Streamflow predictions under climate scenarios in the Boulder Creek Watershed at Orodell

Mountainous areas have complex geological features and climatic variability, which limit our ability to simulate and predict hydrologic processes, especially in face to a changing climate. Hydrologic models can improve our understanding of land surface water and energy budgets in these regions. In this study, a distributed physically-based hydrologic model is applied to the Boulder Creek Watershed, USA to study streamflow conditions under future climatic scenarios. Model parameters were adjusted using observed streamflow data at 1/16th degree resolution, with a NSE value of 0.69. The results from CMIP5 models can give a general range of streamflow conditions under different climatic scenarios. Two scenarios are being applied, including the RCP 4.5 and 8.5 scenarios. RCP 8.5 has higher emission concentrations than RCP 4.5, but not very significant in the period of study. Using pair t-test and Mann-Whitney test at specific grid cells to compare modeled and observed climate data, four CMIP5 models were chosen to predict streamflow from 2010 to 2025. Of the four models, two models predicted increased precipitation, while the other two models predicted decreased precipitation, and the four models predicted increased minimum and maximum temperature in RCP 4.5. Average streamflow decreased by 2% 14%, while maximum SWE varies from -7% to +210% from 2010 to 2025, relative to 2006 to 2010. In RCP 8.5, three models predicted increased precipitation, while the other one model predicted decreased precipitation, and the four models predicted increased maximum and minimum temperature. Besides one model, the other three models predicted increased average streamflow by 3.5% 32%, which results from the higher increasing magnitude in precipitation. Maximum SWE varies by 6% 55% higher than that from 2006 to 2010. This study shows that average daily maximum and minimum temperature will increase toward 2025 from different climate models, while average streamflow will decrease in RCP 4.5 but will increase in RCP 8.5, depending on the changing magnitude in precipitation. Maximum SWE will have larger variations than streamflow, in face to climate change. Variations in maximum SWE and streamflow are related to water storage and supply, and provide guidance for future water resources management.