Abstract

Abstract. Globally, water resources management faces significant challenges from changing climate and growing populations. At local scales, the information provided by climate models is insufficient to support the water sector in making future adaptation decisions. Furthermore, projections of change in local water resources are wrought with uncertainties surrounding natural variability, future greenhouse gas emissions, model structure, population growth, and water consumption habits. To analyse the magnitude of these uncertainties, and their implications for local-scale water resource planning, we present a top-down approach for testing climate change adaptation options using probabilistic climate scenarios and demand projections. An integrated modelling framework is developed which implements a new, gridded spatial weather generator, coupled with a rainfall-runoff model and water resource management simulation model. We use this to provide projections of the number of days and associated uncertainty that will require implementation of demand saving measures such as hose pipe bans and drought orders. Results, which are demonstrated for the Thames Basin, UK, indicate existing water supplies are sensitive to a changing climate and an increasing population, and that the frequency of severe demand saving measures are projected to increase. Considering both climate projections and population growth, the median number of drought order occurrences may increase 5-fold by the 2050s. The effectiveness of a range of demand management and supply options have been tested and shown to provide significant benefits in terms of reducing the number of demand saving days. A decrease in per capita demand of 3.75 % reduces the median frequency of drought order measures by 50 % by the 2020s. We found that increased supply arising from various adaptation options may compensate for increasingly variable flows; however, without reductions in overall demand for water resources such options will be insufficient on their own to adapt to uncertainties in the projected changes in climate and population. For example, a 30 % reduction in overall demand by 2050 has a greater impact on reducing the frequency of drought orders than any of the individual or combinations of supply options; hence, a portfolio of measures is required.

Highlights

  • Climate change projections point to longer or more frequent meteorological droughts in some regions by 2100 but there remain substantial uncertainties as to how rainfall and soil moisture deficits might translate into prolonged periods of reduced streamflow and groundwater levels (IPCC, 2014)

  • The ensemble of rainfall variation shows that there could be substantially greater pressure on water resources – the 10th percentile indicating decreases projected for all seasons; for SCN50 this represents a typical decrease of ∼ 45 % during summer with a small (< ∼ −5 %) decrease in winter

  • We note that a limitation of applying change factors through a weather generator to assess future projections in rainfall is that it does not readily produce the longer sequences of dry periods (Wilby et al, 2004) that may produce multi-seasonal droughts and stress the water supply system

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Summary

Introduction

Climate change projections point to longer or more frequent (or both) meteorological droughts in some regions by 2100 but there remain substantial uncertainties as to how rainfall and soil moisture deficits might translate into prolonged periods of reduced streamflow and groundwater levels (IPCC, 2014). This and other pressures affect and will continue to affect UK water availability into the future. Water resources may increasingly need to be enhanced and managed through new supply or demand management options.

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