In the analysis of precipitation data for the greater Manila area, the following hydrologic problems were encountered:

1. Recognizing alternating series of wet and dry periods which affected fluctuations of groundwater level;

2. Forecasting probability of future occurrences and frequency of storm precipitation;

3, Estimating precipitation from porous and permeable areas with missing record required in the determination of mean areal depth; and

4. Determination of mean areal depth of precipitation from point precipitation data over a significant area such as a river basin or a recharge area.

The first problem was solved through the construction of a 3-year moving mean graph, superimposed upon a precipitation hydrograph, applied to the 90-year period of record gage nt Manila‘s Weather Bureau, Central Office. Interpretation of the graph had shown that peaks of rainfall occur at a mean interval of 11 years. The second was computed through application of the frequency curve to the 90-year period of record, interpretation of which forecasts for the greater Manila area that 9 years out of 10, on the average, the annual precipitation would be equal to, or greater than 48.84 inches. The third problem was determined through the use of several double-mass curves, thus obtaining the annual 1962 precipitation data for Makati and
Tala, Caloocan City which were not recorded by any agency, public or private. The fourth and last which was essential to groundwater computations was evaluated by using the Thiessen polygon method. Analysis revealed that the mean annual depth of precipitation for greater Manila covering an area of approximately 592 square kilometers was 92.3 inches for the year 1962.