1st International Conference on Rain Water Cistern Systems
Honolulu, Hawaii, USA - June 1982

Section 2: Rainfall Analysis

Page 46

Stochastic Dynamic Models for Rainfall Processes

Samir A. Ahmed
Oklahoma State University, USA

Yu-Si Fok
University of Hawaii at Manoa, USA

Introduction

In recent years, there has been a revival of interest in using rain water cistern systems (RWCS) as a supplement to rural and urban residential water supply (Fok et al. 1980; Fok, Murabayashi, and Fong 1979). The reasons for this have been the increasing demand for water and the lack of adequate supply. Curtailment of new urban developments and limits on new house-building permits because of water shortages have been reported in many areas, such as Orange County, California and all the counties o£ Hawaii. In addition, it may not be feasible in some areas-the Hawaii Volcanoes National Park, for example - to install pipelines for water supply (Wentworth 1959). Fok, Murabayashi, and Fong (1979) find that for residential houses located in areas with an annual rainfall of about 508 mm (20 in.), RWCS's may be feasible and cost effective as their main or supplemental source of water supply.

To properly design and operate a RWCS, it is necessary to understand the dynamic and stochastic nature of rainfall processes. These processes evolve continuously in time, thus suggesting models of differential equation form to describe their characteristics. However, since rainfall data are often collected at a series of discrete points in time, differential equation models can be directly used to fit such data. The parameters of the estimated discrete model can then be used to construct continuous time models if the data have been obtained through uniform sampling of the continuous process. The details of such a procedure for modeling, predicting, and simulating rainfall processes are explored in this paper.

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