Distance from the sea, proximity of mountains,continentality and elevation are all useful covariates to assist the mapping of extremerainfalls. Regression models linking these and other variables calculated from a digitalterrain model have been built for estimating the median annual maximum rainfall, RMED.This statistic, for rainfall durations between 1 hour and 8 days, is the index variable inthe rainfall frequency analysis for the new UK Flood Estimation Handbook.The interpolation of RMED between raingauge sites is most challengingin mountainous regions, which combine the greatest variation in rainfall with the sparsestnetwork of gauges. Sophisticated variables have been developed to account for theinfluence of topography on extreme rainfall, the geographical orientation of the variablesreflecting the prevailing direction of rain-bearing weather systems. The differentprocesses of short and long-duration extreme rainfall are accounted for by separateregression models. The technique of georegression combines estimates from regressionmodels with a map of correction factors interpolated between raingauge locations using thegeostatistical method of kriging, to produce final maps of RMED across the UK.
展开▼
