Margulis Research Group

Department of Civil and Environmental Engineering


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Reducing uncertainty of climatic trends in the Sierra Nevada: An ensemble-based reanalysis via the merger of disparate measurements

(Sponsor: NSF Hydrologic Sciences; Collaborator/s: Michael Durand, OSU)

The Sierra Nevada system plays an integral role in the hydrologic cycle, energy cycle, ecological systems, and in water resources supply in Western North America. Trends toward earlier spring snowmelt runoff and decreasing springtime observations of snow water equivalent (SWE) from in situ networks have been observed in the past fifty years. In this project we will develop and apply a SWE reanalysis for a case study basin (Kern River) in the Southern Sierra Nevada. This project will focus on developing a general methodology that could be applied to the entire Sierra Nevada in follow-on work. Additionally, the high-resolution modeling and estimation framework developed here could provide a unique testbed for future climate change studies, where atmospheric model output from regional or global climate models could be used as forcing to the offline model to add to the existing literature on how the Sierra snowpack and spring streamflow is expected to change. We will integrate the models, methods, and results from the work into existing undergraduate and graduate courses at UCLA, and into ongoing outreach work of the Byrd Polar Research Center.

Maps showing: a) Kern River basin location in Sierra Nevada (along with relevant Landsat 5 tiles); and distribution of b) elevation, c) landcover (0=water, 1=bare, 2=groundcover, 3=forest), and d) forest cover fraction.

Distribution of elevation across full Kern basin (black), North Fork (blue), and South Fork (red).

Preliminary results:

Comparison of prior (top row) and reanalysis (bottom row) results to snow-course (left) and pillow (right) observations showing improvement in reanalysis via assimilation of remote sensing data.

Comparison of 27-year seasonal cycle from reanalysis (blue) to snow-course and pillow observations (red). Interannual variability represented by corresponding ranges.


27-year average a) peak SWE and b) day-of-peak (DOP) SWE.

Elevational distribution of a) peak SWE, b) day-of-peak, c) SWE volume, and d) SWE probability. Black, blue, and red lines correspond to full Kern, North Fork, and South Fork respectively.


Maps of annual anomalies in peak SWE. Blue represents above average and red represent below average. Results show anomaly patterns vary from year to year.


Map of diagnosed trends (from 27-year reanalysis) in peak SWE.

Map of diagnosed trends (from 27-year reanalysis) in day-of-peak SWE.

Datasets: All datasets generated as part of this project will be released publically upon publication and completion of the project per NSF data management guidelines. These data will include static datasets for the Kern River basin, dynamic Landsat-derived fSCA over the 27-year period and the daily/90-meter 27-year SWE reanalysis dataset. Data will be available via ftp from the PI's server and/or at the NSIDC website. Please contact the PI about expected release dates, preliminary data availability and consult this site for ftp links when they become available.