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Development of integrated modelling techniques to assess impacts of climate change on pathogens and water quality

Final Report Summary - PACEMOD (Development of integrated modelling techniques to assess impacts of climate change on pathogens and water quality)

The PACEmod project aimed to apply catchment modelling techniques to (a) examine the effects of future climate and land management change on the transport of microbial organisms to freshwater; and (b) assess potential implications for water resource management. It is widely accepted by the scientific community that global climate change (i.e. extremes of the hydrological cycle and global warming) will affect the dispersion of microbial organisms (e.g. E. coli and fecal coliforms) in the environment. However, uncertainty surrounding environmental change (land and climate) impacts on microbial contaminant fate /transport processes makes the assessment of possible human exposure to waterborne pathogens complex and difficult to forecast. If water quality is to be improved and maintained in the future, steps must be taken now to prepare for climate change, examine the exact nature and magnitude of potential climate change impacts, and adapt to possible scenarios that may arise. At present, the major regulatory frameworks in Europe and the USA (i.e. the US Clean Water Act [CWA] and the EU Water Framework Directive [WFD]/Bathing Water Directive [BWD]), do not explicitly address risks posed by climate change. The need for more studies investigating the potential impacts of these changes on freshwater systems, in particular impacts on water quality and the coupling of future climate data with land use change, has been emphasised in recent Intergovernmental Panel on Climate Change (IPCC) reports. Use of catchment models, coupled with monitoring data and future climate and land management projections can permit the assessment of water quality scenarios beyond current records.
This project considered a suite of possible future environmental change scenarios for catchments in the west of Ireland (Fergus and Black rivers) and Virginia, USA (Pigg River). Catchment modelling frameworks were developed to simulate hydrology and microbial transport for all 3 catchments. A catchment model developed using the Hydrological Simulation Program in Fortran (HSPF) was applied for the Pigg River. For the Fergus and Black Rivers, model simulations were conducted using the Soil and Water Assessment Tool (SWAT). Catchment specific data on climate, microbial sources, soils, land use/management, and topography were used for the initial development of modelling frameworks. Observed hydrological data (from catchment located flow gauges) and observed E. coli (Fergus and Black)/fecal coliform (Pigg) sampling data in each catchment were used to calibrate and validate individual models. The developed hydrologic and microbial models provided acceptable prediction of flows and microbial water quality for the Pigg, Fergus and Black Rivers. Post calibration, input data for each catchment were updated to reflect future changes in climate and land management projected for the mid-century period (circa 2050). For Pigg River, 1 future climate scenario and 1 future land management scenarios (LU) were considered to assess impacts on daily stream flow and the daily microbial load. Downscaled General Circulation Model (GCM) projections (ensemble of 7 GCMs) by the Consortium for Atlantic Regional Assessment for the B2 scenario (moderate greenhouse gas emissions) were used to modify historical weather data used in model calibration. For the Irish catchments, 2 future climate scenarios and 1 LU scenario (see Fig. 1) were considered in simulations to assess environmental change impacts on stream flow and the daily microbial load. Downscaling of global modelling outputs was carried out by Met Éireann and the Irish Centre for High-End Computing as partners in the EC-Earth international consortium. Projections were based on two Representative Concentration Pathway (RCPs-4.5 and 8.5) scenarios and used to modify existing weather data (from model calibration). A LU scenario reflecting available data on agricultural production and human population changes was used to update microbial source input data for each study catchment. In all three catchments, variations in stream flow and the daily microbial load were compared to baseline conditions (calibration/validation periods) for the various climate and land management scenarios simulated. Subsequently, possible adaption measures to meet existing US and EU recreational water quality standards were determined from model outputs for all scenarios (baseline and future). Measures were focused on attainable reductions in load from microbial sources.
The simulated scenarios indicated increases of in-stream microbial load annually in all study locations. Trends in microbial load changes were symptomatic of projected seasonal precipitation patterns. Increases of in-stream microbial loads were more pronounced during the winter and autumn months when rainfall is projected to increase. Typically, high and low flow extremes reflected periods when the greatest flux was evident. LU changes (human population and agricultural production increases), in combination with forecasted climate change, caused the most significant increase in daily microbial load. This suggests that future variations in land use/management may be as important as the effects of climate change for in-stream microbial pollutant loads. However, data on future land management were limited in all study catchments. All simulated scenarios (baseline and future) for the Black and Pigg rivers violated numerical criteria guidelines for recreational water quality set by the US CWA. In contrast, all scenarios simulated for each catchment achieved “excellent” status under the EU BWD classifications for freshwater. This signifies that the EU BWD is more tolerant in terms of the allowable in-stream microbial load when compared with the US CWA, and also suggests that EU BWD standards are a more achievable target in all freshwater under future environmental changes. When interpreting the modelling results it should be noted that there are many uncertainties involved in the development of models and the simulation of environmental change scenarios. For example, sources of uncertainty could include sampling errors in observed data, data input errors (microbial source estimates, climate data-existing and downscaled), temporal and spatial variability, failure to capture in-stream processes and others. However, the developed modelling frameworks represent useful tools capable of examining the magnitude of future environmental changes.
Adaptive land management strategies to reduce microbial source loads were subsequently determined in all catchments. Extensive reductions from point and diffuse microbial sources were required in the Pigg and Black catchments to meet the US CWA standard for E. coli. In the US, implementation of best management practices to reduce microbial loads and restore recreational water quality within standards requires extensive funding costs under the Total Maximum Daily Load program. This highlights the difficulties that catchment stakeholders in the US may face (financial and practical) to achieve objectives set out in the CWA under future environmental change. Preparing for the impacts of environmental change, in particular for water quality, is one of the most pressing challenges for water policy globally. Freshwater resources are among the systems that are particularly vulnerable. The PACEmod project represents an initial step towards understanding the possible impacts of environmental change on microbial contaminants in freshwaters and the subsequent implications for recreational water use. In addition, the possible scale of adaptation measures that will be required in future years to maintain microbial water quality within existing water quality standards is examined. Managing risks by adapting existing regulatory frameworks and adjusting to the impacts of environmental change must become a critical component of catchment planning in the intermediate term. Such strategic preparation will improve existing policymaking, and ensure that an optimal context is in place for future decisions based on evolving environmental conditions. This is vital to maintain the quality of all freshwater going forward, and minimize the potential public health risk from pathogenic waterborne microorganisms in recreational freshwater.
Fellow:; Scientist in charge: (School of Biosystems Engineering, University College Dublin, Belfield, Dublin 4, Ireland.)

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