Average annual temperature has warmed 1.1°F since 1900. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century. Extreme heat is of particular concern for the state’s urban areas where high temperatures and high humidity can cause dangerous health conditions.
Ohio has experienced a significant increase in heavy rain events. Increases in winter and spring precipitation are projected and will raise the risk of springtime flooding.
Severe drought is a risk to this agriculture-dependent state. Future projected temperature increases may increase the intensity of naturally-occurring droughts.
Ohio’s mid-latitude location in the interior and away from the coasts of the North American continent results in a climate with a large range in temperature, with warm, humid summers and cold winters. The lack of large mountain barriers to the north or south also contributes to the range of conditions that affect the state, allowing for incursions of very cold air masses from the Arctic in the winter as well as warm and humid air masses from the Gulf of Mexico in the summer. Lake Erie has a large influence on the local climate. Near-shore locations are considerably warmer during the winter and cooler during the summer than locations farther away from the shores. Lake effect snow, caused by the warming and moistening of arctic air masses over the Great Lakes, is a hazard along the southeastern shoreline of Lake Erie.
Since the beginning of the 20th century, temperatures have risen 1.1°F , and temperatures in the 2000s have been warmer than any other historical period (Figure 1). The warming has not been steady. The 1930s through the mid 1950s were generally above the long-term average, followed by the coldest period on record, the 1960s and 1970s. Since the 1970s, mean annual temperature has risen by about 2°F. Based on observations through 2014, 1998 was the hottest on record, with an average annual temperature for the state of 54.1°F. The second hottest year was 2012, with an average temperature of 54.0°F. This warming has been concentrated in the winter and spring. Summers have not warmed substantially in the state, a feature characteristic of much of the Midwest. This trend is reflected in a below average occurrence of very hot days (maximum temperature above 95°F) (Figure 2a). In addition to the overall trend of higher average temperatures, the state has experienced an increase in the number of warm nights (minimum temperature above 70°F; Figure 3). Both Cleveland and Columbus have experienced statistically significant increases in the number of warm nights since 1950. Since 2000, the number has averaged 11 and 14 days per year at Cleveland and Columbus, respectively, compared to an average of 5 days per year at both cities in the 1950s through 1970s. Although both cities also experienced high temperatures in the 1930s, those temperatures were mostly due to extreme high daytime temperatures. Ohio has also experienced a below average number of very cold nights (minimum temperature below 0°F) since 1990 (Figure 2b).
Annual precipitation varies regionally, with the northwestern part of the state averaging 32 inches each year and the south averaging 42 inches each year. Statewide average annual precipitation has ranged from a low of 26.79 inches in 1963 to a high of 55.95 inches in 2011. The driest multi-year periods were in the 1930s and 1960s, and the wettest multi-year periods have been in the 2000s (Figure 2c). Average annual precipitation during the driest and wettest 5-yr periods has ranged from a low of 33.56 inches during 1930–1934 to a high of 42.92 inches during 2003–2007. Snowfall also varies across the state, with the southern shores of Lake Erie receiving 60 inches or more annually, while the southern portion of the state receives less than 16 inches annually.
Ohio has experienced a significant increase in the number of extreme precipitation events (precipitation greater than 2 inches) since the mid 1990s (Figure 4). Past episodes of heavy rains have caused severe flooding in the state. The Great Flood of 1913 was one of the deadliest floods in U.S. history and Ohio’s greatest weather disaster. From March 23 to 26, heavy rains caused extreme runoff from soils saturated from winter storms. Levees along the Great Miami River failed, flooding the entire Great Miami River watershed. Downtown Dayton was particularly hard hit, with floodwaters reaching depths of 20 feet. The flooding caused over $70 million in damages and more than 400 people died. One of the worst floods in recent years occurred in March 1997. Between March 1 and 3, 6–12 inches of rain fell in parts of southern Ohio causing serious flooding, particularly along Brush Creek and the Scioto and Great Miami Rivers. Levels on the main stem of the Ohio River were the highest in over 30 years. Seventeen counties were declared federal disaster areas and more than 5,000 homes were damaged or destroyed, resulting in around $180 million in damages (in 1997 dollars).
Dangerous storms can occur in every season and can cause major impacts, including loss of life, property damage, and disruptions to economic activity. Winter can bring snowstorms and ice storms, while convective storms (including thunderstorms, flood-producing rainstorms, hail, and tornadoes) are common in the warmer months. Although Ohio does not experience as many tornadoes as other states in the Midwest and Great Plains, the state has experienced several deadly tornado outbreaks. On June 28, 1924, Ohio’s deadliest tornado struck the towns of Sandusky and Lorain, killing 85 people and causing more than $1 billion (adjusted to 1997 dollars) in damages. Other notable storms include the Palm Sunday Outbreak (April 11, 1965) which produced 10 tornadoes in the state (4 of which were F4) and caused 60 deaths, the Xenia tornado, an F5 intensity storm in the Super Outbreak of 1974 that killed 34 people, and the outbreak of April 8–9, 1999, which produced 54 tornadoes, including an F4 intensity tornado in Blue Ash and Montgomery that killed 4 people.
Agriculture is an important component of Ohio’s economy, and this sector is particularly vulnerable to extreme weather conditions. In 2007, unusually warm March temperatures, followed by a hard freeze in April, devastated much of the state’s apple crop. This scenario was again observed in 2012, where March temperatures were 9–15°F above average for the state. A cool April again followed with hard freezes. Seasonal precipitation can vary, with no real trend in summer or winter precipitation (Figure 2d). In 2012, an intense drought across the Midwest had severe impacts on Ohio. Rainfall totals for the summer were several inches below average. In addition to low precipitation, the period from January to June was the warmest in 120 years of record, with the warm temperatures compounding the dry conditions. By year’s end, 86 of Ohio’s 88 counties had been declared drought disaster areas.
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 of 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. Increases in extreme heat are of particular concern for Cincinnati, Columbus, and other urban areas where the urban heat island effect raises summer temperatures. High temperatures combined with high humidity can create dangerous heat index values. During July 17–24, 2011, the Ohio River Valley experienced a prolonged heat wave. With temperatures above 90°F for several days in a row and dewpoints in the mid to upper 70s, heat index values rose to between 100°F and 110°F during the day. These occurrences are likely to become more common as temperatures continue to rise. However, there have been exceptionally cold winters in recent years. The winters of 2013–2014 and 2014–2015 had average temperatures from December to February more than 3°F below average, due to persistent weather patterns bringing frigid air southward from the Arctic. Although the state averages approximately 2.3 days below 0°F annually, these two winters averaged 7.5 days. The intensity of such events is projected to decrease in the future.
Although annual precipitation projections are uncertain, winter and spring precipitation are projected to increase (Figure 5). In addition, extreme precipitation is projected to increase, potentially causing more frequent and intense floods. Heavier precipitation and higher temperatures raise the risk of springtime flooding, posing a threat to Ohio’s agricultural industry by delaying planting and resulting in loss of yield.
The intensity of future droughts is projected to increase. Even if precipitation increases in the future, increases in temperature will increase the rate of loss of soil moisture during dry spells. Thus, future summer droughts, a natural part of the Ohio climate, are likely to be more intense.