Seasonal changes in radiation and evaporation implied from the diurnal distribution of rainfall in the Lower Mekong

Tsujimoto Kumiko, Masumoto Takao, Mitsuno Toru

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8 Citations (Scopus)


Solar radiation is an important input to many empirical equations for estimating evaporation, which in turn plays an important role in the hydrologic cycle in the Lower Mekong River Basin due to the high evaporation potential of the tropical monsoon climate. Few proper meteorological data exist for the Lower Mekong River Basin, however, and the region's meteorological conditions, including seasonal variation in radiation and evaporation, have not been clarified. In this study, ground-based hourly hydrometeorological data were collected at three observation stations located in different land-use types (urban district, paddy area, and lake) in the Lower Mekong River Basin. These data were analysed to investigate the seasonal variation in radiation and evaporation related to the diurnal distribution of rainfall. Contrary to common expectations, our results showed that rainy and dry seasons had nearly the same amount of solar radiation in the Lower Mekong River Basin because (1) rainy seasons had a relatively larger amount of extraterrestrial radiation; (2) no rain fell on nearly half of the days during rainy seasons; and (3) the amount of solar radiation on rainy days reached 88% of that on non-rainy days. The third factor was attributed to the high frequency of evening rainfall. Furthermore, this rainfall-radiation relationship meant that rainy seasons had a large amount of net radiation due to the low reduction ratio of solar radiation and an increase in long-wave incoming radiation. Accordingly, rainy seasons bad a high evaporation potential. Moreover, for the rain-fed rice paddies that prevail in this region, sufficient radiation during the rainy season would be a great advantage for rice growing.

Original languageEnglish
Pages (from-to)1257-1266
Number of pages10
JournalHydrological Processes
Issue number9
Publication statusPublished - Apr 30 2008
Externally publishedYes


  • Diurnal distribution of rainfall
  • Evaporation
  • Ground-based hydrometeorological observation
  • Radiation
  • Tropical monsoon climate

ASJC Scopus subject areas

  • Water Science and Technology


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