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 llandrum@nrel.colostate.edu Tague, Christina, Department of Geography, San Diego State University, San Diego, CA, 92182, ctague@mail.sdsu.edu ctague@mail.sdsu.edu Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, jill@nrel.colostate.edu Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, jill@nrel.colostate.edujill@nrel.colostate.edu

2. Rocky Mountains are the geographic source of agricultural, industrial, and municipal water supplies for the western U.S. 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? Rocky Mountain stream and river flows are primarily snowmelt driven Front Range has seen a rapid increase in urbanization Urban and agricultural needs require importing water from the western slope of the divide

3. Changing Landuse: South Platte Watershed

4. South Platte Watershed: Front Range Landuse Change 1930s 1950s 1970s 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 Talus Tundra Forest Rock Forest Tundra

7. Loch Vale Watershed Rocky 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 Snow covered area (photogrammetric image) 21 May 1994 snow no snow RHESSys simulated snow cover 21 May 1994 High snow Med snow Low or 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, 1986-1992 run 1993-1999 LVWS StrataLVWS 1990 ET (*10 cm/yr)

10. RHESSys LVWS 1986-1999 YearObservedRHESSys.RHESSys/Obs 19869509691.02 19877285780.79 19887276500.89 19896775180.77 19907848111.03 19917286930.95 19925905971.01 19937838341.07 19947448421.13 199588510301.16 19969418930.95 199710429910.95 19989067040.78 19999525550.58 86-99 Ave. 8177620.93 Annual Streamflows in mm Obs. Precip.Sim. Precip.Sim/Obs 105611071.05 Annual Precipitation (rain + snow) in mm

11. Global Climate Model scenarios 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: monthly GCM meteorological output LVWS obs. Met. RHESSys 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

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” 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. Spring runoff ~0.5-1 months earlier Similar peak runoff High minimum flow Higher variability (rain on snow events flashier)

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 fluxesLanduse change and C, N, water fluxes Big Thompson Watershed: Climate change extent and duration of wetland floodingClimate change extent and duration of wetland flooding StreamflowsStreamflows Loch Vale Watershed : Loch Vale Watershed : RHESSys simulations of streamflowRHESSys simulations of streamflow Snow distribution scheme addedSnow distribution scheme added Tundra, forest ecosystem development/parameterizationTundra, forest ecosystem development/parameterization Climate change streamflow (spring runoff, peak flows, annual totals)Climate change streamflow (spring runoff, peak flows, annual totals)