Climatology and Sugar Cane — CHANG 
391 
the annual water deficits of the four islands are 
estimated as in Table 1. It is noted that there is 
a large regional variation. The average annual 
deficit for plantation areas on Hawaii, which 
are almost exclusively unirrigated, is only 16.5 
inches. By contrast, the average deficit for Maui 
is as high as 72.8 inches. 
The total annual water deficit for all the 
plantations is estimated at 7.6 million acre- 
inches, or 208 billion gallons. The industry uses 
about 400 billion gallons of water a year for 
irrigation. At first glance, the camp crop in Ha- 
waii seems to be irrigated more than adequately. 
This is, however, not true. Much of the irriga- 
tion water is wasted due to maldistribution. For 
instance, a plantation irrigation at a high level 
of adequacy often loses as much as 60% of its 
water through deep penetration or runoff. Fur- 
thermore, the water supply is often such that a 
plantation over-irrigates in one season and suf- 
fers from drought in another. 
The monthly water-balance charts and the 
water-deficit maps are a valuable guide to agri- 
cultural planning. Such questions as whether or 
not to construct a reservoir, what irrigation sys- 
tem to adopt, and what crop to grow can be 
answered, at least in part, through the use of 
climatic data. 
The monthly water balance presented above 
is by no means precise because the median rain- 
fall is only an approximation of the effective 
rainfall. The amount of effective rainfall varies 
with the rainfall intensity as well as with the 
moisture storage capacity of the soil. To credit 
rainfall correctly, it is necessary to compute the 
daily water balance. 
Fig. 14. Annual water deficit (inches) in Hawaii. 
