Mississippi has exhibited little overall warming in near-surface air temperatures over the 20th and early 21st centuries. However, under a higher emissions pathway, historically unprecedented future warming is projected by the end of the 21st century.
Future changes in average precipitation are uncertain, but increases in extreme precipitation are projected. Higher temperatures will increase the rate of loss of soil moisture during dry spells, increasing the intensity of naturally occurring droughts.
Sea level rise poses widespread and continuing threats to coastal communities of Mississippi. Potential impacts of sea level rise include higher storm surge and disappearing barrier islands.
Mississippi is located on the coast of the Gulf of Mexico and on the southern end of the vast, relatively flat plains of central North America. The state is therefore exposed to diverse air masses, including the warm, moist air over the Gulf of Mexico as well as dry continental air masses, which are cold in the winter and warm in the summer. Relatively mild winters, hot summers, and year-round precipitation characterize Mississippi’s climate. In addition to serving as a predominant source of moisture, the warm waters of the Gulf of Mexico help moderate temperatures along the coast. This mild climate is an important economic driver for agricultural production and tourism. Statewide average annual precipitation is about 56 inches, ranging from 50 inches in the north to about 65 inches along the coast. Historical observed extreme temperatures for the state range from −19°F at Corinth (January 30, 1966) to 115°F at Holly Springs (July 29, 1930).
Temperatures in Mississippi were highest in the 1920s and 1930s, followed by a substantial cooling of almost 2°F throughout the 1960s and 1970s (Figure 1). Temperatures have risen since that cool period by about 2°F, such that the most recent one to two decades have been slightly above the long-term average. Because of the large cooling that occurred in the middle of the 20th century, the southeastern United States is one of the few locations globally that has not experienced overall warming since 1900, while the United States as a whole has warmed by about 1.8°F. The United States as a whole also cooled from the 1930s into the 1960s, but not by nearly as much as Mississippi. Potential hypothesized causes for this difference in warming rates include increased cloud cover and precipitation, increased small particles from coal burning, natural factors related to forest re-growth, decreased heat flux due to irrigation, and multi-decade variability in North Atlantic and tropical Pacific sea surface temperatures. However, the years 2015, 2016, and 2017 were the 10th, 3rd (tied with 1911 and 1923), and 6th (tied with 1998) warmest years on record, respectively, in Mississippi.
A record number of extremely hot days occurred in the early 1950s, with an average of 10 days above 100°F each year. In the 21st century, there has been an average of about 3 such days per year (Figure 2a). The number of days below freezing (maximum temperature at or below 32°F) was well above average in the 1970s and 1980s, but since then has been highly variable (Figure 2b). During the last nine years, both the number of very warm nights (minimum temperature at or above 75°F) (Figure 3) and the daily average summer temperature (Figure 4) have been above average, with a record number of very warm nights (a 5-year average of about 15.5 days per year) in the 2010–2014 period, a little above the previous record set in the 1930–1934 period (about 15 days per year).
Average annual precipitation in Mississippi has generally been above average since the 1970s. (Figure 2c). The driest 5-year period was 1895–1899 averaging less than 48 inches per year, while the wettest was 1970–1974 averaging more than 65 inches per year. Average summer precip has been near to above average since the late 1980s with the highest averages on record occurring in the 2000–2004 and 2015–2018 periods (Figure 2d), although a few individual summers, including 2000 and 2006 have been quite dry. The annual number of extreme precipitation events (days with 3 or more inches) has been near the long-term average (1.5 events per station per year) in the last decade (Figure 5). Agricultural droughts during the summer are frequent occurrences in Mississippi. Since the creation of the United States Drought Monitor Map in 2000, Mississippi has only been completely drought- free for approximately 48% of the time from 2000 to 2018 and has had at least 50% drought coverage for approximately 12% of the time during the same period.
Mississippi experiences an array of extreme weather events including severe thunderstorms, flooding, extreme heat, tornadoes, winter ice storms, and tropical cyclones (hurricanes and tropical storms). Between 2005 and 2018, a total of 20 FEMA disaster declarations were awarded to the state, 15 of which were for severe storms, tornadoes, and flooding events and the other 5 declarations were awarded in response to hurricanes. The typical flood season is November through June when the Mississippi River has its highest flow, although tropical cyclone flooding on smaller rivers occurs in the late summer and fall. Flooding of historic proportions occurred along the Mississippi River in the spring of 2011, following record snowmelt and unprecedented rainfall upstream of the state. Flood damage was estimated at $800 million in agricultural production for Mississippi alone.
Hurricanes can cause catastrophic damage. Hurricane Camille devastated parts of the state in 1969 as either the strongest (peak wind speed) or the second strongest (minimum pressure) storm (Category 5) to strike the United States in the 20th century. Damage estimates approached $950 million (1969 USD) for Mississippi. In 2005, Hurricane Katrina caused extensive damage along the coast of Mississippi as well as inland, including 238 fatalities and billions of dollars in damages. The storm surge at Pass Christian was 22.6 feet for Camille, and 27.8 feet for Katrina. Along the Mississippi coast, surges of approximately 15 feet have an average return period of 25 years, and surges of 20 feet and greater have an average return period of 50 to 100 years (Figure 6).
Tornadoes are another important weather hazard for Mississippi. Over the past 30 years (1985–2014), Mississippi has averaged 43 tornadoes annually, with 4 fatalities per year. The state ranks 12th nationally for the total number of reported tornadoes, but ranks as 1st in the nation in tornado deaths per million people. Since 2005, the state has experienced its three highest annual number of tornadoes: in 2005 (100 tornadoes), 2008 (110 tornadoes), and 2011 (97 tornadoes). Tornadoes occur year-round, but there is a distinct tornado season with occurrences peaking in April and a second, smaller peak in November.
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). Since the 1970s, Mississippi temperatures have generally been within the range, but on the low end, of model-simulated temperatures. Warming is projected despite the lack of a long-term trend in Mississippi temperatures because the increased warming influence of greenhouse gases will become greater than the natural variations that have dominated Mississippi’s temperature climate.
Projected changes in summer precipitation for Mississippi are uncertain through mid-century (Figure 7). This is also the case for the other three seasons. However, future naturally-occurring droughts may be more intense because higher temperatures will increase the rate of loss of soil moisture during dry spells. During such droughts, decreased water availability will likely have important implications for the region and state’s agricultural economy.
Since 1900, global average sea level has risen by about 7–8 inches. Sea level rise along the Mississippi coast may be even higher; the closest tide gauge with long- term data (Alabama’s Dauphin Island) reports a rise of more than 11 inches over the past century. Sea level rise has caused an increase in tidal floods associated withnuisance-level impacts. 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. Nuisance flooding has increased in all U.S. coastal areas, with more rapid increases along the East and Gulf Coasts. Nuisance flooding events in Mississippi are likely to occur more frequently as global and local sea levels continue to rise.
Sea level is projected to rise 1 to 8 feet by 2100, with a likely range of 1 to 4 feet, as a result of both past and future emissions from human activities (Figure 8). Sea level rise has the potential to significantly damage critical transportation assets and negatively impact coastal resort communities along the Gulf Coast of Mississippi. Erosion of the barrier islands may further increase the potential impacts of sea level rise as these islands can shield the densely populated coastal areas, like Gulfport and Biloxi, from storm surge. The rate of erosion is increasing; for example, Ship Island has lost about 40% of its total area since 1970.