The article on climate change and its impact on drainage systems (NCE 18 July) highlighted the importance of taking a precautionary approach to design in light of the future uncertainties. But I would like to clarify some points.
First of all, I wish to correct the misconception - attributed to me - that climate models, such as the Hadley Centre's, do not yet take account of CO 2and CFCs. The Hadley Centre models do represent the complex effects of various scenarios of atmospheric emissions and, through using the rainfall outputs from these models, the impacts on drainage design can be investigated.
This is not the place for detailed discussion on the uncertainties in climate modelling and their representation of CO 2and other emissions, or their prediction of the change in rainfall across the country. However three points raised in the article that might be worthy of brief additional comment include:
lReference to wetter summers in the title is not in keeping with the recent UKCIP02 output, which predicts that summers are going to become significantly drier.
lThe claim that the differences between FEH and FSR are largely attributable to climate change is not in accordance with the views of most hydrologists.
lThe likely worsening of water quality in rivers due to spills from CSOs is more to do with the longer drier spells causing more polluted CSO spills and stormwater discharges in rivers which will have lower summer base flows than 'catastrophic' overflows.
Richard Kellagher, principal engineer, HR Wallingford, Howbery Park, Wallingford, Oxon, OX10 8BA