The relationship between half-hourly rainfall occurrence and daily rainfall

Abstract

Application of satellite rainfall estimation techniques often necessitates an indexing approach in which rain occurrence is accumulated and used as an indicator of total rainfall. This paper describes a simulation to assess the extent to which halfhourly rain occurrence can be used to estimate daily rainfall in a two-month period of the rainfall season in the South African summer rainfall region. The results of the simulation showed that indexing is a valid approach, and that most of the information on daily rainfall totals is contained in rainfall occurrence. At a sampling frequency exceeding 75% (i.e. more than 36 times per day), 90% of variation in daily rainfall could be accounted for by an accumulated rain occurrence index (AROI). At a sampling frequency of 8 samples, equal to the available frequency of Meteosat imagery, for the time period of this study, up to 79% of daily rainfall variation could be accounted for by AROI. It is also shown that estimation accuracy is highly sensitive to rain-rate. *To whom all correspondence should be addressed.

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