End-to-End Ensemble Modelling for Water Resources Planning Under Uncertainty

Counsell, Christian John Adam (2018). End-to-End Ensemble Modelling for Water Resources Planning Under Uncertainty. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000dcf7

Abstract

A hydrological model ensemble, considering two model structures (CatchMOD and PDM), parameter uncertainty and two contrasting methods for estimating potential evapotranspiration (PET), is developed to investigate the relative significance of different sources of uncertainty for water resources planning in the Thames basin. This model ensemble is driven by an ensemble of UKCP09 probabilistic and Future Flows climate change projections, for the 2030s, 2050s and 2080s, to quantify the projected impacts on a range of metrics of relevance to water resources planners using a water resources system model of London.

These sources of supply-side uncertainty are shown to be significant, with the uncertainty associated with the climate change scenarios the largest but hydrological modelling uncertainty, and the method used to estimate PET also shown to be considerable. In terms of overall impacts, the central estimates for the 2030s, 2050s and 2080s are reductions in available resource of around 7%, 11% and 14% respectively. These impacts are shown to equate to economic costs of the order of £360m, £610m and £735m respectively to mitigate such reductions in supply.

The range of uncertainty within each time-horizon is large, greater than the differences between the time-horizons, presenting a significant challenge in deciding the level and timing of investments to mitigate emerging risks. As an example, impacts considered reasonably likely by the 2080s (e.g. a central estimate of 14% impact on deployable output using both PET methods) may be as likely by the 2030s (e. g. using only the modified Penman-Monteith PET method). The estimates of future supply reliability are contrasted with demand forecasts and whilst the pressure associated with the latter is shown to be greater, both are significant and subject to large degrees of uncertainty.

This thesis also highlights the need for detailed examination of hydrological model structures to provide evidence as to their strengths and weaknesses in their representation of key processes, particularly during droughts. The limitations of the climate change products currently used in the industry, particularly with regards to droughts and estimating changes in PET, are also explored.

Significant ongoing research is developing decision-making approaches to support the planning of robust and resilient systems under an uncertain future. This thesis demonstrates that alongside this development, more research is needed to understand, identify and quantify the significant sources of uncertainty that need to be considered as part of the decision-making process.

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