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

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 -->

Conduct research at our CZO -->


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


CZOs at AGU 2018

19 Nov 2018 - The 2018 AGU Fall Meeting will be held December 10-14 in Washington, D.C.


Multiple postdoc and grad student opportunities at UC Merced

12 Sep 2018 - Two postdoctoral scholar positions and multiple MS or PhD research assistantships are currently available at the University of California, Merced....


NSF News Release: Billions of gallons of water saved by thinning forests

11 May 2018 - Too many trees in Sierra Nevada forests stress water supplies, scientists say


NSF Discovery articles focus on the CZOs.

10 May 2018 - The Discoveries section of the National Science Foundation's website on Critical Zone Observatories (CZOs).


NSF Discovery: On World Water Day, scientists study spawning salmon through a riverbed lens

22 Mar 2018 - NSF Southern Sierra CZO researchers peer into North America’s West Coast salmon rivers


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.


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.


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


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: Morgan Barnes

14 Nov 2018 - Say 'Hello!' to biogeochemist Morgan Barnes! Morgan specializes in the study of soil nutrient biogeochemistry, focusing on phosphorus in the Sierras

Congratulations Jill Marshall on receiving the 2018 Luna B. Leopold Young Scientist Award

06 Nov 2018 - Marshall Receives 2018 Luna B. Leopold Young Scientist Award

Researcher Spotlight: Jeff Lauder

24 Oct 2018 - Meet forest ecologist Jeff Lauder! Lauder's research focuses on Sierra Nevada Conifers and how they have been responding to stress during drought!

Research Program Update: September 2018

07 Sep 2018 - Recent activities and findings, funding opportunities, upcoming events, and other updates

Research Program Update: July 2018

17 Jul 2018 - Recent activities and findings, funding opportunities, upcoming events, and other updates

More News >

Example Publications


Mercury sourcing and sequestration in weathering profiles at six Critical Zone Observatories. Richardson, Justin B., Arnulfo A. Aguirre, Heather L. Buss, A. Toby O'Geen, Xin Gu, Daniella M. Rempe, and Daniel deB. Richter (2018): Global Biogeochemical Cycles, doi: 10.1029/2018GB005974 Cross-CZO National


Ideas and perspectives: Strengthening the biogeosciences in environmental research networks. Richter, D.D., S.A. Billings, P.M. Groffman, E.F. Kelly, K.A. Lohse, W.H. McDowell, T.S. White, S. Anderson, D.D. Baldocchi, S. Banwart, S. Brantley, J.J. Braun, Z.S. Brecheisen, C.W. Cook, H.E. Hartnett, S.E. Hobbie, J. Gaillardet, E. Jobbagy, H.F. Jungkunst, C.E. Kazanski, J. Krishnaswamy, D. Markewitz, K. O’Neill, C.S. Riebe, P. Schroeder, C. Siebe, W.L. Silver, A. Thompson, A. Verhoef, G. Zhang (2018): Biogeosciences 15: 4815-4832 Cross-CZO National


Controls on Soil Organic Carbon Partitioning and Stabilization in the California Sierra Nevada. Rasmussen C., Throckmorton H., Liles G., Heckman K., Meding S., and Horwath W.R. (2018): Soil Systems 2(3): 41 Cross-CZO


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 137(3): 297–306 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

Interdisciplinary Teaching about Earth and the Environment for a Sustainable Future Book Chapter: Implementing and Assessing InTeGrate Critical Zone Science Materials in an Undergraduate Geoscience Program. Ashlee Dere, Carol Engelmann, Timothy White, Adam Wymore, Adam Hoffman, James Washburne, Martha Conklin (2018): Springer Cross-CZO National

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

More Publications >