HAPpy Hour Seminar: Spatiotemporal distributions of streamflow extremes over the CONUS during the past four decades and the regionally coherent correlation patterns with ENSO and NAO

Abstract: Streamflow extremes (lower 10th and upper 10th percentiles) over the CONUS during the past four decades are examined using the observations and WRF-Hydro simulations driven by the observation-based AORC (Analysis Of Record for Calibration) and WRF-downscaled CONUS404 datasets. Positive (negative) trends in streamflow upper 10th percentile are found in the Eastern U.S. and Pacific Northwest (Southwest) during the past four decades. Positive (negative) trends in streamflow lower 10th percentile are noted in the Eastern (Western) U.S. Over the CONUS nine climate zones, consistent positive trends in lower 10th and upper 10th percentiles are seen for the Northeast, Southeast, Northern Rockies and the Plains, and consistent negative trends are identified for the Southwest and West. The trends of streamflow upper 10th percentile vary significantly with different forcings and model version. The trends of streamflow upper 10th percentile relate more to those of streamflow means than lower 10th percentile and there is little correlation in the trends between lower 10th and upper 10th percentiles. CONUS404-driven simulations match the observed extremes better than AORC-driven simulations as the latter are associated with many more statistically significant trends in both lower 10th and upper 10th percentiles that are not supported by the observations. The lag 1-year and 2-year correlation patterns of streamflow lower 10th and upper 10th percentiles with the indices of ENSO and NAO show distinctive and regionally coherent correlation patterns over the CONUS. Such regionally coherent correlation patterns of streamflow extremes may indicate significant predictive potential for using the indices of ENSO and NAO to predict streamflow extremes 1 year to 2 years ahead.