A Web‐based rainfall atlas for Southern Africa

Abstract

AbstractWe describe the development of a Web‐based rainfall atlas for southern Africa, a decision support system for the management of water resources. The rainfall atlas, which is accessible online at the URI http://134.76.173.220/rainfall/index.html, was constructed in a number of phases over some 20 years. In the first phase, a 16 parameter model was developed, validated for representative sites, and then fitted to daily rainfall data from 2550 sites. Eight years later the estimates of the model parameters were updated, extended to 5070 sites, and interpolated on a grid of 1 minute of a degree of latitude and longitude over the entire region of southern Africa, namely South Africa, Lesotho and Swaziland. The method of kriging with external drift was used for the interpolation. The interpolated estimates were used to generate long artificial daily rainfall sequences at a spatial resolution of 1 minute of degree square. The sequences were used to compute rainfall‐related statistics, such as percentiles of annual and monthly rainfall distributions, probabilities associated with droughts, and additional measures relating to the timing and intensity of rainfall. The final phase, information transfer, was the construction of the Atlas website, which offers online access to a wide range of rainfall‐related statistics and some 5000 maps. To facilitate the computation of statistics that are not available in the database, the Atlas enables users to generate, and then import, artificial sequences online, for any grid point in southern Africa. These sequences are designed to mirror the properties of real rainfall records (seasonality, serial dependence, distributional properties, etc.) at the required grid point and can be used to compute quantities of interest empirically. Copyright © 2006 John Wiley & Sons, Ltd.