This data release is in support of a comprehensive study to evaluate water-quality trends in the International Souris River Basin, Saskatchewan and Manitoba, Canada and North Dakota, United States. The effort was completed by the U.S. Geological Survey (USGS) in cooperation with the International Joint Commission and International Souris River Board. This data release contains all files necessary to run trend models and produce results published in U.S. Geological Scientific Investigations Report 2023-XXXX [Nustad, R.A., and Tatge, W.S., 2023, Comprehensive Water-Quality Trend Analysis for Selected Sites and Constituents in the International Souris River Basin, Saskatchewan and Manitoba, Canada and North Dakota, United States, 1970-2020: U.S. Geological Survey Scientific Investigations Report 2023-XXXX]. In addition, this data release contains data for reservoir and Canadian streamflow, and water-quality by group (MI = major ion and dissolved solids, NUT = nutrients, PHY = physical parameters) contained in comma separated values (csv) files (site_flow and country/province_data) for selected sites used in trend and spatial analysis of the Souris River Basin. Streamflow data for the selected United States sites were gathered from the National Water Information System (https://nwis.waterdata.usgs.gov/nwis). Water-quality data for the selected sites in the United States were gathered from the National Water Quality Monitoring Council Water Quality Portal (https://www.waterqualitydata.us/) and collected by two additional agencies; the North Dakota Department of Environmental Quality and the U.S. Geological Survey Dakota Water Science Center. For additional information see metadata file specific to each dataset.

i. .\File_Mapping.csv: This file relates historical reconstructed hydrology streamflow from the U.S. Army Corps of Engineers () to the appropriate stochastic streamflow file for disaggregation of streamflow. Column A is an assigned ID, column B is named “Stochastic” and is the stochastic streamflow file needed for disaggregation, column c is called “RH_Ratio_Col” and is the name of the column in the reconstructed hydrology dataset associated with a stochastic streamflow file, and column D is named “Col_Num” and is the column number in the reconstructed hydrology dataset with the name given in column C. ii. .\Original_Draw_YearDat.csv: This file contains the historical year from 1930 to 2017 with the closest total streamflow for the Souris River Basin to each year in the stochastic streamflow dataset. Column A is an index number, column B is named “V1” and is the year in a simulation, column C is called “V2” and is the stochastic simulation number, column D is an integer that can be related to historical years by adding 1929, and column D is named “year” and is the historical year with the closest total Souris River Basin streamflow volume to the associated year in the stochastic traces. iii. .\revdrawyr.csv: This file is setup the same way that .\Original_Draw_YearDat.csv was except that, when a year had over 400 occurrences, it was randomly replaced with one of the 20 other closest years. The replacement process was completed until there were less than 400 occurrences of each reconstructed hydrology year associated with stochastic simulation years. Column A is an index number, column B is named “V1” and is the year in a simulation, column C is called “V2” and is the stochastic simulation number, column D is called “V3” and is the historical year who’s streamflow ratios will be multiplied by stochastic streamflow, and column E is called “Stoch_yr” and is the total of 2999 and the year in column B. iv. .\RH_1930_2017.csv: This file contains the daily streamflow from the U.S. Army Corps of Engineers (2020), reconstructed hydrology for the Souris River Basin for the period of 1930 to 2017. Column A is the date and columns B through AA are the daily streamflow in cubic feet per second. v. .\rhmoflow_1930Present.csv: This file was created based on .\RH_1930_2017.csv and provides streamflow for each site in cubic meters for a given month. Column A is an unnamed index column, column B is historical year, column C is the historical month associated with the historical year, column D provides a day equal to 1 but does not have particular significance and columns E through AD are monthly streamflow volume for each site location. vi. .\Stoch_Annual_TotVol_CubicDecameters.csv: This file contains the total volume of streamflow for each of the 26 sites for each month in the stochastic streamflow time timeseries and provides a total streamflow volume divided by 100,000 on a monthly basis for the entire Souris River Basin. Column A is unnamed and contains an index number, column B is month and is named “V1”, column C is the year in a simulation, column D is the simulation number, columns E (V4 through V29) through AD are streamflow volume in cubic meters, and column AE (V30) is total Souris River Basin monthly streamflow volume in cubic decameters/1,000.

Summary of statistics, regression analyses, LOADEST regressions, mean annual flow-weighted concentrations/values, and Kendal tau trend analyses of flow-weighted constituent concentrations of dissolved chloride, suspended sediment, dissolved oxygen, pH, and Temperature values of water samples collected intermittently at USGS streamgages on the Canadian River or its tributaries from northeastern New Mexico, to Lake Eufaula in Oklahoma from 1949-2013. Water-quality data were retrieved from the USGS NWIS system in 2014.

.\Spring 30 day\ I. .\GrantDevine_Comb.csv: This file contains the total inflow volume to Grant Devine Reservoir for the 30 days with the largest streamflow volume between March and May and the mean of the 3- and 12-month SPEI values for each November 1st. Spring streamflow volume for a given calendar year is paired with SPEI from the previous November 1st value. Column A is an unnamed index number, column B is a year in a stochastic simulation, column C is named “simnum” and is the stochastic simulation number, column D is named “mnspei” and is the mean of the 3- and 12-month SPEI for November 1 of each year in a stochastic simulation, and column E is named “SprintgThirtyTot” and is the total inflow volume for the 30 days with the largest streamflow volume between March and May of the following calendar year. II. .\LakeDarling_Comb.csv: has the same layout as .\GrantDevine_Comb.csv except that it is for local inflows to Lake Darling. III. .\Rafferty_Comb.csv: has the same layout as .\GrantDevine_Comb.csv except that it is for local inflows to Rafferty.

Geographic patterns and time trends of water-quality, modeled streamflow, and ecological data were compared along the Canadian River and selected tributaries in northeastern New Mexico to Lake Eufaula in Oklahoma to determine effects of climate change on water quality, streamflows, fish populations and ecological flows in this watershed from 1939 to 2013. Project participants included staff from the Oklahoma Cooperative Fish and Wildlife Research Unit, Vieux and Associates, USGS New Jersey Water Science Center and the USGS Oklahoma Water Science Center. Principal project funding was by the South Central Climate Science Center, with in-kind matching from the project participant organizations.