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
basin is subdivided into much smaller components (e.g., a fraction of a square kilometer)
that may incorporate single or multiple observations. Consequently, the desired resolution
of climate model output may differ substantially across utilities.
Water supply mass balancing models that integrate hydrologic models, such as Seattle’s
SEAFM or NYCDEP’s integrated modeling project currently under development, seem
to be most capable of incorporating climate model projections. The necessary inputs for
this subset of utility models (i.e., meteorological variables such as temperature and
precipitation) are climate model outputs, and downscaling methodologies can provide
data at the scale of these operating models. However, it should be noted that for some
regions, particular processes, such as coastal storms, are very important for the mass
balance model, but may not be captured by climate models.
Many utility modeling efforts appear to correlate observed variables, such as temperature
and precipitation, with observations or modeled values for the output variable of interest
– usually streamflow. This is typically done in spreadsheets, standalone mass balancing
models, or hydrology models. Because many of these models are based on correlations
with observed data, the modeled relationship, though historically true, may not be true in
the future due to potential nonlinear changes in the relationship between the variables of
interest as climate changes. Nevertheless, because in many cases these models are
updated with new data every year, it may be possible for utility models to adjust over
time to changing climate conditions.
Water quality models may require advances in climate models to be of practical use
because they operate on a finer scale than climate models and they sometimes incorporate
variables not well replicated by current climate models (e.g., cloud cover, intense
precipitation events) to approximate total dissolved solids, turbidity, etc. Higherresolution
or more physically accurate modeling may be necessary to capture the
climatological/weather events of interest for modeling water quality. Furthermore, there
may not be sufficient water quality data (e.g., particle counts, total dissolved solids) with
which to calibrate climate model outputs.
Sometimes hydrologic models and operational (mass balance) models are integrated, and
sometimes they are not. When they are integrated, basic meteorological variables are
used as inputs into the hydrologic models, which then produce streamflow or similar data
for use in the operational models. If the operational models (requiring streamflow data)
are not integrated or not available at all, substantial challenges exist in translating basic
meteorological variables into streamflow or similar data. Other important variables that
may need to be derived from or in addition to climate models to support utility modeling
under changing climate conditions include snowpack, groundwater levels, and water
demand.
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