Low-Flow Trends at Southeast United States Streamflow Gauges

Abstract

Water management and infrastructure design depend on quantifying thresholds in minimum flows. Decreasing trends in low flows have been observed at many stream gauges in the Southeast US; however, a comprehensive quantitative assessment of regional trends and shifts in flow minima is lacking. This study examines trends and abrupt shifts in the annual minimum 7-day mean streamflow in the Southeastern US for four distinct time periods over the last century. A type II error analysis is conducted to evaluate the probability of erroneously declaring that a trend does not exist. A decreasing trend in low-flow magnitude is identified in 80% of the streamflow records. An abrupt shift in low-flow magnitude was identified in 50% of the gauge records, occurring predominantly around 1975–1985 and 1995–2005. Trend slopes indicate an accelerated rate of decline in low-flow magnitude over recent decades compared to the last 50–75 years. Where statistically significant trends are not identified, short record lengths (<50 years) and high variability in flow records result in a high probability of a type II error.