Streamflow drought in the United States during the last century: a mutli-decadal analysis of drought variability, drivers and trends
Abstract
Streamflow drought has received less attention than meteorological and agricultural droughts to date, yet is a significant and recurring problem for water resource management across the United States. Further, multiple simulations project increases in drought duration, severity and variability in future decades. To assess regional patterns in streamflow drought signatures (metrics describing statistical properties of streamflow), their relation to climate, and their trends over time, we used 555 U.S. Geological Survey gages with long-term streamflow data that drain minimally disturbed watersheds. We characterized drought using duration (number of days) and deficit (flow volume below drought thresholds) to calculate values for each signature at each gage for each climate year (April 1 to March 31). Drought signatures were calculated for five drought thresholds (2, 5, 10, 20, and 30 flow percentiles) and two approaches: seasonally variable thresholds with a unique threshold for each day of the year, and a static threshold based on all days and years of record. Correlations with annual climate metrics (e.g. aridity, snowmelt fraction of precipitation, mean air temperature) were computed using climate data from a USGS monthly water balance model, while trend analyses in drought signatures were calculated using the Mann-Kendall test with persistence adjustment for the periods 1921-, 1951- and 1981-2021. Preliminary results suggest that drought signatures calculated with the seasonally variable thresholds tended to reflect shorter drought durations yet larger drought deficits, with greater variability in duration and deficit as compared to signatures calculated using long-term static thresholds. Drought signatures also displayed regional patterns; most notably high interannual variability in the southwest and north central U.S. Drought duration was weakly correlated with climate variables whereas drought deficit was strongly correlated with aridity (P/PET). Drought signatures tended to display similar magnitude correlation coefficients with climate for the current and prior year. Finally, drought duration and deficit were found to have increased from 1951- and 1981-2020 in the western U.S., while decreasing in the northeast U.S., matching concurrent trends in aridity.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMGC23A..01H