Why did the North and Central regions suffer heavy damage from this flood?

Cold air combined with tropical depression has dumped record amounts of rain in the North and Central regions in recent days.

Mr. Le Thanh Hai - Deputy Director of the National Center for Hydro-Meteorological Forecasting, had an interview with VnExpress about the ongoing flood situation.

- Sir, why did the rains of the past few days cause such heavy damage in the North and North Central regions?

- The rain on October 9-10 was caused by the impact of two weather patterns - tropical depression and cold air. Landing in Nghe An - Ha Tinh in the early morning of October 10, the tropical depression only caused moderate rain for these two provinces, but created a pressure wave that spread to the North, causing heavy rain for Thanh Hoa, the southern part of the Northern Delta and some western provinces such as Yen Bai, Son La, Hoa Binh.

The cold air in the early season is not the north or northeast wind but the east and east northeast wind, moving to Guangxi, Guangdong (China) and then spreading down to Vietnam. The cold air combined with tropical depressions or storms causes terrible rain and floods.

I must emphasize that normally in autumn, cold air or tropical depressions alone cause heavy rain. But in the past few days, these two factors have combined to create a heavy rainstorm. Many places have had over 400 mm of rain, with Ben Thuong (Thanh Hoa) seeing up to 536 mm. The water level of the Hoang Long River in Ninh Binh is at a record high, at Ben De (Gia Vien) it is 5.49 m, 29 cm higher than the historic flood in 1985.

Another cause is the impact of climate change, which makes rains more extreme and unpredictable.

Flood map on October 9-12. Graphics: Viet Chung.

- Compared to the pattern of many years, how is the continuous rain in the northern mountainous region for the past three months viewed?

-It must be affirmed that this year's rainfall in most provinces and cities is much higher than the average of many years.

In the northern mountainous region, the rains were particularly heavy and prolonged. The rains in early August caused flash floods and landslides in Yen Bai. According to estimates, in the Nam Pam stream area (Muong La), about one million cubic meters of rock and soil were displaced and eroded. To move that amount of rock and soil, about 5 million cubic meters of water was needed. This amount of water could not have been created from a few days of rain but must have accumulated over the previous month.

In Hoa Binh, on October 9-11 alone, a series of locations recorded rainfall of approximately 500 mm. Water level in Hoa Binh hydroelectric reservoir at noon on October 11 reached nearly 16,000 m³/s, forcing the opening of 8 bottom discharge gates. This is the first time in the history of the plant that 8 out of 12 bottom discharge gates have been opened.

Previously, in August 1996, a tropical depression caused a record flood in Hoa Binh Lake with a flow rate of 22,500 m3/s. But that was in August, and this time it was in October, when summer rains had decreased. Therefore, this is considered a special, rare case.

- Many residential areas were buried by landslides, leaving people unable to react. What do you think about the forecasting of this rain?

- Let the localities and the Central Steering Committee on Natural Disaster Prevention and Control evaluate this.

- For the first time in history, Hoa Binh Lake opened 8 bottom spillway gates. How will this affect the center of Hanoi?

- Hoa Binh Lake opened 8 bottom spillway gates yesterday afternoon. Due to less rain, the water flow to the lake decreased, so by the evening of the same day, the lake only opened 6 gates and this morning, there were only 4 gates. It is expected that by the evening of October 12, the lake will only open 2 bottom spillway gates.

The flood discharge from Hoa Binh reservoir has caused severe flooding in the downstream area of ​​the Da River, from Hoa Binh city to Trung Ha bridge (connecting Hanoi and Phu Tho). As economic activities along the river such as fish cage farming are taking place busily, the impact of floods will be more serious.

The Red River area is not greatly affected by flood discharge, except for the middle banks. Floods on the Red River are mainly at approximately alert level 1 (8-9 m), the dike system will not have any problems.

- What is the forecast for floods in the coming days?

- Rain in the North and Northwest has decreased, and in the Northeast there are still some places. Only Nghe An, Ha Tinh, and Quang Binh have moderate rain and some places have heavy rain. This weather pattern will continue for at least the next three days.

A new storm formed. As it entered the northern East Sea, the storm encountered cold air that poured down on the night of October 15. These two factors combined to deflect the storm to the west.

Therefore, we expect the storm to directly impact, causing moderate and very heavy rain in the provinces from Thanh Hoa to Quang Ngai from the night of October 15 to the end of October 18. The provinces in the Northeast and Northwest will also have moderate rain, some places will have heavy rain.

It is difficult to assess the strength of the storm at the moment, but it is certain that it will reach level 8 - 9.

The river flood rose high, the communal house outside the Hoang Long river dike in Gia Lac commune (Gia Vien, Ninh Binh) was submerged 3m deep. Photo: Viet Linh.

- From now until the end of the year, how many more storms will Vietnam be affected by?

- Due to the influence of weak La Nina, this year's rainy season will start early and end late. We have warned about this in advance. In October, there will be at least 3 storms and tropical depressions, and in November there will also be 1-2 storms. The rains will continue and there is a possibility of many heavy rains.

La Nina is associated with storms. In 2013, the East Sea had 19 storms and tropical depressions. This year there are signs of such.

In the context of climate change, the number of storms will increase slightly, but their intensity will be higher. Extreme and unusual weather patterns such as heavy rains at the end of the season in the Mekong Delta or late storms in November and December directly affecting the South and South Central regions may occur.

Previously, people thought that a storm would hit the South every few decades. But after Typhoon Linda in 1997, storms affected the region in 2006 and 2012, and each storm was more extreme than the last. Therefore, people should not be subjective.

According to VNE