Rainwater is a great resource when timed right and in the right amounts, or stored for later use in rain barrels or in soil pore space.
Unfortunately too much at once can have devastating effects. More people die in flooding than tornadoes, lightning or any other severe weather related causes. Floods cause billions of dollars in damages annually.
Certain precipitation conditions on the basins also showed systematic temporal increases since the 1920s, including annual precipitation, number of seven-day heavy rain events, and the number of days with precipitation. This climatic shift to more multi-day periods of heavy rain appears to be the major reason that hydrologic flooding in the three states has increased since the 1920s. Analysis of the individual major hydrologic floods revealed five different types of precipitation conditions, including snow-melt situations that produced major floods. The primary cause of major floods was prolonged periods of four- to 13-day durations with intermittent moderate to heavy rains, and these events often included heavy, 15-centimeter rainstorms capable of producing flash floods. Causes for Record High Flood Losses in the Central United States
See also HEAVY RAINSTORMS IN CHICAGO: INCREASING FREQUENCY, ALTERED IMPACTS, AND FUTURE IMPLICATIONS
Our recent land management and development practices are also contributing to flooding issues.
Reduction of soil organic matter, loss of wetlands and bare fields in Spring all slow infiltration and increase runoff. Urban sprawl and the increase of impermeable surfaces i.e. rooftops and parking lots; even compacted lawns, also contribute to flood intensity.
A sensitivity analysis was performed to evaluate the effects of urbanization and climate variability on increasing flood peaks. Results indicated that, on average, urbanization caused a 34% greater increase in peak flows than climate variability. In addition, this study indicated that present discharges are, on average, at least 19% larger than regulatory discharges. Ongoing urbanization may cause flood peaks to become even higher. Impacts of Urbanization and Climate Variability on Floods in Northeastern Illinois
Watch for the next post in the series as we look at what this means for water quality.