Environmental Vulnerability

The past decade has seen an increase in severe weather events across the Midwest – a trend which is likely to continue.  Understanding the risks posed by extreme heat and precipitation events can help Missourians prepare against environmental vulnerabilities.

Drought and Heat Stress

According to a report on Missouri’s climate trends, average precipitation is likely to increase in Missouri in the near future. However, summer droughts are likely to be more severe and the number of high heat index days (above 95°F) across the state is expected to double. Recent evidence presented by the U.S. Global Climate Change Research Program shows effects of heat stress and drought are already well known in Missouri – droughts in 2012 restricted flows and disrupted barge traffic. Recently, wildfires across the neighboring Kansas and Oklahoma also caused major damage to farms and ranches. Heat stress can also reduce agricultural yields among both crops and livestock, and in farms without irrigation, prolonged or severe droughts could result in more total crop failures.

Heat stress is also dangerous to population health, especially the health of vulnerable populations in urban areas.  Currently, heat waves kill more people in the United States each year than most other severe weather events combined (hurricanes, tornadoes, floods, and lightning).  Projections from the Union of Concerned Scientists suggest that cities like St. Louis could experience between 10 to 40 days with heat index values exceeding 100°F by the end of the century (up from a baseline of 2 to 3).


Interstate 44 is covered by floodwater in both directions at the intersection of Highway 141 in St. Louis County, Missouri. Source: CNN

According the U.S. Global Climate Change Research Program, extreme rainfall events and flooding have increased during the last century by as much as 20% and these trends are expected to continue.  Much of the increase has been caused by intensification in the heaviest rainfalls. Already in some locations across the Midwest, the 10 rainiest days can contribute as much as 40% of total precipitation in a given year.  Across the state, intense rainfall events can erode and disrupt transportation infrastructure and impact agricultural yields.  In growing urban areas where impervious surfaces (asphalt) reduce the ability of precipitation to infiltrate the soil, sewer systems are particular susceptible to flood events. In particular, overflows of combined storm and sewage drainage systems can result in raw sewage overflows, impacting clean water availability and human health.

Precipitation patterns affect many aspects of life, from agriculture to urban storm drains. These maps show projected changes for the middle of the current century (2041-2070) relative to the end of the last century (1971-2000) across the Midwest under continued emissions (A2 scenario). Left: increases in the amount of rain falling in the wettest 5-day period over a year. This indicates that heavy precipitation events will increase in intensity in the future across the Midwest. Right: change in the average maximum number of consecutive days each year with less than 0.01 inches of precipitation. An increase in this variable has been used to indicate an increase in the chance of drought in the future. (Figure source: NOAA NCDC / CICS-NC).

Invasive Species

Invasive species are a vulnerability to Missouri’s environment. Invasive insects such as the Emerald ash borer and the Gypsy moth can cause extensive damage to Missouri’s hardwood forests. Invasive aquatic species like zebra mussels disrupt river ecosystems by out-competing native species for food and resources. Invasive insects like the Asian tiger mosquito (Aedes aegypti) are vectors for several illnesses including dengue and yellow fever. The economic impacts of invasive species can extend into the billions of dollars and affect multiple sectors, from agriculture to tourism and health. Residential and agricultural property values can also be affected when environmental assets are disrupted by invasive species.

Impaired Waters

Section 303(d) of the federal Clean Water Act requires that each state identify waters not meeting water quality standards and for which adequate water pollution controls have not been required. Water quality standards protect such beneficial uses of water as whole body contact (such as swimming), maintaining fish and other aquatic life, and providing drinking water for people, livestock and wildlife. The 303(d) List helps state and federal agencies keep track of impaired waters not addressed by normal water pollution control programs. For information about designated impaired rivers, lakes, and streams, please visit the Missouri Department of Conservation Missouri Water Quality web page.