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#           Introduction and methods of analysis for peak streamflow trends and their relation to changes in climate in Illinois, Iowa, Michigan, Minnesota, Missouri, Montana, North Dakota, South Dakota, and Wisconsin              

      January 25, 2024    

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Flood-frequency analysis, also called peak-flow frequency or flood-flow frequency analysis, is essential to water resources management applications including critical structure design and floodplain mapping. Federal guidelines for doing flood-frequency analyses are presented in a U.S. Geological Survey Techniques and Methods Report known as Bulletin 17C. A basic assumption within Bulletin 17C is that for drainage basins without major hydrologic alterations, statistical properties of the distribution of annual peak streamflows (peak flows) are stationary; that is, the mean, variance, and skew are constant. The stationarity assumption has been widely accepted within the flood-frequency community; however, a better understanding of long-term climatic persistence and concerns about potential climate change and land-use change has caused a reexamination of the stationarity assumption. Flood-frequency analyses that do not incorporate observed trends and abrupt changes may result in a poor representation of the true flood risk. Bulletin 17C does not offer guidance for incorporating nonstationarities when estimating floods, and it describes a need for studies that incorporate changing climate or basin characteristics. In response to this need and a history of concern regarding nonstationarity peak flows in the region, this study was done by the U.S. Geological Survey, in cooperation with the Departments of Transportation of Illinois, Iowa, Michigan, Minnesota, Missouri, South Dakota, and Wisconsin; the Montana Department of Natural Resources and Conservation; and the North Dakota Department of Water Resources, to assess potential nonstationarity in peak flows in the north-central United States.

This chapter summarizes the methods used to detect hydroclimatic changes in peak-flow data in the study region. A wide range of analyses and statistical approaches are applied to document the primary mechanisms controlling floods and characterize temporal changes in hydroclimatic variables and peak flow. Four periods were selected for analysis of peak flow, daily streamflow, and climate data. The periods are (1) a 100-year period, 1921–2020; (2) a 75-year period, 1946–2020; (3) a 50-year period, 1971–2020; and (4) a 30-year period, 1991–2020. The climate data consist of monthly time series estimates of temperature, precipitation, potential evapotranspiration, actual evapotranspiration, snowfall, soil moisture storage, snow water equivalent, and runoff on a 3.1-mile by 3.1-mile grid for the conterminous United States.

Statistical and graphical analyses were used to investigate potential changes in hydrology and climate. The starting point for these analyses was the initial data analysis of peak flow described in Bulletin 17C, which includes plotting the peak flow and checking for autocorrelation, monotonic trends, and changes points. Analyses were added to examine additional features in the data. To examine potential causal drivers of changes, the climate data were analyzed graphically and statistically. Results are provided in a U.S. Geological Survey data release. The study limitations are documented for users of the results.

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January 25, 2024

####                 Peak Streamflow Data, Climate Data, and Results from Investigating Hydroclimatic Trends and Climate Change Effects on Peak Streamflow in the Central United States, 1921–2020              

Central Midwest Water Science Center

#### Karen R Ryberg, Ph.D.

##### Research Statistician

Dakota Water Science Center

kryberg@usgs.gov

701-250-7422

#### Thomas Over

##### Research Hydrologist

Central Midwest Water Science Center

tmover@usgs.gov

217-328-9757

#### Sara Brandt Levin

##### Physical Scientist

Upper Midwest Water Science Center

slevin@usgs.gov

763-783-3157

#### David C Heimann

##### Hydrologist

Central Midwest Water Science Center

dheimann@usgs.gov

816-554-3489

#### Nancy A Barth

##### Hydrologist

Wyoming-Montana Water Science Center

nabarth@usgs.gov

701-250-7407

#### Mackenzie  Marti

##### Physical Scientist

Central Midwest Water Science Center

mmarti@usgs.gov

217-328-9767

#### Padraic S O'Shea

##### Statistician

Central Midwest Water Science Center

poshea@usgs.gov

319-358-3653

#### Chris Sanocki

##### Geographer

Upper Midwest Water Science Center

sanocki@usgs.gov

763-783-3151

#### Harper Wavra

##### Computer Scientist

Upper Midwest Water Science Center

hwavra@usgs.gov

701-250-7407

#### Roy Sando 

##### Physical Scientist (GIS) 

Wyoming-Montana Water Science Center

tsando@usgs.gov

406-594-9801

#### Steve Sando 

##### Hydrologist (NDAA)

Wyoming-Montana Water Science Center

sksando@usgs.gov

406-457-5928

#### Milan S Liu

##### Geographer

Upper Midwest Water Science Center

msliu@usgs.gov

## Related Content

                  - Data  LabelJanuary 25, 2024                Peak Streamflow Data, Climate Data, and Results from Investigating Hydroclimatic Trends and Climate Change Effects on Peak Streamflow in the Central United States, 1921–2020              Peak-flow frequency analysis is crucial in various water-resources management applications, including floodplain management and critical structure design. Federal guidelines for peak-flow frequency analyses, provided in Bulletin 17C, assume that the statistical properties of the hydrologic processes driving variability in peak flows do not change over time and so the frequency distribution of annuByCentral Midwest Water Science Center 
                  - Connect  Karen R Ryberg, Ph.D.Research StatisticianDakota Water Science CenterEmailkryberg@usgs.govPhone701-250-7422Thomas OverResearch HydrologistCentral Midwest Water Science CenterEmailtmover@usgs.govPhone217-328-9757Sara Brandt LevinPhysical ScientistUpper Midwest Water Science CenterEmailslevin@usgs.govPhone763-783-3157David C HeimannHydrologistCentral Midwest Water Science CenterEmaildheimann@usgs.govPhone816-554-3489Ext206Nancy A BarthHydrologistWyoming-Montana Water Science CenterEmailnabarth@usgs.govPhone701-250-7407Mackenzie  MartiPhysical ScientistCentral Midwest Water Science CenterEmailmmarti@usgs.govPhone217-328-9767Padraic S O'SheaStatisticianCentral Midwest Water Science CenterEmailposhea@usgs.govPhone319-358-3653Chris SanockiGeographerUpper Midwest Water Science CenterEmailsanocki@usgs.govPhone763-783-3151Harper WavraComputer ScientistUpper Midwest Water Science CenterEmailhwavra@usgs.govPhone701-250-7407Roy Sando Physical Scientist (GIS) Wyoming-Montana Water Science CenterEmailtsando@usgs.govPhone406-594-9801Steve Sando Hydrologist (NDAA)Wyoming-Montana Water Science CenterEmailsksando@usgs.govPhone406-457-5928Milan S LiuGeographerUpper Midwest Water Science CenterEmailmsliu@usgs.gov 

### Study Area

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####             Water Resources Mission Area - Headquarters        

USGS Headquarters12201 Sunrise Valley DriveReston, VA20192United States

#### Dakota Water Science Center- Rapid City

1608 Mountain ViewRapid City, SD57702United States

(605) 394-3200

(605) 355-4523

####               Upper Midwest Water Science Center - Madison, WI, Office          

1 Gifford Pinchot DriveMadison, WI53726United States

608-828-9901

608-821-3817

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