A generalized least squares (GLS) technique was used with at-site n-day low-flow time series and frequencies, from SWToolbox (Kiang and others, 2018), and 14 basin characteristics (basin perimeter, drainage area, maximum basin elevation, mean total annual reference evapotranspiration, groundwater head, length of longest flow path, minimum basin elevation, runoff-curve number, relief, ruggedness, slope ratio, percentage of hydrologic soil type B, available water capacity, and total length of streams in a basin) for 28 selected streamflow gaging stations in Puerto Rico to calculate regional n-day low-flow frequency regression equations for ungaged stream locations. The GLS approach assigns weights based on uncertainty of the observations (ie. record length and variance) and accounts for correlated streamflows and time-sampling errors (Eng and others, 2009). Performance metrics from the Weighted-multiple-linear REGression Program (WREG) were analyzed to determine drainage area, mean total annual reference evapotranspiration, and minimum basin elevation as the explanatory variables that provided the best results. Values for the correlation smoothing function in were alpha equal to 0.003 and theta equal to 0.96.
This data release includes a SWToolbox_output_files folder that contains supporting data used to format the WREG input files, xday_lowflow folders (where x refers to 1, 7, 14, or 30) that contain (1) the WREG input files FlowChar, LP3G, LP3K, LP3s, SiteInfo, and the 28 station nday timeseries files (USGSxxxxxxxx); and (2) a WREG_gls_results folder that contains output for the 2yr, 5yr, and 10yr nonexceedance probability flows. References Cited:
Eng, K., Chen, Y., and Kiang, J.E., 2009, User’s guide to the weighted-multiple-linear-regression program (WREG version 1.0): U.S. Geological Survey Techniques and Methods, book 4, chap. A8, 21 p., https://pubs.usgs.gov/tm/tm4a8. Kiang, J.E., Flynn, K.M., Zhai, T., Hummel, P., and Granato, G., 2018, SWToolbox—A surface-water tool-box for statistical analysis of streamflow time series: U.S. Geological Survey Techniques and Methods, book 4, chap. A–11, 33 p., https://doi.org/10.3133/tm4A11.