Grantee Research Project Results
2012 Progress Report: Modeling of the Hydrochemical Response of High Elevation Watersheds to Climate Change and Atmospheric Deposition
EPA Grant Number: R834188Title: Modeling of the Hydrochemical Response of High Elevation Watersheds to Climate Change and Atmospheric Deposition
Investigators: Driscoll, Charles T. , Campbell, John L. , Hayhoe, Katharine , Wu, Wei
Current Investigators: Driscoll, Charles T. , Campbell, John L. , Pourmokhtarian, Afshin , Hayhoe, Katharine , Wu, Wei , Dong, Zheng
Institution: Syracuse University , University of Southern Mississippi , USDA , Towson University
Current Institution: Syracuse University , Towson University , USDA , University of Southern Mississippi
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2009 through July 31, 2012 (Extended to July 31, 2014)
Project Period Covered by this Report: August 1, 2011 through July 31,2012
Project Amount: $800,000
RFA: Consequences of Global Change for Water Quality (2008) RFA Text | Recipients Lists
Research Category: Ecological Indicators/Assessment/Restoration , Climate Change , Watersheds , Aquatic Ecosystems , Water
Objective:
Our overarching goal for this proposed study is to compare model calculations across high elevation watersheds in the United States with a range of climatic conditions to better understand and quantify how the quantity and quality of surface waters might respond to changing climate.
To achieve this goal, we are using the hydrochemical model, PnET-BGC, driven by both past and future simulated climate, to assess the impact of climate change on water quantity and quality. Climate input scenarios are generated with well-documented statistical procedures based on simulations from the latest Atmosphere Ocean Global Circulation Model (AOGCM) outputs available from the Intergovernmental Panel on Climate Change (IPCC) Working Group 1. Using these climate input data, PnET-BGC are being run at the 14 high elevation watersheds. This approach will enable us to evaluate hydrochemical responses intensively at local scales and more broadly at regional and national scales. We are working with cooperating scientists from the intensive study sites to interpret model results and design additional analyses.
Progress Summary:
Modeling potential hydrochemical responses to climate change and increasing CO2 at the Hubbard Brook Experimental Forest using a dynamic biogeochemical model (PnET-BGC)
Dynamic hydrochemical models are useful tools for understanding and predicting the interactive effects of climate change, atmospheric CO2, and atmospheric deposition on the hydrology and water quality of forested watersheds. We used the biogeochemical model, PnET-BGC, to evaluate the effects of potential future changes in temperature, precipitation, solar radiation, and atmospheric CO2 on pools, concentrations, and fluxes of major elements at Hubbard Brook, New Hampshire. Future climate projections used to run PnET-BGC were generated specifically for the Hubbard Brook Experimental Forest (HBEF) with a statistical technique that downscales climate output (e.g., air temperature, precipitation, solar radiation) from AOGCMs to a finer temporal and spatial resolution. These climate projections indicate that over the 21st century, average air temperature will increase at the site by 1.7°C to 6.5°C with simultaneous increases in annual average precipitation ranging from 4 to 32 cm above the long-term mean (1970–2000). PnET-BGC simulations under future climate change show a shift in hydrology characterized by later snowpack development, earlier spring discharge (snowmelt), greater evapotranspiration, and a slight increase in annual water yield (associated with CO2 effects on vegetation). Model results indicate that under elevated temperature, net soil nitrogen mineralization and nitrification markedly increase, resulting in acidification of soil and stream water, thereby altering the quality of water draining from forested watersheds. Invoking a CO2 fertilization effect on vegetation under climate change substantially mitigates watershed nitrogen loss, highlighting the need for a more thorough understanding of CO2 effects on forest vegetation. This work is summarized in [Pourmokhtarian et al., 2012].
Cross site analysis of forested watersheds in the northeastern United States to climate change and increasing CO2 over the 21st century using a dynamic biogeochemical model (PnET-BGC)
We used the biogeochemical model, PnET-BGC, to assess, compare and contrast the effects of potential future changes in temperature, precipitation, solar radiation and atmospheric CO2 on pools, concentrations, and fluxes of major elements at four forested watersheds in the northeastern United States: the HBEF in New Hampshire, East Bear Brook in Maine, Sleepers River Watershed in Vermont, and Huntington Wildlife Forest in New York. Future emissions scenarios were developed from monthly output from three AOGCMs (HadCM3, GFDL, PCM) in conjunction with potential lower and upper bounds of projected atmospheric CO2 (550 and 970 ppm by 2099, respectively).
These climate projections indicate that over the 21st century, average air temperature will increase at all sites with simultaneous increases in annual average precipitation. The modeling results suggest that under future climatic conditions peak discharge in spring will transition from April to March due to less snowmelt and an extended growing season. Higher temperature and a decrease in the ratio of snow to rain, regardless of overall increase in total precipitation, will minimize snowpack development. Over the summer period, higher rates of evapotranspiration are predicted to decrease streamflow. Model results show that under elevated temperature, net soil nitrogen mineralization and nitrification markedly increase, resulting in acidification of soil and streamwater, although the extent varies with site land disturbance history and cumulative inputs of atmospheric nitrogen deposition. The watershed responses of other major elements such as SO42- and Ca2+, and chemical characteristics such as pH and ANC varied based on future climate scenario and site characteristics. Also, we assessed changes in seasonal patterns of concentrations of NO3-, SO42-, Ca2+, DOC, pH, and ANC under all climate change scenarios with and without CO2 effects on vegetation over the period of 2070-2100. These results suggest that in addition to climate change likely altering the overall element concentrations and fluxes, the relative seasonal patterns also will be highly altered. Cross site analysis among different watersheds in the Northeast indicated that historical land disturbances coupled with climate variability will influence future responses of watershed to climate change and variability in hydrochemical response across sites is due to historical land disturbances and soil and geological characteristics.
An assessment of uncertainties due to global climate models, future scenarios, and downscaling on potential hydrochemical response of a forested watersheds to climate change using a dynamic biogeochemical model (PnET-BGC)
Assessments of uncertainties in climate change modeling have generally focused on those inherent to the response of interest. Dynamic hydrochemical models are useful tools to understand and predict the interactive effects of climate change, atmospheric CO2, and atmospheric deposition on the hydrology and water quality of forested watersheds. However, they have inherent uncertainties, which mainly stem from simplifications and assumptions of hydrological and biogeochemical processes depicted in the model. When these models are used to assess the potential impacts of climate change on a watershed, additional new sources of uncertainty become incorporated in the analysis. These include uncertainty in estimates of future emissions due to human activities (scenario uncertainty), the ability of the global circulation model to simulate the response of the climate system to human forcing (model uncertainty), and the observational data and statistical methods used to translate coarse-scale global projections into the high-resolution information required as input to the hydrochemical model (downscaling uncertainty). In this portion of this research, we assessed the degree to which potential future changes in temperature, precipitation, solar radiation and atmospheric CO2 affect projections of pools, concentrations, and fluxes of major elements at the HBEF, using the biogeochemical model, PnET-BGC. We assess, compare and contrast the projections resulting from higher and lower future emissions scenarios SRES A1fi and B1, with potential lower and upper bounds of projected atmospheric CO2 (550 and 970 ppm by 2099, respectively), four CMIP3 global climate models (CCSM4, HadCM3, GFDL, and PCM), and two downscaling approaches (monthly quantile mapping and daily asynchronous quantile regression) based on two different sets of long-term observations (station-based data at Hubbard Brook and PRISM-based gridded temperature and precipitation covering a larger one-eighth degree area).
The climate projections for Hubbard Brook using both downscaling approaches indicate that over the 21st century, average air temperature will increase with simultaneous increases in annual average precipitation. The modeling results from both downscaling approaches suggest that climate change is projected to cause substantial long-term shifts in hydrologic and hydrochemistry patterns. The choice of downscaling approach used, however, had a major impact on the streamflow simulations, which was directly related to the ability of the approach to mimic observed precipitation patterns. Station-based daily asynchronous regression projects increases in annual stream flow, while gridded quantile mapping projection indicates declines in streamflow will occur. The climate and streamflow change signals suggest that the current watershed stream discharge regime, with snowmelt-driven spring-flows in April, will likely change to conditions that are dominated by large winter flows. Model results from BCSD (Bias Correction-Spatial Disaggregation) show that under elevated temperature, net soil nitrogen mineralization and nitrification markedly increase, resulting in acidification of soil and streamwater. In contrast, results from station-based downscaling do not exhibit elevated ecosystem nitrogen loss and associated acidification. Indeed projections show recovery in acid-base status of the ecosystem from historic acid rain. Since NO3- is the main driver of acid-base status of the ecosystem, Ca2+, pH, and ANC follow similar patterns. Model results from BCSD downscaling show that warmer temperatures in the future cause a decrease in soil moisture and an increase in vapor pressure deficit, despite the increase in precipitation. These factors decrease evapotranspiration and cause midsummer drought stress, the extent of which is dependent on the climate-change scenario considered. In contrast, station-based results did not show any pattern of drought.
References:
Pourmokhtarian, A., Driscoll, C. T., Campbell, J. L., Hayhoe, K., (2012) Modeling Potential Hydrochemical Responses to Climate Change and Rising CO2 at the Hubbard Brook Experimental Forest Using a Dynamic Biogeochemical Model (PnET-BGC). Water Resources Research, Vol. 48, W07514, doi:10.1029/2011WR011228
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 26 publications | 7 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Pourmokhtarian A, Driscoll CT, Campbell JL, Hayhoe K. Modeling potential hydrochemical responses to climate change and increasing CO2 at the Hubbard Brook Experimental Forest using a dynamic biogeochemical model (PnET-BGC). Water Resources Research 2012;48(7):W07514 (13 pp.). |
R834188 (2011) R834188 (2012) R834188 (2013) R834188 (Final) |
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Supplemental Keywords:
Climate change, air pollution effects, atmosphere, environmental monitoring, hydrologic models, global climate change, watersheds, hydrochemical response, RFA, Air, climate change, Air Pollution Effects, Atmosphere, environmental monitoring, hydrologic models, atmospheric modelsProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.