What questions are we asking?

1. Modeling water and biogeochemical cycles in the Front Range, Colorado: effects of climate and landuse changes Landrum, Laura L., Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, llandrum@nrel.colostate.edu Tague, Christina, Department of Geography, San Diego State University, San Diego, CA, 92182, ctague@mail.sdsu.edu Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, jill@nrel.colostate.edu

2. Rocky Mountains are the geographic source of agricultural, industrial, and municipal water supplies for the western U.S. Rocky Mountain stream and river flows are primarily snowmelt drivenFront Range has seen a rapid increase in urbanization Urban and agricultural needs require importing water from the western slope of the divide What questions are we asking? How have changes in landuse (primarily urbanization, but also agriculture) affected carbon, nitrogen and water fluxes along the Front Range? How might climate changes affect the extent and duration of flooding in Rocky Mountain wetlands? How might changes in climate affect alpine streamflows?

3. Changing Landuse: South PlatteWatershed

4. South Platte Watershed:Front Range Landuse Change 1970s 1950s 1930s 1990s

5. Big Thompson Watershed • Sub-basin of the South Platte Watershed • Streamflow primarily snowmelt driven • High elevation (~2250-4000+m) • Highly variable weather • SW border –Continental Divide • Landscape mostly forest, but also some wetlands, grasslands, tundra, rock, talus, snowfields

6. RHESSys simulations: Loch Vale Watershed (LVWS) • Sub-basin of the Big Thompson watershed • Alpine-subalpine with comparatively little vegetation Forest Tundra Rock Forest Talus Tundra

7. Loch Vale WatershedRocky Mountain National Park • 660 ha Subalpine and alpine environment • 2 permanent snowfields • Continental Divide forms western border (4000 m peaks) • 80% bedrock outcrop and talus slope (mean slope 32º) • 11% tundra, 5% subalpine fir/Englemann spruce forest, 2% open water and wetlands • Precipitation is orographic (Rocky Mountains) and wind-driven (Loch Vale) • Heaviest precip. months Nov, Feb-Apr. • Most precip (~75%) falls as snow • High winter winds (10/87-4/89 mean for days with snowfall = 5 m/s) • Continuous observations of meteorology, streamflow, water chemistry, 1984-present

8. LVWS: Snow distribution RHESSys simulated snow cover 21 May 1994 High snow Med snow Low or no snow Snow covered area (photogrammetric image) 21 May 1994 snow no snow RHESSys simulated snow cover with snow distribution scheme 21 May 1994 High snow Med snow Low or no snow

9. RHESSys Simulations in LVWS • RHESSys “Base” simulation: • “100 year” spinup • Observed meteorology, 1985-1999 • Annual totals, means 1986-1999 • Parameterization, 1986-1992run 1993-1999 LVWS Strata LVWS 1990 ET (*10 cm/yr)

10. RHESSys LVWS 1986-1999 Annual Streamflows in mm Annual Precipitation (rain + snow) in mm

11. Global Climate Model scenarios • Canadian Centre for Climate Modeling and Analysis Project (CCC) • Hadley Centre • Vegetation-Ecosystem Modeling and Analysis Project (VEMAP) • Topographically adjusted US climate history, 0.5 deg. Grid forms “baseline” • GCM output translated (spline fit) onto the VEMAP grid • Hadley and CCC GCMs • Hadley – warmer, wetter • CCC – warmer • 2 experiments: 1986-1999 and 2000-2099 • 1986-1999: 2030-2050 mean GCM predicted changes in temp., precip. – change observed meteorology accordingly • 2000-2099: RHESSys monthly GCM meteorological output LVWS obs. Met.

12. CCC 1986-1999 LVWS “warming scenario” • Spring runoff ~1-2 months earlier • Lower peak runoff • Earlier decrease in summer flow • Decrease in annual discharge • Higher minimum flow • Flashier discharge (rain on snow) • 1986-1999 CCC: • Temperatures ~3-4 degrees warmer • Precip. At weather station 99% of observed 1986-1999 • Simulated precip. 98% of 86-99 simulated precip. From obs. (less SNOW) • Mean discharge 84% of obs. Sim. 86-99 • EvapoTranspiration 38%, Streamflow 60% of precip. (observations: ET 29%, Flow 69%)

13. Hadley 1986-1999 LVWS “warming scenario” • Spring runoff ~0.5-1 months earlier • Similar peak runoff • High minimum flow • Higher variability (rain on snow events flashier) 1986-1999 Hadley: • Temperatures ~2-2.5 degrees warmer • Precipitation 108% (at weather station and simulated) of observed 1986-1999 • Mean discharge 100% of obs. Sim. 86-99 (snowpack and ET increases) • ET 33%, Streamflow 65% of precip.

14. 2000-2099 GCM runs: CCC • Average precipitation 100% of 1986-1999 mean • Average streamflow 92% of 1986-1999 mean (63% of precip.) • ET 110% of 1986-1999 mean (34% of precip.) • 70% decrease in permanent snowfields • 37% of annual streamflows < 80% 1986-1999 mean (dry) • 12% of annual streamflows < 60% 1986-1999 mean (very dry) • Several 3+ dry years in a row

15. 2000-2099 GCM runs: Hadley • Average precipitation 111% of 1986-1999 mean at weather station • Simulated precip. 103% of 1986-1999 mean (higher rain/snow) • Average streamflow 113% of 1986-1999 mean (70% of precip.) • ET 97% of 1986-1999 mean (27% of precip.) • 30% increase in permanent snowfields • 19% of annual streamflows < 80% 1986-1999 mean (dry) • 42% of annual streamflows > 120% 1986-1999 mean (wet) • A few 3+ dry years in a row • Several 3+ wet years in a row

16. LVWS Climate scenario results • Preliminary results indicate that RHESSys is modeling Loch Vale streamflows well • Warmer, dryer climate scenarios (CCC) lead to • decreased streamflows and increased ET • spring runoffs 1-2 months earlier • flashier flows • decreased snowpack • increased frequency and duration of “dry flow” years • Warmer, wetter climate scenarios (Hadley) lead to: • Increased streamflows • spring runoffs 0.5-1 months earlier • Flashier flows • Increased snowpack

17. What is next for LVWS? Loch Vale Watershed climate change modeling: Nutrients Forest and tundra growth, respiration

18. Modeling water and biogeochemical cycles in the Front Range, Colorado: effects of climate and landuse changes South Platte Watershed: Landuse change and C, N, water fluxes Big Thompson Watershed: Climate change extent and duration of wetland flooding Streamflows Loch Vale Watershed: RHESSys simulations of streamflow Snow distribution scheme added Tundra, forest ecosystem development/parameterization Climate change streamflow (spring runoff, peak flows, annual totals)