Posted on February 21, 2012 10:39 AM
Climate Change Adaptation at a Regional Level
While GO TO 2040 focused on voluntary actions to reduce greenhouse gas emissions, it also noted the need for comprehensive federal action to achieve the reduction goals widely agreed upon within the scientific community. Although the prospects for comprehensive climate legislation look dim, a Policy Update from October 13, 2011, reported on federal agency initiatives to mitigate climate change under their existing authority.
The problem is not just to forestall climate change sometime in the future. Research suggests not only that weather patterns will change, but that patterns have already changed. The most recent assessment report in 2007 from the Intergovernmental Panel on Climate Change concluded that climate change, especially increases in temperature, could already be observed on all continents. For instance, plant hardiness zones in the U.S. have changed noticeably in the past two decades, with more northerly areas now warmer than in the past. The majority of birds that overwinter in North America are now doing so further north. Here in northeastern Illinois, changes in rainfall patterns can also be discerned, although changes in temperature are less evident. The Illinois State Climatologist Office's examination of annual rainfall in northeastern Illinois over the 20th Century suggests that annual rainfall grew noticeably higher after about 1970.
This Policy Update focuses on climate adaptation at a regional level, exploring adjustments that should be made in how we plan, build, operate, and update systems to help cope with weather impacts due to climate change. This piece will use flooding as an illustration of potential policy changes to prepare for these effects. Increasing frequency and intensity of flood events is a real prospect for metropolitan Chicago, a region that has seen its share of disastrous floods. There are good reasons to pay attention to climate change in programs to reduce flood risk, but there are also large uncertainties, design tradeoffs, and a need for new research.
Flood Risk in a Changing Climate
Flooding is one of the main natural disasters threatening the region. Large storms in 1986, 1987, 1996, 2008, 2010, and 2011 caused hundreds of millions of dollars in damage in northeastern Illinois. The floods in the 1980s hastened the adoption of county and municipal ordinances, such as that of DuPage County, to control drainage from developed sites, which stipulated the use of detention basins designed to collect and temporarily store the rainfall from large storm events to lessen flooding downstream.
To size storm sewers, detention basins, and other elements of the drainage system, current ordinances rely on publications by the Illinois State Climatologist Office, the most recent being Bulletin 70, to calculate expected rainfall. Bulletin 70 used weather data from 1901 to 1983 to estimate the frequency and intensity of storms in different areas of Illinois. As noted, recent rainfall appears to be higher than it was during most of that earlier period. While annual rainfall totals may not say much about intensity of storms, the increase in rainfall suggests that Bulletin 70 should be updated. An update, which should involve the input of civil engineering and floodplain management professional societies, could include projections of future rainfall frequency and intensity as region-specific climate models improve. After all, detention basins will be in service for decades, and if storms become more intense, detention volumes required under current ordinances may not be as protective in the future as they are today. Retrofitting to provide more storage at that point may not be feasible because of limited land availability in developed areas.
Federal policy also plays a role in managing future flood risk. The Federal Emergency Management Agency (FEMA) and the Illinois State Water Survey have been working for several years to modernize flood risk maps for the National Flood Insurance Program (NFIP). These maps are used to show areas where local floodplain management requirements -- such as building construction standards -- will be in effect and where flood insurance is mandatory for those with federally-backed mortgages. In many cases, the modeling used to delineate areas that would be flooded in a large storm has not been updated, and it’s possible that flood heights could become higher and floodplains broader as rainfall patterns change. Since there are so many uncertainties in projecting future hydrology, not to mention the engineering studies based on it, it would be worthwhile to re-run the models in a representative watershed based on a range of potential future conditions as a pilot project. This could be done on a local basis. At the federal level, FEMA has initiated a nationwide study to determine the impacts of climate change on the NFIP. It is currently underway.
Infrastructure Design Standards
Design standards may need to change for infrastructure meant to withstand floods. For instance, channel protection for nearly 30 of the 2,000 bridges over streams in the CMAP area are rated as “having failed” or are in severe condition, according to the National Bridge Inventory (see chart below). The inventory also examines “waterway adequacy,” cataloging the bridges that are subject to overtopping during floods. This, too, could become more frequent with increased rainfall. However, the need to overhaul already deficient bridges is an opportunity to review the standards governing reconstruction. For example, should different designs be used to cope with flows that are expected to be higher in the future? This would require updates to the design manuals in use by the Illinois Department of Transportation and other highway departments. Given the length of time bridges will be in service, weather conditions could be significantly different a short ways into their design lives.
Climate Prediction and Climate Readiness
The preceding section discusses building infrastructure to higher standards based on predicted conditions. The many climate models researchers have developed are able to mimic observed conditions fairly well, but only at very large scales. When one attempts to “downscale” these models to the level of smaller areas like states or cities, such as these examples for Illinois, the results can be less satisfactory, with wide variation in predictions and a limited ability to tell which is more probable than another.
As researchers continue to refine climate models for regional application, it may be best to assess vulnerability to a range of potential climatic conditions and take steps to address the biggest risks, rather than plan for a specific target. Designs could be chosen that perform well under a variety of different future scenarios -- an approach known as climate readiness. In engineering practice, a “safety factor” approach is also an option, with an increment added to a standard that would protect against the unknown effects of climate change. More sophisticated approaches will surely evolve in the upcoming years, but it is important to begin thinking about changing practice through policy. Decisions about infrastructure design will be with us for many years -- the region can only be served well by infrastructure that meets its future needs.