Detection of Streamflow Change in the Susquehanna River Basin

Streamflow statistics are commonly used for purposes of planning and managing water resources in the Susquehanna River Basin. For accurately estimating streamflow statistics, it is important to identify whether there are increasing or decreasing changes during the period of records and whether the change is gradual or abrupt. This study employs repeated monotonic trend tests with varying beginning and ending time for detecting changes in streamflow in tributaries within the Susquehanna River Basin. The method is employed to analyze long-term streamflow trends and detect change for annual minimum, median, and maximum daily streamflow for eight unregulated watersheds within the basin. Monthly baseflow and storm runoff are investigated. The results show a considerable increase in annual minimum flow for most of the examined watersheds and a noticeable increase in annual median flow for about half of the examined watersheds. Both these streamflow increases were abrupt, with only a few years of transition centered around 1970. The abrupt change in annual minimum and median flows appears to occur in the summer and fall seasons. The abrupt change in annual minimum and median flows is due to increased flows in the summer and fall seasons. The results also indicate there is no long-term significant increasing or decreasing change in annual maximum flow in the examined watersheds.