Future Temperature and Salinity in Puget Sound, Washington State, Under
CMIP6 Climate Change Scenarios
Abstract
In Washington State, climate change will reshape the Puget Sound marine
ecosystem through bottom-up and, top-down processes, directly affecting
species at all trophic levels. We applied analytical approaches to
better understand future climate change effects on temperature and
salinity in Puget Sound. We used empirical downscaling techniques to
derive high resolution time series of future sea surface temperature and
salinity, based on scenario outputs of two coarse resolution General
Circulation Models, GFDL-CM4 and CNRM-CM6-1-HR, which were created as
part of the CMIP6 - Coupled Model Intercomparison Project Phase 6. We
calculated long-term averages for historical simulations, calculated
anomalies for future years, and applied a delta-downscaling approach to
a Regional Ocean Modeling System (ROMS) time series, yielding short
(2020–2050) and long-term (2070–2100) forecasts. Downscaled output for
Puget Sound showed temperature and salinity variability between
scenarios and models, but overall there was strong model agreement.
Model variability and uncertainty was higher for long-term projections.
Spatially, we found regional differences for both temperature and
salinity: including higher temperatures in the South Basin and higher
salinity in the North Basin. Caveats to our methodology include the
assumption that variable relationships are static and cannot represent
interactions between large scale and local change, but this study is a
first step to translating CMIP6 outputs to higher resolution predictions
of future conditions in Puget Sound. The climate projections for Puget
Sound oceanography will be used to drive the Atlantis ecosystem model
for Puget Sound, an end-to-end ecosystem modeling approach that
represents all trophic levels and evaluates the species-level impacts of
climate change. This project is part of a Washington State Sea Grant
funded project, “Evaluating the effects of Southern Resident orcas
recovery actions and external threats in the marine ecosystem of Puget
Sound.”