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

Abstract

[1] 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 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-term data 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.

Annual Changes in Seasonal River Water Temperatures in the Eastern and Western United States

“…Our approach could easily be applied to systems under more intensive water management practices to better elucidate their effects on thermal habitat. In fact, it has been suggested that examining "minimally human-influenced" sites may help in elucidating climate effects on river water temperature [16]. Although we acknowledge that we were not able to examine truly "minimally-impacted streams", attempts to reduce the effects of water management policies in impoundments is likely important [14].…”

“…Several studies have examined temporal trends in river water temperatures (e.g., [14][15][16][17][18]), and although a direct comparison of findings among studies is not always possible, it is evident from these previous investigations that there is variability in how the thermal habitat of rivers change over time and how they may be responding to drivers of water temperature, such as changes in climate. For example, Kaushal et al [15] found that 50% (20 out of 40) of the U.S. river sites they examined showed statistically significant long-term linear warming trends in annual mean temperature, and Rice and Jastram [18] found substantial variability in the direction and magnitude of trends in river water temperature from the mid-Atlantic region, USA.…”

Rising air and stream-water temperatures in Chesapeake Bay region, USA

“…The literature reflects disagreement regarding the control of air temperature (AT) on WT. Some studies conclude that AT does not control WT (e.g., Johnson 2003;Arismendi et al 2012;Mayer 2012), whereas modeling studies show that AT is a strong predictor of WT (e.g., Webb et al 2003;Moatar and Gailhard 2006;van Vliet et al 2011;Isaak et al 2012). Statistical studies, such as this one, can be complimentary to processoriented studies in identifying factors that may be driving increasing WT trends.…”

Changes in river water temperature between 1980 and 2012 in Yongan watershed, eastern China: Magnitude, drivers and models

“…Although the relationship between air and water temperature is generally strong, the strength of such a relationship varies regionally and temporally, and can be highly site specific due to additional influences from local hydrology and human activities, such as changes in land-use and population density (Arismendi et al, 2012;Orr et al, 2015;DeWeber and Wagner, 2014). It is commonly observed that water temperature is inversely related to river discharge, reflecting a reduced thermal buffering capacity due to decreasing flow volumes, increasing travel time, and diminished dilution capacity for inputs of thermal effluents (Gu and Li, 2002;Webb et al, 2003;Moatar and Gailhard, 2006;Albek and Albek, 2009).…”