MODELING OF THE TIME-SERIES OF SPATIAL COVERAGES OF BRITISH RAINFALL FIELDS

From an analysis of British radar data, it is concluded that the serie s of consecutive rainfall coverages for a given area (e.g. a general c irculation model grid-square) is strongly correlated. Consequently, in application of a rainfall disaggregation procedure, the choice of rai nfall coverage at each time-step should not be independent of previous coverage. The series of areal rainfall depths may be used to represen t part of this correlation by a simple regression based model. Improve ments upon this representation based upon linear time-series models ar e examined here, but they are of limited use. A second model uses the strong correlation between logarithmic transforms of the coverage and of the mean areal depth. It provides a good reproduction of the autoco rrelation structure of the observed time-series. The reproduction of t he marginal distribution can be improved upon by adding a linear time- series component. Another model which uses correlations between the se ries of ratios of consecutive coverages and those of consecutive areal rainfall depths is more successful in reproducing the autocorrelation s of the coverages while preserving the features of the marginal distr ibution of the coverage. It provides a method for the generation of su ccessive coverages conditional-upon the knowledge of the areal rainfal l depths.