Precipitation and flood impact on rice paddies: Statistics in Central Java, Indonesia

Rice, the staple food of most Indonesian people, is mostly produced on Java Island. Flood disasters can cause rice damage, especially during the wet season, when torrential rainfall occurs frequently. The current study investigated the risk of rice damage due to flood disasters. To analyze statistical property and behavior from the 23-years data in Central Java, parametric tests, and the equivalent nonparametric tests were performed. Two-sample t-test and two-sample Kolmogorov-Smirnov (KS) tests were used to identify precipitation threshold that leads to damaging flood. Pearson's r and Spearman's rho coefficients were then computed to measure the strength of association between precipitation and the area of rice paddies affected by flood disasters. The results indicated that there was a clear higher mean (p < 0.05) of the precipitation group causing damaging flood than the other group that did not cause damage. The critical precipitation was about 200 mm in a month. The flood-affected area was not a normal distribution, but the log-transformed data appeared a near-normal distribution. Finally, the correlation tests revealed that the log-transformed affected area is linearly and monotonically dependent on precipitation (Pearson's r = 0.483, Spearman's rho = 0.475, p < 0.05).