A multimodel ensemble approach to assessment of climate change impacts on the hydrology and water resources of the Colorado River basin

Abstract

Abstract. Implications of 21st century climate change on the hydrology and water resources of the Colorado River basin were assessed using a multimodel ensemble approach in which downscaled and bias corrected output from 11 General Circulation Models (GCMs) was used to drive macroscale hydrology and water resources models. Downscaled climate scenarios (ensembles) were used as forcings to the Variable Infiltration Capacity (VIC) macroscale hydrology model, which in turn forced the Colorado River Reservoir Model (CRMM). Ensembles of downscaled precipitation and temperature, and derived streamflows and reservoir system performance were assessed through comparison with current climate simulations for the 1950–1999 historical period. For each of the 11 GCMs, two emissions scenarios (IPCC SRES A2 and B1, corresponding to relatively unconstrained growth in emissions, and elimination of global emissions increases by 2100) were represented. Results for the A2 and B1 climate scenarios were divided into period 1 (2010–2039), period 2 (2040–2069), and period 3 (2070–2099). The mean temperature change averaged over the 11 ensembles for the Colorado basin for the A2 emission scenario ranged from 1.2 to 4.4°C for periods 1–3, and for the B1 scenario from 1.3 to 2.7°C. Precipitation changes were modest, with ensemble mean changes ranging from −1 to −2 percent for the A2 scenario, and from +1 to −1 percent for the B1 scenario. An analysis of seasonal precipitation patterns showed that most GCMs had modest reductions in summer precipitation and increases in winter precipitation. Derived 1 April snow water equivalent declined for all ensemble members and time periods, with maximum (ensemble mean) reductions of 38 percent for the A2 scenario in period 3. Runoff changes were mostly the result of a dominance of increased evapotranspiration over the seasonal precipitation shifts, with ensemble mean runoff reductions of −1, −6, and −11 percent for the A2 ensembles, and 0, −7, and −8 percent for the B1 ensembles. These hydrological changes were reflected in reservoir system performance. Average total basin reservoir storage generally declined, however there was a large range across the ensembles. Releases from Glen Canyon Dam to the Lower Basin (mandated by the Colorado River Compact) were reduced for all periods and both emissions scenarios in the ensemble mean. The fraction of years in which shortages occurred increased by approximately 20% by period 3 in for both emissions scenarios, and the average shortage increased to a maximum of 3.7 BCM/yr for the period 3 A2 ensemble average. Hydropower output was reduced in the ensemble mean for all time periods and both emissions scenarios.

Simulation of Climate Change Effects on Hydropower Operations in Mountain Headwater Lakes, New Zealand

“…Modelling studies in other parts of the world of climate change effects on the hydrology of mountain catchments and hydropower flows are somewhat limited, and findings are variable depending on the location and biophysical characteristics. Studies in North America have found considerable spatial variability in climate change impacts on hydrologic and hydropower systems in large basins, where in general hydropower will be adversely impacted under drier conditions as a result of decreases in flows, and under wetter conditions if inadequate storage exists to allow for seasonal hydrograph changes (Christensen et al, ; Christensen and Lettenmaier, ; Vicuna et al, , ; Minville et al, ; Cherry et al, ; Kerkhoven and Gan, ). Other studies have shown that there is considerable uncertainty among different climate models in simulating river flows and hydropower impacts over space (Markoff and Cullen, ; Kerkhoven and Gan, ), but that most models indicate large decreases in hydropower inflows and production because of greater competition for reservoir storage between hydropower and instream flow goals (Payne et al, ; Markoff and Cullen, ).…”

“…If a lake is not spilling any water, the water is either filling the lake or used to generate electricity. A number of studies on climate change impacts on hydropower generation in other parts of the world have also found that the quantity and variability of annual unproductive spills will likely increase (Christensen et al, ; Christensen and Lettenmaier, ; Vicuna et al, , ; Minville et al, ; Cherry et al, ; Kerkhoven and Gan, ). Very few studies have indicated that flows and hydropower production would increase significantly in the longer term (Minville et al, ).…”

Potential drought stress in a Swiss mountain catchment—Ensemble forecasting of high mountain soil moisture reveals a drastic decrease, despite major uncertainties

“…Ajauro and New [2007] published a comprehensive review on the different ensemble forecast methods that are available and the overall combination approaches. Forecast ensembles have been used in climate change studies in the areas of climatology [ Stott and Forest , 2007], land use change [ Viney et al , 2009], and hydrology [e.g., Christensen and Lettenmaier , 2007; Bastola et al 2011]. Many hydrological studies have simulated ensembles based on different climate models or emission scenarios [ Horton et al , 2006; Jasper et al , 2004].…”

Dynamic Adjustment of Irrigation Technology/Water Management in Western U.S. Agriculture: Toward a Sustainable Future

“…River basin-specific studies indicate that expected increases in future warming trends are expected to exacerbate these water resource impacts. For the Upper Colorado River Basin (UCRB), Christensen and Lettenmaier (2007) applied forecasted changes in temperature and precipitation from 11 climate models and report an 8-11% decrease in UCRB runoff by the end of the 21st century. Hoerling and Eischeid (2007), after examining 42 climate simulations for the UCRB, report likely average decreases in UCRB streamflow of 25% by 2030, and 45% by 2060.…”