The paradox of cooling streams in a warming world: Regional climate trends do not parallel variable local trends in stream temperature in the Pacific continental United States

Temperature is a fundamentally important driver of ecosystem
processes in streams. Recent warming of terrestrial
climates around the globe has motivated concern about consequent
increases in stream temperature. More specifically,
observed trends of increasing air temperature and declining
stream flow are widely believed to result in corresponding
increases in stream temperature. Here, we examined the evidence
for this using long-term stream temperature data from
minimally and highly human-impacted sites located across
the Pacific continental United States. Based on hypothesized
climate impacts, we predicted that we should find warming
trends in the maximum, mean and minimum temperatures,
as well as increasing variability over time. These predictions
were not fully realized. Warming trends were most prevalent
in a small subset of locations with longer time series beginning
in the 1950s. More recent series of observations (1987–2009)
exhibited fewer warming trends and more cooling trends in
both minimally and highly human-influenced systems. Trends
in variability were much less evident, regardless of the length
of time series. Based on these findings, we conclude that our
perspective of climate impacts on stream temperatures is
clouded considerably by a lack of long-termdata on minimally
impacted streams, and biased spatio-temporal representation
of existing time series. Overall our results highlight the need
to develop more mechanistic, process-based understanding
of linkages between climate change, other human impacts
and stream temperature, and to deploy sensor networks that
will provide better information on trends in stream temperatures
in the future. Citation: Arismendi, I., S. L. Johnson, J. B.
Dunham, R. Haggerty, and D. Hockman-Wert (2012), The paradox
of cooling streams in a warming world: Regional climate trends do
not parallel variable local trends in stream temperature in the Pacific
continental United States, Geophys. Res. Lett., 39, L10401,
doi:10.1029/2012GL051448.