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The purpose of this study was to analyze the characteristics of rainfall in the Northern
part of Thailand. The procedures of this study was to collect the available daily rainfall
data from 1952 to 1986 of 70 stations which were recorded by the computer at Royal
Irrigation Department and the Electricity Generating Authority of Thailand. The rainfall
data were analyzed for the rainfall distribution, the months of the maximum rain, annual
coefficient of variation, probability of heavy rain per day, probability of return period
of annual maximum rainfall in 24 hours, the frequency of dry spell, and probability of dry
spell.
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The results of study revealed as following :
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The average of annual rainfall was between 833.4 - 1994.4 millimeters. The area which
had highest rain was on the upper part, eastern and western part, and lowest rain was on
the southwestern and central part of the region.
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The maximum rainfall occurred in August and September in consequence.
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The variation coefficients of rain were least on the eastern and the central, and
greater on the central near to western part of the region.
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The probability of heavy rain per day was between 2.6 - 21.1 percents.
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The probability of return period of annual maximum rainfall in 24 hours was increasing
in accordance with the length of time.
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The frequencies of dry spell in rainy season were greater on the northwestern part,
central part and lesser on the western part, upper one, and some area of the eastern.
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The highest probability of dry spell occurred in June, October and July in consequence.
