Climate Impacts Along the Mississippi River Corridor

Mississippi Basin and Corridor General Info:

Climate Impacts Toplines:

  • According to the 10 cities reporting to CDP in the Mississippi River basin in 2016 (Chicago IL, Cincinnati OH, Cleveland IL, Des Moines IA, Louisville KY, Minneapolis MN, New Orleans LA, Pittsburgh PA, St Louis MO, and Wisconsin Rapids WI), the surveyed cities reported varying susceptibility to the following risks: 60% face river flood as a hazard; 50% face heat waves as a hazard; 30% face severe wind; 80% face flash/surface flood; 40% face drought; 20% face extreme winter conditions; 40% face extreme hot days; 20% face tornadoes; 20% face vector-borne diseases. With the exception of tornadoes all of these hazards have well-documented links and are demonstrably aggravated by climate change.
  • The increasing frequency of heavy rain, both globally and in the Mississippi River Basin specifically, is among the clearest climate change impacts on weather. A warmer atmosphere holds more water vapor. Recent storms along the Mississippi River have been supercharged by running over a warmer ocean and through an atmosphere made wetter by global warming.
  • Heavier rains, combined with intensified snowpack melt on the headwaters, tributaries and mainstem of the Mississippi river, are increasing flood risk for basin communities. The increased precipitation is interspersed with periods of no rain, creating a weather whiplash effect, which increases the risk of severe weather at both extremes. Since 2005, the Mississippi River Valley has sustained successive 100, 200, and 500-year rainfall events, a 50-year drought, Hurricane Katrina and Hurricane Isaac.
  • Recent advances are making it easier to pin specific weather events to climate change. An attribution study published one month after heavy rainfall battered Louisiana in August 2016 found that climate change nearly doubled the chances for the heavy downpours that caused devastating flooding across the gulf state.
  • Average temperatures are increasing in states along both the upper and lower Mississippi, although at varying rates. Increasing heat has costly implications for agricultural yields, labor productivity, public health, energy costs, and infrastructure throughout the corridor. These temperature trends are explored more closely below.
  • Rain and flood related disasters along the Mississippi River have become persistent and systemic, incurring over $50 billion in costs since 2011. Furthermore, the 50-year magnitude drought in 2012 caused an estimated $31.5 billion in damages nationwide and affected at least 5 states bordering the river.
  • In 2015-2016 alone, the Mississippi River Valley incurred over $13 billion in impact costs: an estimated $3 billion in damage from flooding that stretched from Grafton, IL to New Orleans, LA in the span of two months (December 2015 and most of January 2016). And in late August 2016, heavy rainfall and massive flooding caused $10 billion in damages around just the Baton Rouge area of Louisiana.
  • Over the last ten years, ten or more disaster declarations have been designated in thirty states of the basin, while six states have received twenty or more.
  • In 2012, disasters cut into the total revenue of the Mississippi River economy by 8.75 percent in actual losses, and more in follow-on losses. On average, over the last five years, disasters are costing the Mississippi River economy close to 3 percent annually, with damages that carry over into successive years.
  • Of the 10 cities that reported to CDP in 2016, 8 of these cities stated that they consider the effects of climate change could threaten the ability of businesses to operate successfully in their city.
  • In 2016, 7 of the 10 cities of the basin surveyed by CDP identified substantive risks to their city’s water supply in the short or long term. Moreover, 47 companies reported exposure to either current or future water risks in the Mississippi River Basin severe enough to substantively change their operations, revenue or costs. Of these 47 companies, flooding was the top risk reported.

Precipitation (Trends Along a North-South Cross Section)

Along the Upper and Middle Mississippi River:

Annual precipitation has increased in the Midwest by 5 to 15 percent since 1895, while the amount of rain falling in the heaviest downpours increased by 37 percent from 1958 to 2012. According to the most recent National Climate Assessment, the region will also see a higher average number of days without rainfall or snow, which could lead to agricultural droughts, reduced yields, and other economic impacts on key sectors in the future. These longer dry spells reflect precipitation falling in more intense storms.

Long dry spells punctuated by heavy rainfall events create a phenomenon called weather whiplash: While both drought and flood are part of the natural climate pattern, climate change contributes to both, and exacerbates a weather whiplash pattern that matches with observed trends in the basin. As the Mississippi watershed swings between drought and flood, climate change helps push the pendulum out to either extreme, furthering weather whiplash.

Along the Lower Mississippi River:

In the Southeastern US, extreme precipitation increased 27 percent from 1958 to 2012. Significantly, the US National Assessment reports that the long-term trend in the Southeast is larger than natural variation, an indication that changes brought on by global warming are overwhelming natural variation even at the regional level in the Southeast.

Both heavy rainfall and prolonged dry spells cause costly damage to the Mississippi corridor. Heavy rains are a key driver of flooding along the corridor. (Flood trends and resulting damages are explored in the next section.) However, dry spells can be just as destructive.

For instance, in 2012 an extreme dry spell contributed to a severe drought in the upper Midwest that cost the region $35 billion, becoming the second most expensive disaster worldwide that year. The 2012 drought caused water levels to plummet to near-record lows, slowing river traffic and transport of goods along the nation’s busiest waterway. As a result, tugs pulled fewer barges, and barge operators reduced loads to avoid bottoming out. Ultimately, barge cargo for December 2012 totaled 1.1 million metric tons less than the previous year. Disruptions in barge traffic come with a significant price tag for both businesses and government. Every inch drop in water level corresponds to more than 250 fewer tons of barge capacity along the river.

Flooding (Trends Along a North-South Cross Section)

Along the Upper and Middle Mississippi River:

Flooding is a major economic risk in the Midwest. The 1993 Mississippi flood was the costliest flood in modern times after Hurricane Katrina. In 2008, another flood in Cedar Rapids incurred over $10 billion in damages. These historic floods were caused by persistent heavy rainfall. Research shows that the trend towards heavier rainfall events has resulted in an overall increase in flood risk across the region.

Intensifying rainfall and flooding puts levees at greater risk. The risk of levee failure is a significant hazard, as the Midwest contains nearly 4,000 miles of levees, many of which are in poor condition. After the great 2011 flood, about a billion dollars was required to bring the levee system back to the state it was in before is was damaged by the flood.

Along the Lower Mississippi River:

The lower Mississippi River has experienced an increase in both severe flood events and periods of abnormally low water levels, both extremes causing significant disruption and damage to the communities along the river and economy of the region. For instance, in 2011, severe river flooding caused barge crashes and extensive property damage throughout the lower Mississippi region; just one year later, in 2012, a severe drought required the U.S. Army Corps of Engineers to close the river to barge traffic around Greenville, Mississippi for over a week because water levels were too low, delaying around 100 barges and incurring steep financial losses.

With an increase in extreme perception of 27 percent across the Southeast over the last 50 years, the risk of inland river flooding has gone up. This risk is further compounded by the trends in increased precipitation in the Midwest and upper and middle Mississippi river system, which then drain into the lower Mississippi. States of the lower Mississippi corridor are also at increased risk of coastal flooding, driven by sea level rise, increased storm strength and storm surge, which all cause salt water incursions up the Mississippi at greater frequency and further north than previously.

Increasing Heat (Trends Along a North-South Cross Section)

Along the Upper and Middle Mississippi River:

Overall, residents of the Midwest will likely see between two and five times more days over 95˚F in a typical year in the next 5 to 25 years than they have over the past 30 years.

The northern Midwest is likely to experience warmer winters rather than much hotter summers. For instance, of the seven states that currently have sub-freezing average winter temperatures, only two – Wisconsin and Minnesota – are still expected to do so if we continue on our current emissions pathway through the end of the century. However, summer temperatures are likely to increase as well, and by the end of the century, average summer temperatures in Minnesota, Wisconsin and Ohio are anticipated to be higher than current average summer temperatures in Washington, D.C. Lending credence to this trend, Minnesota heat indices climbed above 100˚F at the end of July 2016 and temperatures in St. Louis, Missouri have broken three average winter highs only two months into 2017.

However, the more southern Midwest states will see the most dramatic increase in these extremely hot days. By the end of this century, the average Missouri resident will likely experience 46 to 115 days above 95˚F in a typical year – about as many extremely hot days as the average Arizonan has experienced each year in recent decades. There is a 1-in-20 chance that Missouri will experience more than 125 such days by the end of the century.

Increasing heat in the Midwest will have consequences for agriculture, labor productivity, energy costs and usage, and infrastructure. Over the next 5 to 25 years, without significant adaptation by farmers, some counties in Missouri, Illinois, and Indiana will likely see average commodity crop losses up to 18 to 24 percent due to extreme heat each year, even though warmer winters may extend the growing season enough that farmers can plant two crops. Meanwhile, some states will suffer labor productivity drops as much as 3 percent by the end of this century. In Missouri, there is a 1-in-20 chance that the decline could reach as high as 4.2 percent – a decline comparable to that in absolute labor output during past U.S. recessions. Energy costs in the Midwest are expected to increase as demand for air-conditioning grows across the region. For instance, the most southern Midwest state of Missouri will likely see a 4 to 16 percent jump in energy costs by mid-century, with a 1-in-20 chance this jump will be more than 20 percent by mid-century.

Along the Lower Mississippi River:

The Southeast and Texas will likely be hit harder by temperature rises than any other single part of the country. Overall, residents of the region will likely see between two and four times more days over 95°F in a typical year in the next five to 25 years than they have over the past 30 years. Climate change also threatens to increase humidity, leading to a combination of heat and humidity that creates dangerous outside conditions for people, who must maintain a skin temperature below 100°F in order to effectively cool down and avoid fatal heat stroke. By mid-century, the average Mississippi resident will likely experience 33 to 85 days above 95°F per year, with a 1-in-20 chance of encountering more than 101 extremely hot days—more than three full months— per year.

Just as in the Midwest, increasing heat in Southern Mississippi states will have consequences for agricultural and labor productivity, energy costs and usage, and infrastructure. In particular, the region’s agricultural sector will be damaged by the changing climatic conditions, with several commodity crops likely to face severe yield declines. Meanwhile, residents and businesses will likely be affected by higher heat-related mortality, increased electricity demand and energy costs, and declines in labor productivity, threatening the manufacturing base that is increasingly driving the regional economy. Mississippi is among the top five states in the country likely to have the steepest high-risk labor productivity penalties from warmer temperatures, with up to a 0.8 percent penalty by 2020- 2039, and up to a 1.6 percent penalty in the following 20 years.

Risk and Damage of Recent Disaster Events (A North-South Cross Section)

At the Very Upper Reaches of the Basin System:

In July 2016, multiple rounds of rain showers and thunderstorms with “tornadic-strength winds” hit northeast Minnesota and northwest Wisconsin, compelling Wisconsin Governor Walker to declare a state of emergency in eight northern Wisconsin counties. The heavy rainfall led to two record river gauge readings, ripped up roadways, and caused two fatalities. To explore the storm systems links to climate change, visit Climate Signals.

Mississippi River Flooding 2015-2016:

Between late December 2015 and January 2016, rainfall totals across a huge portion of the Mississippi River basin were two to six times that of an average year, swelling the river to record-worthy levels.

In January 2016, the Mississippi River crested at its third-highest level on record in St. Louis. On Jan. 2, the flood crested at a record level downstream from St. Louis at Cape Girardeau, Mo., where the river reached 48.86 feet — over six feet above major flood stage.

The flooding caused at least $3 billion in damages, killed more than 20 people and breached eleven levees along the Mississippi River. To explore the storm systems links to climate change, see the Climate Nexus backgrounder.

South Central Maya Express Floods 2016:

Starting in March 2016, a “remarkably rare” storm of “unprecedented strength” dumped record amounts of rain on the south central U.S., falling particularly heavily on northern Louisiana where some locations experienced 1-in-1,000 year rains. Three quarters of the state of Mississippi was impacted by flooding, which affected 1.2 million people. As much water fell on the Baton Rouge area over an 18 day period as is carried by the entire Mississippi River. To explore the storm systems links to climate change, visit Climate Signals.

The Deluge that Hit Louisiana and Baton Rouge:

In early August 2016, a slow-moving storm system, fed by near-record warm seas in the Gulf of Mexico and North Atlantic, dumped heavy rains in the Southeastern United States and inundated much of Louisiana, Mississippi, Alabama, Florida and Texas. Five cities in Louisiana reported rainfall totals of over two feet, with some parts of the state recording more than 20 inches of rain in 48 hours, which qualifies as a 1-in-1,000 year rainfall event. Recall that in March of 2016, Louisiana experienced an earlier 1-in-1,000 year rainfall event. Two such events in the space of only a few months completely overwhelmed the state’s coping capabilities. Record flooding was observed on at least ten river gauges in Louisiana.

Thirteen people died in the resulting floods, in what the American Red Cross called the “worst disaster since Superstorm Sandy.” Between March and September of 2016, at least 45,000 homes were damaged or destroyed in Louisiana. To explore the storm systems links to climate change, visit Climate Signals.

Climate change about doubled the chances for the type of heavy downpours that caused the Louisiana flood, according to a climate attribution report.

The global warming signal is present in these numbers. For a precipitation event of this size to occur on the central Gulf Coast, the odds have increased by at least 40 percent and most likely doubled.[8]  – Karin van der Wiel, study lead, researcher and meteorologist at NOAA and Princeton University

Extreme weather records tend to be broken when natural variability happens to run in the same direction as climate change, as here.

The Massive 2011 Mississippi River Flood:

From late April to May 2011, heavy rainfall combined with record-breaking snow-melt runoff into major tributaries of the Mississippi river created a one in 500 year flood event that affected multiple locations along the river system. The flooding swelled the Mississippi River to six times its normal size and hit 119 counties in the middle and lower Mississippi River states of Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri and Tennessee. The river crested in mid-May but stayed above flood stage until mid-June. The flood ultimately incurred at least $2.8 billion in damages. More than 21,000 homes and businesses and 1.2 million acres of agricultural land were inundated, and more than 43,000 people felt some effects. The Army Corps of Engineers spent nearly $60 million while directly fighting the flood from March to August.

Between January and September 2016, the Mississippi River valley sustained $10 billion in impacts. “This is becoming a more and more frequent pattern with escalating costs.” (Mayor Coleman of St. Paul, MN and MRCTI Co-Chair).

The 10 cities that CDP surveyed collectively reported taking more than 35 actions to reduce the risk to, or vulnerability of, the city’s infrastructure, citizens, and businesses from climate change. Respondents from 6 cities regard addressing climate change as an economic opportunity. For instance, a total of 12 climate change-related projects across 7 cities surveyed, reported they are actively working to attract private sector involvement. (CDP Cities 2016 Data)

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