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, Tague, Christina, Department of Geography, San Diego State University, San Diego, CA, 92182, Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523,

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

Changing Landuse: South Platte Watershed

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

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

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

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

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

RHESSys Simulations in LVWS RHESSys “Base” simulation: “100 year” spinup Observed meteorology, Annual totals, means Parameterization, run LVWS StrataLVWS 1990 ET (*10 cm/yr)

RHESSys LVWS YearObservedRHESSys.RHESSys/Obs Ave Annual Streamflows in mm Obs. Precip.Sim. Precip.Sim/Obs Annual Precipitation (rain + snow) in mm

Global Climate Model scenarios Hadley and CCC GCMs Hadley – warmer, wetter CCC – warmer 2 experiments: and : mean GCM predicted changes in temp., precip. – change observed meteorology accordingly : 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

CCC 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) CCC: Temperatures ~3-4 degrees warmer Precip. At weather station 99% of observed Simulated precip. 98% of simulated precip. From obs. (less SNOW) Mean discharge 84% of obs. Sim EvapoTranspiration 38%, Streamflow 60% of precip. (observations: ET 29%, Flow 69%)

Hadley LVWS “warming scenario” Hadley: Temperatures ~2-2.5 degrees warmer Precipitation 108% (at weather station and simulated) of observed Mean discharge 100% of obs. Sim (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)

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

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

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 months earlier –Flashier flows –Increased snowpack

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

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)