Why do storms in Vietnam often hit the Central Region?

There is a saying in folklore, “The husband may forgive, but the wife does not/ Resulting in floods for two or three months in October.” This serves as a reminder and warning about the flood season in the provinces from Thanh Hoa downwards, which typically occurs from early July to October each year. So why does it always happen in Central Vietnam, and what causes these severe storms? Let’s explore the reasons!

According to specialized research on storms in Central Vietnam, there are many subjective and objective factors that lead to this region becoming a center for experiencing unprecedented storms in history.

Major Storms Arise from Geographical Factors

Storms can only form when three conditions are met: Heat, humidity, and a driving force to create a vortex.

The main period for storm and tropical depression activity in the year is during the Summer and Autumn months: from June to November (in the Northern Hemisphere) and from December to March of the following year (in the Southern Hemisphere). Storms are most prevalent in Summer and Autumn because this time provides the most favorable conditions for their formation and development: high sea surface temperatures (at least 26°C or higher), and a tropical atmosphere conducive to strong convective development and large-scale rotational movements.

Storms form in tropical regions because this natural phenomenon requires a very warm water current, at least 26 degrees Celsius at a depth of at least 50 meters. Storms typically form close to the equator and tend to move toward the poles; the further they travel, the faster they become. Consequently, areas near the equator are less affected by storms.

In essence, storms are a means of “discharging heat” for the ocean. Most storms usually follow the edges of high-pressure systems and are pulled by low-pressure areas. In Vietnam, during the months when sea water contains the most energy (July, August, September), the low-pressure trough often stretches across Central Vietnam, which is why storms typically follow this path.

Satellite image of a storm.

In other words, Central Vietnam experiences harsh weather conditions due to the influence of the Southwest monsoon winds. These winds carry a lot of moisture (as they pass over the Indian Ocean), causing frequent rainfall. Due to the impact of the foehn winds, when storms form in the East Sea, they are pushed northward. As the months progress, the winds weaken, leading storms to gradually move toward Central Vietnam.

Each year, sea storms and Northeast monsoon winds commonly result in heavy rain in Central Vietnam. Moreover, global weather changes, such as El Niño and La Niña, exacerbate the severity of these storms and heavy rainfall.

The rainy storm season typically lasts from July to November, averaging 5 – 8 storms per year.

The rainy storm season typically lasts from July to November, with an average of 5 – 8 storms per year. From 2006 to 2017, Central Vietnam was affected by 7 major storms, many tropical depressions, and dozens of Northeast monsoon events. These sea storms and tropical depressions usually originate from neighboring countries like the Philippines, China, etc. After traveling for 3 to 4 days, they reach our coastline.

Flooding Caused by Storms in Upland and Lowland Areas

Compared to the southern and northern regions, the economy of Central Vietnam is relatively underdeveloped. The people of Central Vietnam are accustomed to the scene of “In July the waters jump onto the shore” because “The heavens bring floods every year.”

The coastline of Central Vietnam stretches for 1,200 kilometers and includes provinces from Thanh Hoa to Binh Thuan. The Truong Son mountain range runs along the coast, making the lowlands in Central Vietnam very limited. This area also has a dense system of rivers and canals, with significant rivers like Gianh River in Quang Binh, Thach Han River in Quang Tri, Huong River in Hue-Thua Thien, Thu Bon River in Quang Nam, and Tra Khuc River in Quang Ngai.

River mouths often get silted, obstructing flood drainage for the lowland areas.

Although there are many rivers and streams, most of them are short and have a steep gradient. The river basins are usually hilly, causing rainwater to flow rapidly. Additionally, river mouths often become silted, hindering flood drainage for the lowlands.

Furthermore, flooding has caused significant damage to homes, crops, bridges, and roads, making life even more difficult for the people of Central Vietnam. Being caught in a vicious cycle of natural disasters makes economic development in this region face numerous challenges.

Why Do Floods Cause Severe Damage?

Although local authorities and residents have proactively taken measures to prevent, respond to, and recover from storm-induced floods, the aftermath remains extremely severe. The primary reason is the occurrence of heavy rainfall over a wide area for several consecutive days.

In addition to the main cause being storms in the upland and lowland areas, there are many other reasons commonly mentioned, such as deforestation, sand and gravel exploitation, and the system of dikes and dams.

Storms and floods cause significant damage to the lives of the people.

Research and investigations in the United States and many other places around the world have demonstrated that the leading cause of flooding is excessive rainfall occurring in a short period. Moreover, deforestation can directly impact flooding in narrow river basins like those in Central Vietnam. Trees have the ability to retain water and minimize soil erosion. When forests are cut down, the bare land allows water and soil to wash away, raising water levels in downstream areas.

Unchecked sand and gravel exploitation in rivers also increases flood levels. This situation causes severe erosion along many riverbanks. The erosion of riverbanks and the siltation of river mouths hinder flood drainage and make flooding more severe and prolonged.

Unlike the Red River in the North and the Mekong River in the South, the rivers in Central Vietnam do not have a flood control dike system. Additionally, there are no large reservoirs upstream to mitigate flooding in the lowlands. Therefore, populous areas on both banks of the rivers always face the risk of inundation during heavy rains and storms.

In summary, the primary cause of storms and floods in Central Vietnam is the storms formed in the East Sea and the Northeast monsoon winds, combined with the region’s weather characteristics that are very suitable for the storm paths. As a result, the Central provinces become victims of severe natural disasters. Other factors, such as deforestation, only exacerbate the flooding situation.