Hydrologic metric changes across the conterminous United States

This metadata record describes the following eight attributes: (1) the U.S. Geological Survey streamflow gage identification number, (2) aggregated level 2 ecoregion, (3) hydrologic metric abbreviation, (4) direct-human modification classification of watershed, (5) estimated hydrologic metric values for 1950 to 2014, (6) estimated hydrologic metric values for 1980 to 2014, (7) observed hydrologic metric values for 1980 to 2014, and (8) the direction of streamflow alteration (i.e., inflated, diminished, or indeterminant). Twelve hyrdologic metrics were calculated: low- and high-flow magnitude (LF_MAG(cfs/square km) and HF_MAG(cfs/square km)), low- and high-flow variability (LF_VAR(dimensionless) and HF_VAR(dimensionless)), low- and high-flow frequency (LF_FRE(number of pulses) and HF_FRE(number of pulses)), low- and high-flow duration (LF_DUR(days) and HF_DUR(days)), skewness (OT_SKW(dimensionless)), number of daily rises (OT_RIS(dimensionless)), low- and high-flow seasonality (LF_SEA(dimensionless) and HF_SEA(dimensionless)). The low- and high-flow magnitudes were calculated from the 1st and 99th percentile non-exceedence streamflows divided by the drainage area, respectively. The low- and high-flow variabilities were calculated from the coefficient of variation of the annual minimum and maximum streamflows, respectively. The low- and high-flow frequencies were calculated as the mean of the annual-time series of the number of pulses below the 10th and above the 90th percentile values, respectively. The low- and high-flow durations were calculated from the length of time (in days) that the streamflow was below the 10th percentile or above the 90th percentile, respectively. The skewness values were calculated as the third moment of the daily streamflow values. The number of daily rises values were calculated by the ratio of the number of days where the daily-streamflow was greater than the previous day divided by the total number of days for the period. The low- and high-flow seasonality values were calculated based on frequency of occurrence in different seasons (for more details, please see Eng, K., Carlisle, D.M., Grantham, T.E., Wolock, D.M., and Eng, R.L., 2018, Alteration of streamflow regimes in the United States: U.S. Geological Survey, In Press). USGS NWIS provided the observed daily-streamflow values and the estimated values were calculated by random forest statistical models. The data are in a tab-delimited text format.