Development in Potentially Hazardous Areas

Definition

Percent of development in potentially hazardous areas (500-year flood zone, potential landslide areas, and potential earthquake liquefaction areas)

Why is it Important?

Natural events such as floods, landslides, and earthquakes only become natural hazards if humans are nearby and could be affected by the event. In other words, it is the mixture of natural events and human development that creates the possibility of natural hazards. Due to population growth, more people are living in potentially hazardous areas than ever before.¹ However, through land use planning and proper incentives, it is possible to direct growth away from potentially hazardous areas and reduce risk. This indicator measures the percent of development (commercial, industrial, and residential) that is located in the 500-year flood zone, potential landslide areas, and/or potential earthquake liquefaction areas. The 500-year flood zone includes areas where there is a one in 500 risk of flooding in any particular year. Potential landslide areas are those with significant slopes, which increase the risk of landslides. Potential earthquake liquefaction areas have loose and unconsolidated soils that could lose strength and liquefy in the event of an earthquake.

How are we Doing?

The percent of development in potentially hazardous areas increased from 16.2 percent in the baseline year 2006 to 17.6 percent in 2016.² Development is occurring more in potentially hazardous areas than in the five county area in general (Missouri portion of the region only).³ Specifically, while the amount of development increased by 3.4 percent from 2006 to 2016 in the five county area, the amount of development in potentially hazardous areas increased by 12.3 percent,

Flood zones are the most common type of potentially hazardous area in the Missouri portion of the St. Louis region. The 500-year flood zone covers 364,636 acres, while potential liquefaction areas cover 354,242acres, and potential landslide areas cover 179,980 acres. Most of the development in potentially hazardous areas is located in a potential liquefaction area (50,145 acres) and/or the 500-year flood zone (42,492 acres), while 18,365 acres of development is in potential landslide areas.⁴

Some developments are located in areas with more than one potential hazard.

Geographic Level

Franklin, Jefferson, St. Charles and St. Louis counties and city of St. Louis in Missouri (data for additional areas within the eight county region will be added if it becomes available)

Notes

¹ NASA Earth Observatory, The “Nature” of the Problem: Population and Natural Disasters; accessed on 10 January 2014 at http://earthobservatory.nasa.gov/Features/RisingCost/rising_cost2.php

²The 2006 data reflects NLCD data that was revised and released in 2019 and the flood zones as they were defined in 2006.

³Local data for the counties in Illinois is not available.

⁴These percentages do not add to 100 because some developments are located in areas with more than one potential hazard.

Data Sources

Federal Emergency Management Agency; Missouri Department of Natural Resources; and National Land Cover Database, Multi-Resolution Land Characteristics (MRLC)