Monsoon breaks are key factors to understand summer monsoon rainfall in Cambodia

Long-term Hydrological Observations in a Lowland Dry Evergreen Forest Catchment Area of the Lower Mekong River, Cambodia

Naoki KABEYA (a), Akira SHIMIZU (a), Takanori SHIMIZU (b), Shin’ichi IIDA (b), Koji TAMAI (b), Asako MIYAMOTO (c), Sophal CHANN (d), Makoto ARAKI (b), Yasuhiro OHNUKI (e)

(a) Kyushu Research Center, FFPRI, Kumamoto, Japan.

(b) Department of Disaster Prevention, Meteorology and Hydrology, FFPRI, Tsukuba, Ibaraki, Japan.

(c) Center for Biodiversity, FFPRI, Tsukuba, Ibaraki, Japan.

(d) Forest and Wildlife Science Research Institute, Forestry Administration, Phnom Penh, Cambodia.

(e) Tohoku Research Center, FFPRI, Morioka, Iwate, Japan.

JARQ-Japan Agricultural Research Quarterly, 55(2), April 2021 URL：https://www.jircas.go.jp/ja/publication/list/jarq( External link )

In Cambodia, the summer rainy season is divided into two rainy seasons by breaks known as monsoon breaks (Fig 1). This study analyzed ten years of long -term field observation data of the water budget of Cambodia’s evergreen forest watershed, one of the world’s most data- sparse areas. There were several years during the La Niña years when annual rainfall exceeded 1800 mm; these years were often marked by monsoon breaks during the rainy season. The El Niño years had relatively lower levels of annual rainfall (1100–1200 mm), aside from that in 2016. The strong El Niño years, i.e., 2015-2016, caused a significant reduction in the river and groundwater levels in the Cambodian forest catchment. However, former levels of groundwater and river water were restored by the 953.4-mm rain received during the second half of the rainy season in 2016. Therefore, monsoon breaks may be associated with an increased amount of rainfall in the second half of the rainy season.

Fig1. Monsoon break divide the summer rainy season in the Evergreen Forest Experimental Watershed in Kampong Thom Province, Cambodia.