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

Water Utility Climate Alliance White Paper
Options for Improving Climate Modeling to Assist Water Utility Planning for Climate Change
What water utilities would like from climate science
In general, it is important to note that there does not appear to be a single investment – i.e., the
proverbial “magic bullet” – which will substantially reduce the range of projections at the scale
at which utility planning is conducted. Such projection could be used by utilities to help make
decisions on expensive or long-lived investments such as infrastructure. (This is sometimes
referred to as making the science “actionable” for water utilities.)
Based on our experience working with the water resources community on climate change
adaptation and on our discussions with WUCA members, we identified four topics that we
believe capture the improvements that are desired in the science. The four improvements follow
and the prospects for improvement in the science over the next decade are discussed.
1. Model agreement on change in key parameters. A critical impediment to developing
consistent projections of regional climate change is that GCM projections in many
regions differ on how key parameters such as circulation patterns will change. A number
of the options identified below concern how improvements can be made in simulating a
number of these phenomena. Such improvements may take years to be realized. In the
meantime, we can better understand the sources of uncertainty about regional climate
change and improve techniques for analyzing and applying climate models.
2. Narrowing of the range of model output. The concern by utilities is that across the
numerous emissions scenarios and models, a wide range of projections is given. Only
modest progress is expected because two main sources of uncertainty − emissions
scenarios and model climate sensitivity – have seen only slow progress in narrowing
uncertainty. Enhanced use of observational data to constrain GCMs may help make
progress on this matter.
3. Climate model resolution at a spatial and temporal scale that matches water utilities’
current system models. Ideally, the resolution of GCM output would be at the same scale
in utilities’ systems models. The range of GCM resolution used in climate projections
will likely improve over the next few years from 100–400 km to 50–200 km but for the
most part this resolution will be more coarse than that currently used in utility system
models. Note that increased resolution alone does not guarantee increased accuracy.
4. Improved projections within water utility planning horizons. While long-term
projections of climate change can be useful to utilities, they are also interested in climate
projections for the next few decades. However, in the first few decades of model
projections, simulations of natural modes of climate variability typically have a larger
effect on climate projections than GHG concentrations. Improved simulations of the
drivers of climate variability, such as improved modeling of the Tropical Pacific and
Page S-5