Grantee Research Project Results
Final Report: Consequences of Global Climate and Emissions Changes on U.S. Water Quality: An Integrated Modeling Assessment
EPA Grant Number: R834189Title: Consequences of Global Climate and Emissions Changes on U.S. Water Quality: An Integrated Modeling Assessment
Investigators: Liang, Xin-Zhong , Wuebbles, Donald J. , Srinivasan, Raghavan , Tuppad, Pushpa , Arnold, Jeff
Institution: University of Maryland - College Park
EPA Project Officer: Packard, Benjamin H
Project Period: August 1, 2009 through July 31, 2012 (Extended to July 31, 2014)
Project Amount: $723,559
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:
The objective of this project is to quantify and better understand the impacts and uncertainties of global climate and emission changes from the present to 2050 on U.S. water quality, focusing on the nitrogen cycle and accounting for potential agricultural land conversion to alternative food and biofuel crops, to enable decision makers to design effective management plans and regional adaptive strategies to reduce the risk of harmful impacts. A state-of-the-art modeling systems (GCM: CCSM4 for CMIP5, RCM: CWRF, and hydrology and water quality model: PSWAT) are used to quantify the impacts on future U.S. water quality by a suite of climate changes projected from the present to 2050, including mean and variability (especially extremes). The system integrates climate dynamics, atmospheric physics and chemistry, terrestrial hydrology, agroecology and biogeochemistry, surface emissions, and their nonlinear interactions across a full range of spatial and temporal scales. It consists of one general circulation models (GCMs), which is from National Center for Atmospheric Research – NCAR, NCAR community atmosphere model coupled with the model for ozone and related chemical tracers (MOZART) chemistry (CAM-Chem) to project global changes in climate and chemical transport under 5th intergovernmental panel on climate change (IPCC) accounting for dynamic landuse changes; they represent the likely range of future projections of climatic and chemical lateral boundary conditions (LBCs) that force ESSIC/UMD climate extension of the weather research and forecasting model (CWRF) to downscale regional climate and air quality in North America; they then provide climatic and hydrologic conditions and atmospheric NO3- and NH4+ depositions that drive the soil and water assessment tool (SWAT) to predict water quantity and quality over the entire continental U.S. Such a predictive SWAT (PSWAT) incorporates the most comprehensive pollutant sources (natural and anthropogenic, point and nonpoint), surface and subsurface watershed processes (upland, soil, plant and crop, channel and flood plain, urban, lake and reservoir), agricultural practices (cropping, fertilizer and pesticide use, irrigation, tillage), and other human managements (dam control, sewage discharge, landuse alteration). It determines water yield and supply, streamflow, surface runoff, groundwater recharge, nutrients (N, P), pathogens, bacteria, and sediments, and also feed the changing hydrology and canopy back to CWRF. To enhance result credibility, PSWAT must be objectively calibrated to derive unknown parameters and then validated against surface observations, including precipitation, snow cover, air temperature, vegetation, crop yield, ozone, nitrogen wet deposition, and in-stream nitrogen loading. To this end, the main achievements are given below.
Summary/Accomplishments (Outputs/Outcomes):
Under this EPA STAR support, the Predictive Soil and Water Assessment Tool (PSWAT) that projects future changes in water quantity and quality has been developed through coupling the Climate extension of Weather Research and Forecasting (CWRF) model with the Soil and Water Assessment Tool (SWAT).
The PSWAT has been first calibrated and validated based on its retrospective simulations as driven by the observational reanalysis data to reproduce the observed climate, hydrology, and water quality variations.
We first analyzed variation and distribution characteristics of regional climate model downscaled results from general circulation models for the present and future, and linked the predicted effects of climate change (such as increasing atmospheric water vapor content, changing precipitation patterns, intensity and extremes, reduced snow cover and wide spread ice melting) to hydrology using PSWAT.
We have also updated the PSWAT core code from version SWAT2009 to version SWAT2012; developed an interface allowing PSWAT to cope with changing point sources, manure, and atmospheric deposition for application under different climate change scenarios. Meanwhile we have collected, distributed, and projected point pollutant sources, manure from livestock breeding according to population growth projections; and projected future changes under new representative concentration pathways (RCPs).
Specific achievements include:
- The performance of the PSWAT system is hindered by high frequency input-output operations. The thousands of input files for a large watershed must be combined into a single file to improve the computational performance of the coupled system, especially when run on supercomputing and parallel facilities. This has been accomplished through intensive and careful re-engineering works. First, all input and output variables were classified according to their function and the order of their usage in the program. Then, all categories were written in sequential order into one binary file. Three categories were used: variables to be initialized by reading operation, variables not used in the I/O operation, and output variables. Only a reading interface was needed between input data processing and predicting component in the model.
- Atmospheric depositions from the Community Multiscale Air Quality Modeling System (CMAQ) have been integrated into PSWAT to predict nitrogen distribution. The results indicate that land use (agricultural categories) and atmospheric deposition are the main factors affecting the nitrogen geographic distribution over the U.S.
- A comprehensive input dataset was built for SWAT application over the entire Conterminous United States. The data include: 1) the primary data derived from the Digital Elevation Model (DEM) for the channel length (both the main routing and tributary channel), subbasin channel slope, and Hydrologic Response Unit (HRU) overland slope; 2) the Land Use/Land Cover (LULC) and land management, which are the essential parameters for accurate estimation of various components of the simulating of hydrologic cycle and crop yields; 3) the national State Soil Geographic (STATSGO) soil layer at 1:250,000 scale, which are distributed with ArcSWAT software installation package for the HRU soil characteristics; 4) the climate data of all variables, including daily precipitation and maximum/minimum temperature, derived from the North American Regional Reanalysis (NARR), which is the best available proxy of observations, for the period of 1979-2008. Each HRU is a unique combination of land use, soils, and slope overlay within a subbasin. They are the basic building blocks of SWAT at which all the landscape processes are computed. The slope classes used for this process were 0-1%, 1-3%, 3-5%, 5-8%, and 8% and above, while the land use/soil/slope threshold was 1,000-ha each. As a result, the SWAT predicts hydrologic processes and water quantity and quality variations in 145,581 HRUs over the Conterminous United States.
- All the necessary datasets of pollutant point sources (sewage treatment, fertilizer, and livestock) were constructed and geographically allocated onto PSWAT 8-digital HUCs watersheds over the entire U.S. These pollutant distributions were also projected onto year 2050, including the point sources, fertilizer and the manure from livestock changes based on the IPCC scenarios RCP4.5 and RCP8.5. This projection included key factors such as those related to population growth and land use changes. The outcome will improve understanding of the contributing factors and their relative importance for the projected differences from the current to future by PSWAT. We plan (via other funding resources) to continue some experiments and subsequent diagnostic analyses that will determine the individual and combined impacts of climate and emissions changes, natural and anthropogenic changes, and atmospheric depositions and regional-local sources, on the future U.S. water quality distributions.
- PSWAT performance has been evaluated by comparing the correlation coefficients of the measured streamflow and simulated runoff over the entire U.S. Correlation coefficients are generally high, indicating that PSWAT can be applied to large watersheds and over the entire U.S. for the streamflow distribution prediction. The mountainous regions in the western U.S, however, still require refinement. In a retrospective simulation during 1979-2008, PSWAT faithfully reproduced the observed climate, crop production, and water quality. Reservoir management had a great effect on the streamflow predictions, especially over the western U.S. mountainous region. PSWAT can capture the amount and variability of monthly and annual streamflow over most of the U.S. The model can also predict the corn and soybean yields very well over the upper Mississippi River basin (with percent bias less than 20% for 11 out of four-digit HUCs for both corn and soybean).
- Management prediction system of reservoir has been developed to evaluate the effect due to climate change on to water resources and water quality under the current human management strategy. The simulated water yield with reservoir management scheme was compared with the actual water yield, was found to be more consistent than the simulated one without reservoir managements. It indicates that human management exert significant influence on the allocation of water resources, this is much more obvious on the management-dominated area, such as western U.S. in particular. According experimental simulation, if the current management strategy is extended to near future like 2050 without any adjustment, the reservoirs located in Colorado River basin will be gradually exhausted with the changes of climate.
- A 12-HUC scale PSWAT system has been developed to meet the requirements of future climate assessment at a finer scale. This 12-HUC PSWAT model provides a foundation for the future PSWAT working on the 12-HUC scale over the continent. Proper calibration was critical, as it affects the credibility of the model projection. To develop a physically based distributed hydrologic model requires integrating a huge amount of physical and statistical information and calibrating a large set of unknown parameters for each basin. For this purpose, PSWAT was calibrated at a finer resolution (HUC12 scale) over a large-scale basin Western Lake Erie Basin (WLEB), including Indiana, Michigan and Ohio with an area of ~28,330 km2, as well as calibrated over the Missouri River basin. The traditional approach of calibrating the model only at the catchment outlet cannot account for hydrological and land management differences across the basin. Therefore a new calibration strategy was developed to capture the spatial and temporal variability of hydrologic and land management patterns across the basin. The calibration ensured that gauged and ungauged subunits within the watersheds were represented reasonably well by incorporating wide variations in hydrology and crop management systems produced in different subunits of the large river watersheds due to variations in rainfall, soils, land use and vegetation.
- The effects of projected global changes in climate and human-related emissions for the 2100s compared to the 2000s were investigated for trends in precipitation and temperature, using a regional climate model as driven by large-scale meteorology outputs from the Community Climate System Model version 3. The projected changes in climate are likely to result in lowered precipitation in the west United States. For Rio Grande, Upper Colorado, Lower Colorado, and the Great Basin, variations in trends of future precipitation were always negative. The tendency of lower Colorado is particularly obvious; the basin mean decreased 20.33% (B1), 34.22% (A1B), and 63.93% (A1FI), relative to the current precipitation. However, increases in temperature were expected to be at highest 6.77 (A1FI) or at lowest 1.49 (B1).
- Runoff distribution over the United States was analyzed based on PSWAT simulations. The impacts of climate change on U.S. water resources were evaluated through a comparison of simulated yearly mean runoff under various future climate scenarios (2050s, 2100s) against the ‘present day’ (2000s) conditions. The climate elasticity n was calculated according to the mean annual climatic variables. The results indicate that all of the 18-subbasins in the United Stated can be categorized into three classes (A, B, C) based on n values, which representing the effect of catchment characteristics. Class A basins have n values larger than 2.0, class C basins have n values close to 1, and class B have n values between A and C. Different group of basins have different sensitivity to climatic variables. For example, a 1% precipitation increase will result in an approximately 2.2% increase in runoff in group A, while a 1% increase in radiation Rn, temperature T, wind speedU2, and relative humidity RH will lead to -3.0%, -0.27%, -0.6%, and 1.7% changes in runoff variables, respectively. The effects of climate change on runoff in group C is clearly smaller than those in group A.
- The ratio of annual mean snowmelt to annual mean runoff was analyzed, and can be considered an index to the relative fraction of runoff that is derived from snowmelt. This result emphasized the critical role of snow processes to the hydrology of the western United States, and to a more limited extent, to the northern tier of states. The amount of the snow component in the precipitation during the 2100s decreased greatly compared with that of 2000s (A1B). The pattern of ratio of annual mean snowmelt to annual mean precipitation pushes northward, and narrows its extension. The pattern of the annual mean runoff is surprisingly similar to the physiographic regime which depicts regions grouped together based on similar rock and soil types, which also reflect geographic features such as mountains, plateaus, and valleys. This relationship will be beneficial to the analysis of complex mechanism of essential nexus between runoff and its geographic distribution in PSWAT.
- Changes to the nitrogen loadings were projected under climate change only, keeping all water pollutant sources unchanged from their present-day condition. The outcome provided the first-order estimate of the U.S. water quality’s response to climate change, if all pollutant emissions remained at the present-day level. The future nitrogen loading in the major watersheds shows strong seasonal and spatial variations. Over the upper Mississippi River basin, the nitrogen loading is projected (under the influence of nothing but climate change) to increase significantly in late winter to spring, peaking distinctly in April, but to decrease in summer, variation peaking in June. For this basin, the water quality problem in the future will occur early in the season cycle. The total nitrogen loading will significantly increase over much of the Upper Mississippi River basin, the Ohio River basin and the Mid-Atlantic watershed. Medium-level increases are also projected over the coastal regions, including the Texas-Gulf, South Atlantic-Gulf and Mid-Atlantic watersheds. More detailed analyses are being conducted along with preparing a comprehensive assessment paper that will elaborate on the seasonal variations and geographic distributions of water quantity and quality trends over the whole U.S., and will explain why these trends occur.
Journal Articles on this Report : 6 Displayed | Download in RIS Format
Other project views: | All 8 publications | 6 publications in selected types | All 6 journal articles |
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Choi HI, Liang X-Z, Kumar P. A conjunctive surface–subsurface flow representation for mesoscale land surface models. Journal of Hydrometeorology 2013;14(5):1421-1442. |
R834189 (Final) |
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Gan Y, Liang X-Z, Duan Q, Choi HI, Dai Y, Wu H. Stepwise sensitivity analysis from qualitative to quantitative:application to the terrestrial hydrological modeling of a Conjunctive Surface-Subsurface Process (CSSP) land surface model. Journal of Advances in Modeling Earth Systems 2015;7(2):648-669. |
R834189 (Final) |
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Liang X-Z, Xu M, Yuan X, Ling T, Choi HI, Zhang F, Chen L, Liu S, Su S, Qiao F, He Y, Wang JXL, Kunkel KE, Gao W, Joseph E, Morris V, Yu T-W, Dudhia J, Michalakes J. Regional Climate–Weather Research and Forecasting model. Bulletin of the American Meteorological Society 2012;93(9):1363-1387. |
R834189 (2012) R834189 (2013) R834189 (Final) R833373 (Final) |
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Srinivasan R, Zhang X, Arnold J. SWAT ungauged:hydrological budget and crop yield predictions in the Upper Mississippi River Basin. Transactions of the ASABE 2010;53(5):1533-1546. |
R834189 (2010) R834189 (2011) R834189 (2012) R834189 (2013) R834189 (Final) |
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Wang X, White M, Tuppad P, Lee T, Srinivasan R, Zhai T, Andrews D, Narasimhan B. Simulating sediment loading into the major reservoirs in Trinity River Basin. Journal of Soil and Water Conservation 2013;68(5):372-383. |
R834189 (2013) R834189 (Final) |
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Zhu J, Liang X-Z. Impacts of the Bermuda High on regional climate and air quality over the United States. Journal of Climate 2013;26(3):1018-1032. |
R834189 (Final) R833373 (Final) |
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Supplemental Keywords:
Climate change, hydrological processes, coupled model, nutrient, pathogen, bacteria, sediment, water yield, water supply, streamflow, surface runoff, soil moisture, groundwater recharge, discharge, fertilizer, pesticide, irrigation, drainage, tillage, dam control, urbanization, livestock, GCM, RCM, AQM, WQM , RFA, Air, climate change, Air Pollution Effects, AtmosphereRelevant Websites:
Development of predictive SWAT to assess global change impacts on U.S. water quality (PDF, 1pp, 1mb) Exit
Progress 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.
Project Research Results
- 2013 Progress Report
- 2012 Progress Report
- 2011 Progress Report
- 2010 Progress Report
- Original Abstract
6 journal articles for this project