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

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Water Utility Climate Alliance White Paper Options for Improving Climate Modeling to Assist Water Utility Planning for Climate Change This option can build on work with coupled models and data assimilation used for seasonal (ENSO) and decadal prediction. The tropical Pacific Ocean is comparatively well observed: the Tropical Ocean and Global Atmosphere/Tropical Atmosphere-Ocean Array has been collecting sub-surface ocean data for almost 25 years. Starting around 2000, ARGO floats (http://www.argo.ucsd.edu/) have provided unprecedented spatial and temporal observations of the upper 2,000 meters of ocean with nearly global coverage, including the Tropical Pacific. Cons This option has a low certainty of success. This is a difficult problem given that progress on this has been slow and not systematic across models in the last decade, and it requires innovative ideas. Natural multi-decadal variations in ENSO amplitude may prove too large for useful predictions of change in ENSO characteristics to be reliable. This option requires collaboration across disciplines, which may take time to develop. This option requires cross-modeling center coordination, which may prove technically and organizationally difficult. Availability Some progress could be made in 2–5 years through analysis of existing data to better evaluate climate model performance in the Tropical Pacific. Additional progress could be made by intensively analyzing the Tropical Pacific in coordination with the decadal prediction component of CMIP5 which will start their coupled models using simplified ocean data assimilation methods. However, the larger project of using data assimilation methods to directly improve climate models, and transferring knowledge and techniques from the seasonal prediction models to climate models is much more complex and will likely take longer. Estimate of costs Intensive analysis of climate model performance in the Tropics, including decadal predictions models, could be supported by a research program on the order of $13 million per year. Page 4-13
Water Utility Climate Alliance White Paper Options for Improving Climate Modeling to Assist Water Utility Planning for Climate Change The larger program of coordinated model evaluation and improvement in the Tropical Pacific would likely require a multi-million dollar research program, possibly up to $10 million per year. The main needs are the support of research teams to develop and apply advanced data assimilation techniques to climate models, along with the large computing resources that this would require. GCM-4. Evaluate decadal prediction efforts for water utilities’ planning Prediction of the future climate that takes into account both the climate change signal and the phase of natural climate variability is referred to as “decadal climate prediction” (see Section 3.1.2). Decadal climate prediction is a new methodology with great uncertainties, but also has the potential for great benefit to water utilities. CMIP5 will include the first intercomparison of decadal predictions. Decadal prediction runs are planned to extend to 2035 using GCMs with 50–100 km resolution in the atmosphere. This effort would fund: A climate change specialist to track the progress of decadal prediction efforts worldwide and evaluate the potential for using decadal predictions in water utility planning. Research to integrate predictions of climate variability on annual-to-decadal scales with projections of climate change, thus providing climate change information to address a range of planning horizons. Downscaling efforts only if the potential skill of these prediction can be demonstrated through “hindcast” experiments. Pros Some water utilities have expressed a desire for predictions on a 2–10-year scale. This option may provide improved regional projections because oceans start closer to observed conditions than in free-running GCMs. This option has the potential for skill in predicting Atlantic and Pacific decadal oscillations, potentially improving predictions over most of North America. This will be a large, international effort that is worth following. This option will enhance the understanding of decadal variability and the ability to integrate decadal variability with climate change. Page 4-14
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