Monsoon wind

Monsoon wind are a seasonally dominant climatic agent, determining almost all elements of rainfall and sunshine, water flow, sea waves, and coastal hydrodynamic processes in the Mekong Delta region.

Operating mechanism

The Southwest Monsoon (rainy season, May–October): Originating from the subtropical high-pressure belt in the Southern Hemisphere, crossing the warm equatorial sea, this air mass becomes extremely humid. When blowing inland, the Southwest Monsoon brings abundant rainfall, creating the rainy season for the entire region, with a frequency of occurrence reaching 70-75% during the peak months (June–August). The Southwest Monsoon also plays an important role in transporting a large amount of sediment from the Mekong River to the coastal zone, contributing to the accretion process of the delta.

The Northeast Monsoon (dry season, November–April of the following year): In winter, the Northeast Monsoon from the Siberian high-pressure system moves down. However, due to its geographical location near the equator, upon reaching the Mekong Delta, this air mass is strongly modified, becoming dry and no longer cold as in the North, but only bringing cool, warm weather. This is the cause of the prolonged dry season with very low rainfall.

Impacts of monsoon winds

Shaping a prosperous agricultural foundation

It is the combination of a high and stable year-round temperature and the abundant rainfall brought by the Southwest Monsoon that has created ideal conditions for the development of wet rice agriculture. This is the core foundation helping the Mekong Delta become the "rice granary" of the country, contributing up to 50% of rice production and 90% of exported rice.

The differentiated rhythm of rain and sunshine also shapes the seasonal production calendar and diverse farming models such as rice–shrimp, which is an ingenious adaptation of the people to nature.

Hazards caused by monsoon winds themselves

Besides the benefits, the monsoon regime is also the source of increasingly severe challenges:

Rainy season – Flooding: The large amount of rainfall concentrated seasonally, especially high-intensity thunderstorms, frequently causes widespread flooding. The flat and low-lying terrain of the delta further exacerbates this situation, affecting approximately 50% of the entire region's area.

Dry season – Drought and saltwater intrusion: During the dry season, when the Northeast Monsoon prevails, rainfall sharply decreases, and the water flow from the upper Mekong River is at its lowest level. This is the ideal condition for seawater, driven by tides and the Northeast Monsoon itself, to intrude deep into the interior fields, causing drought and salinity. Studies indicate that the strong operation of the Northeast Monsoon can push the salinity intrusion boundary as deep as 50-65 km inland, seriously threatening freshwater sources for domestic use and production.

In summary

Monsoon winds are the most fundamental climatic agent, playing a role that is both formative and challenging to the existence and development of the Mekong Delta. Their operation is the key to explaining the overall picture of nature and life in this land.