Arkansas has exhibited little overall warming since the early 20th century, but temperatures in the 21st century have been about as warm as the previous record levels of the 1930s and 1950s. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.
The intensity of future naturally occurring droughts is projected to increase because higher temperatures will increase the rate of loss of soil moisture during dry spells.
The number and intensity of extreme heat and extreme precipitation events are projected to increase in the future while the intensity of extreme cold events is projected to decrease.
Arkansas is located in the interior southern United States. The state is close, but not adjacent to the Gulf of Mexico, resulting in a climate that is largely characterized by moderately large variations in temperature and abundant precipitation. Summers are hot and humid, while winters are typically short and cool, with occasional episodes of cold Arctic air. A diagonal line, cutting across the state from northeast and southwest, demarcates the topography of Arkansas. The area northwest of that line includes the Arkansas Ozark Mountains and is generally higher in elevation. Thus, temperatures are generally cooler in this area, particularly in the Boston Mountains portion of the range where some peaks exceed 2500 feet. For example, the average high temperature in July is 90°F at Newport (elevation of 230 feet) in the northeast, while the average high temperature is 82°F at Deer (elevation of 2375 feet) in the northwest. Average low temperatures in January range from 20–25°F in the northwestern tip to 25–30°F in the northeast to 30–35°F in the southwestern portion of the state. Precipitation is abundant throughout the year. Heavy rains can produce totals in excess of 10 inches. Winter and spring are the wettest seasons. The year 1963 was the driest year on record since 1895 with a statewide average of 32.8 inches of precipitation; while the wettest year recorded was 2009, with an average of 72.2 inches of precipitation. Historical extreme temperatures for the state range from a record 120°F in Ozark, set on August 10, 1936 to a record low of -29°F in Gravette set on February 13, 1905.
Arkansas has not seen a significant overall increase in temperature since the early 20th century—similar to the rest of the southeastern United States. Arkansas warmed from the early 20th century into the 1930s followed by a period of cooling into the 1970s of about 2°F. Gradual warming has occurred since the 1970s (at about the same rate as the rest of the United States), but the recent higher temperatures (slightly above the long-term average) have not exceeded those of the 1930s (Figure 1). 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 1.5°F. The United States as a whole also cooled from the 1930s into the 1960s, but not by nearly as much as Arkansas.
The number of extremely hot days (maximum temperature above 100°F) peaked during the 1930s and early 1950s, and both time periods were accompanied by drought (Figure 2a). Since the mid-1950s, the number of such days has been near or below average. Although the number of extremely hot days has not been unusual, mean summer temperatures and very warm nights (minimum temperature above 75°F) during 2010–2014 equaled or exceeded previous record levels, primarily because of an unprecedented warm string of three summers (2010-2012). For 2010–2014, the number of very warm nights was double the long-term average (Figure 3) and annual average summer temperatures were 1.5°F above average (Figure 4), matching or exceeding records set in the 1930s and 1950s. The number of very warm nights in 2015 and 2016 were also well above the long-term average. A winter warming trend is reflected in a below average number of very cold nights (minimum temperature below 0°F) over the past two decades (1990–2014) (Figure 2b).
There is no overall trend in average annual precipitation in Arkansas (Figure 2c). There is also no trend in the annual number of extreme precipitation events, although the highest 5-year average number occurred in 2005–2009, with the number (1.6 days per year) about 40% above the long-term average (1.1 days per year) (Figure 5) because of exceptionally high values in 2008 (3rd highest year since 1900) and 2009 (highest year); the 2nd highest annual value was in 2015. Average annual summer precipitation has been near or below average since the 1980s (Figure 2d). Water levels in the Alluvial Aquifer, the primary source of groundwater in Arkansas, have declined by about 3.7 feet from 2004 to 2014. A vitally important characteristic of the precipitation climatology is its high variability. In recent years, severe drought episodes occurred in the state during 2005–2007 and again during 2010–2012, interrupted by the wettest year on record in 2009 and followed by the fifth wettest in 2015. The driest 5-year period was 1952–1956 with annual average precipitation of 41.97 inches and the wettest was 1990–1994 with 56.62 inches. Arkansas was one of the hardest hit southeastern states during the 2012 drought. Each of the state’s 75 counties received a drought-related disaster declaration. Since the creation of the United States Drought Monitor Map in 2000, Arkansas has only been completely drought-free for approximately 39% of the time (2000–2014) and has had at least 50% or more drought coverage for approximately 19% of the time during that same period.
Extreme weather events in Arkansas include severe thunderstorms, tornadoes, flood-producing heavy rain, and winter ice storms. The most destructive flood in United States history, the Mississippi River Floods of 1927, affected Arkansas by inundating 36 out of 75 counties across the state, with floodwaters as deep as 30 feet in some places. This flood was a result of persistent heavy rainfall across the central United States from August 1926 through the spring of 1927. The unprecedented amounts of rainwater run-off overwhelmed the protective levees. This event led to the Flood Control Act of 1928, allowing for federal government authority to contain the Mississippi River and mitigation efforts that have helped to prevent future flooding events of this magnitude. In May of 2011, floods submerged more than one million acres of Arkansas farmland, costing the state’s agricultural industry approximately $500 million in damages. In the most recent decade, a total of 23 FEMA disaster declarations have been awarded to the state, the majority of which (16 declarations) were for severe thunderstorms, tornadoes, and flooding. Arkansas regularly experiences tornadoes. Over the past 30 years (1985–2014) Arkansas has averaged approximately 32 tornadoes and 5 tornado fatalities per year. The Super Tuesday Tornado Outbreak of February 2008 resulted in 57 fatalities in four states, the second largest number of tornado fatalities since the May 31, 1985 outbreak (88 fatalities). During this tornado outbreak, Arkansas experienced a long-track (122 miles) EF4 tornado, the longest track on record since 1950, causing an estimated $102 million in damages across central and northern Arkansas and 14 fatalities.
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. Heat wave intensity is projected to increase, while cold waves are projected to be less severe.
Winter precipitation is projected to increase in Arkansas by mid-century (Figure 6). In the other seasons, precipitation changes are uncertain. Higher temperatures will increase the rate of loss of soil moisture during dry spells. As a result, naturally occurring droughts are projected to be more intense.