Changes in the Timing of Historical and Future Runoff in Different Snow Regimes

Snow accumulation and ablation characteristics are changing in most watersheds where snow accounts for more than 50% of the annual precipitation. Although snow cover extent is generally decreasing globally, changes in local and regional snowmelt timing can result in faster snowmelt rates and lead to flooding. Flooding may be intensified even in areas where precipitation is projected to decline, which can lead to infrastructure damage including roads, buildings, and industrial facilities where flood protection has been designed for historical conditions. We have been developing a spatially-explicit snow climatology that employs a historical climate record, and global climate model projections of future snow conditions in three domains that encompasses different snow environments. We will present statistical analyses of the changes in the timing of streamflow and Intensity-Duration-Frequency (IDF) curves for our study locations. We will also present our understanding of climate change impacts on IDF curves, with particular attention to the non-stationary relationships among snowmelt, rainfall, and runoff. Further, Generalized Extreme Value (GEV) theorem will be used on maximum and minimum precipitation and streamflow values to develop non-stationary IDF runoff curves. The GEV analysis is complemented by a peak-over-threshold based analysis on index variables such as peak snow water equivalent (SWE), snowmelt onset, and monthly averaged air temperature. Our study outlines a framework how infrastructure decisions in snow-dominated watersheds and projection of climate-induced changes in the intensity and variability of heavy precipitation and runoff events can be improved.