Vietnam has both a tropical climate zone and a temperate climate zone, with all of the country experiencing the effects of the annual monsoon. Rainy seasons correspond to monsoon circulations, which bring heavy rainfall in the north and south from May to October, and in the central regions from September to January. In the northern regions, average temperatures range from 22–27.5°C in summer to 15–20°C in winter, while the southern areas have a narrower range of 28–29°C in summer to 26–27°C in winter. Vietnam’s climate is also impacted by the El Niño Southern Oscillation (ENSO), which influences monsoonal circulation, and drives complex shifts in rainfall and temperature patterns which vary spatially at a sub-national level.
- Mean annual temperature has increased by 0.5-0.7°C since 1960, with the rate of increase most rapid in southern Vietnam and the Central Highlands.
- In the period 1971–2010 the rate of warming is estimated at 0.26°C per decade, this is reported as being almost twice the rate of global warming over the same period.
- Greater warming has been identified in winter months than in summer months.
- The frequency of ‘hot’ days and nights has increased significantly since 1960 in every season, and the annual frequency of ‘cold’ days and nights has decreased significantly.
- Mean rainfall over Vietnam does not show any significant increase or decrease on a national level since 1960.
- The proportion of rainfall falling in heavy events has not changed significantly since 1960, nor has the maximum amount falling in 1-day or 5-day events.
- On a sub-national level some changes are significant: the general trend has been towards increased rainfall in central regions, and reduced rainfall in northern and southern regions. El Niño remains a major influence of trends in precipitation.