Flood-Frequency Analysis in the Midwest: Addressing Potential Nonstationary Annual Peak-Flow Records Active

Executive Summary (or Background):

The U.S. Geological Survey (USGS), in cooperation with the following State agencies:

• Illinois Department of Transportation,
• Iowa Department of Transportation,
• Minnesota Department of Transportation,
• Missouri Department of Transportation,
• North Dakota State Water Commission,
• South Dakota Department of Transportation, and
• Wisconsin Department of Transportation,

has undertaken a multi-year study to research methods for detecting and addressing potential trends in flood frequency distributions because of changes in climate, land use, and other potential drivers of change. This multi-state region represents complex variability in topography, ecoregions, land use, land cover, and climate. The region is characterized by abrupt transitions among high-relief, semi-mountainous areas, well-drained moderate-elevation plains, poorly drained low-elevation glaciated prairies, and other complex geologic and hydrologic features. The land use is mainly pasture and small grains to the west. The Corn Belt covers much of the center and eastern portion of the region and has recently expanded to the west and north. The region also contains major urban-suburban areas, centered on Chicago, Minneapolis-St. Paul, and St. Louis, which have expanded substantially during the proposed study period and thus are another source of non-stationarity.

Peak-flow frequency analysis is essential for flood insurance studies, floodplain management, and the design of transportation infrastructure. In recent decades, better understanding of long-term hydroclimatic persistence, as well as concerns about potential climate change and land-use change have caused the stationarity assumption, underpinning for flood-frequency analysis, to be reexamined. Although many important water-management activities are independently conducted within the sociopolitical state boundaries, regional hydrologic complexities transcend the state boundaries and are more efficiently handled from a regional perspective. This investigation will be conducted in collaboration with a national study funded by the Federal Highway Administration and will focus on specific issues that have the most impact on flood-frequency analysis within the multi-state region.

Sources/Usage: Public Domain.

Objectives:

The overall goal of this study is to evaluate the combined effects of multidecadal climatic persistence (including hydroclimatic shifts), gradual climate change, and some aspects of land-use change on peak-flow frequency analyses in the multi-state region. This study is intended to provide a framework for addressing potential non-stationarity issues in statewide flood-frequency updates that commonly are conducted by the USGS in cooperation with state DOTs throughout the nation on an ongoing basis. This will be achieved through the following primary objectives:

1. Define spatial and temporal characteristics of climatic persistence/change affecting annual peak flows in the multi-state region.
2. Develop and apply a statistical methodology for estimating changes in peak-flow frequency distributions in the multi-state region in relation to climatic persistence/change and urbanization; the effects of rural and land-use change will only be investigated in an exploratory manner.
3. Investigate methods for addressing regional climatic persistence/change and land-use change in peak-flow frequency analysis. To the extent possible, estimates of trend-adjusted flood magnitudes for various exceedance levels (such as the 10-percent or 1-percent annual exceedance probability) will be provided for comparison to previously published estimates.

Sources/Usage: Public Domain.

Tasks:

The results of the proposed investigation will be presented in several peer-reviewed USGS Data Releases, Scientific Investigations Reports (SIR; online only), and journal articles and a USGS Fact Sheet or Story Map. Tasks include efforts to:

1. Publicly release watershed-based climate data (metrics of precipitation and temperature) on a monthly time scale and summed to annual seasonal and annual total values. These data will also contain trend results for trends in climate metrics in annual peak streamflow and climate variables.
2. Characterize the effects of natural hydroclimatic shifts and potential climate change on annual peak flows in Midwest: Illinois, Iowa, Minnesota, Missouri, North Dakota, South Dakota and Wisconsin.
3. Analyze the seasonality of flood peaks in the region and their trends and implications for trend attribution.
4. Evaluate the effect of urbanization on flood-peaks in major metropolitan areas in the study region.
5. Analyze, compile, and publish regional tile drainage data for study reproducibility and documentation
6. Publicly release data that compares adjustment methods at individual sites, such as multiple flood-frequency analysis results.
7. Summarize methods for addressing regional hydroclimatic shifts, climate change, and land-use change in peak-flow frequency analyses in the Midwest.
8. Succinctly summarize the above work in a short fact sheet that provides links to project products to make it easy to find data and results which can be handed out at future meetings, sent to managers for an overview, etc.
9. Receive science communication training from the Alda Center for Communicating Science (funded by USGS Midcontinent Region as an extension to this project).

Sources/Usage: Public Domain.

Sources/Usage: Public Domain.