5.3 Drought and impacts on rice production in the lower Mekong river

CropWatch and DroughtWatch team had monitored the crop conditions affected by drought in the Mekong River Basin (including Cambodia, Laos, Myanmar, Thailand, Vietnam, and the Yunnan Province of China) from February to April of 2020. The results indicated that the five countries of the Mekong River Basin and the Yunnan Province of China had severe deficits of precipitation from February to April 2020, and a meteorological drought occurred in varying degrees (Figure 5.6). The precipitation deficits mainly occurred in the lower Mekong region in February, in Cambodia in March, and along the borders of Myanmar, Thailand and Laos in April.

Since it is the dry season of the Mekong and Lancang Jiang Rivers in February and March and it is not a main season for crop planting, the severe meteorological drought had not produced a significant impact on agriculture (Figure 5.7). Table 5.2 showed the drought situations since February in terms of the proportion of drought-affected area to crop planting area. Laos was hit the hardest: its average proportion reached 38.3% with a peak value of 58.5% in early March. Laos is followed by Cambodia (27.7%), Myanmar and Thailand (18.3% and 17.1%, respectively). The drought impact on Vietnam and the Yunnan Province of China was relatively low, about 13.1% and 11.0% respectively (Table 5.2).

Figure 5.6  Distribution and changes of Standardized Precipitation Index (SPI-3) in the Mekong River Basin in early February, early March and early April 2020

Figure 5.7 Spatial distribution and changes of drought in the Mekong River Basin in mid-February, mid-March and mid-April 2020

Table 5.2. Dekadal crop drought proportion from February to April 2020

   There were differences in the temporal and spatial distribution of drought impact in the countries. The drought occurred mainly in the north of Laos and in the central and western regions of Cambodia (February). The southern and central and eastern regions in Myanmar were heavily affected by drought (February-March). The central and western Thailand (February) and the southern region (March) were relatively hard hit. The Mekong Delta and central Vietnam (February-March) and central and southern Yunnan Province of China (March) also suffered a rather serious drought. By mid-April, the drought situation in the Mekong River Basin had eased as a whole. However, the trend of drought still warrants continuous monitoring, and special attention should be paid to the drought impact as the main crop growing season starts.  

The total rice production in Cambodia, Thailand and Vietnam harvested during September 2019 to April 2020 or to be harvested is estimated to be up by 320 thousand tons. The production of rainy season rice harvested before February 2020 increased 17% compared to the same period of last year. The rice supply of the three countries decreased only by 1%, with a limited impact on their rice exports.

The growth condition of rainy season rice in Cambodia, Thailand and Vietnam in 2019-2020 was generally above the previous five years average (5YA) except for the scattered areas of Kampong Cham and Siem Reap Provinces in Cambodia where rice condition was below the 5YA. In contrast, the rice development during dry season was overall inferior to the average level, among which the growth of rice in western and northwest Thailand, Eastern, northern and southwest Cambodia, the southern and southwest coastal areas of Vietnam were significantly below the 5YA (Figure5.8).

Among the three countries, rice in Vietnam outperformed that of Thailand and Cambodia, with about 85% of rainy season rice in an above-average condition. It is also noteworthy that 16% of the rainy season rice achieved the best condition over the last five years. Meanwhile, about two-thirds of dry season rice presented above-average condition. As for Cambodia, rice growth condition during rainy season was in general favorable, and about 75% of the rainy season rice was in an above-average situation. However, the dry season rice suffered from drought stress with only 29% of the rice area reaching the average level. Similarly, an above-average rice growth condition was also observed during rainy season in Thailand, accounting for 78% of rainy season rice area. However, rice development in dry season was hampered by severe drought with more than half of rice in  a below-average condition(Figure 5.9).

Artificial intelligence algorithms were applied to estimate the cultivated area of dry and rainy season rice from October 2019 to April 2020 in Cambodia, Thailand and Vietnam. The total rice area was estimated at 12,225 thousand hectares, up by 6% compared with the same period last year. The cultivated area of rainy season rice in Cambodia, Thailand and Vietnam increased by 5%, 24% and 8%, respectively. However, the rice area in dry season in the three countries decreased by 23%, 4% and 9% respectively as affected by the severe drought. Remote sensing-based model revealed that the yield of rainy season rice in Cambodia and Thailand increased by 5% and 3% respectively while it remained at same level as the previous season in Vietnam. The rainy season rice production in the three countries increased by 10%, 28% and 8% respectively compared to the same period last year. Their total production of rainy season rice since mid-October 2019 reached 27.22 million tons, with a year-on-year increase of 4.05 million tons (or +17%).

Dry season rice was severely affected by drought although most rice are irrigated. The dry season rice yield in Cambodia, Thailand and Vietnam dropped by 8%, 12% and 1% year-on-year (YoY), respectively, and the production fell by 30%, 15% and 10% respectively. In total the dry season rice production of the three countries was only 19.99 million tons, a decrease of 3.73 million tons or 16%, compared with the same period last year (Table 5.3).

Consequently, the total output of rice harvested or to be harvested in rainy season and dry season from October 2019 to April 2020 was estimated at 47.21 million tons, an increase of 1% or 0.32 million tons. As for each country, Vietnam was less affected by the drought. From mid-October 2019, the total output of rice harvested or to be harvested in Vietnam was 14.84 million tons, a slight decrease of 3% from the same period of last year. Cambodia was the most affected country, with the total output of rice of 9.55 million tons, a decrease of 5% from the same period of last year. A large increase in rice production during the rainy season (major rice) in Thailand more than compensated the loss of dry season rice caused by the drought. Rice production of Thailand increased by 1.24 million tons. Considering the overall stable rice production during the past three years in Cambodia, Thailand and Vietnam, the drought-induced loss of dry season rice over the period monitored had limited impacts on the rice market and the total rice supply of the three countries only dropped by 1% year on year.

Figure 5.8 Rice growth condition in Cambodia, Thailand and Vietnam during the rainy season (left) and dry season (right) in 2019-2020

Figure 5.9 Statistical analysis of different categories of rice growth condition during rainy and dry seasons in Cambodia, Thailand and Vietnam in 2019-2020

Table 5.3. Rainy and dry season rice production in Cambodia, Thailand and Vietnam

Note: the rainy season rice in this report represents the rice whose sowing concentrated from early August to October 2019, and whose harvest concentrated from mid-October 2019 to early February 2020. Each country uses different terminology to name the rainy season rice. For example, it is named as major rice in Thailand, median rice and late rice in Cambodia, and winter-spring rice in southern Vietnam. The dry season rice in the report is a general term for the rice whose sowing period was from late November 2019 to early January 2020, and harvest period was from late March 2020 to late April 2020.