Antecedent Flow Volatility, associated risk, and trends at USGS streamgages across the conterminous United States, 1980-2020

This data release supports the analysis published in Cashman and others (2026), Changing hydrologic volatility and associated risk to freshwater biota across the conterminous United States, 1980–2020. See Larger Work citation.

This data release contains calculated ecoflow metrics, including Natural Flow Anomalies (NFA) and Antecedent Flow Volatility (AFV), volatility-driven ecological risk estimates, and Mann-Kendall trend statistics at U.S. Geological Survey (USGS) streamgages across the conterminous United States (CONUS) for the period 1980-2020.

Natural flow anomalies (NFA) were calculated as the ratio of observed (O) to expected (E) monthly streamflow, where expected flows were predicted using previously trained monthly random forest models applied to NHDPlus V2.1 landscape variables. Antecedent Flow Volatility was computed as the rolling 12-month standard deviation of log10-transformed NFA values. Ecological risk to benthic macroinvertebrates and fish was estimated by applying fitted dose-response models to the AFV timeseries at each gage. Mann-Kendall trend tests were used to evaluate temporal changes in AFV and ecological risk over the study period.

This data release contains the following datasets:

nhd_e_monthly_predicts.parquet - A parquet tabular dataset of monthly natural flow model predictions for all NHDPlus v2.1 catchments across the conterminous United States.

ECO_NRSA_MAJ_CONUS.parquet - A parquet tabular crosswalk of all NHDPlus v2.1 catchments and the majority overlap class of the Ecoregion Level III and their associated EPA National Rivers and Streams Assessment 9-unit aggregated levels.

nwis_swsites_monthly_NFA.parquet - A parquet tabular file that provides the calculated monthly Natural Flow Anomaly for all USGS streamgages used in this analysis.

nwis_swsites_info_comid.parquet - A parquet tabular file that provides additional spatial information and unique NHDPlus v2.1 catchment that has been linked for all USGS streamgages used in this analysis.

nwis_swsites_avgsummer_AFV.parquet - A parquet tabular file that provides the calculated summer average Antecedent Flow Volatility for all USGS streamgages used in this analysis.

nwis_swsites_summer_AFV_trends.csv - A comma separated value tabular file that provides the calculated Mann-Kendall trends on the summer average Antecedent Flow Variability for all USGS streamgages used in this analysis.

nwis_swsites_summer_fish_risk_trends.csv - A comma separated value tabular file that provides the calculated Mann-Kendall trends on the calculated volatility-driven risk to fish communities for all USGS streamgages used in this analysis.

nwis_swsites_summer_bug_risk_trends.csv - A comma separated value tabular file that provides the calculated Mann-Kendall trends on the calculated volatility-driven risk to benthic macroinvertebrate communities for all USGS streamgages used in this analysis.

Ecoflows_1b_swsites_ecometric_12moVar_WY19802020.parquet - A parquet tabular file that provides calculated monthly Natural Flow Anomaly and rolling window calculations of Antecedent Flow Volatility restricted to Water Years 1980-2020 and in specific data format for use in the National Water Availability Assessment data processing pipelines.