Flow-duration statistics at the 99th, 98th, 95th, 90th, 80th, 70th, 60th, and 50th percent exceedance probabilities and annual n-day low-flow statistics for the 1-, 7-, 14-, and 30-day mean low flows with 2-year (0.5 nonexceedance probability), 5-year (0.2 nonexceedance probability), and 10-year (0.1 nonexceedance probability) recurrence intervals were computed for 28 selected streamflow gaging stations in Puerto Rico. The 28 selected streamflow gaging stations were required to have 10 or more years of daily mean streamflow data through water year 2018. The flow-duration statistics and n-day low-flow frequencies were computed using the U.S. Geological Survey program, SWToolbox. Regional regression equations were developed to estimate flow-duration statistics and n-day low-flow frequencies at ungaged stream locations using selected basin characteristics as explanatory variables. These variables were determined from digital spatial datasets and geographic information systems using the most recent data available, as referenced in the U.S. Geological Survey web application, StreamStats, and published in Kolb and Ryan (2021).
An ordinary least-squares procedure in R Studio was used to develop the final regional flow-duration regression equations using drainage area, mean total annual reference evapotranspiration, and minimum basin elevation as the explanatory variables. A generalized least squares procedure in the U.S. Geological Survey program, WREG, was used to account for cross-correlation of sites and develop the final regional n-day low-flow frequency regression equations using drainage area, mean total annual reference evapotranspiration, and minimum basin elevation as the explanatory variables. This data release includes two child pages: Puerto Rico Flow-Duration Regression Files and Puerto Rico N-day Low-Flow Regression Files, a BasinCharacteristics.csv file that contains 47 basin and climatic characteristics considered in the analyses, a BasinCharacteristics_corrrelation_charts folder that contains .pdf files showing correlation matrices, a R_regsubsets_output folder that contains .txt and .pdf files showing results of the "regsubsets" analyses, a Trend_statistics_nday_lowflow_timeseries.csv file that contains the SWToolbox Mann-Kendall tau statistics, and a NWIS_rdb_files folder that contains the .rdb files used in the analyses. References Cited:
Kolb, K.R., and Ryan, P.J., 2021, Basin Characteristic Rasters for Puerto Rico StreamStats, 2021: U.S. Geological Survey data release, https://doi.org/10.5066/P9HK9SSQ.