finding 21.5 : key-message-21-5

Storm water management systems, transportation networks, and other critical infrastructure are already experiencing impacts from changing precipitation patterns and elevated flood risks (medium confidence). Green infrastructure is reducing some of the negative impacts by using plants and open space to absorb storm water (medium confidence). The annual cost of adapting urban storm water systems to more frequent and severe storms is projected to exceed $500 million for the Midwest by the end of the century (medium confidence).

This finding is from chapter 21 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The chapter lead authors were identified in October 2016, and the author team was recruited in October and November 2016. Authors were selected for their interest and expertise in areas critical to the Midwest with an eye on diversity in expertise, level of experience, and gender. The writing team engaged in conference calls starting in December 2016, and calls continued on a regular basis to discuss technical and logistical issues related to the chapter. The Midwest chapter hosted an engagement workshop on March 1, 2017, with the hub in Chicago and satellite meetings in Iowa, Indiana, Michigan, and Wisconsin. The authors also considered other outreach with stakeholders, inputs provided in the public call for technical material, and incorporated the available recent scientific literature to write the chapter. Additional technical authors were added as needed to fill in the gaps in knowledge.

Discussion amongst the team members, along with reference to the Third National Climate Assessment and conversations with stakeholders, led to the development of six Key Messages based on key economic activities, ecology, human health, and the vulnerability of communities. In addition, care was taken to consider the concerns of tribal nations in the northern states of the Midwest. The Great Lakes were singled out as a special case study based on the feedback of the engagement workshop and the interests of other regional and sector chapters.

Note on regional modeling uncertainties

Interaction between the lakes and the atmosphere in the Great Lakes region (e.g., through ice cover, evaporation rates, moisture transport, and modified pressure gradients) is crucial to simulating the region’s future climate (i.e., changes in lake levels or regional precipitation patterns).fe83e7d3-3f29-4aef-81ae-28abd70dda2e,94a4d51e-96a4-4155-926d-31be60e2206a Globally recognized modeling efforts (i.e., the Coupled Model Intercomparison Project, or CMIP) do not include a realistic representation of the Great Lakes, simulating the influence of the lakes poorly or not at all.9db319af-7cec-440e-8dda-41526fed6cd0,5295673e-703b-42f8-9792-4ccf8e3cf747,03f91fdd-6d7d-431b-997b-91f63f52fe45,ee7f8311-bd00-4353-87a9-61ffb7813bf0,1cd8ac44-e9d5-4a2e-ab8e-e48c8988bbc2 Ongoing work to provide evaluation, analysis, and guidance for the Great Lakes region includes comparing this regional model data to commonly used global climate model data (CMIP) that are the basis of many products practitioners currently use (i.e., NCA, IPCC, NOAA State Climate Summaries). To address these challenges, a community of regional modeling experts are working to configure and utilize more sophisticated climate models that more accurately represent the Great Lakes’ lake–land–atmosphere system to enhance the understanding of uncertainty to inform better regional decision-making capacity (see for more information).

Description of evidence base:

The patterns of increased annual precipitation, and the size and frequency of heavy precipitation events in the Midwest, are shown in numerous studies and highlighted in Melillo et al. (2014)dd5b893d-4462-4bb3-9205-67b532919566 and Easterling et al. (2017).e8089a19-413e-4bc5-8c4a-7610399e268c Increases in annual precipitation of 5% to 15% are reported across the Midwest region.e8089a19-413e-4bc5-8c4a-7610399e268c In addition, both the frequency and the intensity of heavy precipitation events in the Midwest have increased since 1901.e8089a19-413e-4bc5-8c4a-7610399e268c

For the early 21st century (2016–2045), both lower and higher scenarios (RCP4.5 and RCP8.5) indicate that average annual precipitation could increase by 1% to 5% across the Midwest, suggesting that the observed increases are likely to continue. By mid-century (2036–2065), both scenarios (RCP4.5 and RCP8.5) indicate precipitation increases of 1% to 5% in Missouri and Iowa and 5% to 10% increases in states to the north and east. By late century (2070–2089), precipitation is expected to increase by 5% to 15% over present day, with slightly larger increases in the higher scenario (RCP8.5). Model simulations suggest that most of these increases will occur in winter and spring over the 21st century. Similar to annual precipitation, the amounts from the annual maximum one-day precipitation events (a measure of heavy precipitation events) are projected to increase over time in the Midwest. The size of the events could increase by 5% to 15% by late century.e8089a19-413e-4bc5-8c4a-7610399e268c

Gray literature documents that heavy rains in the Midwest are overwhelming storm water management systems, leading to property damage. Kenward et al. (2016)e9ccb2ed-ba08-43aa-8895-a21908f6d691 provide examples of rain-related sewage overflows in the Midwest. These include an overflow of 681 million gallons during heavy rains in April 2015 in Milwaukee and an overflow of over 100 million gallons from December 26–28, 2015, in St. Louis. Winters et al. (2015)0fe1cea1-aae3-4a35-b78f-61dcb5d6df49 document that failure of storm water management systems in heavy rain leads to property damage, including basement backups.

The disruption of transportation networks by heavy precipitation in the Midwest has been documented by collecting contemporary news reports and by compiling state government reports. Posey (2016)d9754ccb-d173-4624-8e6a-1efb9a37b556 relates that four storms between April 2013 and April 2014 forced evacuations or damaged cars in St. Louis, Missouri. In the same period, there were 18 flood-related closures on Missouri roads, a figure that excludes closures on small local roads. Flooding in May 2017 led to the closure of more than 400 roads across Missouri, a figure that again excludes local roads. Closed roadways included multiple stretches of Interstate 44, as well as sections of I-55, affecting interstate traffic between St. Louis and Memphis.bb613b8d-1aae-425c-b4b5-5274d1460d42 News reports document that the same stretch of I-44 was shut down during the floods of December 2015–January 2016.7529ed72-74b6-4f77-bf19-8aeeb1ab5ae0

Flood-related disruptions to Midwest barge and rail traffic in 2013 were documented by several articles in Journal of Commerce, a shipping trade magazine.cad15039-4add-470a-bac2-adeb08e201c4,3a526a0c-963a-46d5-a774-1673ff962adc WorkBoat, a trade journal of the inland shipping industry, documents that Mississippi River navigation has been halted by flooding in 2013, 2015, 2016, and 2017. It also documents low river conditions affecting navigation in 2012 and 2015.69f02922-508b-4bd8-9062-5ec8e4014e6c,39081664-4e4d-4cbc-aa98-7d33f8f87491,126256c6-a9c1-4b9f-bb8f-c43638c7db15,9478fde6-be0e-4ddf-b79e-348a4dc7b9b1,ef115408-09f5-4c76-a817-a428b078dc1b Disruptions to rail service caused by the floods of 2017 were documented in news media accounts.1e28d91b-3344-4106-8fe5-49c6a9c84431 Changon (2009)9baccf7b-275b-400c-8432-c8c92651c318 documents that flooding in 2008 resulted in extensive damage to railroads in Illinois and adjacent states, with costs exceeding $150 million due to direct damage and lost revenue.

Although there is ample documentation of transportation systems in the Midwest being disrupted by floods in recent years, there is a lack of long-term time series data on disruptions with which to determine whether these incidents are becoming more frequent. Development of long-term data on transportation disruptions in the Midwest is a research need. It is clear that flood frequency and severity on major rivers in the Midwest have increased in recent decades, although additional research is needed on the relative contributions of climate change and land-use change to increases in flood risk.aa980625-eab7-45f5-9bcb-d8dbbd36e6c7,80446a6f-156b-48ee-9b50-faabef3a1e52,64e82a6d-9331-443b-9329-74e5e25536bf

The EPA estimated economic costs related to infrastructure and transportation in the Midwest, including costs associated with bridge scour and pavement degradation.0b30f1ab-e4c4-4837-aa8b-0e19faccdb94 The use of green infrastructure to reduce impacts associated with heavy precipitation is also documented in gray literature, including municipal planning documents. Using planted areas to absorb rainfall and reduce runoff has become a common approach to storm water management.b71cbf27-2a1d-477e-9d0a-4d49b427ed47,b0449e10-e122-4c04-a967-f2aef8b905b8,4c84ded1-6381-469a-bf07-50f9dc76cb45,6c1de119-8509-4e82-8aee-3c2c1163748e,ac04db1a-16ad-4ca0-91c1-b08a981eec1c,e611137a-7d8d-4fda-be01-d438c7c25ec2,6a5b4177-6cae-4aed-949e-aade35b943f7 Dechannelization and restoration of streams as a technique for improving storm water management is described in Trice (2013)4efa8307-3b25-4b9a-96f7-ebcab2cfdecb and Milwaukee Metropolitan Sewer District (2017).0a2139b3-514c-4784-8fed-37831138aa6e Preservation of open space is described in Ducks Unlimited (2017)a373ebb7-290f-4513-8719-2d0a7005d9c3 and the Ozaukee Washington Land Trust (2016).7badb8b5-90d3-4124-9b87-e79982c57c62 The use of urban forestry as an adaptation method is documented in the Minneapolis Marq2 Project (2017)f89cf6b7-1c12-4cb8-b1c3-3f218a948dc5 and the Cleveland Tree Plan (2015).c69f166d-6658-44f5-82dd-16e8130500ab Projected costs to storm water systems are based on EPA projections.0b30f1ab-e4c4-4837-aa8b-0e19faccdb94

New information and remaining uncertainties:

Although there is very high confidence that flood risk is increasing in the Midwest, there remains uncertainty about the relative contributions of climate change and land-use change. There is, however, sufficient evidence that changing precipitation patterns are leading to changes in hydrology in the Midwest,c9d0a7e9-2bba-48cb-bd53-9e8c4209976d,43a6ac94-f12c-4ed4-b942-02c9480acc93,397fc975-a56c-4d94-a91d-76ba800562d4,ab5a35f8-2e28-4dd1-ba18-ded6a6d4c710,d2af0d06-91aa-4e53-99e1-4dad2ac9195a and that heavier precipitation patterns are consistent with projections from climate models, to justify a rating of medium confidence to the assertion that climate change is contributing to changes in flooding risk. There is high confidence that local governments and nongovernmental organizations are turning to green infrastructure solutions as a response to increased flooding risk. Additional research is needed to quantify the aggregate benefits of these approaches.

While it is clear that flood frequency and severity on major rivers in the Midwest have increased in recent decades, it must be emphasized that the change in precipitation levels is not the only factor contributing to the increase in flood risk. Land-use change, particularly the destruction of floodplains by levee systems, has also been documented as a key contributor to increasing flood risk in the Midwest.aa980625-eab7-45f5-9bcb-d8dbbd36e6c7,80446a6f-156b-48ee-9b50-faabef3a1e52,64e82a6d-9331-443b-9329-74e5e25536bf On smaller streams, tile drainage systems have been shown to exacerbate flood risk.80341782-104c-4415-8650-70dd485b2246 Determining the relative contribution of land-use change and climate change to increases in riverine flood risk is an important research need.

Assessment of confidence based on evidence:

There is medium confidence that climate change is contributing to increased flood risk in the Midwest; there is medium confidence that green infrastructure is reducing flood risk. There is much uncertainty associated with specific numerical projections. This leads to medium confidence that costs will exceed $500 million. However, the EPA projections are sufficient to provide high confidence that increasing the capacity of existing storm water systems in order to maintain current levels of service would require significant expenditures on the part of urban sewer districts.

References :

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