Projected Hydrologic Changes Under Mid-21st Century Climatic Conditions in a Sub-arctic Watershed

The potential effects of mid-21st century climate change on the hydrology of the Cook Inlet watershed in south-central Alaska was analyzed in this study. Climate datasets representing a set of potential change scenarios for the period 2041-2070 were developed from the North American Regional Climate Change Assessment Program (NARCCAP) archive of dynamically downscaled climate products. The NARCCAP 50-km scale regional climate output was converted to realistic daily weather time series using a change factor method in which observed meteorological time series used for model calibration are perturbed. The perturbations are based on statistical summaries of change for the different climate scenarios, by month, as calculated from the differences between the 1971-2000 and 2040-2070 climate model simulation periods. The downscaled climate datasets were then used to run the Soil and Water Assessment Tool (SWAT) for the Cook Inlet watershed. Generally, it was observed that increasing rainfall and warmer temperatures across the Cook Inlet watershed led to a predicted increase in the stream flow in the major rivers, increase in 7-day low flows, and considerable increase in 100-year peak flow. Furthermore, under future climatic conditions precipitation is expected to increase in the Cook Inlet watershed but the amount of snowfall is expected to decrease. Also, the amount of snowmelt is expected to increase due to warmer temperature thereby causing the average annual fraction of snowfall as precipitation to decrease leading to a reduction in the glacial mass balance in the watershed. Moreover, average annual water yield, runoff, baseflow, snowmelt across the basin is expected to increase. More specifically the different hydrologic components varied seasonally and monthly driven by the seasonal and monthly changes in precipitation and temperature. However, the overall hydrology of the watershed is projected to remain snowmelt dominated through the mid-21st century without a major shift in regime. These simulations provide a benchmark of hydrologic sensitivity to potential future climate change in this watershed useful for identifying vulnerabilities and informing the development of adaptation responses.