A Method for Developing Climatological Rainfall Information: A Preliminary Application to Luzon

A method for developing climatological information of monthly rainfall for the Philippines is described. The information consists of monthly rainfall at a uniform array of grid points. This array can be used to construct climatological rainfall maps and other types of graphical representations with the aid of a geographical information system. The method, which has been developed, is based on combining three types of rainfall information. These consist of grid point rainfall values from a fluid dynamical model of the atmosphere, rainfall observations from rain gauge stations and satellite estimates of rainfall. These three types of information are combined by an objective analysis technique in order to obtain rainfall at a uniform network of grid points.

The present paper describes an initial application of the method to the island of Luzon for the month of June. In this application, only model-generated rainfall and rainfall from rain gauge stations are used. Satellite data are not included in the application because these are still not available. The atmospheric model, which is used in this initial application, is a simple model–the mixed layer model. The climatological rainfall information, which is produced by the method, is used to construct a climatological map of rainfall for the month of June. The map is compared with a corresponding map prepared by the Climate Branch, Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA). The map which is produced by the present method, exhibits higher horizontal resolution and greater accuracy.