Long-Term Changes in the Continental United States Streamflow and Teleconnections with Oceanic-Atmospheric Indices

We investigated the changes in streamflow (water-year basis) and evaluated the spatial and temporal relationship of the streamflow (averaged for three seasons) across the U.S. with Pacific and Atlantic Ocean climate variability using data from 240 naturalized flow stations for the period 1951 to 2010. Statistical tests (Mann-Kendall and Pettitt’s Tests) were used to evaluate the gradual (trend) and abrupt (step) changes. Walker test was used to compute the field significance. The coupled relationship between oceanic-atmospheric indices [Sea surface temperature (SST) and geopotential height at 500-mbar (Z₅₀₀)] and the seasonal continental U.S. streamflow was evaluated utilizing singular value decomposition. Majority of streamflow stations in the eastern U.S. showed increasing streamflow trend, while most of the stations in Pacific Northwest showed trend that were decreasing. Early period of 1970s and late period of 1980s were detected with shift, following the long term trend. Z₅₀₀ represented the seasonal variability in streamflow better, compared to SST. Strong correlation with the streamflow stations in the Midwest, Arkansas-White-Red, Souris-Red-Rainy, Pacific Northwest regions were noticed mainly by the Pacific and Atlantic Z₅₀₀. Strong correlations between Pacific SST and the streamflow stations in southern South-Atlantic-Gulf, Midwest and regions of Pacific Northwest were detected. Likewise, the SST of the Atlantic Ocean showed statistically significant correlations with the New England, Midwest and regions of South-Atlantic-Gulf. The findings from the current study helped in understanding the long term changes and can be used to improve streamflow forecasting models, which may help managing water resources in response to climate change.