Saltwater intrusion in Mekong Delta increasingly severe, unseasonable

Saltwater intrusion from the sea up rivers has affected the Mekong Delta’s freshwater supply more than a month earlier and more badly than normal, an agriculture ministry agency has reported.

In Vietnam’s rice basket, the intrusion is five to seven kilometers deeper than normal for this period, the Directorate of Water Resources said in the report on the lack of water and mitigating saltwater intrusion it released on Thursday.

Before 2012 upstream impacts were minimal and flow patterns in the Mekong were close to natural.

But since then, countries in the Mekong River basin had built 128 reservoirs (13 on the main river and 115 on its tributaries) with a capacity of 88 billion cubic meters, expected to increase to 90-95 billion by 2030 and 120 billion upon the completion of the 231 reservoirs planned in 2040-60.

In future, as upstream countries completed their reservoirs, sea levels rose and the climate changed, saltwater intrusion was expected to become more severe and irregular.

Saltwater intrusion had now started 1 to 1.5 months earlier than previously observed during the dry season, which lasted from late November to early May in southern Vietnam.

In years with low upstream flows, the intrusion started as early as December end and peaked in February or early March.

Before 2012 salinity would appear between February and April, peaking at the end of March.

This year the salinity had spiked significantly.

For instance, between April 18 and 22, it was measured at over 3-4 gm/liter in Kien Giang Province and over 10 gm in Bac Lieu Province.

The directorate blamed this on low upstream water levels, prolonged heat and high evaporation rates.

The sowing of summer-autumn crops caused a rapid decrease in water levels.

The unrelenting heat has exacerbated the impacts in some places like Ca Mau Province.

As of now, in the delta, some 1,580 hectares of rice, mostly in Soc Trang Province, and 4,640 ha of lime and other fruit trees in Long An Province face reduced productivity due to a water shortage.

More than 73,900 families in seven provinces suffer from a lack of fresh water for daily use.

But to put things in perspective, this is lower than in 2019-2020, when 96,000 families were affected.

Besides, in seasons like 2015-2016 and 2019-2020, the salinity levels were higher than the recent four-gram level.

Water depletion also causes land subsidence and erosion along water bodies in Ca Mau and Kien Giang.

A total of 901 subsidence and erosion sites span 23.4 kilometers in the two provinces.

It is forecast that the saltwater intrusion would decrease from May as the rainy season begins, and stop affecting water sources from early June.

By Viet An – VnExpress.net – April 26, 2024