**2. Climate Change and the Water Cycle**

Even cursory examination of the evidence shows the importance of water in relation to climate change. The impact of water in the decline of civilisations has been examined and reviewed [13]. Climate change is likely to affect the water cycle across the globe [14] with potential influences on surface and groundwater quality; it will lead to changes in atmospheric water vapour content, changes in cloud types and cover, and changes in the frequency of severe storms. Over time, it is likely that there will be increased melting of glaciers and icecaps [15] and ocean warming (and associated thermal

expansion) that will cause sea levels to rise [16]. It remains possible that the release of permafrost methane may contribute to further warming [12,17]. These changes in atmospheric conditions and moisture content are expected to result in an increase in floods, famine, hurricanes and tropical storms, drought [18], wild fires, chronic water shortages, decreased water quality, periods with increased mosquito vectors, alterations to the seasonality of diseases, contaminated recreational waters and rising sea levels. Most assessments of the risks to health from climate change are conducted over time periods ranging from the present to 80 years. However, there are potentially much larger risks over longer timescales, particularly if there is a substantial sea level rise, and prolonged periods with much-increased average and peak temperatures [19].

Although scientific understanding of how climate may affect weather patterns has increased enormously over the past few years, especially in relation to extreme weather, the consequences for, and influences on, water quality (e.g., microbiological quality) are far less studied [20]. Changes in water arise from interactions with the weather, affecting ecosystems, changing the flow of nutrients and pathogens in catchments, and influencing water quality. Climate change may influence the microbiological quality of river water, which may present risks to bathers [21]. A modelling approach involving Quantitative Microbial Risk Assessment found that although climate change increased the fluxes of a number of pathogens, the overall change in risk was limited. Part of this was due to the dilution effect of increasing rainfall. As risks are likely to be location specific, wider generalisations are difficult. The approach used in such studies could be transferred to other locations. In summary the IPCC states that in overall terms, climate change is projected to reduce the quality of raw waters [22].
