CUMULATIVE PERCENTAGE OF RAINFALL 
Fig. 5. Relationship between per cent of days with rain and per cent of total rainfall. 
one in every 5 or 6 years. Furthermore, storm 
damages are usually restricted to Kauai and the 
east coast of Hawaii. 
The frequency distribution of daily rainfall in 
Hawaii is extremely skewed. Figure 5 shows the 
relationship between the percentage of rainy 
days and the percentage of rainfall amounts 
cumulated from the least to the heaviest. At 
Ewa, for example, 10% of the days with the 
heaviest rain accounted for nearly 60% of the 
total, while 50% of days with least rainfall 
amounted to only 6% of the total rain. The 
skewness of the daily rainfall frequency curve 
decreases slightly with the increase of annual 
rainfall. 
The skewed rainfall distribution has at least 
two important implications. First, a large 
amount of the annual rainfall will probably be 
lost as runoff. Second, the mean monthly rain- 
fall will be considerably higher than the median, 
and the former is a poor indicator of the 
"normal” condition. For this reason median 
rainfall is used extensively in Hawaii. 
As rainfall variability is very high in the 
tropics (Biel, 1929), even the use of the 
median is inadequate for many agricultural pur- 
