Progress in Earth and Planetary Science (Aug 2018)
Diurnal pattern of rainfall in Cambodia: its regional characteristics and local circulation
Abstract
Abstract We analyze the hourly rainfall data of 30 rain gauges in Cambodia from 2010 to 2015 to focus on the diurnal pattern of rainfall and its regional characteristics, with the underlying mechanisms inferred from the observed data. The observed annual rainfall in inland Cambodia ranges from 1087 to 1528 mm on station-average. Approximately 5–20% of the annual rainfall occurs during the pre-monsoon season, 50–78% during the summer monsoon season, and 12–36% during the post-monsoon season. During the pre-monsoon season, rainfall is dominant on the coast and over the Cardamom Mountains, with a maximum in the afternoon. The rainfall amount is smaller around the Tonle Sap Lake. During the summer monsoon season, rainfall is larger in the northern region and smaller in the western region in inland Cambodia, in both amount and proportion to annual rainfall. The rainfall amount on the coast is distinctively large. The diurnal rainfall maximum occurs in the early afternoon in the Cardamom Mountains, in the afternoon on the plain at the southwestern side of the Tonle Sap Lake, in the evening on the wide area of the northeastern side of the lake, and in the early morning on the coast. The clear regional characteristics in the diurnal rainfall pattern suggest significant effects of local features, even during the Asian summer monsoon season. During the post-monsoon season, rainfall is larger on the southwestern side of the Tonle Sap Lake with dominant nocturnal rainfall. These diurnal patterns are, however, not clear on some days, and analysis of the synoptic-scale atmospheric condition suggests the effect of the large-scale low-pressure system and disturbances on the appearance of the clear diurnal rainfall pattern. The effect of land–lake and mountain–valley circulations on forming the diurnal rainfall pattern is also implied from ground-observed meteorological data, although further numerical studies are required to examine the detailed mechanisms. The study of local effects on rainfall with consideration of the land-surface dynamics may aid flood and drought management in Cambodia by facilitating a greater understanding of its rainfall pattern.
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