Final Report: Prediction of Effects of Changing Precipitation Extremes on Urban Water Quality

EPA Grant Number: R835195
Title: Prediction of Effects of Changing Precipitation Extremes on Urban Water Quality
Investigators: Lettenmaier, Dennis P. , Baptiste, Marisa , Nijssen, Bart , Sun, Ning , Yearsley, John
Institution: University of Washington
EPA Project Officer: Hiscock, Michael
Project Period: June 1, 2012 through May 31, 2016
Project Amount: $699,905
RFA: Extreme Event Impacts on Air Quality and Water Quality with a Changing Global Climate (2011) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Global Climate Change , Water and Watersheds , Climate Change , Air , Water

Objective:

The objectives of the proposed project were to:  (1)  integrate a system of existing physically based distributed hydrology models, dynamical and statistical downscaling methods, and urban water quality models to provide a framework for predicting of the effects of changes in climate extremes on urban water quality at regional scales; and (2)  demonstrate application of the framework to assess the implications of 2007 IPCC (Intergovernmental Panel on Climate Change) AR4 climate change scenarios (and AR5 scenarios as they become available) on water quality for the next half century at the scale of large urban regions.

The project successfully integrated water quality components based on EPA’s SWMM (Stormwater Management Model) model into DHSVM (Distributed Hydrology Soil Vegetation Model) and linked DHSVM to RBM (River Basin Model). The resulting modeling system was then used to simulate stream temperature and water quality basins in the Puget Sound region in Washington State and for the Connecticut River Basin in the northeastern United States. In particular, the effects of changes in climate and land use on stream temperature and water quality were evaluated for selected basins. The resulting computer codes are publicly available and the work has resulted in a five manuscripts in print (2), revision (1) and preparation (2).

Summary/Accomplishments (Outputs/Outcomes):

Our research has led to the following components that enhance our understanding of environmental problems and provide important insights into potential climate change adaptation measures that may benefit stream temperature regimes. In particular: 

  • We have developed mechanistic models that account for land use, riparian vegetation, and climate controls on stream temperature at high spatial resolution. Our findings emphasize the necessity of representing riparian shading in assessing the impacts of climate and land cover change on urban streams
  • Using this modeling system for basins in the Pacific Northwest, we have found that riparian vegetation is more important than basin-wide land cover change in determining stream temperature, even though both have minor effects on stream temperatures in winter high flow periods, because of lower heat inputs from solar radiation, and lower sensitivity of water temperature to the input of solar radiation with higher water depths in winter.
  • However, during summer months, the effect of riparian vegetation on stream temperatures is comparable with that of climate change. This leads to a finding with important implications for riparian management: Restoration of riparian vegetation over a fairly narrow streamside corridor can mitigate some (over half in some cases) of the effects of future climate change in summer low flow period (at least in the Pacific Northwest).
  • We have developed a mechanistic modeling framework that is applicable to the evaluation of potential changes in urban water quality and associated hydrologic changes in response to ongoing climate and landscape alteration. The grid-based spatially distributed model, DHSVM-WQ, is an outgrowth of the DHSVM that incorporates modules for assessing hydrology and water quality in urbanized watersheds at a high spatial and temporal resolution. DHSVM-WQ simulates surface runoff quality and in-stream processes that control the transport of nonpoint-source (NPS) pollutants into urban streams.
  • Using this model in three urban watersheds in the Puget Sound region, we have found that urbanization has a much greater effect than climate change on both the magnitude and seasonal variability of streamflow, TSS(Total Suspended Solids) loads, and TP (Total Phosphorus) loads largely due to substantially increased streamflow, and particularly winter flow peaks. Water temperature is more sensitive to climate warming scenarios than to streamflow changes associated with precipitation changes and urbanization.

Conclusions:

  • Our grid-based modeling system, DHSVM-RBM, dynamically couples the spatially distributed hydrologic model DHSVM and semi-Lagrangian, one-dimensional stream temperature model RBM. It facilitates characterization of the impacts of climate, landscape and near-stream vegetation changes on stream temperature and allows modelling of spatially distributed water temperature for the entire stream network. As applied to the Mercer Creek urban watershed, the model results suggest that DHSVM-RBM is able to produce reasonable streamflow and water temperature predictions at fine temporal and spatial scales.
  • In the Mercer Creek urban watershed: Notwithstanding general warming as a result of climate change over the last century, which has resulted in somewhat warmer stream temperatures, there have been concurrent increases in low flows as a result of urbanization and deforestation, which more or less offset the effects of a warmer climate on stream temperatures.
  • In the Mercer Creek urban watershed: […] loss of riparian vegetation has had a much larger impact on stream temperature and, in particular, on annual maximum stream temperature (around 4°C), which could be mostly reversed by restoring riparian vegetation in a fairly narrow corridor – a finding that has important implications for vegetation management in the riparian corridor. Our findings also emphasize the necessity of representing riparian shading in assessing the impacts of climate and land cover change on urban streams.
  • As applied to 15 sub-basins in Puget Sound, our results show that the model is able to produce streamflow and stream temperature predictions at fine temporal and spatial scale that mostly match available observations well.
  • For those 15 sub-basins: Through a set of simulations with different assumptions about future land use and climate change, we find that:

(1) riparian vegetation has a much greater effect on stream temperatures than does basin-wide land cover change especially during summer low flow periods when maximum stream temperatures occur;

(2) riverine inflows account for up to 1/8 of the overall thermal inputs to Puget Sound in winter, and this fraction increases with both urbanization and climate change, although the increase is relatively modest in both cases. The fraction in summer, however, will decrease with climate change.

(3) the effect of riparian vegetation on stream temperatures is comparable with that of climate change in summer months; hence, the restoration of riparian vegetation over a fairly narrow streamside corridor can mitigate some (over half in some cases) of the effects of future climate change in summer low flow periods;

(4) both basin-wide land cover and riparian vegetation have minor effects on stream temperatures in winter high flow periods, because of lower heat inputs from solar radiation, and lower sensitivity of water temperature to the input of solar radiation with higher water depths in winter. In contrast, climate change results in stream temperature changes year round mainly due to air temperature changes.

  • In this study, we develop and demonstrate the application of a hydrologic/water quality model, DHSVM-WQ, for predicting hydrology and water quality in urbanized watersheds at a high spatial and temporal resolution. The water quality module uses conceptual representations of physical processes associated with pollutant sources, transport, and transformation, in a manner similar to SWAT (Soil and Water Assessment Tool), HSPF (Hydrological Simulation Program--Fortran), and SWMM. DHSVM-WQ is grid based and spatially distributed, which facilitates a pathway to investigate the implications of changes in climate and landscape on urban water quality in space and time, and allows approximation of pollutant pathways to surface waters and determining priority areas to be targeted for possible remediation. As applied to three urbanized catchments, the model provides plausible predictions of streamflow, stream temperature, TSS, and TP.
  • By conducting simulations using a set of scenarios that characterize future climate and land use change for three urbanized catchments in the Pacific Northwest, we find that:
  • The urbanization scenario (LC2050), as compared to the precipitation change scenario (RCP8.5[P]) and warming scenarios (RCP4.5[T] and RCP8.5[T]), has a much greater effect on increasing both magnitude and seasonal variability of streamflow, TSS and TP loads due to substantially increased streamflow year round, particularly during winter flow peaks; Water temperature is more sensitive to RCP4.5[T] and RCP8.5[T] than to the streamflow changes driven by LC2050 and RCP8.5[P];
  • By conducting simulations using a set of scenarios that characterize future climate and land use change for three urbanized catchments in the Pacific Northwest, we find that:
    1. Extreme water quality events in urban watersheds are expected to change primarily as a result of changes in the hydrologic regime (e.g., changes in precipitation intensity and duration);
    2. The timing and magnitude of high-load events of TSS and TP are strongly correlated with those of high-flow events, especially in the forest dominated Issaquah catchment where the predominant source of TSS loads is soil erosion;
    3. Urbanization and climate change together are predicted to yield significantly higher annual mean streamflow (up to 55% increase), water temperature (up to 1.9ºC increase), TSS load (up to 182% increase), TP load (up to 74% increase), when comparing against the current condition.
    4. The effect of water quality parameter uncertainty on TSS and TP load predictions was generally greater than the effect of Global Climate Models  uncertainties, particularly during high-load events.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 8 publications 3 publications in selected types All 3 journal articles
Type Citation Project Document Sources
Journal Article Cao Q, Sun N, Yearsley J, Nijssen B, Lettenmaier DP. Climate and land cover effects on the temperature of Puget Sound streams. Hydrological Processes 2016;30(13):2286-2304. R835195 (Final)
  • Full-text: ResearchGate-Abstract & Full Text PDF
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  • Abstract: Wiley Online-Abstract
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  • Journal Article Sun N, Yearsley J, Voisin N, Lettenmaier DP. A spatially distributed model for the assessment of land use impacts on stream temperature in small urban watersheds. Hydrological Processes 2015;29(10):2331-2345. R835195 (2013)
    R835195 (2014)
    R835195 (2015)
    R835195 (Final)
  • Full-text: Wiley-Full Text PDF
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  • Abstract: Wiley-Abstract & Full Text HTML
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  • Other: ResearchGate-Prepublication PDF
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  • Journal Article Sun N, Yearsley J, Baptiste M, Cao Q, Lettenmaier DP, Nijssen B. A spatially distributed model for assessment of the effects of changing land use and climate on urban stream quality. Hydrological Processes 2016;30(25):4779-4798. R835195 (2014)
    R835195 (Final)
  • Full-text: Wiley-Full Text PDF
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  • Abstract: Wiley-Abstract & Full Text HTML
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  • Other: ResearchGate-Abstract & Full Text PDF
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  • Supplemental Keywords:

    Urban water quality, water quality, urban streams, precipitation, hydrology model

    Relevant Websites:

    RBM Semi-Lagrangian Stream Temperature Model | University of Washington Exit

    UW-Hydro / DHSVM-RBM GitHub Site Exit

    Progress and Final Reports:

    Original Abstract
    2012 Progress Report
    2013 Progress Report
    2014 Progress Report
    2015 Progress Report