A multivariate spatial-temporal model of rainfall in southwest Saudi Arabia. I. Spatial rainfall characteristics and model formulation

Abstract

Hourly data from a network of 100 autographic raingauges have been collected as part of an extensive hydrological investigation of five wadis in southwest Saudi Arabia. The general spatial and temporal characteristics of these data are presented. Seasonality of catchment rainday occurrence is illustrated and gauge rainday occurrence shown to be strongly associated with elevation. Most point rainfalls are of 1–2 h duration, initiated in mid to late afternoon. Spatial distribution is highly localised so that for the minimum intergauge distances of 8–20 km, probability of joint occurrence and cross-correlation of hourly rainfall are small. On the basis of these data, a stochastic model of the spatial distribution of hourly rainfall has been formulated. Catchment and gauge rainday occurrence are well reproduced, as are point rainfall depths and durations. Spatial performance is reasonable for daily rainfall. However, the weak spatial dependence in the data leads to some clustering of occurrence at the hourly level, which the model is unable to reproduce.