Changes in precipitation extremes for New Zealand: climate model predictions
An analysis of daily precipitation output from a regional climate model was undertaken in order to estimate future changes in precipitation extremes for New Zealand. Daily rainfall for present (1971—2000) and future (2071—2100) climate under the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios A2 and B2 emission scenarios, was simulated by the regional climate model PRECIS, developed at the UK Met Office Hadley Centre. Return values of 1-day precipitation extreme for a 5-year return period were calculated from a generalized Pareto extreme value model fitted to the tail of the rainfall distribution. A test of the statistical analysis in several regions of New Zealand revealed that the generalized Pareto model was appropriate for estimating daily precipitation extremes over the country for short return periods, but was unable to realistically capture the changes in longer return periods under transient climate change. For long return periods, a separate analysis of the regional climate model simulations suggested that the increase in the heaviest rainfall extremes in the country has an upper limit in the range of between 7 to 9% per Kelvin of warming. Similarly, an ensemble of global climate models from the Coupled Model Intercomparison Project 3, suggested an increase of 5 to 12% per Kelvin. For New Zealand, increases in precipitation extremes greater than that predicted by the widely used Clausius Clapeyron relationship (6.5% per Kelvin), should be considered in future planning.