Integrating watershed-scale and river-reach protection and restoration planning to promote climate resilience in the South Fork Nooksack River (SFNR)

The Nooksack Indian Tribe reservation is located at the foot of the North Cascades Mountains, approximately 13 miles east of Bellingham, WA and the Salish Sea. The Tribe relies on a harvestable surplus of Pacific salmon in the Nooksack River for cultural, subsistence, and commercial purposes. Today, Pacific salmon runs are less than 10 percent of the runs in the late 1800’s. Causes of the declines are complex; however, it is well understood that the legacy of commercial forestry, agriculture, and development has increased sediment loading and water temperature. Climate impacts will cumulatively add to the legacy impacts, which are still evident today. The Tribe has been an effective member of a collaboration of agencies, tribes, universities, contractors, and NGOs aimed at addressing both current and projected impacts on water quality and streamflow. Whereas many restoration and planning efforts focus exclusively on either the stream corridor or adjacent upland land use when considering water quality, the Tribe has successfully integrated watershed-scale planning with reach-scale planning to more fully address the needs of fish in the South Fork Nooksack River. In particular, the tribe initiated a federally-funded comprehensive watershed conservation planning effort. The watershed-scale approach includes assessment of upland land use impacts and adaptation strategies to ameliorate downstream water quality issues. The results are driving the development of silvicultural and in-stream strategies to restore natural water storage functions. Concurrently, the Tribe received NEP grant funding as administered by WA Department of Ecology to develop a reach-scale protection and restoration plan for the SFNR. The reach-scale approach involves engaging riparian landowners to determine interest in protecting and restoring buffers along the SFNR and tributaries, and developing implementation plans for such action. Together, these efforts provide a case study in identifying in-stream, riparian, and upland protection and restoration strategies to support fish survival

Forest gap effects on snow storage in the transitional climate of the Eastern Cascade Range, Washington, United States

Forest thinning and gap creation are being implemented across the western United States of America (USA) to reduce wildfire and forest mortality risk as the climate warms. The Eastern Cascades in Washington, USA, is in a transitional zone between maritime and continental climate conditions and represents a data gap in observations describing the relationship between forest density and snowpack. We collected 3 years of snow observations across a range of forest densities to characterize how forest management efforts in this region may influence the magnitude and duration of snow storage. Observations indicate that peak snow storage magnitude in small gaps ranges from the same to over twice that observed in unburned forest plots in the Eastern Cascades. However, differences in snow duration are generally small. Across all Eastern Cascade sites and years, we observed a median difference of snow storage lasting 7 days longer in gaps as compared to nearby forest plots. A notable exception to this pattern occurred at one north-facing site, where snow lasted 30 days longer in the gap. These observations of similar snow storage duration in the Eastern Cascades are attributed to minimal differences in canopy snow interception processes between forests and gaps at some sites, and to higher ablation rates that counterbalance the higher snow accumulation in the gaps at other sites. At the north-facing site, more snow accumulated in the gap, and ablation rates in the open gap were similar to the shaded forest due to the aspect of the site. Thus, snow storage duration was much longer in the gap. Together, these data suggest that prescriptions to reduce forest density through thinning and creating gaps may increase the overall amount of snow storage by reducing loss due to sublimation and melting of canopy-intercepted snow. However, reducing forest density in the Eastern Cascades is unlikely to buffer climate-induced shortening of snow storage duration, with the possible exception of gap creation in north-facing forests. Lastly, these observations fill a spatial and climatic data gap and can be used to support hydrological modeling at spatial and temporal scales that are relevant to forest management decisions

Quantifying and Modeling the Influence of Forest on the Magnitude and Duration of Mountain Snow Storage in the Pacific Northwest, USA

Thesis (Ph.D.)--University of Washington, 2016-08Forests strongly influence the amount and duration mountain snow storage because forest cover modifies both snow accumulation and ablation processes. Quantifying and predicting forest effects on snow processes and snow storage is critical for understanding the effects of forest change on snow storage, and subsequent impacts on downstream water resources. However, both the magnitude and direction of forest modifications of individual snow processes vary with climate, topography, and forest characteristics. Accurate prediction of the net effects of forest change on mountain snow storage, particularly in a warming climate, depends on accurately representing the spatiotemporal variability of forest-snow interactions. With a goal to better understand forest-snow processes in the maritime snow zone, we collected snow observations over four winters within diverse forest types in western Washington, USA. We utilize these new observations to quantify forest effects on snow duration, as well as to assess the robustness of remote methods to observe snow-covered area within a forest. We find that mean snow duration is 8 days longer in forest gaps than in forested plots, but that snow duration in thinned forest and dense forest are indistinguishable at the 1600 m2 plot-scale. We additionally show that time-lapse cameras and spatially distributed ground temperature sensors are both robust methods for observing snow duration, and make suggestions about the optimal spatial density of snow observations within forests. The entire four-year dataset and related metadata are extensively described, and are now publicly available for potential use in numerous modeling applications. To expand our focus on forest-snow interactions to the Pacific Northwest, USA, regional-scale, we collaborate with other research institutions and engage citizen scientists. Regional synthesis and analysis of snow depth and duration at 12 out of 14 paired open-forest locations show that differential snow duration ranges from synchronous, to snow lasting up to 13 weeks longer in the open. The differences in snow duration are attributed to forest effects on snow accumulation, with larger differences between snow accumulation rates than between ablation rates in the open and forested sites through the duration of the forest snowpack. In 2 out of the 14 locations, differential snow duration is 2-5 weeks longer in the forest. These 2 sites are subject to hourly average wind speeds ranging up to 8 and 17 m s-1. Therefore, longer snow duration in the forest likely results from a combination of enhanced deposition of snow and reduced snow loss from canopy interception in the forested sites. These findings suggest that a regional framework to understand forest effects on snow storage in the maritime to maritime-continental transitional climate across the Pacific Northwest must account for high interception efficiencies in warmer climates as well a high winds due to topographic exposure and climate. Lastly, we assess the influence of forest structural characteristics on snow storage in western Washington by linking lidar-derived forest canopy metrics to snow depth and snow duration. By using a matrix decomposition method to collapse the variance of spatially distributed observations of snow depth onto a few dominant modes, we show that the top two modes represent forest effects on snow accumulation and ablation, respectively. Furthermore, gridded metrics of canopy cover and height that quantify the canopy directly overhead, rather than to the south, correlate equally strongly (r2 of up to 0.74) with the spatial coefficients that scale both of these modes. This finding suggests that the role of forests in shading the snowpack from sunlight is diminished at this site. Furthermore, multivariate analysis of physiographic predictors of snow duration across a range of elevations and years quantifies the important role of canopy characteristics in controlling snow duration. At the study site in western Washington, the binary simplification of considering forested versus open locations is supported by evidence for a stepped response, in which snow duration shifts from longer to shorter around values of 60-70% canopy cover. Collectively, the findings demonstrate that forest effects on snow accumulation dominate the overall influence of forest on snow storage in the Pacific Northwest, USA, resulting in larger magnitude and longer duration snow storage in canopy gaps, except in locations subject to high wind speeds

Snow, forest, and meteorological data collected in the Cedar River Municipal Watershed, Washington, USA

See associated paper: Dickerson-Lange, S.E., Lutz, J.A., Gersonde, R., Martin, K.A., Forsyth, J.E., and J.D. Lundquist (2015, in preparation for Water Resources Research), Field observations of distributed snow depth and snow duration within diverse forest structures in a maritime mountain watershedSpatially distributed snow depth and snow duration data were collected over two to four snow seasons during water years 2011-2014 in experimental forest plots within the Cedar River Municipal Watershed, 50 km east of Seattle, Washington, USA. These 40 m × 40 m forest plots, situated on the western slope of the Cascade Range, include un-thinned second-growth coniferous forest as control treatments, variable density thinned forests, forest gaps in which a 20 m diameter (approximately equivalent to one tree height) gap was cut in the middle of each plot, and old growth forest. Together, this publicly available dataset includes snow depth observations from manual snow courses, distributed snow duration observations from ground temperature sensors and time-lapse cameras, meteorological data collected at two open locations and three forested locations, and forest canopy data from airborne light detection and ranging (LiDAR) data and hemispherical photographs. These co-located snow, meteorological, and forest data have the potential to improve understanding of forest influences on snow processes, and provide a unique model-testing dataset for hydrological analyses in a forested, maritime watershed.National Science Foundation, CBET-093178

Development and Testing of a Snow Interceptometer to Quantify Canopy Water Storage and Interception Processes in the Rain/Snow Transition Zone of the North Cascades, Washington, USA

Tree canopy snow interception is a significant hydrological process, capable of removing up to 60% of snow from the ground snowpack. Our understanding of canopy interception has been limited by our ability to measure whole canopy water storage in an undisturbed forest setting. This study presents a relatively inexpensive technique for directly measuring snow canopy water storage using an interceptometer, adapted from Friesen et al. (2008). The interceptometer is composed of four linear motion position sensors distributed evenly around the tree trunk. We incorporate a trunk laser-mapping installation method for precise sensor placement to reduce signal error due to sensor misalignment. Through calibration techniques, the amount of canopy snow required to produce the measured displacements can be calculated. We demonstrate instrument performance on a western hemlock (Tsuga heterophylla) for a snow interception event in November 2011. We find a snow capture efficiency of 83 ± 15% of accumulated ground snowfall with a maximum storage capacity of 50 ± 8 mm snow water equivalent (SWE). The observed interception event is compared to simulated interception, represented by the variable infiltration capacity (VIC) hydrologic model. The model generally underreported interception magnitude by 33% using a leaf area index (LAI) of 5 and 16% using an LAI of 10. The interceptometer captured intrastorm accumulation and melt rates up to 3 and 0.75 mm SWE h−1, respectively, which the model failed to represent. While further implementation and validation is necessary, our preliminary results indicate that forest interception magnitude may be underestimated in maritime areas