High water tables, high flows, and climate change
Water tables remain well above normal, and the Huron River is flowing higher season-for-season compared to any period in recent memory. Since May of 2019, the flow of the river is consistently higher than average. Many creeks repeatedly overflow their banks, and many normally seasonal wetlands hold standing water through late summer. In Hamburg Township, the river has remained near or above flood stage for months. Parts of Milford have seen their highest water levels in a generation. Downriver communities have seen both the effects of high river flows and coastal flooding from record high Lake Erie water levels —conditions magnified when winds blow on shore out of the east. The challenges are widespread.
High water levels are more than a nuisance. They create public health risks. Water in basements can lead to mold and lasting structural damage. Farm fields remain wet well into the planting season, interfering with growers’ ability to earn a living. Flooding in contaminated sites can result in pollution spreading to surrounding areas. High flows on the river can be dangerous for anglers and paddlers— several canoe and kayak rental businesses along the Huron River, including Skip’s near Dexter and the Ann Arbor liveries, have had to delay or limit their services due to unsafe, high flows.
More than a passing trend
The high water levels and water tables in the watershed are part of a larger pattern. The 2010s were the wettest decade in Michigan’s recorded history, and 2019 was the 2nd wettest year on record for the U.S., the wettest ever for Michigan, and the 2nd wettest in Southeast Michigan. These circumstances have all coincided with severe flooding across much of central North America, resulting in widespread damage.
Beyond natural water level variation, the Great Lakes have been at or near record levels over the past year. From Lake Superior to Lake Ontario, the effects on coastal communities and ecosystems has been dramatic. Beaches have been claimed by the lakes. Sensitive, rare wildlife habitats have been swept away or inundated.
Climate change makes the water cycle more chaotic
These events are all symptoms of climate change. Several climate factors affect how much water is in the Great Lakes basin over any given period of time. Evaporation, precipitation, and ice cover are the dominating climatic characteristics.
A warming world increases evaporation over the long term. Once water evaporates from a watershed, it falls anywhere the wind takes it—potentially removing available water from the region. Warmer temperatures therefore tend to lead to drier soil and lower water levels in the affected region.
Precipitation and ice cover in the region, however, have become more variable with rising temperatures. Warmer air holds more moisture. For every 1°F rise in temperature, the atmosphere holds around 4% more water vapor, providing more readily available fuel for storms.
When the Great Lakes freeze over in late winter, the ice effectively shuts down evaporation from the lakes and, counterintuitively, a warming world can lead to variable periods of greater ice cover. As the polar regions warm faster than the rest of the planet, the temperature gradient that keeps cold air trapped in the arctic weakens. Cold air masses can break away to the south (the “polar vortex” outbreaks) and cause the lakes to freeze, thus reducing evaporation even as more moisture and precipitation arrives from outside the region. Since 2014, this has been a recurring pattern and, as the world continues to warm, variability in ice cover could become even less predictable. The Great Lakes and our watershed could see higher highs and lower lows in water levels.
Increased precipitation, flooding, and pollution
Since 1951, precipitation has increased by 14% across the Great Lakes region. The frequency of heavy storms has risen by 35%, a major cause of widespread flooding. In some hotspots, including parts of Southeast Michigan, the increase has been greater. Perhaps
more important is how and when that precipitation is reaching us. The most intense storms have become more powerful and more frequent, delivering a greater proportion of our precipitation in downpours rather than gentle sprinkles. Fall snow is coming later, and spring snow is melting earlier.
These seasonal changes affect the timing and volume of water moving through the system, requiring adaptations in how the water is managed. In Dexter, for example, the new storage basin the city installed to hold wastewater during large events overflowed twice in the first year. Disrupted spring weather means that rain falls on rapidly melting snow and still-frozen ground, causing abrupt flooding that carries road salt and other recently thawed contaminants to streams.
Unless global greenhouse gas emissions are drastically reduced, the current trends will likely continue and worsen. Even if emissions are reduced enough to avoid the worst impacts of climate change, some amount of change is inevitable for decades to come due to the residual warming effect of greenhouse gases already emitted. That means local communities need to be prepared for unprecedented weather events in addition to working to reduce emissions and slow global warming.
Planned climate resiliency
HRWC has been working with communities to adapt to the increasing volume of water flowing through the watershed. Recent partnerships include:
- The City of Wixom—installing rain gardens to restore a section of Norton Creek;
- The City of Ann Arbor—installing green infrastructure to help reduce runoff; and
- The City of Ypsilanti—removing Pen Dam to restore the natural ability of the river to absorb high flows through Ypsilanti.
Working at this scale in our home communities is where individuals and groups can have the greatest positive impact. As we try to avoid the worst impacts of climate change by reducing greenhouse gas emissions, we can work to adapt to the unavoidable and keep our heads above water.
This blog post was originally included in the Huron River Report, Spring 2020.