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The Southern Institute for Water Resources Research forecasts that the 2026–2027 dry season in the Mekong Delta will be a low-water year. The 4 g/l salinity line is expected to reach 55–70 km inland on the Cuu Long river mouths in the first half of March 2027. For fruit orchards and raw-material growing areas, what matters is not only how much water can be stored, but which block gets it, when, and based on what data.
Key points
- Average flow into the delta at Kratie for November 2026–January 2027 is forecast at about 4,712 m³/s, 24.7% below the long-term average. The Institute recommends completing water storage before November 2026.
- According to AGRIVI, farms that irrigate on one schedule for the whole farm typically make decisions several days later than farms with block-level data.
- According to FAO, crop water requirements differ widely between crops; among the fruit crops in the FAO table, pineapple has the lowest mid-season crop coefficient (0.30).
- FAO classifies pummelo, orange, lemon, mango and passion fruit as salt-sensitive, and pineapple as moderately tolerant. Irrigation water with total dissolved solids above 450 mg/l (about 0.45‰) already calls for restrictions on use.
The 2026–2027 dry season: the official forecast
The Winter–Spring 2026–2027 seasonal bulletin of the Southern Institute for Water Resources Research (data to 29–30 September 2026) expects water flows into the delta to be close to the 2015–2016 dry season; in a bad scenario, flows could fall to 2019–2020 levels for some periods.
| Indicator | 2026–2027 dry-season forecast |
|---|---|
| Average flow at Kratie, Nov 2026–Jan 2027 | About 4,712 m³/s; 24.7% below the long-term average and about 53.3% below the same period of 2025–2026 |
| Average flow at Kratie, Feb–May 2027 | About 3,089 m³/s; 20.3% below the long-term average |
| 4 g/l salinity line, Cuu Long river mouths | 30–40 km (December 2026); 50–65 km (January–February 2027); 55–70 km (first half of March 2027) |
| 4 g/l salinity line, the two Vam Co rivers | 40–45 km (December 2026); 80–85 km (January–February 2027); up to 100–125 km (March–April 2027) |
| Compared with the long-term average | Salinity reaches generally 5–15 km further inland on the Cuu Long river mouths and 12–36 km further on the Vam Co rivers |
The Institute recommends that areas short of water due to salinity intrusion store water from the flood season, finish before November 2026 and top up whenever possible. Conditions in the second half of March 2027 will depend on releases from upstream Mekong reservoirs, so the weekly and monthly bulletins that follow should be monitored.
Why a single irrigation schedule is no longer enough
An article by AGRIVI (Croatia), a farm management software developer, on the 2026 dry season in the Mediterranean sets out a principle that also applies to Vietnam: in perennial orchards, water demand differs by variety, rootstock, soil type and block position, so a uniform schedule over-irrigates some blocks and under-irrigates others.
According to AGRIVI, water decisions lose time in three places:
- Late detection. By the time leaves curl, wilt or change colour, the tree has been short of water for about 3–5 days. These are late indicators.
- Uniform irrigation. The same daily volume for every block. In a drought year, the water over-applied to one block is the water another block is missing.
- Weather forecasts not linked to irrigation planning. If rain is forecast, irrigation on less-stressed blocks can be deferred and water redirected to blocks that need it now.
AGRIVI also notes that damage to perennial crops can carry over for two or three seasons after a drought year. The examples in the AGRIVI article come from Spain and Morocco; they illustrate the principle only and are not applied to Vietnam.
Water requirements differ by crop: FAO data
FAO Irrigation and Drainage Paper 56 calculates crop water requirement (ETc) as the crop coefficient (Kc) multiplied by reference evapotranspiration (ET0), which is set by weather. One millimetre of water over one hectare equals 10 m³. Mid-season Kc values for selected crops:
| Crop (FAO-56, Table 12) | Mid-season Kc | Salt tolerance (FAO-29) |
|---|---|---|
| Pineapple, bare soil | 0.30 | Moderately tolerant |
| Citrus, no ground cover, 70% canopy | 0.65 | Sensitive (orange, lemon, pummelo) |
| Citrus, with ground cover, 50% canopy | 0.80 | Sensitive |
| Avocado, no ground cover | 0.85 | Sensitive |
| Coffee, bare ground | 0.95 | Not listed |
| Banana, second year | 1.20 | Not listed |
Illustrative example (an assumption, not a measurement in Vietnam): on a day with ET0 of 5 mm, an orange block with 70% canopy needs about 0.65 × 5 = 3.25 mm, or 32.5 m³/ha. A second-year banana block on the same day needs about 6 mm, or 60 m³/ha. Two blocks on the same farm can differ by almost a factor of two.
Pineapple is a special case: according to FAO, the plant closes its stomata during the day, so most of the water lost is evaporation from the soil. The coefficients above assume 50% of the ground is covered by black plastic mulch and sprinkler irrigation; with drip irrigation under the mulch, Kc drops by a further 0.10. For MD2 pineapple growing areas, bed mulching matters as much as the irrigation volume. FAO-56 has no data for durian or mango; Kc for these two crops should not be guessed.
Saline water: measure before you irrigate
FAO Irrigation and Drainage Paper 29 on water quality classifies irrigation water by salinity: below 450 mg/l total dissolved solids, no restriction; 450 to 2,000 mg/l, slight to moderate restriction; above 2,000 mg/l, severe restriction. In the parts-per-thousand units commonly used in the delta, the thresholds are roughly 0.45‰ and 2‰. The 4 g/l salinity line in the forecast bulletin, i.e. 4‰, is well above the severe-restriction threshold.
According to FAO-29, orange yields start to decline when the electrical conductivity of irrigation water exceeds about 1.1 dS/m, and grapefruit at about 1.2 dS/m. FAO classifies pummelo, orange, lemon, mango, passion fruit and avocado as salt-sensitive; pineapple, papaya and pomegranate as moderately tolerant; durian is not listed. This is a relative comparison; actual tolerance also depends on climate, soil and irrigation practice.
Unplanned irrigation and pumping caused by drought and salinity will push costs away from budget; how to track this is covered in Budget vs actual by block, and the shared block code for irrigation logs is discussed in Block-level data.
What companies should do
The following are AgrifoodV’s recommendations.
- Calculate the water needed for the whole dry season block by block: area, crop, tree age, with or without ground cover. Compare it with the volume stored in ponds and reservoirs. Complete water storage before November 2026, as recommended by the Southern Institute for Water Resources Research.
- Set priorities before water runs short: salt-sensitive blocks carrying fruit, young-tree blocks, more drought-tolerant blocks. When water covers only part of the need, it is already decided which blocks get full irrigation and which get reduced irrigation.
- Measure salinity every time water is taken into ponds or reservoirs during the peak salinity period; record it in the log by block code together with irrigation volumes. Check the Institute’s weekly bulletin when setting the weekly irrigation schedule.
- Reduce evaporation before increasing irrigation: mulch around trunks, mulch beds, use drip irrigation where feasible. For MD2 pineapple this is particularly useful, because most of the water lost is evaporation from the soil.
AgrifoodV helps companies organise growing-area management, field logs and block-level water planning.
References
- Southern Institute for Water Resources Research. Bản tin dự báo mùa: Dự báo nguồn nước và kế hoạch phân phối, sử dụng nước trong hệ thống công trình thủy lợi phục vụ sản xuất vùng ĐBSCL, năm 2026 (vụ Đông Xuân 2026–2027) [Seasonal bulletin: water resources forecast and water allocation plan for irrigation systems in the Mekong Delta, 2026 (Winter–Spring 2026–2027)], data to 29–30 September 2026. siwrr.org.vn.
- Busic, B. Mediterranean Specialty Crop Water Management in a Drought-Pressured Season. AGRIVI Blog, published 11 June 2026, updated 28 September 2026. agrivi.com/blog/specialty-crop-water-management-mediterranean.
- Allen, R.G., Pereira, L.S., Raes, D., Smith, M. Crop evapotranspiration: Guidelines for computing crop water requirements. FAO Irrigation and Drainage Paper 56, 1998, Chapter 6, Table 12 and footnote 16. fao.org.
- Ayers, R.S., Westcot, D.W. Water quality for agriculture. FAO Irrigation and Drainage Paper 29 Rev.1, 1985, Table 1 (Chapter 1) and crop salt tolerance tables (Chapter 2). fao.org (Chapter 1); fao.org (Chapter 2).
Article by AgrifoodV, compiled from the sources above (accessed 23 October 2026). European figures in the AGRIVI article are used only to illustrate the principle; the irrigation example is an AgrifoodV assumption, not a measurement in Vietnam. Water and salinity forecasts may change with updated bulletins. This content is not a substitute for technical advice for individual orchards. This content is not a substitute for legal advice. Cover image: Nelli Neufeld / Pexels.
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