Discontinuous Changes of Precipitation in Japan after 1900 Detected by the Lepage Test
1992 Volume 70 Issue 1 Pages 95-104
Details
1992 Volume 70 Issue 1 Pages 95-104
Regional changes in precipitation are studied by means of a statistical hypothesis test. Precipitation data used are records at 52 meteorological stations in Japan where observation has been carried out since before 1900. The test used is the Lepage test, which is a distribution-free two-sample test.
The detection is made in the following way: Two data sets of precipitation records during N-year period till (Y-1) year and after Y year are statistically tested. The Y year is moved so as to cover the time series data at each station, and when the test rejects the null hypothesis of no difference with a 1% or 5% significance level, the change is determined.
The time variation of the number of the stations where the change in the annual precipitation amount is detected with a 1 % significance level shows that the number of the stations sharply increases around 1924, 1949 and 1960 when N=25. This large number indicates that the change occurred in a wide area, and the sharp variation of the number indicates that these changes are discontinuous. A change in 1915 can be added to these by referring to a previous study.
Spatial distributions of the difference between the means for 25-year periods prior to and from the years mentioned above illustrate that every change shows a trend of being consistent within one region but different among other regions. Thus, regional discontinuous changes are presented.
The same test is applied to the seasonal data. The change in 1949 is strongly detected in the AprilJuly season when it falls on Baiu, an East Asian rainy season. The change in 1915 is also detected in the November-March season, an East Asian winter monsoon season. The changes in 1924 and in 1960 were dominant only in the annual precipitation amount. Dependence of the detection upon the sample size is also studied.
Because a few papers reported that discontinuous climate changes occurred on a global scale in 1920s and around 1950, regional changes in precipitation corresponding to these global changes are shown in Japan.
