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The Southern Sierra Critical Zone Observatory is a community platform for research on critical zone processes, with ongoing investigations and measurements at several sites along a 2300-m elevation gradient on the western slope of the southern Sierra Nevada.

We encourage the research community to utilize our intesively studied field sites.

Observatory research is framed by multiple spatial and temporal scales.

Spatial differences along the elevation gradient characterizing our Critical Zone Observatory's field areas - from forest ecology to preciptation phase to bedrock composition - create a natural laboratory to study changes in critical zone characteristics and processes across the landscape. While this elevation transect experiences rapid seasonal changes, from snow cover to wet soil to dry soil in a 1-2 month period, climate warming will shift this transition to an earlier time and a higher elevation. Researchers can also use the gradient then as a substitution of space for time to research how critical zone processes respond to natural and anthropogenic environmental changes, including warmer average temperatures and forest thinning.

Our growing community of critical zone scientists from multiple institutions and areas of research expertise are carrying out investigations in the Sierra National Forest, Kings River Experimental Watershed, San Joaquin Experimental Range, and Sequoia National Park.

Learn more about our field areas and instrumentation -->

Our integrated research is centered on several interdisciplinary questions and goals:


Critical Zone researchers are currently investigating a tightly linked set of research questions at our Observatory, including:

  • How do soil moisture and topographic variability interact to influence soil-formation and weathering?
  • How is the response of soil moisture to snowmelt and rainfall controlled by variability across the landscape, and how do these responses both reflect and constrain streamflow and ET?
  • How does vegetation, and ecosystem distribution and function (species, plant functional type, production), vary with climate (elevation); and what physiological mechanisms regulate these interactions?
  • How does vegetation influence land-atmosphere exchange of water, energy, and CO2?
  • How do soil/landscape heterogeneity and water fluxes influence nutrient cycling and retention?
  • What is the role of aeolian fluxes in controlling nutrient availability and NPP?

While some research is centered on a single discipline, many questions require a multi-disciplinary approach. Our measurements and monitoring efforts overlap with other observatories in the National Science Foundation's U.S. Critical Zone Observatory Network in order to rapidly improve Earth systems models.

Explore examples of current research topics in detail -->

Initial research focus and findings

Since it was initiated in 2007, the Southern Sierra CZO has become a platform for a wide variety of research. Much of the research during the first five years addressed these questions:

  • How does landscape variability control how soil moisture, evapotranspiration and stream flow respond to snowmelt and rainfall?
  • How is soil moisture linked to topographic variability, soil formation and weathering?
  • What physiological mechanisms are controlling how vegetation distribution and function vary with climate
  • How do vegetation attributes influence cycling of water, energy, and CO2?
  • What is the link between soil heterogeneity, water fluxes and nutrient availability?

Among the many results to date at our CZO, four key findings stand out:

  • A strategically distributed measurement suite provides the data needed to close the water balance at multiple scales, providing a foundation for further process research. At the headwater catchment scale our estimates of evapotranspiration (ET) using a water-balance approach are in good agreement with flux-tower measurements. Similarly, our estimate of the water balance across the entire Upper Kings River basin also matches observations.
  • Mid-montane forests have a year-round growing season, avoiding summer water-stress shutdown through deep rooting and avoiding winter shutdown cold tolerance, explaining high productivity and biomass in the mid-montane belt.
  • In contrast to high rates of evapotranspiration (ET) at mid-elevation, we observed reduced ET and productivity at lower elevations owing to summer moisture stress and at high elevations due to cold stress. This confirms the inverse drought and energy limitation conceptual model, with implications for effects of warming on ET.
  • Deep rooting and soil development are important for sustaining high rates of net primary productivity (NPP). At our main instrumented headwater catchment, we found that over one-third of the ET came from depths below 1 m.
For more information on our activities and findings, view our annual reports and publications.





© University of California, Merced

© Sierra Nevada Research Institute

Through late September, the stream at the Providence subcatchment 301 was muddy but had no running water, even after a few small storms. Now, enough rain and snow has fallen to start flow again.  © SSCZO

The forest around Soaproot Saddle is showing extreme water stress. At the end of the water year, the eddy covariance flux tower was only showing respiration and decay, no water usage! © SSCZO

This view from a helicopter above Soaproot Saddle shows the patchy nature of the tree death. As more trees are impacted by insects, these patches are growing. © M Meadows

Observatory research is framed by multiple spatial and temporal scales.

Major questions and goals of current research at the Southern Sierra Critical Zone Observatory

Research News


Watch Online: AGU 2017 Nye Lecture by Roger Bales

17 Jan 2018 - Dr. Roger Bales's Nye Lecture, "Making up for lost snow: lessons from a warming Sierra Nevada", is now available to watch online.


White paper of 2017 CZ Science Meeting in Arlington, VA

01 Jan 2018 - New Opportunities for Critical Zone Science Following the June 2017 Arlington Meeting for Critical Zone Science (hosted by CZO), a white booklet...


CZOs at AGU 2017

05 Dec 2017 - Information on CZO award recipients, events, presentations, etc. at the 2017 AGU Fall Meeting.


Observatory scientists volunteer with students at new STEAM Center in Merced

02 Nov 2017 - UC Merced scientists are sharing their research, stories, and expertise at Merced City School District's new STEAM Center.


Water Resources Research Special Collection: Concentration-discharge relations in the critical zone

30 Oct 2017 - Water Resources Research published a new special collection in September 2017 featuring concentration-discharge research from multiple CZOs.


UCTV: Southern Sierra CZO researchers featured on Sustainable California channel

21 Jun 2017 - University of California Television (UCTV) features Bales, Conklin, Glaser, Safeeq, and others on the new Sustainable California channel


Southern Sierra CZO Videos

04 May 2017 - Onward California - University of California television spots showcase Southern Sierra CZO research


The frontier beneath our feet — an AGU commentary on the critical zone

21 Apr 2017 - AGU has published a collection of commentaries highlighting the important role Earth and space science research plays in society.


2017 CZO Webinar Series: Critical Zone and Society

06 Apr 2017 - 2017 CZO Webinar Series: Critical Zone and Society.


NY Times: Sierra Nevada Snow Won’t End California’s Thirst

11 Apr 2016 - New York Times reporter, Henry Fountain spoke with Southern Sierra CZO PIs Roger Bales and Martha Conklin and investigtor Mohammad Safeeq as they...


Critical Zone Profiles - Meet the people doing CZO science (Southern Sierra CZO)

07 Sep 2015 - Get a sense of the people and the work. Several members of the Southern Sierra CZO are profiled here, including students and professors.

Researcher Spotlight: Kimber Moreland

18 Jan 2018 - Meet the people behind the research!

Updates for Researchers: January 2018

17 Jan 2018 - Funding opportunities, recent publications, upcoming webinars, and other important information for southern Sierra researchers

Visiting the Water Source: A Tour of the Kings River Headwaters

06 Nov 2017 - By Michelle Gilmore and Leigh Bernacchi   Ever wonder how we know what we know about water? Twenty-five intrepid water and forest managers,...

UCSB graduate team working on collaborative forest restoration strategies in Sierra Nevada

03 Oct 2017 - Five master's students at the UCSB Bren School are incentivizing restoration strategies for private landholders with Sierra RCD.

New SSCZO comic artfully communicates research

19 Jul 2017 - Wonder what soils and sponges have in common? Or why some trees in the Sierra Nevada are dying while others are surviving? Find out in our new comic.

More News >

Example Publications


Beyond clay: towards an improved set of variables for predicting soil organic matter content. Rasmussen C., Heckman K., Wieder W.R., Keiluweit M., Lawrence C.R., Berhe A.A., Blankinship J.C., Crow S.E., Druhan J.L., Hicks Pries C.E., Marin-Spiotta E., Plante A.F., Schädel C., Schimel J.P., Sierra C.A., Thompson A., Wagai R. (2018): Biogeochemistry (online) Cross-CZO


Growing new generations of critical zone scientists. Wymore Adam S., Nicole R. West, Kate Maher, Pamela L. Sullivan, Adrian Harpold, Diana Karwan, Jill A. Marshall, Julia Perdrial, Daniella M. Rempe and Lin Ma (2017): Earth Surface Processes and Landforms 42 (14): 2498-2502 Cross-CZO National


Regional sensitivities of seasonal snowpack to elevation, aspect, and vegetation cover in western North America. Christopher J. Tennant, Adrian A. Harpold, Kathleen Ann Lohse, Sarah E. Godsey, Benjamin T. Crosby, Laurel G. Larsen, Paul D. Brooks, Robert W. Van Kirk, Nancy F. Glenn (2017): Water Resources Research 53 Cross-CZO National


Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth. Brantley, S.L., McDowell, W.H., Dietrich, W.E., White, T.S., Kumar, P., Anderson, S., Chorover, J., Lohse, K.A., Bales, R.C., Richter, D., Grant, G., and Gaillardet, J. (2017): Earth Surface Dynamics, 5, 841–860 Cross-CZO National


Reviews and syntheses: on the roles trees play in building and plumbing the critical zone. Brantley, Susan L., David M. Eissenstat, Jill A. Marshall, Sarah E. Godsey, Zsuzsanna Balogh-Brunstad, Diana L. Karwan, Shirley A. Papuga, Joshua Roering, Todd E. Dawson, Jaivime Evaristo, Oliver Chadwick, Jeffrey J. McDonnell, Kathleen C. Weathers (2017): Biogeosciences, 14, 5115-5142 Cross-CZO National


Prevalence and magnitude of groundwater use by vegetation: a global stable isotope meta-analysis. Jaivime Evaristo and Jeffrey J. McDonnell (2017): Scientific Reports 7 Cross-CZO National


Controls on deep critical zone architecture: a historical review and four testable hypotheses. Riebe, C. S., Hahm, W. J., Brantley, S. L. (2017): Earth Surface Processes and Landforms, 42 (1): 128–156 Cross-CZO National


Special issue of The Earth Scientist about the Critical Zone and the US NSF Critical Zone Observatory (CZO) program. CZO Education/Outreach team (2016): The Earth Scientist, Volume XXXII, Issue 3, Fall 2016 Cross-CZO National


Variation of organic matter quantity and quality in streams at Critical Zone Observatory watersheds. Miller, Matthew P., Boyer, Elizabeth W., McKnight, Diane M., Brown, Michael G., Gabor, Rachel S., Hunsaker, Carolyn T., Iavorivska, Lidiia, Inamdar, Shreeram, Johnson, Dale W., Kaplan, Louis A., Lin, Henry, McDowell, William H., Perdrial, Julia N. (2016): Water Resources Research, 52 (10): 8202–8216 Cross-CZO

Mechanisms controlling the impact of multi-year drought on mountain hydrology. Bales, R. C.; Goulden, M. L.; Hunsaker, C. T.; Conklin, M. H.; Hartsough, P. C.; O'Geen, A. T.; Hopmans, J. W.; Safeeq, M. (2018): Hydrological Processes: 10.1038/s41598-017-19007-0

Subsurface plant-accessible water in mountain ecosystems with a Mediterranean climate. Klos, P. Z.; Goulden, M.; Riebe, C. S.; Tague, C.; O’geen, A. T.; Flinchum, B. A.; Safeeq, M.; Conklin, M. H.; Hart, S. C.; Berhe, A. A.; Hartsough, P. C.; Holbrook, S.; Bales R. C.; (2018): Hydrological Processes: 10.1002/wat2.1277

Global patterns of dust and bedrock nutrient supply to montane ecosystems. Arvin, L.J.; Riebe, C.S.; Aciego, S.M.; Blakowski, M.A. (2017): Science Advances, Vol. 3, no. 12, eeao1588

Concentration-discharge relationships in headwater streams of the Sierra Nevada, California. Hunsaker, C. T., Johnson, D. W. (2017): Water Resources Research 53, 7869–7884

Snowmelt controls on concentration‐discharge relationships and the balance of oxidative and acid‐base weathering fluxes in an alpine catchment, East River, Colorado. Winnick M.J., Carroll R.W.H., Williams K.H., Maxwell, R.M., Dong, W., Maher K. (2017): Water Resources Research 53, 2507–2523 Cross-CZO National

Insights into hydrologic and hydrochemical processes based on concentration‐discharge and end‐member mixing analyses in the mid‐Merced River Basin, Sierra Nevada, California. Liu F., Conklin M.H., Shaw G.D (2017): Water Resources Research 53, 832–850

Quantifying nutrient uptake as driver of rock weathering in forest ecosystems by magnesium stable isotopes. Uhlig, D., Schuessler, J.A., Bouchez, J., Dixon, J.L., von Blanckenburg, F. (2017): Biogeosciences 14, 3111-3128

More Publications >