Welcome to RiSaWa

RiSaWa is the acronym for Rice Production Caught Between Salinity and Drought – Future Options for Sustainable Use of Water in the Mekong Delta Region.

The project RiSaWa will link several aspects of water management in the Vietnamese Mekong Delta (VMD) to create a comprehensive study of water management in coastal regions of the VMD.

The overall aim of RiSaWa is to contribute to food security and protect essential resources, such as water and soil, by mitigating the impacts of climate change in the VMD, sea level rise and salt intrusion. Seasonal best practice scenarios will be developed for each district to avoid salinization of rice fields and effectively use water for sustainable rice production, while avoiding negative impacts on the fragile VMD ecosystem.

Status quo

Vietnamese Mekong Delta Fig.1: Lantsat image of the Vietnamese Mekong Delta. Source: http://www.stelar-s2s.org

The Vietnamese Mekong Delta (VMD) covers 39,000 km2 of fertile alluvial plain and is home to over 18 million people (Hagenvoort and Trí, 2013). It is considered one of the most agriculturally productive areas in the world. Its main products are rice, fruits, fish and shrimp (CGIAR, 2016), and accounts for 50% of rice, 65% of aquaculture, and 70% of fruit production in Vietnam, and 90% of its rice exports (Kakonen, 2008; Trung, 2014; Trinh et al., 2014). For 60% of the local populace, rice cultivation is their primary livelihood.

Sea level rise, seasonal freshwater deficit, and seasonal freshwater excess are major threats to rice production in river deltas and along rivers in the Asian-Pacific region (Wassmann et al. 2004; Adamson and Bird, 2010). Sea level rise will increase salt intrusion into river deltas, such as the VMD, seriously threatening rice production (Shamsudduha et al., 2009; Toan, 2014). Salt intrusion refers to the infiltration of groundwater aquifers and generally increased salinity gradients as seawater makes its way further inland, often during the dry season (Smajgl, 2015). In the VMD during the dry season, an estimated 1.8 million ha of land is affected by saline water above 5 gl-1 (Carew-Reid, 2008; Mekong River Commission, 2010). Freshwater use upstream for domestic or industrial activities is increasing in the VMD, limiting irrigation and allowing greater seawater encroachment during the dry season as a result of negative river discharge (Hashimoto, 2001). Therefore, the VMD faces the dual threat of drought and salinity. According to the CGIAR, severe drought combined with salt intrusion strongly affected 11 of the 13 provinces in the VMD in 2016, resulting in 400,000 ha of damaged cropland, of which 25,900 ha was left fallow as a result. Rice areas affected by drought and salinity intrusion rapidly increased from 139,000 ha in mid-March 2016 to 224,552 ha by mid-April 2016. The impact of increased seasonal drought and salt intrusion is not only limited to agriculture, but threatens the quality of life for a growing regional population. In the Ben Tre Province in 2013, around 2,000 ha of rice were affected by saline intrusion, while 63,000 households lacked access to freshwater (Khoi, P., Thinh, H., 2013).

Caught between salinity and drought Fig.2: Rice production in the Vietnamese Mekong Delta caught between salinity and drought

To mitigate the effects of seasonal salt intrusion and dwindling freshwater resources, several management strategies have been implemented by government and farmers over the past few years. For example, costly sluices and sea dikes have been constructed to reduce coastline erosion and salt intrusion (Trung, 2014). Mostly in response to limited freshwater availability, farmers have turned to water saving irrigation technologies (WSIT), such as alternative wetting and drying or saturation soil culture to improve water use efficiency (WUE) (Oliver et al., 2008; Dong et al., 2012). However, WSIT applied in saline soils may in fact exacerbate salinity due to capillary rise.

Vietnamese Mekong Delta Fig.3: Land-cover map of the Vietnamese Mekong Delta showing different rice cropping systems. Source: Son et al., 2014

Land-use change could have a significant impact on salt intrusion and conserving freshwater resources. Across the VMD, irrigated rice is often double- or even triple-cropped (Son et al., 2014; Smaigl et al., 2015). Reducing cropping cycles in selected areas could decrease freshwater use without seriously impacting yield. The favorable economics of shrimp farming and fruit production have led to a shift away from rice cultivation. However, shrimp farming also suffers from increasing risks due to climate change, as shown by a disease outbreak in 2011 from the combination of extreme heat and salt intrusion (Hung, 2011). Shrimp farming can be integrated into a paddy rice system, by using rice with short rotation periods during the wet season (Bergkvist, 2012), and farming shrimp in the same paddy during the dry season. However, the brackish water needed for shrimp farming has been shown to further increase soil salinity, and can lead to crop failure (Tho, 2008). This can be avoided by replacing shrimp with fish within the rotation (CGIAR, 2016). Finally, efforts to identify and breed high-yielding rice genotypes tolerant to salinity stress as well as the conditions found in the VMD remain ongoing (Lang et al., 2018). Field trials have shown that if salt-sensitive are replaced with more tolerant varieties, rice production can be maintained at the same level up to 3 ‰ salinity (Smaigl et al., 2015).

Looking to the future, the food and economic security as well as ecosystems of the VMD are fundamentally threatened by the effects of climate change. These include sea level rise, higher frequency of extreme weather events, rising average temperatures, and increased salinity intrusion (CGIAR, 2016). Beyond improvements in water infrastructure, salt intrusion and freshwater scarcity can be mitigated through a combination of land-use change, management practices, and genotype selection.

References

Adamson, P., & Bird, J. (2010). The Mekong: a drought-prone tropical environment?. International Journal of Water Resources Development, 26(4), 579-594.

Bergqvist, A., Eitrem Holmgren, K., & Rylander, P. (2012). Impacts of saline water intrusion on the daily lives in the Mekong Delta Viet Nam.

Carew-Reid, J. (2008). Rapid assessment of the extent and impact of sea level rise in Viet Nam. International Centre for Environment Management (ICEM), Brisbane, 82.

CGIAR. (2016) The drought and salinity intrusion in the Mekong River Delta of Vietnam: Assessment Report. Ben Tr, Tra Vinh, Kien Giang, Vietnam: CGIAR.

Dong, N. M., Brandt, K. K., Sørensen, J., Hung, N. N., Van Hach, C., Tan, P. S., & Dalsgaard, T. (2012). Effects of alternating wetting and drying versus continuous flooding on fertilizer nitrogen fate in rice fields in the Mekong Delta, Vietnam. Soil Biology and Biochemistry, 47, 166-174.

Hagenvoort, J. E. J., & Văn, P. Đ. T. (2013). Adaptation to Saline Intrusion in the Coastal Area of Vĩnh Châu, the Vietnamese Mekong Delta.

Hashimoto, T. (2001). Environmental Issues and Recent Infrastructure Development in the Mekong Delta: review, analysis and recommendations with particular reference to large-scale water control projects and the development of coastal areas. Australian Mekong Resource Centre.

Hung, N., (2011). Disease outbreaks for intensive shrimp farming system according to climate change (in Vietnamese: Toˆm bi dich beˆnh do bieˆn đổi kh ́ı haˆu). Kinh Te Sai Gon Online. Käkönen, M. (2008). Mekong Delta at the crossroads: more control or adaptation?. AMBIO: A Journal of the Human Environment, 37(3), 205-213.

Khoi, P., Thinh, H., (2013). An alarm for saline intrusion in the Vietnamese Mekong Delta (in Vietnamese: Ba ́o đoˆng xaˆm ma ̆n tai Ðoˆng ba ̆ng soˆng Cửu Long). Dien Dan Dau Tu - Kinh Doanh.

Lang, N. T., Phuoc, N. T., Van Khoa, B., & Buu, B. C. (2018). Development of Rice Genotypes Tolerant to Salinity Stress in the Mekong Delta, Vietnam using Marker-Assisted Selection. SABRAO Journal of Breeding & Genetics, 50(3).

Mekong River Commission. (2010) Impacts of Changes in Salinity Intrusion. Assessment of Basin-Wide Development—Technical Note 8. Mekong River Commission.

Oliver, M. M. H., Talukder, M. S. U., & Ahmed, M. (2008). Alternate wetting and drying irrigation for rice cultivation. Journal of the Bangladesh Agricultural University, 6(2), 409-414.

Shamsudduha, M., Chandler, R. E., Taylor, R. G., & Ahmed, K. M. (2009). Recent trends in groundwater levels in a highly seasonal hydrological system: the Ganges-Brahmaputra-Meghna Delta. Hydrol Earth Syst Sc, 13(12), 2373-2385.

Smajgl, A., Toan, T. Q., Nhan, D. K., Ward, J., Trung, N. H., Tri, L. Q., ... & Vu, P. T. (2015). Responding to rising sea levels in the Mekong Delta. Nature Climate Change, 5(2), 167.

Son, N. T., Chen, C. F., Chen, C. R., Duc, H. N., & Chang, L. Y. (2014). A phenology-based classification of time-series MODIS data for rice crop monitoring in Mekong Delta, Vietnam. Remote Sensing, 6(1), 135-156.

Tho, N., Vromant, N., Hung, N. T., & Hens, L. (2008). Soil salinity and sodicity in a shrimp farming coastal area of the Mekong Delta, Vietnam. Environmental Geology, 54(8), 1739-1746.

Toan, T. Q. (2014). Climate change and sea level rise in the mekong delta: flood, tidal inundation, salinity intrusion, and irrigation adaptation methods. In Coastal Disasters and Climate Change in Vietnam (pp. 199-218). Elsevier.

Trung, N. H. (2014). Possible impacts of seawater intrusion and strategies for water management in coastal areas in the Vietnamese Mekong delta in the context of climate change. In Coastal Disasters and Climate Change in Vietnam (pp. 219-232). Elsevier.

Wassmann, R., Hien, N. X., Hoanh, C. T., & Tuong, T. P. (2004). Sea level rise affecting the Vietnamese Mekong Delta: water elevation in the flood season and implications for rice production. Climatic change, 66(1-2), 89-107.