 a warning of increasingly common severe heatwaves, flash floods and droughts was given by scientists yesterday (Hannah Devlin writes).  a report on extreme weather by the Intergovernmental Panel on Climate Change suggested that developing countries would be hit hardest by these outcomes of climate change.  a report by the panel in 2007 was found to contain an exaggerated claim about how fast Himalayan glaciers were melting.  But Rajendra Pachauri, the panel's chairman, said at a conference in Kampala, Uganda, that its credibility remained intact and that its findings would be a vital contribution to the UN Conference on Climate Change in Durban, South africa, next month.  The two-year study involving 100 scientists and policy experts is far more confident about the prospect of intense heatwaves and heavy downpours than the effect of climate change on hurricanes and tornados.