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

Location: Southwest Watershed Research Center

2020 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
This project is the sole focus of the management unit (MU), and this annual report describes progress for the 3rd year of this 5 year project cycle. A major challenge faced during the year was the preparation for construction of the Unit’s new building. In that process, four smaller buildings were torn down, personnel were moved into temporary workspaces, and then construction was halted as the contractor backed out of the agreement. Currently, new construction is at a stand-still until a new contractor and agreement can be made. Office space is not a limiting factor for research, but there is no room for domestic or international collaborators until the new building is completed. On a positive note, the Unit’s two scientist vacancies at the start of this project cycle have been filled, and their contributions, supplementing original plan objectives primarily through rainfall simulation and rainfall manipulation experiments, have been included below. Under Objective 1, substantial improvements were made in observational capabilities at the Walnut Gulch Experimental Watershed (WGEW) Long Term Agro-Ecosystem Research (LTAR) site. For Sub-objective 1.1, a suite of improvements were developed and deployed to enhance rainfall simulation, overflow instrumentation, and methodologies for application in rangeland hydrology and erosion experiments on brush management. Improvements include adoption of new datalogger technologies for rainfall simulators and new overland flow methodologies for measuring flow velocity, runoff, and erosion. Mini-disk infiltrometer methods for assessing soil water repellency were also evaluated and compared with more traditional methods. A new approach for measuring hillslope overland flow during natural rainfall was field tested with collaborating scientists from New Mexico State University. Furthermore, under Sub-objective 1.1, an internal report on the differences in above-ground rain gauges and ground-level pit gauges as related to wind direction and speed was completed, and rainfall drop size data are being incorporated into the analysis. Also, for Sub-objective 1.1, the variation of stable isotopes in rainwater were measured at high frequency within storm events. Also, in collaboration with other LTAR locations, research was conducted on the flow of dissolved organic matter resulting from intense summer rainstorms over Walnut Gulch. A dataset was developed including the concentrations of carbon and nitrogen. Fluorescence spectra were used to infer whether organic matter derived from plant litter or soil microbial decomposition. Coupling these concentration data with the high-quality water balance measurements in this long-term research watershed allowed determination of mass fluxes. For Sub-objectives 1.2 and 1.3, in collaboration with the Soil Health Institute samples were taken to quantify the health of WGEW and Santa Rita Experimental Range (SRER) soils using a wide variety of soil metrics. Field samples were taken and results are being analyzed. To improve vegetation monitoring, fifty-three research plots, totaling 193 hectares on the SRER, were photogrammetrically sampled by a Real-Time Kinematic Unmanned Aerial Vehicle at 1 cm ground sampling distance. Computer code was written to process the resulting imagery into ortho photos, digital surface and terrain models and point clouds using graphical processing units on a high performance computer and to classify the resulting 3-dimensional imagery products by vegetation life form. Similar vegetation measurements were also started in Walnut Gulch. For Sub-objective 1.4, in collaboration with ARS researchers in Boise, Idaho, vegetation, soils, and infiltration experiments were conducted within multiple tree removal treatments and untreated areas at two woodland sites, 13 years after the treatment applications. The experiments evaluated the long-term effectiveness of the various tree removal practices to reduce tree cover, re-establish sagebrush steppe vegetation, and improve hydrologic function. For Sub-objective 1.5, in collaboration with the National Park Service, a field campaign was conducted that utilized ARS rainfall simulation technologies and historical rainfall data to evaluate the effects of prolonged rainfall events on erosion of traditionally-built adobe walls. Lastly, analysis for six LTAR Experimental Watersheds, testing for trends for sub-daily rainfall intensification was completed. The data for the analysis from the six locations was collected and thoroughly vetted for errors with consultation of staff at the various locations. Under Objective 2, progress continued 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, under Sub-objective 2.1, research continued on quantifying the effects of brush management on land- atmosphere water and carbon exchanges by collecting a fourth year of post-treatment flux tower data along with vegetation cover in control and treated areas. These data are being used in conjunction with ecosystem water and carbon dioxide flux measurements within the control and treated areas to understand the efficacy of the pesticide application for brush management. Also, riparian vegetation water use research continued by comparing the water use of a riparian woodland and an upland grassland to determine how much water was used by plants as opposed to evaporating from the soil. Moreover, in collaboration with the University of Arizona, a facility for experimental manipulations of rainfall was completed in a semiarid rangeland ecosystem. The site was protected from storm damage with culverts and other drainage work. Sixty plots were planted with native perennial bunchgrass seedlings inside six covered high tunnels to exclude natural rainfall. Each tunnel was fitted with rainfall harvesting equipment, with the harvested rainfall applied to plots according to one of twelve rainfall scenarios. Automated remote cameras were installed to track vegetation greenness. Soil moisture observations and modeling were carried out to quantify the severity and duration of drought stress in the root zone. The facility is now ready and the first summer season field campaigns have started. For Sub-objective 2.2, a study was conducted to evaluate long-term erosion rates on sagebrush steppe following pinyon and juniper encroachment and control treatment. Sites in Idaho, Nevada, and Utah were selected. These sites have been the subject of previous experiments since 2006 including rainfall simulations and have been closely monitored. A total of 160 samples were prepared (dried and homogenized) and analyzed to measure cesium concentrations that can be used to measure long-term soil loss rates due to erosion. Under Objective 3, a new conceptual framework and corresponding experimental methods were developed to understand and model the dynamics of semiarid upland and channel erosion processes. For Sub-objective 3.1, the effects of surface condition (distribution of vegetation, slope steepness and roughness) on infiltration, runoff, concentrated flow dynamics, sediment transport processes, and surface evolution were quantified. Under Objective 4, the widely-used hillslope Rangeland Hydrology and Erosion Model (RHEM) and watershed Automated Geospatial Watershed Assessment (AGWA) models were improved by developing methods to incorporate remotely-sensed, meteorological, and land surface information into them. In support of Sub-objective 4.1, for RHEM, model inputs for thousands of locations around the world were created, and the results were validated on known data values within the United States. Also, a rainfall event data generator was developed that can automatically convert long-term rainfall and runoff data into input that can be readily used by the model. For Sub-objective 4.2, experimental study sites were identified, assessed, and selected in Arizona and Utah to evaluate the effects of brush management on hydrology and erosion processes. Pinyon and juniper savannas at the San Carlos Apache Tribe Indian Reservation were field surveyed in collaboration with tribal land managers and United States Geological Survey scientists. Additional research sites have been targeted at the Grand Staircase-Escalante National Monument, and an internal proposal and full experimental design has been submitted to assess the impacts of vegetation restoration practices on sagebrush vegetation recruitment and infiltration, runoff, and erosion processes. Also, a tool was created to generate customized reports containing remotely sensed information and climate data for public land allotments in southern Arizona to highlight areas with anomalously low cover and grass growth to focus attention by public rangeland managers. Under Sub-objective 4.3, a study was completed on the effect of incorporating time-varying remotely sensed estimates of foliar canopy cover data on modeled runoff volume and peak runoff flow rate.

Accomplishments
1. Unmaintained rangeland erosion control structure database developed to assist restoration efforts. Thousands of erosion control structures, such as small water supply dams, stock tanks, check dams, water spreaders, and earthen contour berms have been built over the last century to control water and sediment across western rangelands. Many of these structures are not maintained and have failed. ARS scientists in Tucson, Arizona, developed a spatially explicit database of water and sediment control structures in a sparsely populated semiarid watershed. More than 1000 structures were identified, their condition assessed, and altered runoff and sediment transport pathways were documented. Knowledge of these impacts is critical to landowners and managers who seek to restore degraded rangelands. In many cases restoration potential is limited because altered runoff patterns are contributing to gullying and erosion. The results highlight the influence of human made structures on rangeland landscapes, providing information to prioritize sites with the greatest potential for restoration.

2. Interaction of wind and runoff amplifies soil loss after wildfire and has profound implications for post-fire modeling and risk assessment. Increasing wildfire activity and associated water and soil impacts are a major concern for public and private land managers, scientists, and policy makers throughout the western United States. ARS scientists in Tucson, Arizona, and Boise, Idaho, conducted a two-year study of wildfire impacts on water and soil movement and found that fire-induced increases in soil erosion were attributed to wind movement of fine sediment along hillslopes and subsequent flushing of those sediments by winter runoff. These novel results aid land managers and scientists by quantifying the interacting effects of wind and water processes on post-fire erosion, paramount for advancing post-fire risk assessment.

3. Forest conditions have a major influence on snowpacks of the semiarid southwest United States. In the southwest United States, wintertime snow accumulation in mountain snowpacks is a major, but highly variable, water source for rivers. Snowpacks in these regions may accumulate and disappear several times during a given winter, depending upon the weather and shelter from nearby trees. ARS researchers from Tucson, Arizona, collaborated with scientists from the University of Arizona to quantify how forest conditions interact with weather to regulate the accumulation and disappearance of snow. While treeless clearings can accumulate up to 30% more snow than dense forests, the rate of snow disappearance in those clearings depends on the degree of shade from nearby trees. Generally, snowpack is maximized when forest covers between 30-50% of the land. Collectively, these results demonstrate the potential for adaptive forest management to conserve and enhance water supplies. These results are being used by water managers of Arizona's largest surface water supply to improve streamflow forecasting and reservoir operations. Furthermore, these results are informing multi-criteria forest management plans overseen by the US Forest Service and The Nature Conservancy. Finally, the results are being applied in a new partnership to improve USGS hydrologic modeling in the Upper Colorado River Basin.

4. Southwest United States forests are an important buffer against rising temperatures. In the semiarid western United States, forecasted warming and changes to precipitation could affect mountain forest health with implications for their ability to buffer carbon dioxide emissions and provide water for people. ARS and university scientists in Tucson, Arizona, measured water and CO2 inputs and outputs from a mountain forest in Arizona for nine years between 2009 and 2018. Because of its southerly location, the forest was relatively warmer than other mountain forests in the western United States, which allowed for increased forest growth during the winter. Although it was also drier than other forests regionally, it received more rain during the summer, and the combination of winter snow accumulation and summer precipitation promoted generally favorable moisture conditions for most of the year. Consequently, the forest removed more carbon dioxide from the atmosphere annually than other monitored forests in the western United States. Our results suggest that the effect of rising temperatures on the future health of mountain forests may depend on the consistency of moisture availability throughout the year. This research directly informs atmospheric CO2 projections and can also be used by water managers to infer the timing and magnitude of streamflow processes that are affected by forest water use.

5. Vegetation, soils, hydrology, and erosion plot data from western rangelands provides improved understanding of rangeland conservation practices. Rainfall simulation and overland-flow experiments advance understanding of surface hydrology and erosion processes and provide valuable data for testing and improving predictive models. This study led by ARS scientists in Tucson, Arizona, and Boise, Idaho, compiled a unique long-term dataset of rainfall simulation and overland flow plot data paired with measures of vegetation and ground surface conditions before and after various conservation practices. The dataset enables new evaluations and improvements of runoff and erosion models that managers can use to guide and assess management practices for more effective and cost efficient conservation of western rangelands.

6. Remotely sensed vegetation cover improves watershed modeling of runoff. Watershed vegetation cover conditions are dynamic, yet they are difficult to monitor over long time scales and over large areas that are an important factor in runoff response and erosion. Ranchers and land managers need to assess vegetation conditions to make stocking decisions and target conservation practices to mitigate areas at risk of erosion. ARS researchers in Tucson, Arizona, evaluated the effects of different vegetation cover datasets on simulated storm runoff from a watershed. They found that remotely-sensed vegetation cover from satellites improved simulated runoff when compared to measured runoff. The developed framework provides a means for a simple but improved parameterization for watershed-scale modelling where vegetative data may be scarce or unobtainable for long-term analysis.

7. Remote sensing improves the evaluation of semiarid rangeland conservation practices. Ranchers and conservationists need to evaluate watershed and vegetation conditions to make rangeland stocking decisions to maintain long-term rangeland health, the economic viability of grazing operations and, to preserve ecosystem services. In this study, ARS scientists in Tucson, Arizona, used state-of-the-art ARS simulation tools to provide estimates of runoff and erosion to evaluate conservation investments on a large watershed in southeast Arizona that were implemented under the Conservation Effects Assessment Project. Numerous well documented conservation practices were conducted on the watershed, allowing an assessment of how satellite remotely-sensed images can capture on-the-ground conditions. The assessment demonstrated the utility of remotely sensed estimates of plant cover and type, and detection of mechanical and fire treatment of brush removal for runoff and erosion model inputs, but the commonly-used National Resource Inventory data were only capable of estimating the effects of large watershed changes like drought and wet years. Thus, widely-available satellite data should prove useful for decision making by rangeland managers.

8. Semiarid grassland nitrous oxide emissions increase with warmer temperatures. Although much climate change research focuses on carbon dioxide, there are other important greenhouse gases occurring in smaller quantities, but with greater potency than carbon dioxide, including nitrous oxide (N2O). ARS researchers in Tucson, Arizona, and colleagues from China analyzed 46 published studies worldwide in which temperature or precipitation were artificially altered to test for effects on N2O emissions. They found that increased temperature drove increased N2O release from soils by an average of 33%, although the results varied across biomes, with the biggest response in shrublands. Increased precipitation also enhanced N2O emissions, while decreased precipitation suppressed emissions. Collectively, these results suggest that globally warming temperatures may increase N2O release, representing a reinforcing effect on climate change.

Review Publications
Korgaonkar, Y., Guertin, D., Goodrich, D.C., Unkrich, C.L., Kepner, W., Burns, I. 2019. Modeling urban hydrology and green infrastructure using the AGWA urban tool and the KINEROS2 model. Frontiers in the Built Environment. 4:58. https://doi.org/10.3389/fbuil.2018.00058.
Vega, S., Williams, C.J., Brooks, E., Pierson Jr, F.B., Strand, E., Robichaud, P., Brown, R., Seyfried, M.S., Lohse, K., Glossner, K., Pierce, J., Roehner, C. 2020. Interaction of wind and cold-season hydrologic processes on erosion from complex topography following wildfire in sagebrush steppe. Earth Surface Processes and Landforms. 45(4):841-861. https://doi.org/10.1002/esp.4778.
Smith, W., Dannenberg, M., Yan, D., Hermann, S., Barnes, M., Barron-Gafford, G., Biederman, J.A., Ferrenberg, S., Fox, A., Hudson, A., Knowles, J.F., Macbean, N., Moore, D., Nagler, P., Reed, S., Rutherford, W., Scott, R.L., Wng, X., Yang, J. 2019. Remote sensing of dryland ecosystem structure and function: Progress, challenges and opportunities. Remote Sensing of Environment. 233. https://doi.org/10.1016/j.rse.2019.111401.
Lucas-Borja, M., Zema, D., Yu, Y., Nichols, M.H., Bombino, G., Denisi, G., Denisi, P., Labate, A., Carrà, B., Xiangzhou, X., Rodrigues, B., Cerdá, A., Zimbone, S. 2020. Influence of site and check dam characteristics on sediment retention and structure conservation in a Mexican river. In: Innovative Biosystems Engineering for Sustainable Agriculture, Forestry and Food Production. Coppola, A., Di Renzo, G.C., Altieri,G., D'Antonio, P. Springer International Publishing.
Knowles, J.F., Scott, R.L., Minor, R., Barron-Gafford, G. 2020. Ecosystem carbon and water cycling from a sky island montane forest. Agricultural and Forest Meteorology. 281. https://doi.org/10.1016/j.agrformet.2019.107835.
Nicosia, A., Di Stefano, C., Pampalone, V., Palermi, V., Ferro, V., Polyakov, V.O., Nearing, M.A. 2020. Testing a theoretical resistance law for overland flow under simulated rainfall with different types of vegetation. Catena. 189. https://doi.org/10.1016/j.catena.2020.104482.
Dwivedi, R., Eastoe, C., Knowles, J.F., Wright, W., Hamann, L., Minor, R., Mitra, B., Meixner, T., Mcintosh, J., Ferre, P., Castro, C., Niu, G., Barron Gafford, G., Abramson, N., Papuga, S., Stanley, M., Hu, J., Chorover, J. 2020. Vegetation source water identification using isotopic and hydrometric bservations from a subhumid mountain catchment. Ecohydrology. 13(1). https://doi.org/10.1002/eco.2167.
Belmonte, A., Sankey, T., Biederman, J.A., Bradford, J., Goetz, S., Kolb, T., Woolley, T. 2019. UAV-derived estimates of forest structure to inform ponderosa pine forest restoration. Remote Sensing in Ecology and Conservation. 6(2):181-197. https://doi.org/10.1002/rse2.137.
Meles, M.B., Goodrich, D.C., Demaria, E.M., Heilman, P., Nichols, M.H., Levick, L., Unkrich, C.L., Kautz, M.A. 2019. Multi-parameter regression modeling for improving the quality of measured rainfall and runoff data in densely instrumented watersheds. Journal Hydrologic Engineering. 24(10). https://doi.org/10.1061/(ASCE)HE.1943-5584.0001825.
Polyakov, V.O., Nearing, M.A., Nichols, M.H., Cavanaugh, M.L. 2019. An improved excavation method for measuring bulk density of rocky soil using terrestrial LiDAR. Journal of Soil and Water Conservation. 74(3):265-268. https://doi.org/10.2489/jswc.74.3.319.
Li, L., Zheng, Z., Wang, W., Biederman, J.A., Xu, X., Ran, Q., Qian, R., Xu, C., Zhang, B., Wang, F., Zhou, S., Cui, L., Che, R., Hao, Y., Cui, X., Xu, Z., Wang, Y. 2019. Terrestrial N2O emissions and related functional genes under climate change: A global meta-analysis. Global Change Biology. 26(2):931-943. https://doi.org/10.1111/gcb.14847.
Edwards, B.L., Webb, N.P., Brown, D.P., Elias, E.H., Peck, D.E., Pierson Jr, F.B., Williams, C.J., Herrick, J.E. 2019. Climate change impacts on wind and water erosion on US rangelands. Journal of Soil and Water Conservation. 74(4):405-418. https://doi.org/10.2489/jswc.74.4.405.
Demaria, E.M., Hazenberg, P., Scott, R.L., Meles, M.B., Nichols, M.H., Goodrich, D.C. 2019. Intensification of the North American Monsoon rainfall as observed from a long-term high-density gauge network. Geophysical Research Letters. 46(12):6839-6847. https://doi.org/10.1029/2019GL082461.
Alves, G., Mello, C., Beskow, S., Junqueira, J., Nearing, M.A. 2019. Assessment of the soil conservation service–curve number method performance in a tropical Oxisol watershed. Journal of Soil and Water Conservation. 74(5):500-512. https://doi.org/10.2489/jswc.74.5.500.
Potts, D., Barron-Gafford, G., Scott, R.L. 2019. Ecosystem hydrologic and metabolic flashiness are shaped by plant community traits and precipitation. Agricultural and Forest Meteorology. 279. https://doi.org/10.1016/j.agrformet.2019.107674.
Nouwakpo, S.K., Williams, C.J., Pierson Jr, F.B., Weltz, M.A., Arslan, A., Al-Hamdan, O. 2020. Effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and ecohydrologic function on woodland-encroached sagebrush rangelands, Great Basin, USA: Part II: runoff and sediment transport at the patch scale. Catena. 185. https://doi.org/10.1016/j.catena.2019.104301.
Goodrich, D.C., Wei, H., Burns, I., Guertin, D., Spaeth, K., Hernandez Narvaez, M.N., Holifield Collins, C.D., Kautz, M.A., Heilman, P., Levick, L., Ponce Campos, G.E., Carrillo, E., Tiller, R. 2020. Evaluation of Conservation Effects Assessment Project Grazing Lands conservation practices on the Cienega Creek Watershed in southeast Arizona with RHEM/KINERSO2/AGWA modeling tools. Journal of Soil and Water Conservation. 75(3):304-318. https://doi.org/10.2489/jswc.75.3.304.
Snyder, K.A., Scott, R.L. 2019. Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange. Hydrological Processes. 34(2):223-236. https://doi.org/10.1002/hyp.13639.
Stoy, P.C., El-Madany, T.S., Fisher, J.B., Gentine, P., Gerken, T., Good, S.P., Klosterhalfen, A., Liu, S., Miralles, D.G., Perez-Priego, O., Rigden, A.J., Skaggs, T.H., Wohlfahrt, G., Anderson, R.G., Coenders-Gerrits, A.M.J., Jung, M., Maes, W.H., Mammarella, I., Mauder, M., Migliavacca, M., Nelson, J.A., Poyatos, R., Reichstein, M., Scott, R.L., Wolf, S. 2019. Review & syntheses: Turning the challenges of partitioning ecosystem evaporation and transpiration into opportunities. Biogeosciences. 16(19):3747-3775. https://doi.org/10.5194/bg-16-3747-2019.
Li, L., Nearing, M.A., Nichols, M.H., Polyakov, V.O., Winter, C., Cavanaugh, M.L. 2020. Temporal and spatial evolution of soil surface roughness on stony plots. Soil & Tillage Research. 200. https://doi.org/10.1016/j.still.2019.104526.
Li, L., Nearing, M.A., Nichols, M.H., Polyakov, V.O., Cavanaugh, M.L. 2019. Using terrestrial LiDAR to measure water erosion on stony plots under simulated rainfall. Earth Surface Processes and Landforms. 45(2):484-495. https://doi.org/10.1002/esp.4749.
Polyakov, V.O., Nearing, M.A., Stone, J. 2019. Soil loss from small rangeland plots under simulated rainfall and run-on conditions. Geoderma. 361. https://doi.org/10.1016/j.geoderma.2019.114070.
Li, L., Nearing, M.A., Nichols, M.H., Polyakov, V.O., Guertin, D., Cavanaugh, M.L. 2020. The effects of DEM interpolation on quantifying soil surface roughness using terrestrial LiDAR. Soil and Tillage Research. 198. https://doi.org/10.1016/j.still.2019.104520.
Williams, C.J., Snyder, K.A., Pierson Jr, F.B. 2020. Ecohydrology of pinyon and juniper woodlands. In: Miller, R.F., Chambers, J.C., Evers, L., Williams, C.J., Snyder, K.A., Roundy, B.A., Pierson, F.B., editors. The Ecology, History, Ecohydrology, and Management of Pinyon and Juniper Woodlands in the Great Basin and Northern Colorado Plateau of the Western United States, General Technical Report, RMRS-GTR-403. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. pp. 129-163.
Nicosia, A., Di Stefano, C., Pampalone, V., Palermi, V., Ferro, V., Nearing, M.A. 2020. Testing a theoretical resistance law for an overland flow on a stony hillslope. Hydrological Processes. 34(9):2048-2056. https://doi.org/10.1002/hyp.13709.
Baffaut, C., Baker, J.M., Biederman, J.A., Bosch, D.D., Brooks, E.S., Buda, A.R., Demaria, E.M., Elias, E.H., Flerchinger, G.N., Goodrich, D.C., Hamilton, S.K., Hardegree, S.P., Harmel, R.D., Hoover, D.L., King, K.W., Kleinman, P.J., Liebig, M.A., McCarty, G.W., Moglen, G.E., Moorman, T.B., Moriasi, D.N., Okalebo, J., Pierson Jr, F.B., Russell, E.S., Saliendra, N.Z., Saha, A.K., Smith, D.R., Yasarer, L.M. 2020. Comparative analysis of water budgets across the U.S. long-term agroecosystem research network. Journal of Hydrology. 588. https://doi.org/10.1016/j.jhydrol.2020.125021.
Broxton, P., Van Leeuwen, W., Biederman, J.A. 2020. Forest cover and topography regulate the thin, ephemeral snowpacks of the semiarid Southwest United States. Ecohydrology. 13(4). https://doi.org/10.1002/eco.2202.
Li, L., Zheng, Z., Biederman, J.A., Qian, R., Zhang, B., Che, R., Wang, F., Xu, Z., Cui, X., Hao, Y., Wang, Y. 2020. Drought and heat wave impacts on grassland carbon cycling across hierarchical levels. Plant, Cell & Environment. 1-12. https://doi.org/10.1111/pce.13767.
Meles, M.B., Jackson, C., Goodrich, D.C., Younger S.E., Griffiths, N., Vaché, K., Rau, B. 2020. Dynamic domain kinematic modeling for predicting interflow over leaky impeding layers. Hydrological Processes. 34(13):2895-2910. https://doi.org/10.1002/hyp.13778.
Fullhart, A.T., Nearing, M.A., McGehee, R., Weltz, M.A. 2020. Temporally downscaling a precipitation intensity factor for soil erosion modeling using the NOAA-ASOS weather station network. Catena. 194. Article 14709. https://doi.org/10.1016/j.catena.2020.104709.
Williams, C.J., Pierson Jr, F.B., Kormos, P., Al-Hamdan, O.Z., Johnson, J. 2020. Vegetation, ground cover, soil, rainfall simulation, and overland-flow experiments before and after tree removal in woodland-encroached sagebrush steppe: the hydrology component of the Sagebrush Steppe Treatment Evaluation Project (SageSTEP). Earth System Science Data. 12(2):1347-1365. https://doi.org/10.5194/essd-12-1347-2020.