Research Project: Understanding Ecological, Hydrological, and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

2022 Annual Report

Objectives
Objective 1. Quantify the magnitude and variability of the water balance components in semiarid landscapes and identify their controlling processes. 1.A: As an LTAR observatory, continue to collect and curate WGEW datasets including precipitation, runoff, sediment, pond runoff and sediment, meteorology, soil moisture, fluxes, vegetation, spatial datasets, and make datasets available under FAIR principles. 1.B: Quantify intra-storm variation in stable isotope values of precipitation over WGEW and identify relative influence of moisture source, season, local weather and sub-cloud processes. 1.C: Track daily watershed water balance components for rangeland ecosystems in the WGEW and SRER for improved assessment of water status and associated productivity. 1.D: Incorporate a variety of enhancements into watershed and erosion models maintained by the SWRC to add additional sub-processes, reduce predictive uncertainty, make them easier to use, enhance integration with land management agency workflows, and expand their use geographically. Objective 2: As part of the Long-Term Agroecosystem Research (LTAR) network, characterize and quantify impacts of water and agriculture/water management on semiarid watershed and agroecosystem processes. 2.A: Assess how novel remote sensing tools and low-cost, automated optical imagery can be used to quantify evapotranspiration and vegetation carbon uptake in water-limited regions. 2.B: Improve large-scale mapping of rangeland vegetation cover, lifeform, and biomass to classify rangeland ecological sites and states. 2.C: Quantify the long-term variability of riparian woodland evapotranspiration and CO2 exchange and their controls. 2.D: Assess impacts of altered temporal rainfall regime on semiarid grassland water and carbon cycling processes. Objective 3: Quantify and predict effects of climatic change, plant community transitions, and conservation practices on ecological, hydrological, and erosion processes. 3.A: Develop new conceptual and quantitative frameworks to assess the impacts of brush management on ecosystem structure and function and enhanced delivery of ecosystem services. 3.B: Assess impacts of climate change, wildfire, and vegetation management on hydrology and erosion processes across spatial scales within the rangeland-dry forest continuum. Two Goals are included for this Sub-objective. 3.C: Conduct field-based experiments on southwestern U.S. rangelands to assess the impact of woodland encroachment/infilling and tree removal conservation practices on vegetation, surface soils, and hydrology and erosion processes. 3.D: Evaluate the hydrologic, geomorphic, and ecologic impacts of failed soil and water conservation structures in Southwest rangelands. 3.E: Quantify how weather variability and potential changes in climate impact ecosystem net and gross carbon uptake in the water-limited Southwest. 3.F: Quantify how snowmelt amount and timing are impacted by vegetation structure under changing climate, wildfire, and vegetation management in the semiarid interior western U.S. 3.G: Estimate runoff and erosion risks over western U.S. rangelands.

Approach
Objective 1. A. Collect and make available Walnut Gulch Experimental Watershed (WGEW) datasets including precipitation, runoff, sediment, pond runoff and sediment, meteorology, soil moisture, fluxes, vegetation, spatial datasets. B. Quality-control and collate precipitation samples during summer rainfall events using a custom autosampler. C. Make measurements of precipitation, soil water content, runoff and evapotranspiration in the headwater watersheds of the WGEW and Santa Rita Experimental Range from the SECA network to track daily water balance components. D. Add functionality to existing runoff and erosion models to improve the applicability and ease of use for watershed management and assessments. Objective 2. A. Evaluate novel remote sensing spectral tools across the gradients of spatial and temporal dryland measurements. B. Use field measurements of cover, biomass and lifeform along with remotely sensed data to classify states on ecological sites. Structure from Motion will be used to estimate the distribution of cover and biomass by lifeform using machine learning (ML) and estimate erosion and runoff model parameters within the common site/state combinations. C. Use eddy covariance flux data from a riparian woodland site to better understand what controls annual ET and productivity. D. Utilize the Rainfall Manipulation facility in the SRER to fully control precipitation (using rainout shelters and irrigations) over hydrologically isolated plots with equal mixtures of multiple semiarid grassland plants and initiate hydroclimate disturbance treatments. Objective 3. A. Test for impacts on measured runoff after brush management treatments and demonstrate Rangeland Hydrology and Erosion Model (RHEM) capability to accurately simulate runoff and erosion processes for tree canopy and intercanopy areas on untreated and treated sites. B. Conduct a series of field studies quantifying impacts of fire on vegetation, ground cover, soil water repellency, infiltration, and runoff and erosion processes, and evaluate climatic and vegetation controls on surface water supplies using daily streamflow records in watersheds of the Colorado River Basin. C. Use artificial rainfall simulation and overland flow experiments to quantify infiltration, runoff, rainsplash, and erosion on tree-encroached sagebrush with tree-removal practices. D. Quantify the impacts of failed conservation structures using LiDAR data, aerial photographs, and satellite imagery. E. Use water and carbon flux data to better understand ecosystem responses to short and long term climate variability and improve models. F. Combine various datasets to quantify how snowmelt amount and timing are impacted by vegetation structure. G. Employ ML methods complemented by auxiliary data to develop relationships to field-collected variables from monitoring locations across the West and determine if ML techniques can predict RHEM parameters and runoff and erosion predictions directly.

Progress Report
Under Sub-objective 1A, data collection on Walnut Gulch continued and various hydrological datasets were compiled, quality checked, and made available to the public. Additionally, five new tools based on physical principles of watershed response to rainfall events were developed and applied to the rainfall-runoff records of the Walnut Gulch Experimental Watershed (WGEW) that have been collected since 1953. The new tools identified 13% of the days with rainfall and 7% of the runoff events sampled had errors. Omitting these events improved the quality and reliability of the WGEW dataset for hydrologic modeling and analyses. The revised database has been reloaded into the Unit’s web site. As other observations from the WGEW (meteorology, soil moisture, etc.) underwent quality assurance/quality control (QA/QC) procedures, the data was uploaded to the Unit’s web site and the Long-Term Agroecosystem Research (LTAR) databases. Under Sub-objective 1B, scripts were developed to summarize isotopic values of precipitation and associate them with meteorological conditions and moisture sources. Under Sub-objective 1C, scripts were developed for computing and plotting watershed water balances variables. New webpages were developed in collaboration with the University of Arizona for posting these figures on the new Santa Rita Experimental Range webpages and for a Unit newsletter that is distributed to ranching stakeholders on WGEW. Under Sub-objective 1D, substantial progress has been made on incorporating improvements to the watershed hydrologic modeling tools. A snow module was completed for Rangeland Hydrology and Erosion Model (i.e., RHEM-Snow) that passed outputs into the KINEROS2 (K2) watershed model. The snow module requires hillslope elevation, aspect, and slope. The Automated Geospatial Watershed Assessment (AGWA) model was modified output these data to RHEM-Snow. RHEM-Snow was tested in data-rich locations in Arizona, New Mexico, Utah, Idaho, Colorado, and Wyoming. In the coming year RHEM-Snow will more fully integrated within K2 to speed execution. The second task under this sub-objective was successfully accomplished for the continents of Africa and portions of South America. With climate generator (CLIGEN) parameters defined, and their uncertainty, for these data sparse regions, a variety of watershed modeling tasks (e.g., flood prediction, erosion risk, etc.) can be conducted with much greater confidence. Also, with our LTAR partner sites (R.J. Cook Agronomy Farm), we have identified data sets suitable for testing the model's ability to track and predict carbon and nitrogen. For Sub-objective 2A, spectrometers, thermal cameras, phenocams, and global positioning system (GPS) receivers have been deployed at the Bigelow and Kendall sites to understand how novel remote sensing techniques can capture various ecosystem processes like photosynthetic activity, photosynthetic capacity, and evapotranspiration. Furthermore, at the RainMan global change experimental facility, we have deployed spectrometers, red, green, blue (RGB) cameras, and thermal cameras to assess photosynthesis, evapotranspiration, and plant access to soil moisture. Under Sub-objective 2B, to develop a map of ecological states on the Santa Rita Experimental Range, we conducted a ground survey of over 70 transects and a drone survey of almost 200 hectares with remotely sensed data to distinguish between two states based on the amount of bare soil and how connected the bare soil areas are. The Largest Patch Index proved superior to mean fetch and bare ground, and the 10 m Sentinel-2 data was better than 30 m Landsat or 3-m Planetscope imagery. For Sub-objective 2C, a new post-doctoral scientist will analyze the 20-year Charleston Mesquite Woodland data to understand what controls the interannual variability of land-atmosphere carbon dioxide and water fluxes. Also, data from this site was quality checked and submitted to AmeriFlux for data archiving and sharing. For Sub-objective 2D at RainMan, we introduced winter rainfall manipulations to cross with existing (since 2020) summer rainfall manipulations. We made regular measures of plant community composition, plant traits, ecosystem exchanges of carbon dioxide and water, soil moisture, and spectral traits. For Sub-objective 3A, a prototype web interface with annual brush cover estimates from 2000-2021 for Major Land Resource Areas 65, 71, 73, and 69 in Nebraska, Kansas, and Colorado that we developed is being evaluated by range managers and other stakeholders. For Sub-objective 3A, Goal 3.A.ii, experimental plot data from the Sagebrush Steppe Treatment Evaluation Project (SageSTEP) Hydrology Study were compiled and used to develop Rangeland Hydrology Erosion Model (RHEM) runs and to evaluate RHEM predictions of measured runoff and erosion responses from rainfall simulation plots on woodland-encroached sagebrush sites. Further, hillslope-scale plot data were used to evaluate RHEM frameworks for modeling runoff and erosion in untreated and treated woodlands. Results from the plot- and hillslope-scale model study were utilized to publish RHEM frameworks assessing impacts of woodland encroachment and tree removal treatments on woodland-encroached sagebrush rangelands. In support of Sub-objective 3B, Goal 3.B.i, vegetation, ground cover, infiltration, and soil water repellency data collected in the Pinaleños Mountains Hydrology Study were compiled and analyzed. Additionally, multiple unburned and burned forested sites were sampled in Santa Catalina Mountains, consistent with methodologies in the Pinaleños Mountains Hydrology Study. Data collected in the Santa Catalina Mountains Hydrology Study were compiled for future analyses. Under Goal 3.B.ii, we conducted a literature review to determine the knowledge gaps specifically related to lower and warmer watersheds having ephemeral snowpacks and multiple snowmelts per winter with higher and colder watersheds having a single snowmelt period. This allowed us to contrast the streamflow response to wildfire at lower/warmer vs. higher/colder watersheds in the Salt River Basin, Arizona. For Sub-objective 3C, research sites were established on Grand Staircase Escalante National Monument in Utah. Rainfall simulation and overland flow experiments were conducted at untreated sagebrush and woodland sites and included sampling vegetation, ground cover, soil crusts, and soil physical attributes. For Sub-objective 3D, we developed a geospatial information system-based schema for managing, documenting, and displaying spatial-distributed rangeland soil and water conservation structures. A post-doctoral research scientist was hired to assist with developing automated methods for identifying soil and water conservation structures in high resolution digital elevation models that are derived from aerial lidar data. Algorithm development and testing is being implemented in Cochise County, Arizona. For Sub-objective 3E, micrometeorological data collection continued for the Semiarid ECohydrological Array (SECA) sites. Site data was quality-checked twice yearly and submitted to the AmeriFlux network where the dataset was published and made publicly available. Progress was also made on several studies looking at the 2020 extreme southwestern United States drought using the SECA dataset together with other datasets either collected in-situ at the sites or remotely via satellites. Furthermore, SECA data was used to evaluate earth-system model performance to understand how model structure and model parameterization impacts the agreement between model predictions and the site flux data. Under Sub-objective 3.F, analysis of Snowtography and SNOTEL datasets of snowpack, temperature, and soil moisture was completed. As well, an algorithm was developed to estimate whether precipitation at a snow station is rain or snowfall, and whether winter rain is absorbed by existing snowpack. We developed an algorithm using Snowtography to quantify daily water inputs to soils and quantified how forest cover regulates the amount and timing of snowmelt water inputs at both high/cold and low/warm sites. For Sub-objective 3G, RHEM was used to estimate runoff and erosion at nearly 60,000 National Resources Inventory (NRI) and Assessment, Inventory, and Monitoring (AIM) locations by the Natural Resources and Conservation Service and the Bureau of Land Management, respectively. Auxiliary remote sensing, climate, and soils data have been collected and collated with observations made in the field at all the NRI and AIM sampling locations. Promising results have been obtained using the NRI, AIM, and auxiliary data using Machine Learning to replicate the RHEM results in a fraction of the time required by the RHEM model.

Accomplishments
1. Climate warming in the western United States is amplifying drought impacts on agroecosystems. Droughts are among our costliest and deadliest natural disasters. Human-caused warming enhances the severity of drought and its impacts on ecosystems both by quickening soil drying and through plant responses to warming-enhanced atmospheric dryness. ARS researchers in at Tucson, Arizona, in collaboration with university researchers, examined the 2020 southwestern U.S. drought. During the summer and autumn of 2020, much of the U.S. Southwest experienced its hottest and driest conditions since the late 1800s, resulting in large reductions in plant photosynthesis across the region (enough to feed approximately 50 million cattle for a month across shrublands and grasslands alone). Importantly, exceptionally high heat and atmospheric dryness, both largely the result of recent warming, drove much of this reduction in productivity, suggesting amplified impacts of drought on Earth’s ecosystems in a hotter future world.

2. The Rangeland Hydrology and Erosion Model effectively predicts benefits of conservation practices on pinyon-juniper woodlands. Land managers throughout the western United States are challenged with effective application and assessment of tree removal conservation practices to mitigate ecohydrologic impacts of woodland encroachment on sagebrush rangelands. A primary challenge is forecasting the hydrologic and erosion benefits of potential treatments without expensive and laborious hydrologic field studies. ARS researchers in Tucson, Arizona, used data from rainfall simulation studies to evaluate Rangeland Hydrology and Erosion Model performance in predicting hillslope runoff and erosion responses on woodland-encroached sagebrush sites before and nine years after tree removal. RHEM effectively predicted measured hydrologic and erosion responses for untreated woodlands and for treated conditions following tree removal by fire, cutting, and shredding treatments. Results from the model testing yielded multiple RHEM frameworks for applying the model to diverse woodlands conditions. This study is the first published direct assessment of RHEM application to woodlands and provides land managers valuable insight for applying RHEM in assessment of hydrologic vulnerability and erosion potential and targeting effective conservation practices for diverse woodland scenarios.

3. State-of-the-art land surface models underestimate carbon cycling in the semiarid southwestern United States. Recent studies have shown that arid regions are an important component of the global carbon cycle. However, unlike wetter regions, the state-of-the-art land surface models used in these studies have not yet been extensively evaluated for arid regions. ARS scientists in Tucson, Arizona, along with university researchers, addressed this gap by comparing 14 models against data from 12 arid monitoring sites in the southwestern United States, encompassing a range of climate and vegetation (forest, shrub- and grassland). Models underestimate both the average carbon uptake and release as well as the annual change in these quantities, suggesting that these regions may play an even more important role in the global carbon cycle than previously thought. Discrepancies are explained by the models’ muted response of photosynthesis to soil moisture - particularly in the spring for high elevation forested sites, and during the monsoon for low elevation desert shrub and grass sites. A range of hypotheses related to plant physiology and phenology for why model photosynthesis does not respond sufficiently to soil moisture are offered to serve as a guide for future model developments.

4. Forest thinning to reduce wildfire risk reduced soil moisture stress for remaining trees. Western forests are a critical source of water supply, and they face increasing pressure from climate change, which increases their susceptibility to die-off from drought, fire, and insect infestation. Tree stress depends largely on the depth, duration and intensity of soil moisture stress. ARS scientists in Tucson, Arizona, collaborated with university partners to measure soil moisture stress in the root zone of a ponderosa pine forest for two years following a range of thinning treatments and compared this against an unthinned control stand. Forest thinning was effective at reducing soil moisture stress for the remaining trees. Post-thinning stands with taller trees experienced less stress than stands with shorter trees, possibly due to different water use or to the effects of short trees in reducing snow accumulation. Collectively, our results demonstrate new ways to assess objectively, the impacts of forest thinning on the health of remaining trees.

5. Timing influences the sensitivity of a semiarid grassland to drought. The impacts of short-term “pulse” droughts lasting several days to weeks are generally negative for grassland ecosystems. However, we lack specific information about how the impacts of drought vary with the timing of the drought during the growing season. ARS scientists in Tucson, Arizona, collaborated with Chinese scientists working in Inner Mongolia to evaluate results of a rainfall manipulation experiment by imposing drought alternatively during early, middle, and late portions of the summer growing season in a semiarid grassland. They found that pulse drought occurring during early or mid-growing season had positive impacts on root production, while late-season drought decreased root biomass. Drought most strongly reduced carbon dioxide uptake early in the growing season. Collectively, these results suggest that plants faced with drought early in the growing season have reduced capacity to take up carbon through photosynthesis, but they are able to respond to the challenging environment by producing more roots.

6. Valuation of riparian ecosystem services developed and compared for the San Pedro and Middle Rio Grande. Creating measurable ecological accounting units has become a point of emphasis in valuing ecosystem services. Understanding which ecological endpoints, emanating from biophysical production functions, are important to individuals could help to create measurable ecological accounting units. ARS scientists in Tucson, Arizona, and others created ecological endpoints for the semi-arid riparian ecosystems of Upper San Pedro River in Arizona and Middle Rio Grande River in New Mexico. Benefit transfer techniques were used to compare their ability to be transferred to similar riparian ecosystems. If clearly defined, ecological accounting units can be developed for comparable ecosystem services. This could lead to ecosystem services being properly incorporated into benefit cost analyses that maximize economic product of both market and nonmarket goods and services.

7. Streamflow response to wildfire differs with season and elevation in the Lower Colorado River Basin. In the western United States, wildfires are impacting the forested mountains important to agricultural and urban water supply. While peak streamflow and soil erosion often increase immediately after fires, it is unknown whether water supplies are altered over multiple years. ARS scientists in Tucson, Arizona, quantified streamflow in eight watersheds within Arizona’s Salt River basin during 15 years following two of the largest fires in the modern history of the western United States. Four independent methods suggested that streamflow declined or remained the same. Dominant winter/spring streamflow was unchanged in higher/colder headwaters but decreased in lower/warmer headwaters. Summer flows increased in two of the most heavily burned watersheds. With greater than 80% of the annual streamflow generated during winter, winter response to vegetation change dominates annual response. They demonstrate the importance of separately analyzing wet and dry years to detect wildfire impacts on hydrology in the 21st century, which has been warmer and drier than most of the pre-fire record. Climatological asynchrony of snowmelt and transpiration in warmer, lower-elevation or lower-latitude watersheds may reduce streamflow benefits of fire.

8. Precipitation repackaging into fewer, larger storms delayed seasonal timing of peak production in a semiarid grassland. Against a backdrop of rising temperature, large portions of the western United States are experiencing fewer, larger, and less frequent rainstorms. We do not know how this intensification of rainfall patterns will affect the amount and timing of photosynthesis by drylands plants, but this is important for decisions made in ranching, land management and carbon cycle science. ARS scientists in Tucson, Arizona, with university collaborators, conducted a field experiment that excluded natural rainfall and replaced it with irrigation in fewer, larger simulated rainstorms, while keeping the total amount the same over the summer growing season. They found that repackaging rainfall into a few, large storms delayed the timing of peak plant photosynthesis up to one month. Meanwhile, the magnitude of greatest weekly photosynthesis was not affected. Future management decisions should consider the delay in peak productivity shown here for optimal use and timing of grassland resources.

9. Vegetation diversity following shrub removal enhanced the carbon uptake and water use efficiency of a rangeland savanna, especially during the dry season. Vegetation in dryland agroecosystems is undergoing rapid change due to human management and climate change. Therefore, it is critical to know how vegetation change alters the water and carbon cycling in drylands. Here, ARS scientists in Tucson, Arizona, collaborated with academic partners in Mexico to analyze records of water and carbon exchanges between the atmosphere and two adjacent sites in the Sonoran Desert: one was a native shrubland, and the other had been transformed into a shrub-grass savanna through shrub removal several decades prior. They found the two sites functioned similarly during the rain summer season, but that the more diverse vegetation in the savanna allowed this site to take up more carbon and use water more efficiently during the relatively dry winter season. The savanna was always a net sink of atmospheric carbon dioxide, while the shrubland was sometimes a sink and sometimes a source. These results show how vegetation management can enhance ecosystem water use and productivity.

10. Improved methods to accomplish quality assurance and quality control (QA/QC) for ARS experimental watershed observations. Long-term records of rainfall and runoff are crucial to understanding hydrologic processes within a watershed or landscape and predicting how these interactions will respond to future climatic, land use, and biophysical changes. The semi-arid USDA-ARS Walnut Gulch Experimental Watershed (WGEW) in Arizona has measured rainfall and runoff since 1953. Despite several improvements in data collection and storage over the years, undetected errors still exist within these datasets. To identify these errors and inconsistencies, ARS researchers in Tucson, Arizona, utilized five different hydrologic methods to develop a suite of quality control tools. These semi-automated data quality checking tools were applied in WGEW to improve the quality of the dataset. The implementation of the methods described in this work uncovered several previously undetected errors, providing researchers with more accurate data and means for improved hydrologic analyses and model predictions.

11. Rangeland milkweed plants provide critical habitat in the lifecycle of the monarch butterfly. The distribution and condition of milkweed communities in North America is a key concern of ecologists and land managers due to downward population trends in monarch butterflies. Yet, there have been no recent extensive regional or national assessments of milkweed conditions in the United States. Researchers from the Natural Resources Conservation Service (NRCS, Fort Worth, Texas), ARS (Tucson, Arizona), and Iowa State University (Ames, Iowa) used the NRCS National Resource Inventory rangeland dataset to evaluate the distribution, density, and condition of milkweeds and associated habitats and environmental conditions on non-federal western U.S. rangelands. The study documents the previously unknown extent of milkweed availability and associated changes in trends in ecosystem health throughout the western United States. The findings provide a valuable reference for future assessments of milkweed population trends and pollinator habitat in the western United States and offer guidance in recovery efforts for the monarch butterfly regarding milkweed availability and habitat requirements.

Review Publications
Novick, K., Ficklin, D., Baldocchi, D., Davis, K., Ghezzehei, T., Konings, A., MacBean, N., Raoult, N., Scott, R.L., Shi, Y., Sulman, B., Wood, J. 2022. Confronting the water potential information gap. Nature Geoscience. 15(3):158-164. https://doi.org/10.1038/s41561-022-00909-2.
Williams, C.J., Nouwakpo, S.K. 2022. Introduction to the special issue “Ecohydrologic feedbacks between vegetation, soil, and climate”. Water. 14(5). Article 760. https://doi.org/10.3390/w14050760.
Spaeth Jr., K., Barbour, P., Moranz, R., Dinsmore, S., Williams, C.J. 2022. Asclepias dynamics on US rangelands: Implications for conservation of monarch butterflies and other insects. Ecosphere. 13(1). Article e03816. https://doi.org/10.1002/ecs2.3816.
Al-Hamdan, O.Z., Pierson Jr., F.B., Robichaud, P., Elliot, W.J., Williams, C.J. 2022. New erodibility parameterization for applying WEPP on rangelands using ERMiT. American Society of Agricultural and Biological Engineers. 65(2):251-264. https://doi.org/10.13031/ja.14564.
Williams, C.J., Pierson Jr., F.B., Al-Hamdan, O., Nouwakpo, S.K., Johnson, J.C., Polyakov, V.O., Kormos, P., Shaff, S., Spaeth, K. 2022. Assessing runoff and erosion on woodland-encroached sagebrush steppe using the Rangeland Hydrology and Erosion Model. Ecosphere. 13(6). Article e4145. https://doi.org/10.1002/ecs2.4145.
Dannenberg, M., Yan, D., Barnes, M., Smith, W., Johnston, M., Scott, R.L., Biederman, J.A., Knowles, J., Wang, X., Duman, T., Litvak, M., Kimball, J., Williams, A., Zhang, Y. 2022. Exceptional heat and atmospheric dryness amplified losses of primary production during the 2020 U.S. Southwest hot drought. Global Change Biology. 28(16):4794-4806. https://doi.org/10.1111/gcb.16214.
Young, A., Friedl, M., Novick, K., Scott, R.L., Moon, M., Frolking, S., Li, X., Carrillo, C., Richardson, A. 2022. Disentangling the relative drivers of seasonal evapotranspiration across a continental-scale aridity gradient. Journal of Geophysical Research-Biogeosciences. 127(8). Article e2022JG006916. https://doi.org/10.1029/2022JG006916.
MacBean, N., Scott, R.L., Biederman, J.A., Peylin, P., Kolb, T., Litvak, M., Krishnan, P., Meyers, T., Arora, V., Bastrikov, V., Goll, D., Lombardozzi, D., Nabel, J., Pongratz, J., Sitch, S., Walker, A., Zaehle, S., Moore, D. 2021. Dynamic global vegetation models underestimate net CO2 flux mean and inter-annual variability in dryland ecosystems. Environmental Research Letters. 16(9). Article 094023. https://doi.org/10.1088/1748-9326/ac1a38.
Javadian, M., Smith, W., Lee, K., Knowles, J.F., Scott, R.L., Fisher, J., Moore, D., van Leeuwen, W., Barron-Gafford, G., Behrangi, A. 2022. Canopy temperature is regulated by ecosystem structural traits and captures the ecohydrologic dynamics of a semiarid mixed conifer forest site. Journal of Geophysical Research-Biogeosciences. 127(2). Article e2021JG006617. https://doi.org/10.1029/2021JG006617.
Zhang, X., Ma, Z., Barron-Gafford, G., Scott, R.L., Niu, G. 2022. A microbial-explicit soil organic carbon decomposition model (MESDM): development and testing at a semiarid grassland site. Journal of Advances in Modeling Earth Systems. 14(1). Article e2021MS002485. https://doi.org/10.1029/2021MS002485.
Wang, X., Biederman, J.A., Knowles, J.F., Scott, R.L., Turner, A., Dannenberg, M., Kohler, P., Frankenberg, C., Litvak, M., Flerchinger, G.N., Law, B., Kwon, H., Reed, S., Parton, W., Barron-Gafford, G., Smith, W. 2022. Satellite solar-induced chlorophyll fluorescence and near-infrared reflectance capture complementary aspects of dryland vegetation productivity dynamics. Remote Sensing of Environment. 270. Article 112858. https://doi.org/10.1016/j.rse.2021.112858.
Biederman, J.A., Robles, M., Scott, R.L., Knowles, J. 2022. Streamflow response to wildfire differs with season and elevation in adjacent headwaters of the Lower Colorado River Basin. Water Resources Research. 58(3). Article e2021WR030687. https://doi.org/10.1029/2021WR030687.