporal=monthly%20Soil%20temperature%20daily%20mean/average/0.1m
The information is now accessible at https://products.climate.ncsu.edu/cardinal/request/ (account registration and sign-in required). See these stored documents at the following links for the mentioned reports from the Lake Wheeler and Reedy Creek weather stations accessed in 2023 and 2024:
[34] https://www.deq.nc.gov/legislative-reports/north-carolina-drought-management-advisory-council-report/open [ Predictions and a non-sensical statement at end of paragraph omitted, see above for full text of quote].
[35] https://www.drought.gov/historical-information?state=north-carolina&countyFips=37183, 1895-Present Monthly
[36] https://stateclimate.org/pdfs/journal-articles/2021_1-Lisonbee.pdf
[37] September 11, 2020 post on Nextdoor.com.
[38] https://climate.ncsu.edu/climate/hurricanes/statistics. While this particular bar chart has been removed by the State Climate Office of North Carolina from its website, its current search function for the same type of storms does not reveal any such storms after 2019: https://products.climate.ncsu.edu/weather/hurricanes/affecting/?state=NC&buffer=150. All data accessed for this section in February, 2024.
[39] https://mrcc.purdue.edu/CLIMATE/index.jsp
Daily observed data, Seasonal, Seasonal Statistics
Growing season/ ≤ 32°/1887–2023, Find a station, NC, ThreadEx/Raleigh Area (Station ID: RDUthr). Sign up for free account and sign in. Once logged in, change the daily station to KRDU at the top of the screen. Historical first and last freeze dates are located in the menu on the left under Daily-Observed Data — Seasonal- Seasonal Statistics. Select the Frost Season and if necessary, change the temperature threshold to ≤ 32°. Figures for years 1893, 1894, 1925 and 1926 included from report accessed on 3/21/2023. A 2/9/2024 email sent to mrcc@purdue.edu inquiring about the missing data for these four years in the report accessed on 2/8/2024 did not receive a response. NOAA has designated the Midwestern Regional Climate Center (MRCC) as the lead climate center for determining average freeze dates around the country.
[40] Definition per the MRCC.
