Difference of hydrological cycle between Islands and surrounding oceans over the Indonesian maritime continent

The climate of the maritime continent is characterized by huge amounts of precipitation throughout the year and plays an essential role as a major atmospheric heat source of the Earth's climate system. The unique environment in this region with complex distribution of islands and warm pool favors the development of deep and frequent convection. The deep convection accompanied by heavy precipitation is generally observed over islands and its surrounding ocean rather than open seas. Major islands combined with surrounding warm seas, therefore, are most likely to play an important part in the energy and water cycle processes driving the complex atmospheric circulation pattern. To understand the time-space characteristics of the hydro-climate in Borneo, and its surrounding ocean, we examined the climatological hydrological cycle on monthly mean basis by using TRMM and JRA25/JCDAS reanalysis data from 1999-2010. The interactive nature between the hydro-climate and the tropical rainforest were also discussed. Seasonal variation of precipitation over Borneo and the surrounding ocean is very small compared with it in other tropics. The vertically- integrated moisture flux from surface to 100 hPa shows divergence throughout the year over the Borneo, suggesting that this island plays moisture source to atmosphere. In contrast, other major islands in the maritime continent, such as New Guina and Sumatra, seasonal cycle of the moisture flux convergence is clearly observed. The evapotranspiration, as defined by residual from precipitation and moisture flux convergence, contributes to precipitation over Borneo throughout the year. On the other hand, the contribution of moisture flux convergence for precipitation is noticeable over the surrounding ocean of Borneo, particularly during the boreal winter. The seasonal cycle of circulation pattern influences water budget over coastal area. These results strongly suggest that precipitation in the Borneo is basically occupied by evapotranspiration from tropical rainforests in the island.