Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

2019 Annual Report

Objectives
1:As part of the LTAR network, and in concert with similar long-term, land-based research infrastructure in the region, use the Walnut Gulch LTAR site to improve the observational capabilities and data accessibility of the LTAR network and support research to sustain or enhance agricultural production and environmental quality in agroecosystems characteristic of the semiarid Southwest region. Research and data collection are planned and implemented based on the LTAR site application and in accordance with the responsibilities outlined in the LTAR Shared Research Strategy, a living document that serves as a roadmap for LTAR implementation. Participation in the LTAR network includes research and data management in support of the ARS GRACEnet and/or Livestock GRACEnet projects. 1.1:Improve & continue long-term measurements & analysis of water budgets on WGEW & Santa Rita Experimental Range (SRER) watersheds. 1.2:Expand variables measured on WGEW & SRER watersheds based on recommendations of the LTAR Meteorology, Hydrology, CO2, Non-CO2 Gas, Soil, Biology, & Wind Erosion Committees. 1.3:Develop a long-term monitoring program. 1.4:Implement an experiment on the SRER watersheds to quantify the effects of brush management on a set of ecosystem services. 1.5:Compute trends in sub-daily & daily precipitation intensity across LTAR sites. 1.6:Evaluate National Weather Service dual pole radar precipitation data & its ability to improve flash flood forecasting. 2:Quantify how seasonal, annual, and decadal-scale variations in climate, plant community composition, and management impact processes controlling the cycling of water, energy, and carbon in semiarid rangelands 2.1:Determine how changes in vegetation structure & climate affect ecosystem-atmosphere water vapor & CO2 exchange using long-term flux tower observations. 2.2:Use isotopes in pond deposition sediments to understand & quantify erosion & sediment yields in semiarid landscapes as a function of ecological sites. 2.3:Quantify the impact of erosion control structures on runoff & sediment transfers in semiarid landscapes. 2.4:Estimate annual production & minimum total foliar cover using Landsat & MODIS satellite. 2.5:Develop methods to assess climate impacts on rangeland vegetation composition & production across the West. 3:Develop a new conceptual framework and corresponding experimental methods to understand and model the dynamics of semiarid upland and channel erosion processes. 3.1:Conduct experiments to quantify the effects of surface condition. 3.2:Conduct experiments to develop a remote sensing method to estimate hydraulic roughness. 4:Improve hillslope (RHEM) and AGWA/KINEROS2 watershed models and develop methods to incorporate new remotely sensed, meteorologic, & land surface information. 4.1:Complete development & post-disturbance testing of the RHEM for application in Western rangelands. 4.2:Develop a mechanism to extend the findings from the Walnut Gulch LTAR site across Arizona & New Mexico & support collaborative vegetation management of public lands to improve watershed function. 4.3:Incorporate a variety of KINEROS2 (K2) / AGWA model enhancements.

Approach
Objective 1: 1. Use co-located rain gauges to quantify uncertainties in long-term precipitation datasets. 2. Use radar stage measurements to test remote methods to measure runoff stage 3. Deploy mobile x-band Doppler radar and compare with Dual Pole radar rainfall rain-gauge observations, and runoff observations on the WGEW. 4. Meet LTAR objectives by: a) using observational datasets to quantify the individual components of the watershed water balance in Walnut Gulch Experimental Watershed WGEW), b) using satellite and ground measurements of vegetation to document changes in watershed vegetation, c) determining trends and magnitude of precipitation intensities and precipitation extremes across the continental US, and d) implementing the LTAR common experiment to assess the effects of brush management on a set of ecosystem services. Objective 2: 1. Use long-term flux tower observations to determine how changes in vegetation structure and climate affect ecosystem-atmosphere water vapor and carbon dioxide exchange. 2. Use 210Pb pond stratigraphy to determine erosion rates and their historical dynamics on small watersheds over the past 50-100 years. 3. Quantify runoff and sediment yields on watersheds to quantify the impact of erosion control structures on runoff and sediment transfers. 4. Use satellite, climate, site productivity and management data to estimate annual production and minimum total foliar cover. 5. Use LiDAR, point cloud, and new satellite datasets to construct canopy height models to assess climate impacts on rangeland vegetation composition and production. Objective 3: 1. Use rainfall simulator experiments to quantify the effects of surface condition on infiltration, runoff, concentrated flow dynamics, sediment transport processes, and surface evolution. 2. Use radar backscatter roughness and hydraulic roughness at a laboratory, rainfall simulator, and small watershed scales using airborne and satellite active radar imagery to develop a remote sensing methods to estimate hydraulic roughness. Objective 4: 1. Complete development and post-disturbance testing of the Rangeland Hydrology and Erosion Model (RHEM) for application in Western rangelands. 2. Create a web interface to identify problem areas in watersheds, compare across watersheds, and assess trends in time prior to KINEROS2 modeling. 3. Incorporate RHEM, improved process model representations, and higher-resolution, model inputs, sub-surface and variable width routing, and interstorm processes into KINEROS2.

Progress Report
Substantial progress was made on all four objectives and their sub-objectives. Under Objective 1, researchers in Tucson, Arizona, made substantial improvements in observational capabilities at the Walnut Gulch Experimental Watershed (WGEW) Long Term Agro-Ecosystem Research (LTAR) site. Related to Sub-objective 1.1, evaluation and improvement of the WGEW observational capabilities continued by assembling data from standard above-ground and pit rain gauges and use of innovative radar technology to collect and test stage flow data at flume measurement locations. Annual water balance data were assembled for grassland, shrubland and savanna watersheds and this long-term data is being used to better understand semiarid rangeland water flows as well as to compare with LTAR sites around the country. In support of Sub-objective 1.2, data from our meteorology sites and carbon dioxide (CO2) measurements are being uploaded regularly into national databases to facilitate data sharing, and a further intensive effort is underway to perform quality assurance/quality control on our historic observational database. Substantial work has been done to estimate rangeland grass cover using unmanned aerial vehicles (UAV) photo imagery, which is related to Sub-objective 1.3. Vegetation and rainfall simulation experiments were conducted within adjacent treated and untreated areas to evaluate effectiveness of herbicide application to reduce shrub cover, enhance grass cover, and limit runoff and erosion, in support of Sub-objective 1.4. Extensive reformatting and error checking was made after acquiring precipitation data from other LTAR locations to test the hypothesis of sub-daily precipitation intensification, in support of Sub-objective 1.5. In cooperation with National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Lab, we deployed their mobile ground-based X-band radar near the Walnut Gulch during the monsoon during both FY17 and FY18. In support of Sub-objective 1.6, the data is undergoing post processing and error checking. Under Objective 2, researchers in Tucson, Arizona, made substantial progress on quantifying how seasonal, annual, and decadal-scale variations in climate, plant community composition, and management impact processes controlling the cycling of water, energy, and carbon in semiarid rangelands. Accordingly, research continued on quantifying the effects of brush management on land-atmosphere water and carbon exchanges by collecting a third year of post-treatment flux tower data along with vegetation cover in control and treated areas. Research continued on riparian vegetation water use by examining effects of biocontrol on a tamarisk-invaded site and by looking at how access to groundwater affects precipitation used by the vegetation. Results were published on the long-term water balance of a brush-encroached grassland site and on the controls of soil respiration in Arizona rangelands, in support of Sub-objective 2.1. A sampling protocol was created for collecting isotope samples on semiarid land forms located on hillslopes in Arizona. The focus of this work shifted from the use of the isotopes in depositional areas to the understanding of loss rates by erosion on hillslopes. In support of Sub-objective 2.2, one hillslope has been sampled, and currently the samples are being processed with the gamma ray spectrometer. Field sites across Arizona, New Mexico, and Colorado have been identified and a database has been populated with locations of prior rangeland water and erosion control work. Several of these sites have been visited and structures have been evaluated for their structural and functional integrity. Research is ongoing to quantify the legacy impacts of these structures. In collaboration with the National Park Service’s (NPS) Vanishing Treasures Program, a field campaign utilizing USDA-ARS rainfall simulation technologies and historical rainfall data from WGEW was conducted to evaluate the effects of varying rainfall intensities and amounts on erosion of traditionally-built adobe walls, related to Sub-objective 2.3. Under the goals of Objective 2, a new research thrust was developed by an ARS scientist, who installed a new rainout shelter experiment on a semiarid rangeland ecosystem. Site investigations included vegetation and soil mapping, soil coring and analysis for texture and bulk chemistry, and topographic analysis. Site preparation included road improvements and construction of one mile of new fencing to exclude grazing. This facility will be used to test scenarios of altered amounts of winter precipitation as well as changes in the timing of summer rainfall into fewer/larger or more/smaller storm events. Responses to be measured include the competition, growth and mortality of grasses, water use, and productivity. Results from this study will help ranchers and other land managers plan stocking rates, determine grazing allotments, and predict productivity of grasslands at seasonal to decadal time scales. Finally, in support of Sub-objective 2.4, a suite of machine learning models was tested on two remotely-sensed estimates of cover and two of forage production based on Landsat for 1987-2016 across southeastern Arizona. Predictors in the models included interpolated climate inputs from PRISM, slope, aspect, years since a fire, and distance from a channel, which supports Sub-objective 2.5. Under Objective 3, researchers in Tucson, Arizona, worked on developing a new conceptual framework and corresponding experimental methods to understand and model the dynamics of semiarid upland and channel erosion processes. Accordingly, a series of rainfall events were simulated on stony plots at three slope gradients and rock cover was measured. Surface elevations were sampled by terrestrial light detection and ranging (LiDAR) at high resolutions. Calculated roughness indices included random roughness, fractal dimension and generalized fractal dimension. Data from these experiments has been analyzed and results have been drafted for publication, which supports Sub-objective 3.1. There was a delay in the development of the radar with our collaborating university to measure hydraulic roughness. This prevented the running of simulations, which has been rescheduled for next fiscal year. Existing post-processed airborne and satellite-active radar images over portions of the Walnut Gulch have been documented, which relates to Sub-objective 3.2. Under Objective 4, researchers in Tucson, Arizona, improved widely-used hillslope Rangeland Hydrology and Erosion Model (RHEM) and watershed Automated Geospatial Watershed Assessment (AGWA) models and developed methods to incorporate new remotely-sensed, meteorological, and land surface information into them. Fact sheets were developed and posted on the RHEM model website, including for post-oak savannas in central Texas and short grass prairie ecological sites in west Texas. In support of Sub-objective 4.1, examples show the user how to assess ecological site descriptions and how plant community transitions impact hydrologic function of the sites through changes in plant lifeform, plant canopy, and ground cover. Study sites were assessed and selected in New Mexico and Utah for experiments in collaboration with ongoing LTAR research on the effects of vegetation management on hydrology and erosion processes. Numerous, persistent pinyon and juniper woodlands in New Mexico were field surveyed by ARS and National Park Service staff for experimental research on the long-term effects of tree cutting on vegetation production, infiltration, and soil loss/retention. In particular, the study will provide insight on whether tree removal practices are sustainable and thus economically viable. An NPS-internal research proposal for the field experiments by ARS is being written in collaboration with NPS staff. Additional research sites have been targeted at the Grand Staircase-Escalante National Monument in collaboration with NPS staff, and an NPS-internal proposal with a full experimental design has been submitted by ARS scientists to assess the impacts of vegetation restoration practices (tree removal) on sagebrush vegetation recruitment, infiltration, runoff, and erosion processes. For the national parks, a suite of vegetation, rainfall simulation, overland flow, and soil water experiments have been proposed to improve understanding of the ecohydrologic impacts of various management practices. The proposed work includes applications of various ARS-developed hydrology and erosion models to assess and target management practices over watershed-scales and should meet the needs of a growing number of grassroots watershed management efforts across the West. This work supports Sub-objective 4.2. The assorted tasks to improve AGWA and the KINEROS2 model, except for diffusion wave routing, have been completed, related to Sub-objective 4.3.

Accomplishments
1. Intensification of growing season rainfall observed from a long-term high-density gauge network. The hypothesis that a warmer and wetter climate will result in increased precipitation intensity has typically been tested only at the daily time scale due to the lack of high-quality, long-term observations at sub-daily time scales. Quantifying precipitation intensity is critical to local, state, and federal planners as they design infrastructure to accommodate storm-induced flooding. Scientists in Tucson, Arizona, used unique long-term, high-resolution datasets from an ARS Long-Term Agro-ecosystem Research (LTAR) watershed and found that summer rainfall has become more intense since the 1970s for the southwestern U.S., meaning that similar duration storms now deliver more rainfall. As more intense storms result in more storm runoff, engineering designs to accommodate runoff like culverts and bridges may encounter larger floods and may need modification.

2. Long-term semiarid rangeland water balance. One of the most enduring and important questions for hydrology is how precipitation is partitioned among evapotranspiration, runoff, groundwater recharge, and storage of moisture in the soil. Scientists in Tucson, Arizona, measured how precipitation was partitioned at a semiarid savanna site with 13 years of data. Almost all of the precipitation goes into evapotranspiration with only a small amount of runoff and negligible recharge. Contrary to expectations, researchers saw significant, episodic carryover of soil moisture from the summer/fall growing season to the subsequent springtime when the plants awake from winter dormancy and extract the stored moisture. These comprehensive, long-term measurements support expectations about the overriding importance of evapotranspiration in semiarid watershed water budgets and reveal a surprising degree of inter-seasonal water storage.

3. Improved understanding of ecohydrologic impacts of pinyon and juniper removal in the western U.S. Private and public land managers throughout the western U.S. need science-based understanding to aid management of extensive pinyon and juniper woodlands. Considerable research has been completed on the ecohydrologic impacts of pinyon and juniper reductions; however, no broad synthesis of the literature has been compiled to date. ARS scientists in Tucson, Arizona, Reno, Nevada, and Boise, Idaho, reviewed nearly 300 scientific publications to assess the ecohydrologic impacts of pinyon and juniper tree reductions across plot to watershed scales, short- and long-term periods, and regional climatic gradients. The synthesis found that plot- to watershed-scale ecohydrologic and erosion impacts of tree reduction (by management or natural events) on pinyon and juniper woodlands depend on: (1) the degree to which tree removal alters vegetation and ground cover structure, (2) initial conditions, and (3) inherent site attributes. The literature is inconclusive regarding tree reduction impacts on watershed-scale changes in groundwater and streamflow. The synthesis provides guidance to help land managers analyze the potential ecohydrologic impacts of both climatic- and human-driven changes to woodland landscapes and identifies key knowledge gaps.

4. Improved snow water equivalent maps with machine learning of snow survey and laser snow depth measurements. Knowing the quantity of water in the snowpack, known as the snow water equivalent (SWE), is critical for water supply forecasts and management of rivers and streams for water delivery and hydropower, as most western surface water originates from mountain snowmelt. Scientists from the University of Arizona and the ARS in Tucson, Arizona, developed a new method to estimate SWE by combining aerial remote sensing maps of snow depth with snow density maps generated through machine learning of hundreds of field measurements of snow density. The study found that snow density can vary by as much 75%, highlighting the importance of considering the spatial variability when estimating SWE. In addition, spatially variable maps of snow density can impact watershed-scale SWE estimation up to 20% as compared to using snow density measurements from commonly used snow monitoring stations. The new method will improve SWE estimates for water supply monitoring, evaluating snow models, and understanding how changing mountain forests might impact SWE.

5. Soil losses from small rangeland plots under simulated rainfall and run-on conditions. Understanding the mechanisms of detachment by raindrops and surface runoff is needed to predict and mitigate soil erosion. Researchers in Tucson, Arizona, conducted an experiment using simulated rainfall on 56 small natural plots located on 7 arid rangeland sites in Arizona, U.S. Sediment yield was best predicted by flow discharge for both rainfall and surface runoff treatments. Rainfall erosion generated 2 to 44 times more sediment than runoff alone at the same discharge rate. Among 19 variables related to surface conditions, a weak correlation was found between sediment yield and plant foliar cover, structure, and surface litter; however, there was no single best cover predictor common for all ecological sites tested. This study aids in the ability to construct erosion models for rangeland soils.

6. Evolution of rock cover, surface roughness, and flow velocity on stony soil under rainfall. Soil surface roughness (SSR), typically a result of rock fragments accumulating as the result of preferential erosion of fine materials, is an important factor influencing water erosion processes. ARS scientists in Tucson, Arizona, simulated a series of rainfall events on a stony plot (2 × 6.1 meters) at three slope gradients (5%, 12%, and 20%) and rock cover was measured. Surface elevations were sampled by terrestrial light detection and ranging (LiDAR) at high resolutions. Calculated roughness indices included random roughness (RR), fractal dimension and generalized fractal dimension. Results showed: 1) SSR increased as the rainfall simulation proceeded; 2) the steeper slope developed greater surface roughness; and 3) both the increase of surficial exposed rocks and the formation of rills contributed to the variations of SSR. These results improve scientists' understanding of the evolution of semiarid stony hillslopes, and improve their ability to construct erosion models for rangeland soils.

7. Environmental and vegetative controls on soil carbon dioxide efflux in three semiarid ecosystems. Soil carbon dioxide emissions are due to belowground plant and microbial respiration and biogeochemical processes, and they are a major component of the total amount of carbon moving from the land to the atmosphere. Increased understanding of the processes underlying these natural emissions in globally expansive semiarid ecosystems is necessary to reduce uncertainty in the earth’s carbon budget and feedbacks to climatic change. Researchers in Tucson, Arizona, combined field measurements with statistical models to investigate how soil temperature, soil moisture, and photosynthesis control emissions in three semiarid ecosystems with similar climate but with different vegetation. Results indicate that the combination of soil moisture, soil temperature and photosynthesis are required to appropriately account for the spatial and temporal behavior in emissions. Accounting for the interactive effects of the three drivers on carbon dioxide emissions, typically not accounted for in current models, will be important to determine the response of extensive semiarid lands to changes in climate and land cover.

8. Hydrologic and geomorphic process response to check dams. Rock structures in small channels, known as check dams, are a common practice used in rangeland restoration projects; however, there is little documented information on their efficacy. ARS scientists in Tucson, Arizona, measured the hydrologic and geomorphic response to check dams in southern Arizona since 2008. The installation of check dams have produced mixed results with some leading to less runoff and erosion and others resulting in land degradation. In addition, over time, check dams may create new concentrated flow paths and incision that will result in enhanced rangeland degradation. Watershed restoration must address both channel and upland degradation.

9. Semiarid agro-ecosystem response to timing of heavy rainfall events. Heavy rainfall events are an aspect of climate change that has been observed and is expected to become more important in the future, but we don’t understand how heavy rainfall impacts semiarid agroecosystems. Scientists in Inner Mongolia, China, and Tucson, Arizona, conducted experiments using rainfall shelters and hand watering of a semiarid grassland to test the effects of a heavy rainfall event applied at different times of the growing season. Impacts were not immediately apparent, because above-ground plant productivity was not affected by the heavy rainfall. However, root production was inhibited by heavy rainfall when applied late in the growing season. These results suggest that if plants respond to heavy rainfall by reducing their root production, they may be more susceptible to future drought periods.

10. Cooperative Observer Network (COOP) for evaluation of precipitation extremes at daily time scales the LTAR network. The national Cooperative Observer Network (COOP) weather observer network is run by volunteers who report daily precipitation and temperature, but do not record these observations at a consistent time across the county. The COOP network is widely used by climatologists and scientists to understand the climate across the country and to detect trends in extreme events as they relate to climate change. The LTAR network of precipitation gauges is professionally operated and was used as an extra layer of quality control to evaluate the COOP network. Scientists in Tucson, Arizona, showed consistency between the COOP and Long Term Agro-ecosystem Research (LTAR) networks when precipitation extremes are analyzed. Despite discrepancies at the daily time step, the extreme precipitation observed by COOP rain gauges can be reliably used to characterize changes in the hydrologic cycle due to natural and human causes.

11. Improving the United Kingdom’s Meteorological Office weather forecasts. The United Kingdom’s Meteorological (Met) Office makes routine regional and global weather forecasts, but the computer models have substantial errors in surface temperature, particularly over arid regions, which causes errors in their weather forecasts. To investigate these errors and improve the weather model forecasts, researchers from the ARS in Tucson, Arizona, and the Met Office, conducted an experimental campaign using ground, airborne and satellite measurements at the Walnut Gulch Experimental Watershed. The model temperatures were confirmed to be too cold with respect to the ground-based temperatures, and this bias was related to the model bare soil fractions that are too low and not adequately simulating the patchy, shrub-covered landscapes found in many arid lands. Improving the model representation of vegetation and soil demonstrated better simulation of the surface temperatures and moistures, which will improve European weather forecasts.

Review Publications
Williams, C.J., Pierson, F.B., Kormos, P.R., Al-Hamdan, O., Nouwakpo, S., Weltz, M.A. 2019. Vegetation, hydrologic, and erosion responses of sagebrush steppe 9 yr following mechanical tree removal. Rangeland Ecology and Management. 72(1):47-68. https://doi.org/10.1016/j.rama.2018.07.004.
Wang, W., Yin, S., Xie, Y., Nearing, M.A. 2019. Minimum inter-event times for rainfall in the Eastern region of China. Transactions of the ASABE. 62(1):9-18. https://doi.org/10.13031/trans.12878.
Abercrombie, S., Koprowski, J., Nichols, M.H., Fehmi, J. 2018. Native lagomorphs suppress grass establishment in a shrub-encroached, semi arid grassland. Ecology and Evolution. 9(1):307-317. https://doi.org/10.1002/ece3.4730.
Zhao, Y., Nearing, M.A., Guertin, D. 2019. A daily spatially explicit stochastic rainfall generator for a semi-arid climate. Journal of Hydrology. 54:181-192. https://doi.org/10.1016/j.jhydrol.2019.04.006.
Scott, R.L., Biederman, J.A. 2019. Critical zone water balance over thirteen years in a semiarid savanna. Water Resources Research. 55:574-588. https://doi.org/10.1029/2018WR023477.
Zhou, C., Biederman, J.A., Zhang, H., Cui, X., Wang, Y., Hao, Y. 2019. Extreme-duration drought impacts on soil CO2 efflux are regulated by plant species composition. Plant and Soil. 439(1-2):357-372. https://doi.org/10.1007/s11104-019-04025-w.
Turpin-Jelfs, T., Michaelides, K., Biederman, J.A., Anesio, A. 2019. Soil nitrogen response to shrub encroachment in a degrading semi-arid grassland. Biogeosciences. 16:369-381. https://doi.org/10.5194/bg-16-369-2019.
Williams, C.J., Snyder, K.A., Pierson Jr, F.B. 2018. Spatial and temporal variability of the impacts of pinyon and juniper reduction on hydrologic and erosion processes across climatic gradients in the Western US: A regional synthesis. Water. 10(11). https://doi.org/10.3390/w10111607.
Demaria, E.M., Goodrich, D.C., Kunkel, K. 2019. Evaluating the reliability of the U.S. Cooperative Observer Program precipitation observations for extreme events analysis using the LTAR network. Journal of Atmospheric and Ocean Technology. 36:317-332.
Hinojo-Hinojo, C., Castellanos, A., Huxman, T., Rodriguez, J., Vargas, R., Romo-Leon, J., Biederman, J.A. 2019. Native shrubland and managed buffelgrass savanna in drylands: implications on ecosystem carbon and water fluxes. Agricultural and Forest Meteorology. 268:269-278. https://doi.org/10.1016/j.agrformet.2019.01.030.
Nichols, M.H., Polyakov, V.O. 2019. The impacts of porous rock check dams on a semiarid alluvial fan. Science of the Total Environment. 664:576-582. https://doi.org/10.1016/j.scitotenv.2019.01.429.
Roby, M., Scott, R.L., Barron-Gafford, G., Hamerlynck, E.P., Moore, D. 2019. Environmental and vegetative controls on soil CO2 efflux in three semiarid ecosystems. Soil Systems. 3(1):6. https://doi.org/10.3390/soilsystems3010006.
Lahmers, T., Gupta, H., Hazenberg, P., Castro, C., Gochis, D., Yates, D., Dugger, A., Goodrich, D.C. 2019. Enhancing the structure of WRF-Hydro-Hydologic Model for semi-arid environments. Journal of Hydrometeorology. 20:691-714. https://doi.org/10.1175/JHM-D-18-0064.1.
Brooke, J., Harlow, R., Scott, R.L., Best, M., Edwards, J., Thelen, J., Weeks, M. 2019. Evaluating the Met Office Unified Model land surface temperature in Global Atmosphere/Land 3.1 (GA/L3.1), Global Atmosphere/Land 6.1 (GA/L6.1) and limited area 2.2km configurations. Geoscientific Model Development. 12:1703-1724. https://doi.org/10.5194/gmd-12-1703-2019.
Zhang, X.J., Polyakov, V.O., Liu, B., Nearing, M.A. 2018. Quantifying geostatistical properties of 137Cs and 210Pbex at small scales for improving sampling design and soil erosion estimation. Geoderma. 334:155-164. https://doi.org/10.1016/j.geoderma.2018.08.002.
Reinmann, A., Susser, J., Demaria, E.M., Templer, P. 2018. Declines in northern forest tree growth following snowpack decline and soil freezing. Global Change Biology. 25:420-430. https://doi.org/10.1111/gcb.14420.
Hao, Y., Zhang H., Biederman, J.A., Li, L., Cui, X., Xue, K., Du, J., Wang, Y. 2018. Seasonal timing regulates extreme drought impacts on CO2 and H2O exchanges over semiarid steppes in Inner Mongolia, China. Agriculture, Ecosystems and Environment. 266:153-166. https://doi.org/10.1016/j.agee.2018.06.010.
Fu, C., Wang, G., Bible, K., Goulden, M., Saleska, S., Scott, R.L., Wofsy, S., Cardon, Z. 2018. Hydraulic redistribution affects modeled carbon cycling via soil microbial activity and suppressed fire. Global Change Biology. 24:3472-3485. https://doi.org/10.1111/gcb.14164.
Spiegal, S.A., Bestelmeyer, B.T., Archer, D.W., Augustine, D.J., Boughton, E., Boughton, R., Clark, P., Derner, J.D., Duncan, E.W., Cavigelli, M.A., Hapeman, C.J., Harmel, R.D., Heilman, P., Holly, M.A., Huggins, D.R., King, K.W., Kleinman, P.J., Liebig, M.A., Locke, M.A., McCarty, G.W., Millar, N., Mirsky, S.B., Moorman, T.B., Pierson, F.B., Rigby, J.R., Robertson, G., Steiner, J.L., Strickland, T.C., Swain, H., Wienhold, B.J., Wulfhorts, J., Yost, M., Walthall, C.L. 2018. Evaluating strategies for sustainable intensification of U.S. agriculture through the Long-Term Agroecosystem Research network. Environmental Research Letters. 13(3):034031. https://doi.org/10.1088/1748-9326/aaa779.
Lee, E., Kumar, P., Baron-Gafford, G., Hendryx, S., Sanchez-Cohen, E., Minor, R., Colella, T., Scott, R.L. 2018. Impact of hydraulic redistribution on multispecies vegetation water use in a semi-arid savanna ecosystem: An experimental and modeling synthesis. Water Resources Research. 54:4009-4027. https://doi.org/10.1029/2017WR021006.
Yan, D., Scott, R.L., Moore, D., Biederman, J.A., Smith, W. 2019. Understanding the relationship between vegetation greenness and productivity across dryland ecosystems through the integration of PhenoCam, satellite, and eddy covariance data. Remote Sensing of Environment. 223:50-62. https://doi.org/10.1016/j.rse.2018.12.029.
Li, L., Zheng, Z., Biederman, J.A., Xu, C., Xu, Z., Che, R., Wang, Y., Cui, X., Hao, Y. 2019. Ecological responses to heavy rainfall depend on seasonal timing and multi-year recurrence. New Phytologist. 223:647-660. https://doi.org/10.1111/nph.15832.
Polyakov, V.O., Nearing, M.A. 2019. A simple automated laser profile meter. Soil Science Society of America Journal. 83:327-331. https://doi.org/10.2136/sssaj2018.10.0378.
Broxton, P., Van Leeuwen, W., Biederman, J.A. 2019. Improving snow water equivalent maps with machine learning of snow survey and LiDAR measurements. Water Resources Research. 55:3739-3757. https://doi.org/10.1029/2018WR024146.
Williams, C.J., Pierson, F.B., Nouwakpo, S., Al-Hamdan, O., Kormos, P.R., Weltz, M.A. 2018. Effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and ecohydrologic function on woodland-encroached sagebrush rangelands, Great Basin, USA: Part I: Vegetation, hydrology, and erosion responses. Catena. https://doi.org/10.1016/j.catena.2018.02.027.
Williams, C.J., Pierson, F.B., Nouwakpo, S., Kormos, P., Al-Hamdab, O.Z., Weltz, M.A. 2019. Long-term evidence for fire as an ecohydrologic threshold reversal mechanism on woodland-encroached sagebrush shrublands. Ecohydrology. 12(4):e2086. https://doi.org/10.1002/eco.2086.
Wi, S., Ray, P., Demaria, E.M., Steinschneider, S., Brown, C. 2017. A user-friendly software package for VIC hydrologic model development. Journal of Environmental Modeling and Software. 98:35-53. https://doi.org/10.1016/j.envsoft.2017.09.006.
Singh, I., Dominguez, F., Demaria, E.M., Walter, J. 2018. Extreme landfalling atmospheric river events in Arizona: Possible future changes. Journal of Geophysical Research Atmospheres. 123:7076-7097. https://doi.org/10.1029/2017JD027866.
Kautz, M.A., Holifield Collins, C.D., Guertin, D., Goodrich, D.C., Van Leeuwen, W., Williams, C.J. 2019. Hydrologic model parameterization using dynamic Landsat-based vegetative estimates within a semiarid grassland. Journal of Hydrology. 575:1073-1086. https://doi.org/10.1016/j.jhydrol.2019.05.044.
Roy, T., Valdes, J., Lyno, B., Demaria, E.M., Serrat-Capdevila, A., Gupta, H., Valdes-Pineda, R., Durcik, M. 2018. Assessing hydrological impacts of short-term climate change in the Mara River Basin of East Africa. Journal of Hydrology. 566:818-829. https://doi.org/10.1016/j.jhydrol.2018.08.051.
Chandler, D.G., Cheng, Y., Seyfried, M.S., Madsen, M.D., Johnson, C.E., Williams, C.J. 2018. Seasonal wetness, soil organic carbon, and fire influence soil hydrological properties and water repellency in a sagebrush-steppe ecosystem. Water Resources Research. 54(10):8514-8527. https://doi.org/10.1029/2017WR021567.
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