Location: Southwest Watershed Research2013 Annual Report
1a. Objectives (from AD-416):
1. Improve watershed management by developing the capacity to more accurately predict soil and plant water dynamics utilizing a combination of remote sensing, modeling and in-situ measurements. 2. Quantify how seasonal, annual, and decadal-scale variations in climate (including climate forecasts) and plant community composition impact the cycling of energy, water and carbon in semiarid rangelands. 3. Develop improved watershed model components and decision support systems that more fully utilize and assimilate economic and remotely sensed data for parameterization, calibration and model state adjustment.
1b. Approach (from AD-416):
Methods of investigation include field and laboratory experimentation, as well as the development and use of state-of-the-science watershed models and the use of remote sensing for watershed characterization. Multiple methods and techniques will be employed to improve the prediction of plant-water soil dynamics under objective one. They include data assimilation techniques to incorporate both in-situ and remotely sensed measurements into simulation models. In addition, algorithms for enhanced retrieval of watershed characteristics and state variables will be developed. Results from this research are critical for extension of results to large-areas using remote sensing and critical for improved inputs and parameter estimates for the models addressed under objective three. Research undertaken to address objective two more closely focuses on ecohydrology and determining changes in the cycling of energy, water and carbon as well as changes in the composition of plant communities across a wide range of time scales. This includes global change impacts on ecohydrologic processes (including water, nutrient and energy cycles) that underpin ecosystem structure and function. Thus, objective two also focuses on the relationship between global change, ecohydrology and watershed response, which will allow the evaluation of the combined impacts of climate change, intensive land use and species invasions on ecohydrological processes that are critical to maintaining ecosystems. It includes three Multi-Location Projects (MLPs) led or co-led by scientists in this research unit, which will examine observations across decadal and continental scales using observations from USDA’s national network of experimental watersheds, ranges and forests. To address objective three we will develop tools and methods to enhance watershed and rangeland management through wider accessibility of databases from our long-term experimental watersheds, and by development and testing of watershed and decision support models which can assimilate remotely sensed data and incorporate economic and ecosystem service information.
3. Progress Report:
This is the second year of the five-year plan and we are reporting progress on the 24 month milestones and accomplishments. Good progress was made on each of the three objectives and two of the three Multi-Location Projects (MLPs) during this year. Briefly, for Objective 1, a number of new experiments and analyses of remotely sensed imagery to improve watershed management through more accurate prediction of soil and plant water dynamics were successfully initiated. Using data from several ARS locations and other sites around the world, analysis revealed that water demand by many plant communities can fluctuate in response to water availability, but the research also suggests that a limit to this resilience could ultimately threaten the survival of these plant communities in sensitive environments such as the grasslands in the Southwest. Another major finding for this objective was that forecasted changes in precipitation patterns may lead to decreased vegetation productivity, even if precipitation totals stay the same. For Objective 2, long-term field ecohydrological studies were maintained and new ones initiated to quantify climate interactions on the cycling of energy, water and carbon in semiarid rangelands. For Objective 3, the KINEROS2 watershed model developed and maintained by the Management Unit (MU) was further improved. Within KINEROS2 an “urban” model element was validated and used with careful field observations to estimate the amount of new, manageable water, that arid and semi-arid communities will have due to urbanization for beneficial uses such as aquifer recharge. A rangeland state-and-transition model information was also completed and tested for the Empire Ranch in southeastern Arizona, supporting our cooperative efforts with the Natural Resources Conservation Service (NRCS) for the Congressionally mandated rangeland Conservation Effects Assessment Project (CEAP).
1. New source of “manageable water” from urbanization estimated with ARS KINEROS2 watershed model. Growth and urbanization occurred rapidly in the American Southwest and is projected to exceed the growth of other regions of the United States. Computer models used to predict the effects of urbanization on runoff typically account for the impervious areas (e.g. roads, roofs, driveways) but not the effect of changes in the soil’s ability to absorb rainfall in the constructed area (e.g. yards, common areas). In this study ARS researchers from Tucson, Arizona, working with colleagues from the U.S. Geological Survey collected detailed hydrologic measurements in a residential development and adjacent natural watershed in southeast Arizona. These measurements were used with a novel ARS watershed model (KINEROS2). Results indicated that urbanization resulted in a nearly 20-fold increase in runoff over the natural watershed and compaction of soils done for construction accounted for about 15-20% of the total increase in runoff. This “new” manageable water from storm runoff in developed areas, that would have otherwise been lost to evaporation and plant water use, can be detained and used for groundwater recharge of aquifers to be used again for agriculture or thirsty communities.
2. Plant water demands shift with water availability. ARS scientists at Tucson, Arizona, and their partners around the world have determined that water demand by many plant communities can fluctuate in response to water availability, indicating a capacity for resilience even when changing climate patterns produce periodic droughts or floods. But their research also suggests that an observed limit to this resilience to climate change could ultimately threaten the survival of these plant communities. Sensitive environments such as the arid grasslands in the Southwestern U.S. are already approaching this limit. This work can help resource managers develop agricultural production strategies that incorporate changes in water availability linked to changing precipitation patterns.
3. Consequences of cool-season drought-induced plant mortality to Chihuahuan Desert grassland ecosystem and soil respiration dynamics. Current climate trends have led to winter drought across the arid Southwest United States that have induced wide-spread plant mortality and substantially altered the plant community structure of these critical rangeland ecosystems. However, how these mortality-induced shifts affect seasonal ecosystem carbon dioxide exchange and the processes regulating this are unclear. ARS researchers in Tucson, Arizona, and University of Arizona scientists quantified carbon dioxide exchange and soil respiration following two extensive perennial grass diebacks in a semidesert grassland. They found winter drought-associated mortality strongly modulated the grasslands ability to effectively use rainfall over the following summer rainy season, and that surviving plant condition, not overall plant mortality, had a strong effect on the soil respiration portion of ecosystem carbon flux. These results suggest current climate trends towards drier winters are likely to strongly, and negatively affect the processes underlying productivity in Southwest grassland grazing systems.
4. Extreme precipitation patterns will decrease vegetative productivity. One recurring forecast effect of global climate change is that, in general, precipitation patterns will become more extreme, with fewer, larger storms and longer dry spells. ARS scientists at Tucson, Arizona, and colleagues conducted an investigation into the observed effect of precipitation variability from 2000 to 2009 on 11 different sites within the continental United States. Results showed that for most biomes tested, a more extreme precipitation pattern had a negative effect on vegetative productivity, and resulted in, on average, a 20% reduction in rain use efficiency. With predictions of more extreme weather events, forecasts of ecosystem production should consider these non-linear responses to altered extreme precipitation patterns associated with climate change.
5. Cool-season whole plant gas exchange of exotic and native semiarid bunchgrasses. The invasive South African perennial grass, Lehmann lovegrass, alters community structure and ecosystem processes across a wide area of Southwestern US desert grassland grazing systems. Past research suggested a critical feature in the invasive success of this grass was its ability to exploit cool season rainfall that native bunchgrasses typically do not. ARS researchers in Tucson, Arizona, and University of Arizona and University of California scientists quantified whole-plant gas exchange performance of Lehmann lovegrass and a native bunchgrass (bush muhley), over two contrasting winter and springtime periods. They found the two species performed as well under drier, warmer cool-season conditions, but the exotic grass performed more poorly than the native under very wet, cool-season conditions. These results demonstrated that cool-season rain was not a critical feature in driving the higher productivity critical to the invasive success of Lehmann lovegrass, but that predicted warmer and drier cool season conditions are likely to enhance the continued regional spread of this exotic grass.
6. Satellite estimates of rainfall validated with ARS Experimental Watershed rain gauge data. Water is a critical resource in rapidly growing arid and semiarid regions and accurate estimates of rainfall are essential to manage agricultural productions and critical water resources. In many places rain gauges cannot be deployed and ground based radar estimates of rainfall are blocked by mountains. ARS researchers from Tucson, Arizona, working with colleagues from the National Aeronautics and Space Administration (NASA) compared rain gauge observations from the densely instrumented USDA, ARS Walnut Gulch Experimental Watershed (WGEW) to rainfall intensity estimates from the TRMM or Tropical Rainfall Measurement Mission satellite between 1999-2010. Results indicate a very good agreement between the TRMM and WGEW estimates of rainfall rates. This is an important finding as rainfall is not well measured over large parts of the globe and the TRMM satellite design is the basis for the new NASA Global Precipitation Mission.
7. Remote sensing of total canopy cover on rangelands. Rangelands are extensive and expensive to monitor. Researchers at Applied Geosolutions LLC, Michigan State University, and ARS in Tucson, Arizona, developed a method to quantify the foliar canopy cover of both green and senescent vegetation using remote sensing. The method links field-scale observations with Landsat imagery, which is free and can provide pasture and ranch scale information (30m), to Moderate-resolution Imaging Spectroradiometer (MODIS) imagery. MODIS is also free and can be used to assess a time series of cover across states or regions at a coarser resolution (500m). The amount of total canopy cover indicates how well protected rangelands are from rainfall induced erosion. Remotely sensed total cover could be used to parameterize rangeland watershed models that would otherwise be very expensive to run.
8. Assessing phenological change in China from 1982 to 2006 using Advanced Very High Resolution Radiometer (AVHRR) imagery. China's rapid economical growth attributes largely to the policy of opening special economic zones launched in 1978. The heterogeneous nature of the policy implies spatial variation of the policy’s impacts on vegetation growth across the country. ARS researchers in Tucson, Arizona, and the Michigan State University mapped the annual vegetation growth across China from 1982 to 2006 based on remote sensing imagery and quantified the temporal trend at the 8km X 8km pixel scale. The spatial pattern of the historical trend reveals great variation across the country and coincidence with several national policies launched by the government since 1978. Significant decreasing trends were found along the coastal area of the Pacific Ocean and some areas along the Yangtze River, which are likely due to the opening of economic zones and inland cities and associated anthropogenic causes such as rapid urbanization and deforestation. Significant increasing trends detected in Northeast, Northwest and Central China indicate the effect of the ‘Three-North Shelter Forest Programme’ and these areas, while the significant decreases in the grassland area of Inner Mongolia indicate desertification.
Goodrich, D.C., Burns, I., Unkrich, C.L., Semmens, D., Guertin, D., Hernandez, M., Yatheendradas, S., Kennedy, J., Levick, L. 2012. KINEROS2/AGWA: Model use, calibration, and validation. Transactions of the ASABE. 55(4):1561-1574.