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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


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.


NSF: Dust contributes valuable nutrients to Sierra Nevada forest ecosystems

28 Mar 2017 - NSF Press Release: New research finding provides insight into role dust may play as ecosystems change


CZOs at AGU 2016

22 Nov 2016 - CZOs at AGU 2016: Agenda and award recipients


Living with less snow in the West: What Global Warming means for our water supplies

15 Apr 2016 - The story in The Desert Sun, shows insight into the research at SSCZO and efforts being made to understand the shift in the Sierra snowpack.


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...


“Natural Inquirer” education journal features study by Southern Sierra researchers

01 Apr 2016 - A study by Southern Sierra Critical Zone Observatory researchers was featured in a recent issue of Natural Inquirer, a middle school...


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.

Gobi Desert Dust Helps Sustain California’s Sierra Nevada

28 Mar 2017 - A team of researchers found that dust provides a much greater amount of nutrients to vegetation in the Sierra Nevada than previously thought.

Pushing the Limits on Water Isotope Measurement:  Lawrence Livermore and UC Merced

20 Dec 2016 - Lawrence Livermore and UC Merced researchers are tracking water through the critical zone using cutting-edge technology and new collection methods.

Critical Zone Q&A with researcher Adrian Harpold

19 Oct 2016 - University of Nevada Reno's Adrian Harpold reflects on his past and present time researching at Critical Zone Observatories.

Vegetation Matters: Type conversion could impact Sierra stream flow more than changing climate alone

02 Sep 2016 - This is an excerpt of a press release originally published on 30 August 2016 by James Badham, covering a new peer-reviewed article published by...

Shale Hills CZO hosts Jorden Hayes for All-Hands 2016

16 May 2016 - Jorden Hayes (Southern Sierra CZO) was an invited speaker and visitor to the Shale Hills CZO All-Hands meeting in May 2016

More News >

Example Publications


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


Influence of terrain aspect on water partitioning, vegetation structure, and vegetation greening in high elevation catchments in northern New Mexico. Zapata-Rios X., Brooks P.D., Troch P.A., McIntosh J. and Guo Q. (2016): Ecohydrology 9(5): 782-795 Cross-CZO National


Hydrological partitioning in the critical zone: Recent advances and opportunities for developing transferable understanding of water cycle dynamics. Brooks P.D., Chorover J., Fan Y., Godsey S.E., Maxwell R.M., McNamara J.P., and Tague C. (2015): Water Resources Research 51 (9): 6973-6987 Cross-CZO


Chapter 2 – The Role of Critical Zone Observatories in Critical Zone Science. White T., Brantley S., Banwart S., Chorover J., Dietrich W., Derry L., Lohse K., Anderson S., Aufdendkampe A., Bales R., Kumar P., Richter D., McDowell B. (2015): Developments in Earth Surface Processes 19: 15–78 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 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 Discussions Cross-CZO National

Dust outpaces bedrock in nutrient supply to montane forest ecosystems. Aciego, S.M.; Riebe, C.S.; Hart, S.C.; Blakowski, M.A.; Carey, C.J.; Aarons, S.M.; Dove, N.C.; Botthoff, J.K.; Sims, K.W.; Aronson, E.L. (2017): Nature Communications

The impact of wildfire on baseflow recession rates in California. Bart, R.L.; Tague, C. (2017): Hydrological Processes

Using Scientist-Teacher Partnerships to Create Student-Driven Environmental Field Research Experiences in Primary and Secondary Education Classrooms. Gilmore, M., Stacy, E.., Meadows, M. and Sullivan, L. (2016): The Earth Scientist XXXII, no. 3 (Fall 2016): 28–32 Cross-CZO National

Characterizing Runoff and Water Yield for Headwater Catchments in the Southern Sierra Nevada. Safeeq, M., Hunsaker, C. (2016): Journal of the American Water Resources Association

Effects of Model Spatial Resolution on Ecohydrologic Predictions and Their Sensitivity to Inter-Annual Climate Variability. Son, K., Tague, C., Hunsaker C. (2016): Hillslope and Watershed Hydrology

More Publications >