1. Seasonal Cycle Shifts in Hydroclimatology Over the Western US Satish Regonda, Martyn Clark, Balaji Rajagopalan and John Pitlick Goals 1. Examine changes in the timing of spring snowmelt 2. In relation to a. Elevation b. Snow water equivalence (SWE) c. Temperature d. Precipitation

3. Data and Methods 1. Streamflow: For each year, compute the day on which 50% of the water-year flow is equaled or exceeded (89 stations)

4. 2. Trends in April 1 SWE (501 stations) 3. Trends in temperature and precipitation (hundreds of stations)

9. SUMMARY: Runoff appears to be occurring earlier in PNW; not much change in the Sierras or Rockies Change is greatest in low-elevation basins April 1 SWE is less in PNW, northern Rockies; little change in Sierras or southern Rockies Temperature appears to be increasing throughout the west. Precipitation also increasing, except in PNW Shift in timing of runoff in PNW appears to be related to both an increase in temperature and a decrease in precipitation