Evaluation of streamflow trends and the drivers of long-term change for 33 river basins in the southeastern U.S.

Growing water demands and climate change are altering the timing and magnitude of streamflows. To further understand streamflow changes over time, we assessed long-term streamflow trends for 33 basins in the South Atlantic-Gulf Drainage, southeastern United States. We gathered daily streamflow data and calculated the annual (1957 – 2022) mean, minimum and maximum of streamflows (m 3 /s; n = 373 gages). We used Mann-Kendall to indicate significant changes and Sen’s slope to indicate the magnitude of changes and averaged them for the 33 basins. Our results indicated that mean annual streamflows were increasing in the western and southern regions (24.2% of basins) but decreasing in the larger central region (69.7% of basins). Minimum streamflows indicated a large percentage of significant declines (34.0% of gages) whereas maximum streamflows indicated a larger magnitude of declines (– 0.30 ± 1.7 (m 3 /s)/year). To further understand where streamflows were changing we assessed the relationship between streamflows and static spatial indicators including drainage area, elevation and ecoregions. To understand why streamflows were changing we assessed long-term trends for total precipitation, maximum and minimum temperatures, population and groundwater level. Using regression analysis and AIC model selection, we found that total precipitation explained 17% of streamflow variation and drainage area explained 14%. Temperatures and population increased across the region but were not related to variation in streamflow changes. Understanding the contributions of different drivers of streamflow changes provides insight for predicting water quantity changes, which affect water quality, ecological relationships and biodiversity.