Global warming and the demand for water

More than a decade has passed since the International Panel on Climatic Change began to study (in depth) the possibility that the global climate was changing. Increasing attention is also being paid to the impact of such changes on society in general, and on the planning and management of water resources. Not least among the water resources planning problems is the estimation of the changes which might occur in public water-supply demands. Such changes are notoriously difficult to evaluate, particularly in the UK where most domestic premises remain un-metered. Elsewhere, econometric models involving climatic parameters as independent variables have had some success, but a recent application of this approach in the UK was unable to identify particular parameters which had a consistent influence over the summer period. This lack of success might be partly caused by the public reaction to summer conditions being a complex function of several parameters, such as duration of sunshine, temperature and rainfall. This complexity has already been recognised by climatologists, who have devised forms of summer indices involving weighted combinations of climatic variables to determine how 'good' or 'bad' a particular period might be perceived by the general public. The use of one such summer index to explain the variations in an index of demand for public water supply in the London supply area has shown that simple and consistent relationships can be derived. Application of these relationships to scenarios of changes in temperature, sunshine duration and rainfall totals for the year 2050 shows an increase of 0.6- 2.9 index points in water-supply demand over the 1950-1990 period average.