Modeling water and biogeochemical Modeling water and biogeochemical cycles in the Front Range, Colorado: cycles in the Front Range, Colorado:

effects of climate and landuse changeseffects of climate and landuse changes

Landrum, Laura L., Natural Resource Ecology Laboratory, Colorado State Landrum, Laura L., Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, University, Fort Collins, CO, 80523, llandrum@nrel.colostate.edullandrum@nrel.colostate.edu

Tague, Christina, Department of Geography, San Diego State University, Tague, Christina, Department of Geography, San Diego State University, San Diego, CA, 92182, San Diego, CA, 92182, ctague@mail.sdsu.eductague@mail.sdsu.edu

Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado Baron, Jill S., USGS, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, 80523, State University, Fort Collins, CO, 80523, jill@nrel.colostate.edujill@nrel.colostate.edu

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 (~2250-4000+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 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

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 1994High snowMed snow

Low or no snow

RHESSys Simulations in LVWSRHESSys “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)

RHESSys LVWS 1986-1999

Year Observed RHESSys. RHESSys/Obs

1986 950 969 1.02

1987 728 578 0.79

1988 727 650 0.89

1989 677 518 0.77

1990 784 811 1.03

1991 728 693 0.95

1992 590 597 1.01

1993 783 834 1.07

1994 744 842 1.13

1995 885 1030 1.16

1996 941 893 0.95

1997 1042 991 0.95

1998 906 704 0.78

1999 952 555 0.58

86-99 Ave.

817 762 0.93

Annual Streamflows in mm

Obs. Precip. Sim. Precip. Sim/Obs

1056 1107 1.05

Annual Precipitation (rain + snow) in mm

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

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%)

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)

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

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

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

What is next for LVWS?

Loch Vale Watershed climate change modeling:

Nutrients

Forest and tundra growth, respiration

Modeling water and biogeochemical Modeling water and biogeochemical cycles in the Front Range, Colorado: cycles in the Front Range, Colorado:

effects of climate and landuse changeseffects of climate and landuse changesSouth Platte Watershed:South Platte Watershed:

•Landuse change and C, N, water fluxesLanduse change and C, N, water fluxes

Big Thompson Watershed:Big Thompson Watershed:•Climate change extent and duration of wetland floodingClimate change extent and duration of wetland flooding

•StreamflowsStreamflows

Loch Vale WatershedLoch 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)