According to updated data from the Institute for Climate and Social Research (IRI), in the period from August to October 2025, ENSO is in a neutral state with a probability of occurring about 68%. Next, in September-November and October-December 2025, neutral ENSO tends to decrease slightly, down to 49% and 50% respectively. However, the likelihood of maintaining a neutral state is still higher than La Niña or El Niño.
As of September 12, the total water storage capacity in reservoirs in the Mekong River basin reached about 54.18 billion m3. Of which, reservoirs in China are about 20.98 billion m3, reservoirs in the downstream of the Mekong Delta are about 33.20 billion m3. On average, the entire basin reached 82.8% of the total useful capacity of the lake system, lacking about 11.32 billion m3 compared to the requirements.
The water level of Tonle Sap Lake in Kampong Luong on September 12 reached 7.04m, equivalent to a reserve of 35.9 billion m3.
According to the forecast of the Southern Hydrometeorological Station (September 9, 2025), the Southern region will have rainfall from September to November 2025, generally at a level close to or higher than the average of many years, with a total standard rainfall of 50-150 mm. Specifically, in September 2025, the total rainfall is approximately 10-20% higher than the average of many years, the number of common rainy days is 18-23 days.
In October, the total rainfall is approximately 10-20% higher than the average of many years, the number of common rainy days is 15-20 days. In November, the total rainfall is approximately 5-15% higher than the average of many years, the number of common rainy days is 10-15 days.
The Southern Institute of Water Resources Research predicts that in the central Mekong Delta, the flood peak will appear during the high tide period from October 8-11, 2025, with the peak in Can Tho about 2.15-2.25m.
The main flood peak in the 2025 high tide crop is forecast to be high, many flood control beds are at risk of being affected all year round, especially in the central Mekong Delta region. According to calculations, with the main flood season of 3.7m in Tan Chau combined with the peak tide in 2025, there are about 220 bays at risk of being affected, with a total area of about 56,302 hectares. Of which, Can Tho City (including the old Can Tho City and the old Hau Giang Province) was most affected with 116 bays, an area of 21,729 hectares; the province least affected was Tay Ninh, with only 1 bay with an area of 4,032 hectares (belonging to the old Long An area).
The Southern Institute of Water Resources also forecasts the possibility of saline intrusion in the Mekong Delta in the 2025-2026 dry season at approximately the multi-year average (TBNN) of 2013-2025, lower than the 2024-2025 dry season. Specifically, in the last 2 months of 2025, the salinity level of 4 g/l will penetrate 20-30 km, not affecting the ability of irrigation works to collect water.
In January - February 2026, the salinity level of 4 g/l will be 40-50 km deep, equivalent to TBNN; 5-11 km lower than in 2025, 12-20 km lower than in 2020 and 8-15 km lower than in 2016.
From March 2026, it will depend on the amount of water regulated from reservoirs upstream of Me Cong. If the water source increases like in recent years, saline intrusion will decrease; otherwise, the salinity intrusion will remain at the same level as in February 2026.
The Southern Institute of Water Resources Research recommends that coastal areas should proactively build temporary dams and dredge canals early in the rainy season to store water, ensuring reasonable regulation for production. For areas at risk of water shortage due to saline intrusion, it is necessary to store water early from the end of the flood season (November), especially during high tides.
For closed irrigation systems such as Go Cong, Nam Mang Thit, Nhat Tao - Tan Tru, Long Phu - Tiep Nhat, it is necessary to closely monitor salinity developments, close drainage to prevent salinity from the sea to the upstream from November 2025 (after the flood recedes); at the same time, increase dredging of canals to improve water storage and regulation capacity.
For areas in the Quan Lo - Phung Hiep, Cai Lon - Cai Be irrigation systems, it is necessary to develop a project operation plan to ensure a reasonable balance between fresh water and saltwater, serving different water users.
