Small-scale hydropower systems are popular both in the United States and much of the developing world due to the emphasis on renewable energy and the general cost-competitiveness of hydroelectric power generation. We present a novel modeling package, referred to as the Hydropower Potential Assessment Tool (HPAT), to assess historic and projected future small-scale run-of-river hydropower resource potential at a single location or distributed over a study region. HPAT implements a fully-distributed streamflow model, which is coupled to a digital elevation model to assess hydropower resource potential. To demonstrate HPAT, we implement the models for a privately-owned run-of-river facility on Falls Creek outside of Sweet Home, Oregon, USA. We use an ensemble of Global Climate Models (GCMs) for two future climate scenarios to project a plausible range of future changes at this site. For the Falls Creek facility, HPAT projects that the timing of peak streamflow will shift from spring to winter and that mean annual hydropower potential will likely decrease slightly from average 1980-2010 historic conditions through the end of the 21st century. All inputs to HPAT are globally available, except for streamflow observations necessary for calibration. (C) 2016 Elsevier Ltd. All rights reserved.