The most profound effect of climate change that is already evident in Indiana is the increase in total precipitation and extreme precipitation events.
Statistics compiled by Purdue University show that, since records began in the late 1800s, annual precipitation across Indiana has increased between 3 and 7 inches, with the largest gains occurring in south central Indiana. These increases are forecast to continue as greenhouse gas concentrations rise because of the burning of fossil fuels.
Warmer temperatures lead to increased precipitation in a couple of ways. First, warmer air can hold more water vapor. For example, at 70 degrees Fahrenheit, a kilogram of dry air can hold 16 grams of water vapor, while at 80 degrees a kilogram of dry air can hold 22 grams of water vapor. Warmer ocean temperatures also contribute as warmer water evaporates into the atmosphere more readily than cooler water. This principle is illustrated by the fact that ocean temperatures must be near 80 degrees before they can infuse the atmosphere with enough moisture to support hurricane development. If you are wondering why ocean temperatures are important to landlocked Indiana, most of the low level atmospheric moisture that fuels precipitation in the Ohio Valley comes from the Gulf of Mexico, where it is drawn up by southerly winds that rotate counterclockwise ahead of approaching low pressure systems.
In addition to the increases in annual precipitation, extreme precipitation events — defined as 2 or more inches in a day — are also increasing. This has been particularly evident in the spring and early summer in recent years including 2015, 2017 and 2019. While the heaviest rainfall in 2015 was concentrated in the northern portion of the state, it was more widespread in 2017 and 2019. At my home in southeastern Madison County, I recorded 36 inches of rain between April 25 and July 25 in 2017. This is nearly 90% of our normal average annual precipitation in just three months.
These wetter conditions are having a profound effect on Indiana’s agriculture. Wetter springs are delaying field work and planting. This was such a problem in 2019 that many local fields were not planted at all since it was too late to sow corn and soybeans by the time the rains abated and the field conditions improved in July.
More extreme rainfall events are also affecting our urban storm water infrastructure. These events are causing more sewer overflows into our rivers from our antiquated combined sewer systems, increasing both nutrient pollution and bacterial contamination. While communities are required to update their infrastructure to eliminate these discharges, these events are making these upgrades more challenging to engineer.
For more important information about climate change in Indiana, visit the Purdue Climate Change Research Center website at https://ag.purdue.edu/indianaclimate/indiana-climate-report.