Average annual temperature has increased about 1°F over the last two decades. Although there has been a general lack of summer warming, with little change in the occurrence of high summer daytime extremes, Indiana has experienced a below average number of very cold days since the 1990s. Under a higher emissions pathway, historically unprecedented warming is projected, with corresponding decreases in cold wave intensity and increases in heat wave intensity.
Precipitation in spring and summer has generally been above average over the past two decades (1995–2014), affecting agriculture in both positive (adequate soil moisture) and negative (delays in spring planting) ways. Precipitation in winter and spring is projected to increase, which poses a continuing risk of spring planting delays.
Severe flooding and drought have occurred periodically in recent years. Future increases in extreme precipitation events may increase the frequency and intensity of floods. Increases in evaporation rates may increase the intensity of naturally-occurring droughts.
Merry Lea Environmental Learning Center of Goshen College near Wolf Lake, Indiana.
Photo by David Cornwell
Indiana’s location in the interior of the North American continent exposes it to a climate with large ranges in temperature, resulting in warm, humid summers and cold winters. The lack of mountains to the north or south allows very cold air masses from the Arctic in the winter and warm, humid air masses from the Gulf of Mexico in the summer to move into the state, further increasing the range of conditions that affect Indiana. Average annual temperature ranges about 10°F from north to south. Lake Michigan moderates the temperature of the far northwest portion of the state, causing cooler summers and warmer winters. Lake Michigan also is the source of lake-effect snows, which can extend as far inland as Elkhart (north-central Indiana).
Since the beginning of the 20th century, temperatures in Indiana have risen approximately 1°F (Figure 1). Temperatures in the 2000s have been higher than any other historical period with the exception of the early 1930s “Dust Bowl” era. Warming has been concentrated in winter and spring while summers have not warmed substantially in the state, a feature characteristic of much of the Midwest (Figure 2a). The lack of summer warming is reflected in a below average occurrence of very hot days (maximum temperature above 95°F) (Figure 2b) although the number of very warm nights (minimum temperature above 75°F) has been average since the mid 1990s (Figure 2c). Due to extreme drought and poor land management practices, the summers of the 1930s remain the warmest on record. The winter warming trend is reflected in a below average number of very cold nights (minimum temperature below 0°F) since the 1990s (Figure 3).
Annual precipitation has varied from a low of 29.11 inches in 1963 to a high of 55.21 inches in 2011. The driest multi-year periods were in the 1930s, 1940s, and 1960s, and the wettest in the 2000s (Figure 4). The driest 5-year period was 1940-1944 and the wettest was 2007-2011. Annual precipitation also varies widely across the state, ranging from 47 inches annually in the south to 37 inches in the north. For snowfall, the pattern is reversed, with the southwest averaging 14 inches, while some northern locations near Lake Michigan average over 70 inches. The proximity to Lake Michigan occasionally results in heavy winter precipitation from lake-effect snows. On January 21–22, 2014, a lake-effect storm dropped 18 inches of snow in Gary over a 5-hour period.
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 snow and ice storms, while convective storms capable of producing floods, hail, and tornadoes are common in the warmer months. One of the state’s worst winter storms occurred on December 22–23, 2004. More than 20 inches of snow fell across the southern part of the state. Many locations reported record snowfall amounts, including the city of Washington, with 32 inches of snow. With temperatures below freezing, the snow lingered for several days, shutting down airports and interstates and stranding holiday travelers. The storm killed 5 people and a state of emergency was declared for 50 counties.
Indiana has a long and deadly history of tornadic storms. On March 18, 1925, the deadliest tornado in U.S. history—the “Tri-State Tornado”—struck southwestern Indiana after tracking across Missouri and Illinois. The tornado destroyed parts of Griffin, Owensville, and Princeton and caused hundreds of injuries and 76 deaths. The Palm Sunday Outbreak on April 11, 1965 included several tornadoes in Indiana, eight of them at F4 intensity. The outbreak injured hundreds in the state and killed more than 130 people. Indiana’s largest tornado outbreak occurred on June 2, 1990, when 37 tornadoes occurred, several of which were classified as F4 intensity.
Agriculture is an important sector of Indiana’s economy and is particularly vulnerable to a variety of extreme weather conditions. In 2007, unusually warm March temperatures, followed by a hard freeze in April, devastated much of the state’s fruit crops, with total agricultural losses estimated at $48 million. In 2012, a large drought across the Midwest severely impacted the state. Rainfall for May, June, and July totaled 6.57 inches, more than 5 inches below average, and the 4th driest such period (after 1936, 1930, and 1988) in 120 years of record. By early August, almost 70% of the state was in extreme drought, with a quarter of the state experiencing exceptional drought. The drought caused major damage to crops, particularly in the southern third of the state.
On average, Indiana has experienced wet springs and summers over the past two decades (Figure 2d). While precipitation during these critical growth months is important for adequate soil moisture, it can also make it difficult for farmers to plant crops. Indiana has also experienced an increase in the number of heavy precipitation events (more than 2 inches of precipitation) (Figure 5), which can cause severe flooding. The Great Flood of 1913 was the worst flood in Indiana history. Heavy rains fell from March 23 to 26, causing many rivers across the state to reach flood stage. More than 100 people were killed, with damages estimated at $25 million (in 1913 dollars). Heavy rains on saturated ground were also responsible for severe flooding in June 2008. From June 6 to 7, heavy rain fell across central and southern Indiana, with some stations reporting up to 10 inches of rain. Many streams reached record flood levels. In total, 39 counties were declared disaster areas and damages were estimated at hundreds of millions of dollars. In the summer of 2015, central Indiana experienced historic levels of rainfall characterized by the wettest July on record at Indianapolis (8.6 inches above normal). Flooding in June and July exceeded flood control capacity in three reservoirs for the first time since they were built in the late 1960s. The extremity of this event rivals in magnitude the exceptional drought that impacted the state in 2012, highlighting the extremes in climate that the state has experienced in recent years.
Water levels in the Great Lakes have fluctuated over a range of three to six feet since the late 19th century (Figure 6). Higher lake levels were generally noted in the latter part of the 19th century and early 20th century, the 1940s, 1950s, and 1980s. Lower lake levels were observed in the 1920s and 1930s and again in the 1960s. Overall, Lake Michigan-Huron has shown a statistically significant downward trend over the past 150 years. The trend is largely due to the high levels early in the period and the extremely low levels in the past 10 years. However, rapid increases in water levels have been observed in the Great Lakes following historic lows in 2013. In fact, Lakes Michigan and Huron have experienced a remarkable recovery with a rise of more than 3 feet from low levels in 2013. This unexpectedly rapid rise in water levels have been associated with negative impacts along lakeshore areas during high wind and wave events, including beach erosion and damage to piers and other structures built during “low” water years.
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. If the warming trend continues, future heat waves are likely to be more intense. Extreme heat is of particular concern for Indianapolis and other urban areas where high temperatures, combined with high humidity, can cause dangerous heat index values, a phenomenon known as the urban heat island effect. By contrast, the intensity of cold waves is projected to decrease.
Precipitation is projected to increase in Indiana, with increases most likely during the winter and spring (Figure 7). Extreme precipitation is also projected to increase, potentially increasing the frequency and intensity of floods. Heavier precipitation not only increases the risk of springtime flooding, but also poses a threat to Indiana’s important agricultural economy 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 evaporation rates and the rate of loss of soil moisture. Thus, future summer droughts, a natural part of the Indiana climate, are likely to be more intense.