Statistical Analysis in Rainfall Estimation Case Study in Upstream of Ciliwung

Abstract

Determining for distribution of rainfall is a very important part in determining the plans of rainfall in a region. This study used daily rainfall data in 1992-2009 from three rainfall stations,namely Gunung Mas, Citeko and Gadog. Thiessen polygon method is used to determine the average rainfall region. The distribution of rainfall is determined by using statistical analysis with Chi-Square test. Based on the results of distribution suitability testing by using Chi-Square (?_r²) with significance (?) we obtained ?_r² value of 6.50 while the ?_r² table is 7.185. Since the calculated ?_r²< ?_r² table, then the Gumbel distribution is eligible. So that the distribution pattern of the right to Ciliwung upstream is the Gumbel distribution. The amount of planned rainfall-plant the upstream Ciliwung watershed based on the Gumbel distribution for the return period of 2, 5, 10, 25, 50, and 100 years, respectively are 70.98 mm, 88.98 mm, 99.55 mm, 113.93 mm , 124.59 mm and 135.18 mm.