Northern Alaskan rivers have experienced changes in runoff patterns over the past 19 years. Initially, there was sharp snowmelt runoff and summer drought. Then, there was higher and earlier snowmelt runoff. In the most recent years, there was even higher runoff with sustained late summer flows. This shift is likely due to more rainfall and less snowmelt. The decline in sea ice is connected to increased late summer rainfall. To manage flood risks, erosion, permafrost degradation, and ecosystem impacts, ongoing monitoring and planning are crucial in the National Petroleum Reserve in Alaska.