Spatiotemporal variability of Hokkaido's seasonal precipitation in recent decades and connection to water vapour flux

摘要

Based on 169 stations, annual, seasonal and monthly precipitation trends for the northern Japanese island of Hokkaido were analysed for the period 1980-2011 using the Mann-Kendall test and geostatistical interpolation techniques. Possible association with water vapour flux was explored using ERA-Interim reanalysis data. Precipitation increased in Hokkaido over the study period at both the annual and seasonal scales. In general, the northwest had higher precipitation than the southeast in winter, autumn and on an interannual basis and precipitation tended to be concentrated in the southeast in both spring and summer. There was also more precipitation during warm times of the year. For example, precipitation occurred mainly during the summer, ranging from 233 to 751mm and autumn, ranging from 218 to 724 mm, while precipitation was significantly less in winter and spring. Most stations with declining precipitation trends were located in areas with higher precipitation, such as the west in winter and autumn and the southeast fringe in summer and scattered across the areas with lower precipitation in spring. Increases in precipitation were mainly seen in February, May, June, July, September, November and December atmore than 100 stations. Amongst these, almost all of the stations showed positive trends in May (168 stations) and July (165 stations). Finally, the changes of the water vapour transport and budget in whole-layers between the period 1980-2011 possibly explained the spatiotemporal distribution of precipitation trends in Hokkaido.