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Categorized | IN OUR COMMUNITY

Ready and Resilient

Posted on 10 May 2016 by Calvin

Patterns tend toward extreme rain events as the norm by 2025

By TRUDY DUNHAM

Extreme rainfall. Kenny Blumenfield, a Senior Climatologist at the Minnesota Department of Natural Resources, told the recent Gov­ernor’s Water Summit that our MN rainfall pattern is beyond the range of historical probability. Annual precipitation increased 10-15 percent from 1985 to 2007. Heavy downpours are twice as frequent as they were 100 years ago.

“Unprecedented” rainfall events are possible in the coming years, and will become the norm by 2025.

Warmer temperatures increase the evaporation of water into vapor. Warmer air can hold more water vapor than cooler air. When the vapor condenses into rain, there’s more of it to fall. Blumenfield called the increasing intensity and frequency of rainfall the “smoking gun” of climate change.

What is extreme rainfall? A lot of rain falling in a very short time. It can be several inches within a few hours, or rain falling for days at a time. The July 1987 “Superstorm” dropped 9 inches of rain at the Minneapolis–Saint Paul International Airport in 6 hours.

While heavy rain can make travel dangerous and result in power outages, the real problem is stormwater runoff: when the rain cannot soak into the ground. Water runs off our yards, driveways, parking lots and streets. Sometimes it flows into our rain gardens and stormwater ponds, but too often it runs directly into our storm sewers.

Stormwater runoff threatens our water quality. Sediment, litter, leaves, pesticides, fertilizers and oil waste flow through our storm sewers into our waterways. Lakes and rivers are polluted, aquatic ecosystems impaired, and recreational use spoiled.

The runoff contributes to flooding. Infrastructure built for 20th-century precipitation patterns cannot handle the rapid influx of rainwater. Drainage systems, roads, and stormwater holding ponds are overwhelmed. Since 2000, federal, state and local government agencies have spent $350 million in Minnesota to repair flood damage.

Finally, we need the rainwater to recharge our groundwater supply. Minnesota’s groundwater use has increased 35% in the last 25 years. Rain held in the soil has time to filter contaminants and seep down to replenish aquifers. We need this water to prevent future water shortages.
What can we do to adapt to the extreme rainfall and stormwater runoff?

Let’s start with our yards:
Aerate your lawn. Residential lawns tend to be highly compacted and absorb little water. Removing small plugs of soil or punching holes in the ground with an aerator helps the lawn to soak up more water.
Let your grass grow taller. Grass roots are about as long as grass blades. Longer roots mean better water absorption, so consider letting your grass grow to a height of 2.5–3.5 inches.
Replace some grass with native plants. Even if taller, grass is inferior to native shrubs and wildflowers at absorbing and retaining water. The extensive root systems of native plants keep soil from washing away and increase the amount of water the soil can absorb. Plants are especially important in areas where stormwater runoff collects. Consider installing a rain garden.
Add mulch and compost. Cover any bare soil with mulch or wood chips to reduce runoff and prevent soil from washing away. Compost can improve the soil structure and nutrient content, reducing the need for chemical fertilizers. It also retains a lot of water, reduces runoff and filters pollutants. Consider adding 2-4” of organic material each year.
Protect urban trees. The root system of a single large tree can absorb up to 100 gallons of water in a day. Tree canopies also slow the rainfall and spread it over a larger area.

Some maintenance issues to consider:
Keep your trees trimmed. Branches are more likely to break off in severe storms, falling on roofs, cars and power lines where they can inflict more damage.
Pick up pet waste. When pet waste becomes part of the storm runoff, it adds disease-producing organisms, further impairing the water quality.
Clean your gutters. Flush your gutters to keep rainfall away from your house foundation. If they still overflow, consider installing wider “elbows.”
Pick up trash. Pick up litter in your street and along the boulevard so it isn’t swept down the storm sewer in a storm. If leaf debris collects between City street sweepings, consider raking and recycling it. Clear debris from around the storm drains.

If you arRain gardene considering renovation or landscaping:
Use permeable surfaces. If you are replacing a driveway or patio, consider permeable pavers. Gravel, flagstones, and bricks allow water to soak in between them.
5% slope: Make sure that the yard slopes away from the house a minimum of 5%, to minimize possible drainage into your basement.
Catch or slow the runoff: If your lawn slopes, consider installing a rain garden or berm to prevent or slow stormwater from flowing into the street. Install a rain barrel or cistern to catch stormwater runoff from your roof.
Channel the water: Direct your gutter downspout into your yard, not onto a paved surface. Consider incorporating slight slopes or ditches into your landscaping to slow the runoff, and channel it where you want it to go.

Be ready—the storms are coming! Do what you can to prevent stormwater runoff. We’ll need it for the water shortages to come.

The Ready and Resilient Hamline Midway project is an initiative of the Hamline Midway Environmental Group (HMEG) to build climate change resiliency in our community.

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