This dataset contains annual peak and seasonal maximum streamflow data from the USGS National Water Information System (NWIS) and the results of an analysis of spatial and temporal patterns for those data for the conterminous U.S. An interpretation of the analysis of these data will be published in a journal article. The streamflow data were compiled for the years 1966 to 2015 for 415 streamgages that are part of the USGS HCDN-2009 network. The HCDN-2009 network contains streamgages in watersheds with minimal anthropogenic change. The dataset contains the annual peak and the maximum daily streamflow for the months of October through December (OND), January through March (JFM), April through June (AMJ), and July through September (JAS). The maximum daily streamflow for OND, JFM, AMJ, and JAS was determined as the largest daily streamflow over those months. This dataset contains the following files for the annual peaks and maximum daily streamflow. The files labeled "raw" contain the water year and the raw annual peaks from NWIS and the selected maximum daily streamflow from NWIS. The files labeled "SPI" contain the water year and the standardized peaks and maximum daily streamflow by using the Standardized Precipitation Index method. The files labeled "cluster_assignments" contain (in columns) the gage name (two letter abbreviation of the state in which the gage is located and the USGS site number), the latitude and longitude (NAD 83) of the gage, an integer that is an identifier of the cluster that the gage was assigned, and the Pearson correlation coefficient between the standardized streamflow and the average standardized streamflow of all gages in its cluster. The annual peaks were clustered into 4 groups, the OND maximum flows were clustered into 7 groups, the JFM maximum flows were clustered into 9 groups, and the both the AMJ and JAS maximum flows were clustered into 5 groups. The files with the term "cluster_means" in the file name contain the water year and the mean of the standardized streamflow of all gages in the clusters of peaks and maximum daily streamflow for OND, JFM, AMJ, and JAS.

The U.S. Geological Survey (USGS) recently completed a report documenting methods for peak-flow frequency analysis following implementation of the Bulletin 17C guidelines (https://doi.org/10.3133/tm4B5). The methods provide estimates of peak-flow quantiles for 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities (AEPs) for selected streamgages operated by the USGS and Environment Canada. In association with the report, this data release presents peak-flow frequency analyses for 148 streamgages (127 stations in Maine, 16 in New Hampshire, and 5 in New Brunswick, Canada). Included are 148 individual ".PRT" text files that contain results of the flood-frequency analyses of annual peak flows from all of the selected streamgages. The files were generated using version 7.3 of USGS software PeakFQ (https://water.usgs.gov/software/PeakFQ/; Veilleux and others, 2014) to conduct flood-frequency analyses using the expected moments algorithm (England and others, 2018). The peak-flow files used as input to PeakFQ were obtained from the USGS National Water Information System (NWIS) database (https://nwis.waterdata.usgs.gov/usa/nwis/peak) and contained annual peak flows ending in water year 2019. Results of the flood-frequency analyses at streamgages that did not have storage or regulation in the watershed (124 of the total 148) were used to develop peak-flow regression equations for estimating the selected AEPs at ungaged sites in Maine. Results from the unregulated streamgages that had periods of record of at least 20 years (51 of the 124) were used for a Maine skew analysis also outlined in the report. This data release also includes eight Excel tables summarizing the results of the peak-flow frequency analyses and peak-flow regionalization. Tables include basin characteristics used in the regionalization, information needed for flood-frequency analyses including periods of record used in analyses and skew values, maximum instantaneous floods , flood frequency estimates , information needed for advanced accuracy analyses for the streamgages and information needed for calculation of the 90-percent confidence intervals of the peak-flow equations for the AEPs.

The U.S. Geological Survey (USGS) recently completed a report documenting methods for peak-flow frequency analysis following implementation of the Bulletin 17C guidelines (https://doi.org/10.3133/tm4B5). The methods provide estimates of peak-flow quantiles for 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities (AEPs) for selected streamgages operated by the USGS and Environment Canada. In association with the report, this data release presents peak-flow frequency analyses for 148 streamgages (127 stations in Maine, 16 in New Hampshire, and 5 in New Brunswick, Canada). Included are 148 individual ".PRT" text files that contain results of the flood-frequency analyses of annual peak flows from all of the selected streamgages. The files were generated using version 7.3 of USGS software PeakFQ (https://water.usgs.gov/software/PeakFQ/; Veilleux and others, 2014) to conduct flood-frequency analyses using the expected moments algorithm (England and others, 2018). The peak-flow files used as input to PeakFQ were obtained from the USGS National Water Information System (NWIS) database (https://nwis.waterdata.usgs.gov/usa/nwis/peak) and contained annual peak flows ending in water year 2019. Results of the flood-frequency analyses at streamgages that did not have storage or regulation in the watershed (124 of the total 148) were used to develop peak-flow regression equations for estimating the selected AEPs at ungaged sites in Maine. Results from the unregulated streamgages that had periods of record of at least 20 years (51 of the 124) were used for a Maine skew analysis also outlined in the report. This data release also includes eight Excel tables summarizing the results of the peak-flow frequency analyses and peak-flow regionalization. Tables include basin characteristics used in the regionalization, information needed for flood-frequency analyses including periods of record used in analyses and skew values, maximum instantaneous floods , flood frequency estimates , information needed for advanced accuracy analyses for the streamgages and information needed for calculation of the 90-percent confidence intervals of the peak-flow equations for the AEPs.

This data release identifies 555 Hydro-Climatic Data Network (HCDN) streamgages in the conterminous United States during the period 1981-2019 which were grouped according to similarity in their temporal patterns of mean monthly streamflow.

This data release identifies 555 Hydro-Climatic Data Network (HCDN) streamgages in the conterminous United States during the period 1981-2019 which were grouped according to similarity in their temporal patterns of mean monthly streamflow.

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 annual peak flows is stationary. Better understanding of long-term climatic persistence and further consideration of potential climate and land-use changes have caused the assumption of stationarity to be reexamined. This data release contains input data and results of a study investigating hydroclimatic trends in peak streamflow (peak flow) in the Central United States, including nine states (Iowa, Illinois, Michigan, Minnesota, Missouri, Montana, North Dakota, South Dakota, and Wisconsin). Peak flow records from unregulated U.S. Geological Survey (USGS) streamgages were used to evaluate changes over 30-, 50-, 75-, and 100-year trend periods, all ending in water year 2020. This data release contains station lists of the streamgages used in each of the nine states, the peak streamflow input data and peak streamflow analysis results, and the climate input data and climate analysis results. See "Station_Lists.zip" on the landing page for station lists (in text file format) for each state included in the study.

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 annual peak flows is stationary. Better understanding of long-term climatic persistence and further consideration of potential climate and land-use changes have caused the assumption of stationarity to be reexamined. This data release contains input data and results of a study investigating hydroclimatic trends in peak streamflow (peak flow) in the Central United States, including nine states (Iowa, Illinois, Michigan, Minnesota, Missouri, Montana, North Dakota, South Dakota, and Wisconsin). Peak flow records from unregulated U.S. Geological Survey (USGS) streamgages were used to evaluate changes over 30-, 50-, 75-, and 100-year trend periods, all ending in water year 2020. This data release contains station lists of the streamgages used in each of the nine states, the peak streamflow input data and peak streamflow analysis results, and the climate input data and climate analysis results. See "Station_Lists.zip" on the landing page for station lists (in text file format) for each state included in the study.

This data release contains trend results computed on the basis of modeled and observed daily streamflows at 502 reference gages across the conterminous U.S. from October 1, 1983 through September 30, 2016. Modeled daily streamflows were computed using the deterministic Precipitation Runoff Modeling System (PRMS), and five statistical techniques: Nearest-Neighbor Drainage Area Ratio (NNDAR), Map-Correlation Drainage Area Ratio (MCDAR), Ordinary Kriging of the logarithms of discharge per unit area (OKDAR), Nearest-Neighbor nonlinear spatial interpolation using flow duration curves (NNQPPQ), and Map-Correlation nonlinear spatial interpolation using flow duration curves (MCQPPQ). Observed daily streamflow data for the study gages were retrieved from the National Water Information System (NWIS). Study gages were selected from among Hydro-Climatic Data Network 2009 (HCDN-2009) gages in the GAGES-II dataset considered to be minimally affected by regulation, diversion, mining, or other anthropogenic activities. Results include trends in annual and monthly means, annual percentiles (1, 5, 10, 25, 50, 75, 90, 95, 99), annual 1-day high, 3-day high, and 7-day low, and annual snowmelt-related runoff timing for a subset of snowmelt dominated basins. Bias and volumetric efficiency statistics between observed and modeled streamflows also are provided.

This data release contains trend results computed on the basis of modeled and observed daily streamflows at 502 reference gages across the conterminous U.S. from October 1, 1983 through September 30, 2016. Modeled daily streamflows were computed using the deterministic Precipitation Runoff Modeling System (PRMS), and five statistical techniques: Nearest-Neighbor Drainage Area Ratio (NNDAR), Map-Correlation Drainage Area Ratio (MCDAR), Ordinary Kriging of the logarithms of discharge per unit area (OKDAR), Nearest-Neighbor nonlinear spatial interpolation using flow duration curves (NNQPPQ), and Map-Correlation nonlinear spatial interpolation using flow duration curves (MCQPPQ). Observed daily streamflow data for the study gages were retrieved from the National Water Information System (NWIS). Study gages were selected from among Hydro-Climatic Data Network 2009 (HCDN-2009) gages in the GAGES-II dataset considered to be minimally affected by regulation, diversion, mining, or other anthropogenic activities. Results include trends in annual and monthly means, annual percentiles (1, 5, 10, 25, 50, 75, 90, 95, 99), annual 1-day high, 3-day high, and 7-day low, and annual snowmelt-related runoff timing for a subset of snowmelt dominated basins. Bias and volumetric efficiency statistics between observed and modeled streamflows also are provided.

This metadata record describes data that characterize low-flow period duration and seasonality, as well as trends and climate linkages at streamgages across the conterminous United States. These data are associated with a publication which looks to answer three questions about low-flow periods in the conterminous United States: (1) how long are these periods and when do they typically start and end, (2) how are these properties changing through time, and (3) how does climate influence these properties? These data include 1145 U.S. Geological Survey streamgages with historical periods from 1951-2020. This data release contains the following: ===== 1) low_flow_characteristics.csv: Annual low-flow period characteristics for selected streamgages, for each climate year from 1951-2020. 2) low_flow_trends.csv: Trends in low-flow period characteristics for selected streamgages, from 1951-2020. 3) climate_trends.csv: Trends in climate variables for selected streamgages related to low-flow periods from 1951-2020. 4) monthly_low_flows.csv: The number of low-flow days in each month for selected streamgages. 5) site_metadata.csv: Metadata for describing each of the selected streamgages. 6) climate_correlations.csv: Correlations between low-flow period characteristics for selected streamgages and climate variables. 7) all_percentiles_1951_2020.zip: A zip file containing all streamflow percentile data used in this analysis.