Options for Improving Climate Modeling to Assist Water Utility ...

More documents

Recommendations

Info

Water Utility Climate Alliance White Paper Options for Improving Climate Modeling to Assist Water Utility Planning for Climate Change This study explores the impact that climate change will have on the Bull Run watershed and PWB’s ability to provide reliable water to its customers. It uses a series of linked models to address the potential impacts of climate change on hydrologic processes and management of the water supply system. The results of this study also included an evaluation of the impacts of changes in temperature on water demand. The PWB has used this study as a first look at how climate change might impact both water supplies and demands. This study has been cited as part of water rights extensions for the PWB’s secondary groundwater supply as well as development of a Habitat Conservation Plan for Endangered Species Act listed fish in the Bull Run watershed. Changes in temperature and precipitation were used as inputs into a Distributed Hydrology, Soil- Vegetation Model (DHSVM) developed for PWB to simulate hydrologic processes in 150-meter grid boxes with physical data layers that are unique to the watershed. The output of DHSVM is streamflow data. These data, in turn, are fed into PWB’s Supply and Transmission Model, a system operation model used in this study to examine the impacts of climate change on the water supply performance of the existing system, as well as two planning scenarios from the Infrastructure Master Plan. This study concluded “that climate change will have a significant impact on the hydrology of the Bull Run watershed and will impact the safe yield of the Portland water system.” Finally, PWB indicated an interest in repeating its climate change study using the DHSVM again, but with either using the UW Climate Impacts Group RCM outputs as parameters for input to the DHSVM (because the RCM attempts to do a better job of the storm track/topography factors for watersheds where the ocean conditions are very important), or using more GCMs than the four used in the Bull Run watershed study (Lorna Stickel, Water Resources Planning Manager, Portland Water Bureau, personal communication, April 24, 2009). 2.1.4 Seattle Public Utilities Seattle Public Utilities (SPU) partnered with King County, Washington; the UW Department of Ecology; and Cascade Water Alliance to fund the UW Climate Impacts Group to conduct a downscaling study of three potential future climate scenarios in November 2007 (Polebitski et al., 2007). Three scenarios were used: a warm scenario – GISS ER, with SRES emission scenario B1; a warmer scenario – ECHAM5, with SRES scenario A2; and a warmest scenario – IPSL_CM4, with SRES scenario A2. These three scenarios produced future, climate-altered, meteorological datasets for the Puget Sound region at four different time periods: 2000, 2025, 2050, and 2075. These meteorological datasets were run through the DHSVM hydrology model to produce hydrologic datasets for the four time periods. This project utilized a statistical downscaling approach that produces long records – 77 years – of hydrologic and meteorological data for each climate scenario. SPU subsequently fed the hydrologic data directly into its Conjunctive Use Evaluation systems model, rather than running the raw climate model output Page 2-5
Water Utility Climate Alliance White Paper Options for Improving Climate Modeling to Assist Water Utility Planning for Climate Change through SPU’s hydrology model – the Seattle Forecast Model (SEAFM). This allowed SPU to use a scenario approach to determine the effects of different potential climate futures on the operation of the SPU water system (Seattle Public Utilities, 2009). SPU then explored adaptation scenarios by investigating intra-system modifications, mostly the elimination of conservative assumptions from their system supply calculations that effectively increased the usable storage capacity for water with no new supply infrastructure. While the climate scenarios reduced supply to between 79% and 94% of historic levels by 2050, these adaptations would restore between 9% and 16% of supply. Consequently, these adaptive actions would mitigate for the loss of supply in two of the three climate scenarios by 2050, but additional adaptive measures would be needed for the third climate scenario in 2050 and all three climate scenarios by 2075 to restore supply to historic levels. SPU identified potential options for these additional adaptive measures. SPU also examined the impacts of the three climate scenarios on water demand by using a historical regression analysis of monthly data for consumption, maximum temperature, and rainfall at SeaTac Airport. Assuming that this relationship would hold into the future, SPU projected that peak season consumption could increase 4% to 13% between 2000 and 2075 under the three climate change scenarios assuming no additional demand management or conservation programs. In a separate study, SPU engaged Northwest Hydraulic Consultants in a dynamic downscaling study (Northwest Hydraulic Consultants, 2009) that took outputs generated by two GCMs/scenario combinations – CCSM3 under an A2 scenario and ECHAM5 under an A1B scenario – and used them as inputs in the UW’s Weather Research and Forecasting RCM (WRF). The GCM output consisted of meteorological data developed for two 31-year periods: one for 1970−2000 and one for 2020–2050. The WRF output was produced in two grid sizes: 20 km 2 and 36 km 2 . The output of these models was fed into the Hydrologic Simulation Program-Fortran hydrologic model for the entire Thornton Creek basin to determine changes in a number of creek flow parameters. This study concluded: While this pilot study demonstrates the feasibility of applying such temporally and spatially detailed data to assess climate change effects on urban streams and drainage infrastructure, future projections of both precipitation and stream flow from different GCM-RCM combinations are widely divergent and there appears as yet to be insufficient information or knowledge to demonstrate that one model combination is more or less accurate than another. Additional work is needed to improve confidence in future projections and before applying dynamically downscaled data to stormwater planning, policy, or design standards (Northwest Hydraulic Consultants, 2009, p. 22). Page 2-6
Page 2: Options for Improving Climate Model
Page 5 and 6: Water Utility Climate Alliance Whit
Page 8: Water Utility Climate Alliance Whit
Page 88 and 89:
Water Utility Climate Alliance Whit
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118:
Page 121 and 122:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142:
show all

Options for Improving Climate Modeling to Assist Water Utility ...

Create successful ePaper yourself

Delete template?

Save as template?