Search - NW Climate Science Digest

Use this page to search climate science digests beginning in 2015.

Digests from 2013-2014 are archived here.

Digest Articles

Aquatic Resources, Stream Flow, Hydrology in the Western U.S.

Future projections of streamflow magnitude and timing differ across coastal watersheds of the western U.S.

Burke, W. D. and Ficklin, D. L. (2017), Future projections of streamflow magnitude and timing differ across coastal watersheds of the western United States. Int. J. Climatol. doi:10.1002/joc.5099

While streamflow timing of western U.S. watersheds has shifted earlier in mountainous snow-dominated watersheds due to earlier snowmelt, timing for rain-dominated coastal watersheds has shifted to later in the year. Despite these dissimilarities, coastal watersheds have received little attention in the literature. This research assessed changes in projected climate and hydrology for five small coastal basins in Washington, Oregon, and California. Projections of temperature and precipitation were coupled with the Soil and Water Assessment Tool hydrologic model to simulate future hydrology for each watershed. The response of climate, streamflow discharge, and timing was analyzed for each watershed by comparing the projected mid-21st century and late-21st century to the historical period. While temperature is projected to increase at each watershed from 1 to 6°C by the end of the 21st century, precipitation varies widely with the median and mean change across all watersheds and GCMs being close to zero. Changes in the magnitude of peak winter streamflow discharge differ across the region compared to the historical period. The projected decreases in peak winter streamflow magnitude have critical implications for water supply, which is already strained from extensive drought and high demand.

Snowmelt rate dictates streamflow

Barnhart, T. B., Molotch, N. P., Livneh, B., Harpold, A. A., Knowles, J. F., & Schneider, D. (2016). Snowmelt Rate Dictates Streamflow. Geophys. Res. Lett. Geophysical Research Letters. doi:10.1002/2016gl069690

A recent paper in Geophysical Research Letters presents a possible mechanism linking snowmelt rate to streamflow generation. The results of the study indicate that there is a strong correlation between snowmelt rate and baseflow efficiency, which supports the idea that greater snowmelt rates increases subsurface flow. As temperatures continue to increase this may lead to earlier, slower snowmelt, decreasing streamflow production.

EPA Announces Climate Adjustment Tool for the Storm Water Management Model

EPA's Storm Water Management Model (SWMM) is widely used throughout the world and is considered the "gold standard" in the design of urban wet-weather flow pollution abatement approaches. It is a dynamic hydrology-hydraulic water quality simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas, and allows users to include any combination of low impact development (LID)/green infrastructure controls to determine their effectiveness in managing stormwater and sewer overflows. The new Climate Adjustment Tool (SWMM-CAT) is a simple to use software utility that applies monthly climate adjustment factors onto historical precipitation and temperature data to consider potential impacts of future climate on stormwater. Learn more and access the tool and download the SWMM-CAT user’s guide.

Earlier snowmelt reduces carbon storage

Winchell, T. S., D. M. Barnard, R. K. Monson, S. P. Burns, and N. P. Molotch (2016), Earlier snowmelt reduces atmospheric carbon uptake in midlatitude subalpine forests, Geophys. Res. Lett., 43, 8160–8168, doi:10.1002/2016GL069769.

A team of researchers from the University of Colorado examined the relationship between carbon uptake and snow ablation periods in this new study. The authors used 15 years of eddy covariance data in Colorado and found that the colder ablation-period air temperatures during years with earlier snowmelt led to reduced carbon uptake. From this observed phenomenon, the authors then projected net carbon uptake for an average mid-century ablation period using a multilinear regression. Findings from this projection show a possible 45% reduction in carbon uptake due to earlier snowmelt caused by increased global temperatures.

Population Fluctuations of Coastal Cutthroat Trout in Irely Creek, Washington

In the Irely Creek watershed (upper Quinault River drainage) within Olympic National Park, coastal cutthroat coexists with anadromous coho salmon and two resident-fish and several amphibian species. During 2001-2002, cutthroat redds and fry were abundant in the mainstem, particularly in its middle segment, with escapement estimates being 48-106. More recently, the population has declined by an order of magnitude, reflecting summer/fall droughts that have often dried up adult habitat in Irely Lake. Although redd counts have risen when summer/fall seasons have been wetter during 2003-2010, they haven’t reached 2001-2002 counts via regular lake dry-outs, including two consecutive dry-outs during 2002-2003. Hence, the population is showing an overall downward trend with some smaller-scale oscillations coupled with escapement estimates during 2003-2010 ranging from 4 to 32.

Selecting climate change scenarios for specific impacts

Vano JA, Kim JB, Rupp DE, Mote, PW (2015). Selecting climate change scenarios using impact-relevant sensitivities. Geophys Res. Lett 42(13), 5516-5525. Doi: 10.1002/2015GL063208

Climate change studies oftentimes involve the selection of a small number of climate scenarios, with varied methods for how to select which climate models and scenarios should be chosen. Vano et al. develop a method that characterizes climate projections on an impacts spectrum that uses a sensitivity analysis technique described in Vano and Lettenmaier (2014). Performance of the climate models is specific to the Pacific Northwest region. Rather than selecting climate models based on which models best approximate climate in the Pacific Northwest, this method shows how climate models (and scenarios) are chosen for particular impacts. This is a “bottom-up meets top-down” approach that makes the climate impact in question of primary importance in the climate model and scenario selection process. Once the climate models and scenarios are selected, simple sensitivity analysis was used to understand how a particular variable responds to incremental temperature and precipitation changes. Examples highlighted in the study include changes in streamflow and annual vegetation carbon in the Pacific Northwest.

Next Steps for Managing Freshwater Resources in a Changing Climate

Next Steps for Managing Freshwater Resources in a Changing Climate summarizes recommendations for implementing the National Action Plan: Priorities for Managing Freshwater Resources in a Changing Climate. The report was developed by the Water Resources Adaptation to Climate Change Workgroup that supports the Advisory Committee on Water Information - a national federal advisory committee made up of representatives of a diverse set of stakeholders and federal agencies. The Workgroup organized five subgroups based on the major recommendation topics in the National Action Plan: data and information for decision-making; vulnerability assessment; water use efficiency and conservation; integrated water resource management; and capacity building in training and outreach. The report is the result of discussions that took place at a two-day meeting of the Workgroup members in February 2014.  

Storm Surge Inundation & Scenario-Based Projected Changes Map

Developed by the EPA, the storm surge inundation map is an interactive map illustrating the current worst-case storm surge and inundation scenarios on the American Gulf and Atlantic coasts. The map incorporates data layers from FEMA’s 100 and 500 year flood maps, NOAA’s Sea, Lake and Overland Surge from Hurricanes (SLOSH), and the National Hurricane Center's coastal county hurricane strike maps. The second map, EPA’s scenario-based projected changes map, is an online map that provides access to localized scenarios of projected changes in annual total precipitation, precipitation intensity, annual average temperature, 100-year storm events, and sea-level rise from EPA’s Climate Resilience Evaluation and Awareness Tool. 

Evaluating climate model simulations of drought for the Northwestern U.S.

Abatzoglou, J.T. and Rupp, D.E. In press. Evaluating climate model simulations of drought for the northwestern United States. International Journal of Climatology. DOI:10.1002/joc.5046

Researchers from Oregon State and the University of Idaho developed a framework to help evaluate the fidelity of global climate models (GCMs) to simulate regional drought. They focused on the northwestern United States and found that model fidelity was generally higher for drought metrics evaluated with evapotranspiration versus precipitation and for seasonal/annual timescales versus multi-year timescales. They also found that models systematically underestimated the severity of regional drought in the region of focus. Their research aims to do two things: help those who use regional climate projections where drought plays an important role and highlight shortcomings of model simulations of hydroclimate variability.

Flaws Detected in Models that Predict Future Changes in Stream Temperature

Ivan Arismendi, Mohammad Safeeq, Jason B Dunham and Sherri L Johnson, Can air temperature be used to project influences of climate change on stream temperature? Environmental Research Letters,vol 9, 084015,

Researchers found that regression-based statistical models that predict stream temperatures based on more widely available air temperature data did not accurately predict long-term changes in stream temperatures, likely due to additional influential variables, such as groundwater contributions or riparian shading. This model evaluation shows that other alternatives are needed.