Flooding is one of the key public concerns identified through the OneSTL public engagement process. Between 1993 and 2013, the Mississippi River at St. Louis crested above the major flood stage 11 times. Serious flash floods have also hit the region several times in recent years, including 2008 and 2013.
Levees play an indispensable role in flood management, protecting communities, businesses and farmland. Much of the region’s heavy industry is located in levee-protected areas. Maintaining and improving existing levee systems is critical for protecting the region’s industrial base, as well as riverfront communities, against major flood events. Equally important is preserving existing floodplains, such as the area around the confluence of the Mississippi and Missouri rivers, as open space.
Impervious surfaces such as parking lots, roads and roofs play a role in flash floods, directing water into sewers and channelized waterways. When the runoff exceeds the capacity of stormwater sewers, overflow results, leading to property damage and erosion. Many communities in St. Louis have taken effective steps to reduce flooding risk. There are several construction techniques that can be used to allow more rainwater to be stored in the ground, near where it falls. 
Bioswale at Missouri Botanical Garden.These methods, sometimes referred to as Low Impact Development (LID), are already playing an important role in reducing the risk of flash floods in the St. Louis area. A program known as the Community Rating System (CRS), part of the National Flood Insurance Program, gives communities financial incentives to take measures to reduce flooding risk.
Publicly available climate projections suggest that the risk of flooding could increase in coming decades, with increases in the number of heavy precipitation events and increases in winter and spring precipitation. The potential for increases in flooding risk underscores the importance of levee maintenance, the use of LID techniques, and programs such as CRS.
Climate models also project increases in average temperatures, as well as increases in the number of days with heat in excess of 95 degrees. Extreme heat affects public health and the use of electricity, and also creates material stress on pavement and bridge expansion joints. Communities throughout St. Louis are already taking actions to reduce the impacts of extreme heat. Promoting energy conservation can partially offset increased demand for electricity in summer. Special needs registries allow public health officials to reach out to individuals that may be vulnerable during heat waves. Abatement strategies such as street trees help combat the urban heat island effect. These measures, already beneficial, grow in importance in the context of a changing climate.
