Climatology and Sugar Cane — CHANG 
385 
poses. A knowledge of the extremes and fre- 
quency probabilities is indispensable. Because 
the basic cause of rainfall variation in Hawaii 
is rather uniform, the rainfall probabilities for 
different stations can be related in a simple, 
empirical manner (Landsberg, 1951). Figure 6 
shows the probabilities (slanting lines) of hav- 
ing an annual amount of less than a given quan- 
tity (ordinate) as a function of the median 
annual amounts (abscissae), based on at least 
60 years’ records of 20 plantation stations. It is 
evident that Figure 6 could be used as a risk 
chart. Monthly rainfall probabilities could also 
be presented in the same manner. 
TEMPERATURE 
The mean annual temperatures in the low- 
land plantation areas vary from 72.5 F along 
the east coast of Hawaii to 75 F for the drier 
stations. The temperature decreases with eleva- 
MEDIAN ANNUAL RAINFALL (INCHES) g 
co 
Fig. 6. Probabilities of having individual rainfall 
amounts in Hawaii as a function of median annual 
rainfall. 
tion at an average rate of 4 F per 1,000 ft. The 
coldest plantation stations, at an elevation of 
about 3,000 ft, have a mean annual temperature 
of 62-63 F. 
All the stations in Hawaii below an altitude 
of 5,000 ft have an annual temperature range 
of less than 9 F (Jones, 1942) ; thus a station at 
an elevation of 2,000 ft with an annual temper- 
ature of 65 F would have a minimum monthly 
temperature as high as 62 F. The isothermal 
climate is favorable for the growth of a peren- 
nial crop like sugar cane. 
In Hawaii, as in many other tropical coun- 
tries, the daily temperature range exceeds the 
annual mean daily temperature range and ex- 
hibits greater areal differences than does the 
mean annual temperature. Figure 7 shows the 
distribution of the annual mean daily tempera- 
ture range in the cane-growing areas. In general 
the dry leeward stations have the greater tem- 
perature range. The daily temperature range is 
subject to a small seasonal variation, being 
slightly higher in the winter. According to the 
results of phytotron experiments at the Cali- 
fornia Institute of Technology, daily tempera- 
ture range exerts a profound influence on fruit 
quality (Went, 1957). 
The distribution of soil temperature in the 
tropics can be deduced fairly accurately from 
observations of air temperature (Chang, 1958). 
The mean annual soil temperature at any depth 
differs only slightly from the mean annual air 
temperatures. The annual temperature range at 
the soil surface under the cover of a sugar-cane 
crop is reduced to half of the air temperature 
range. Thus, in most of the lowlands in Hawaii 
soil temperature exceeds 72 F throughout the 
year. Studies at the Experiment Station have 
established that temperatures of 62 F are ex- 
tremely limiting for cane growth and nutrient- 
and water-uptake. Such low temperatures are 
observed only in the mountains above 2,000 ft. 
The lowest soil temperature recorded on sugar 
cane land was 61 F at Hamakua plantation at 
an elevation of 3,000 ft. 
RADIATION 
Radiation measurements have been taken at 
35 plantation stations by photochemical tubes 
which use oxalic acid as agent and uranyl sul- 
