Statistical and geostatistical analysis of rainfall in central Japan

To obtain fundamental information for assessing water resources and predicting natural hazards caused by heavy rains, rain precipitation data in central Japan have been analyzed statistically and geostatistically using data of AMeDAS (Automated Meteorological Data Acquisition System) established by Meteorological Agency of Japan. The study area is the mountainous Chubu and plain Kanto districts, central Japan, and the starting data was August 14, 1999, when severe floods affected some areas in Kanto. For the distribution of hourly, daily and annual precipitations, lognormal distributions were fitted well in both districts, but exponential distribution was more suited for monthly precipitations. Experimental variograms of annual precipitations show clearly nuggets and sills as well as ranges. The range is about 130 km in both districts. If it rains heavy in a wide area, variograms of hourly precipitations show clear ranges, which are generally 50–70 km. Ranges of variograms increase with increasing accumulation time, and become constant as 120–150 km over 3–5 hours. Introduction Water is essential for all living things including human beings, and hence one of the most important resources. All necessary water for life on land originates for rain. Estimation of rain precipitation, accordingly, is very important for assessing water resources. The result of the assessment contributes to not only water supply but also making plans to keep the environmental conditions. Many environmental problems are caused by water pollutions in rivers, lakes and sea. The estimation of rain precipitation is also important for predicting natural hazards caused by heavy rain. To estimate rain precipitation properly, it is necessary to have optimally distributed locations of rain gauges, and to apply an appropriate technique for the estimation. We have used geostatistical approach to tackle the problem. In geostatistical approach, the variogram would suggest how to optimally distribute the locations of rain gauges, and the kriging should be able to estimate rain precipitation. We have used rain precipitation data in Chubu and Kanto District in August 1999. Data and Areas The Meteorological Agency of Japan has established an automated meteorological observation system named AMeDAS (Automated Meteorological Data Acquisition System). AMeDAS has 1536 stations in the whole area of Japan (377,800 km). Each station records rain precipitation and other meteorological data such as temperature, velocity of wind, and so on at every hour. The station density is about 1/250 km (41 stations in 100x100 km). If the stations are arranged on a tetragonal grid, the average distance between the neighboring stations is 16 km. If they are arranged on a trigonal grid, the average distance is 17 km. Meteorological Agency of Japan have published data of AMeDAS every year as a CD-ROM. The present study uses the data in 1999. One of the main purposes of this study is to evaluate the station density. Japan is one of the most