Climate

Rainfall, Winds , Temperature

Cambodia’s climate is tropical monsoonal with a pronounced wet and dry season . During the wet season from May until early October , rainfall is largely derived from the southwest monsoon drawn landward from the Indian Ocean. The dry season, from November to April, is associated with the northeast monsoon which sends drier and cooler air .

1. Rainfall

Most of Cambodia can be described as sub humid. The wet season accounts for 80% of the annual rainfall. The average annual rainfall varies across the country from between 1,000 to 2,50mm. Rainfall in the central area covering the Tonle Sap Basin - Lower Mekong Valley averages 1,200 to 1,900mm annually. East of the Mekong River rainfall is generally between 1,800 and 3,000mm.

The heaviest rainfall ,over3,000mm per year, occurs along the coastal lowlands in the west

The lowest rainfall occurs in the rainshadow region of the Elephant Mountains and the Cardamom Mountains. This area is often subject to drought.

Precipitation also varies widely from year to year. From the latter part of July there may be periods without significant rainfall for ten or fifteen days or more at a time , referred to as the short dry season’( farmers tend to delay planting on this account to minimize the risk of damage to rice seedlings ).

2. Winds

There are few reliable records of windspeed data for Cambodia . Observations and extrapolation from neighboring Thailand and Vietnam tend to indicate that mean windspeeds are low , in the order of 2m/s for much of the country. Between February to April there are strong winds for the south east and these should lead to relatively strong winds in southern Cambodia . In May to July the winds move more to the southwest crossing the Thailand Coast and the Gulf of Siam before entering the south of Cambodia. From August to October general turbulence in the upper layers leads to unstable conditions across the continent of South East Asia. In November to January the wind moves to the northeast and sometimes leads to a strong steady wing. December is known as the month for kite flying, with a strong steady wind from the north .

Typhoons ( tropical cyclones ), which often devastate coastal Vietnam, rarely cause damage in Cambodia.

3. Temperature

Mean monthly temperatures range from a minimum of 25^oC in January to 29^oC in April. There is little spatial variation in temperatures. Temperatures higher than 32^oC are common, and just before the range of the rainy season they may rise to more than 38^oC. The temperature rarely falls below 10^oC.

Relative humidifies range from 65-70% in January and February to 85-90% in August and September. Annual evaporation is of the order of 2,000 to 2,200 mm, being highest in March and April at 200 mm to 240 mm , and lowest in September/October at 120 mm to 150 mm. Evapotranspiration (EPT) varies from a monthly average of 90 mm during the rainy season to 120 mm in the dry season.