Watershed Management Plan - Mason County

Appendix
B Key Issues and Options – Water Quantity
Following are options the Planning Unit and its partners could pursue to
better understand and prepare for the likely effects of climate change in
WRIA 16.
Option 22.
Conduct a modeling and research effort to
predict future hydrographs under climate change
Over the next few decades increasing global and regional air temperatures
are expected to lead to reduced snowpack and receding glaciers. Due to the
dependence of many WRIA 16 streams on snowpack, these changes are
expected to lead to increased winter-time flows, as more precipitation will
fall as rain rather than snow, and decreased spring and summer-time flows,
as snowpack and glaciers are reduced. Furthermore, spring peak flows are
predicted to occur two to six weeks earlier in streams fed significantly by
snowpack. Changes in quantity and timing of flow of this magnitude can
affect the availability of water for all users (particularly agricultural), and
could be detrimental to migrating juvenile salmon, which depend on cool
and ample flows in the late spring for migration. Understanding how global
climate change affects the Pacific Northwest’s climate and water resources
can help watershed planning units more effectively manage water supplies
for current and future water supply needs (UW Climate Impacts Group,
2004).
Accordingly, the WRIA 16 Planning Unit could partner with an appropriate
scientific organization to conduct a modeling and research effort to predict
more specifically what the streamflow impacts are likely to be. An excellent
resource and potential partner for this effort would be the University of
Washington Climate Impacts Group, which has developed a streamflow
scenario tool to estimate and plan for possible future scenarios (Sniver et al,
2003). The Planning Unit’s existing stream gauge date would be the starting
point for this effort.
Option 23.
Develop adaptive capacity to efficiently manage
climate impacts on the water supply
One of the likely effects of climate change on WRIA 16 is that reduced
snowpack will lead to lower summer stream flows. In addition, if spring
peak flows occur weeks earlier (as predicted), the time between peak spring
runoff and fall rains may be even longer, further affecting a basin’s ability to
meet water demands during the driest time of year. Finally, warmer
summers may increase demand for water, even as flows are decreasing.
Water conservation, water banking, and greywater use are three strategies
addressed by options presented elsewhere in this plan, but other approaches
may also be needed to extend water supplies into the dry summer months.
In particular, the Planning Unit could seek to develop adaptive capacity to
prepare for and manage climate impacts. For example, increasing usable
water storage (both surface water and aquifer storage and recovery) can be
an effective means of saving water for summer use. When and if water
page 106 Final Plan for County Adoption – May 11, 2006