Abstract
In this article, the mean daily streamflow at 139 streamflow-gaging stations (sites) in the southern and southeastern United States are analyzed for spatial and temporal patterns. One hundred and thirty-nine individual time-series of mean daily streamflow were reduced to five aggregated time series of Z scores for clusters of sites with similar temporal variability. These aggregated time-series correlated significantly with a time-series of several climate indices for the period 1950–2015. The mean daily streamflow data were subset into six time periods—starting in 1950, 1960, 1970, 1980, 1990, and 2000, and each ending in 2015, to determine how streamflow trends at individual sites acted over time. During the period 1950–2015, mean monthly and seasonal streamflow decreased at many sites based on results from traditional Mann–Kendall trend analyses, as well as results from a new analysis (Quantile-Kendall) that summarizes trends across the full range of streamflows. A trend departure index used to compare results from non-reference with reference sites identified that streamflow trends at 88% of the study sites have been influenced by non-climatic factors (such as land- and water-management practices) and that the majority of these sites were located in Texas, Louisiana, and Georgia. Analysis of the results found that for sites throughout the study area that were influenced primarily by climate rather than human activities, the step increase in streamflow in 1970 documented in previous studies was offset by subsequent monotonic decreases in streamflow between 1970 and 2015.
Highlights
Significant changes in the natural streamflow regime for streams throughout the United States (U.S.)have been identified using analysis of spatial and temporal trends in streamflow [1,2,3]
Results from the seasonal Mann–Kendall analysis for each of the 365 streamflow quantiles using the Q-K analysis [26,27] for each of the six multi-decadal trend analysis periods were combined for visual analysis and interpretation into a single graph, termed the stacked Quantile-Kendall (Q-K)
Results for all six trend periods are stacked vertically in the graph: Symbols plotting in the region near the bottom of the graph, corresponding to starting in 1950, indicate significant trends for the 66-year period 1950–2015; symbols plotting near the top of the graph, corresponding to starting in 2000, represent significant trend test results for the 16-year period 2000–2015
Summary
Have been identified using analysis of spatial and temporal trends in streamflow [1,2,3]. These deviations, resulting from both anthropogenic and climatic influences, affect local communities and aquatic biology in many ways, including changes in streamflow, community composition, and alterations to habitat that are necessary to support indigenous wildlife. McCabe and Wolock [7] examined the spatial correlation of trends and identified 14 clusters of streamflow-gaging stations across the U.S with similar “temporal patterns.”. Seasonal variability of trends in regions with similar geographic patterns was identified by Dettinger and Diaz [9], who found similar spatial clusters of trends in streamflow
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