Salinity intrusion, caused by global sea-level rise, is a major threat to paddy cultivation in the Mekong Delta of Vietnam (MKD). Salinity exposure reduces crop yields, increases soil salinity, and exacerbates fresh water scarcity, resulting in altered land use decisions and decreased paddy farming profitability. This study evaluates the effects of salinity intrusion on paddy yields and planted acreage, using a 21-year district-level panel dataset from the 13 provinces in the MKD. Specifically, we analyze the relationship between current salinity levels and paddy yield, as well as the relationship between lagged salinity levels and the paddy planted area. We examine these relationships across all districts, as well as for salinity-prone and non-salinity-prone districts and by proximity to the coast (20 km, 20-60 km, and 60+ km). The results indicate that salinity intrusion poses a significant challenge to paddy production in salinity-prone and coastal regions. Salinity level significantly and adversely affects paddy yields in salinity-prone and coastal districts. Similarly, high salinity levels in the past five years significantly reduce planted paddy acreage in these same regions. We also find that paddy yields in the MKD peaked in 2015 and have been declining since. The study highlights the regional differences in challenges associated with salinity intrusion in paddy production. Policymakers and agricultural managers need to take a region-specific approach to ensure that interventions are tailored to the specific needs and challenges faced by farmers. This entails supporting intensified paddy production in less salinity-prone areas and facilitating transitions to economically profitable alternatives to paddy in more salinity-prone areas. / Master of Science / Salinity intrusion, resulting from rising sea levels worldwide, poses a significant threat to paddy cultivation in the Lower Mekong Delta, Vietnam (MKD). The increased exposure to salinity adversely affects crop yields, exacerbates soil salinity levels, and contributes to freshwater scarcity. Consequently, this study aims to assess the effects of salinity intrusion on paddy yields and planted acreage in the MKD. By using a 21-year dataset covering thirteen provinces within the MKD, this study examines the relationship between current salinity levels and paddy yield, as well as the association between lagged salinity levels and the planted area of paddy crops. The analysis considers all districts within the region, distinguishing between salinity-prone and non-salinity-prone districts, as well as the proximity to the coast (20 km, 20-60 km, and 60+ km). The findings indicate that salinity intrusion presents a significant challenge to paddy production in both salinity-prone and coastal regions. High salinity levels substantially and adversely affect paddy yields in these districts. Furthermore, elevated salinity levels within the past five years significantly reduce the planted acreage of paddy crops in the same regions. Notably, paddy yields in the MKD reached their peak in 2015 and have been declining since. This study highlights the need for tailored strategies to address the diverse challenges faced by farmers in different regions. Policymakers and agricultural managers must support intensified rice production in areas that are less prone to salinity, while also promoting alternative crops in regions more vulnerable to salinity. By doing so, we can help sustain agricultural productivity and livelihoods in Vietnam's Mekong Delta, even in the face of salinity intrusion.

A 3-D numerical model of the Head of Passes and Bird’s Foot Delta of the Mississippi River- was developed. The model was based on Delft3D and simulates the hydrodynamics and salinity transport for Head of Passes area from RM 6.5 to Gulf of Mexico. The model was calibrated, validated, and used to predict the response of the river to certain stimuli, such as - channel closures, channel modifications and diversions. The model includes West Bay, Southwest Pass, South Pass, Pass-A-Loutre and Main Pass. Three basic cases were developed: existing conditions, closure of Southwest Pass with a levee of 1.5m with dredging of Pass-A-Loutre to 13.7 meter depth, and closure of Southwest Pass and South Pass with dredging of Pass-A-Loutre to 13.7 meter (45 ft) depth. Salinity has been added to the model. It has been proved that salinity intrusion has a significant impact on the model instantaneous discharge. For all passes except Southwest Pass instantaneous discharge decreases almost in half. Closure of Southwest Pass and dredging of Pass-A-Loutre leads to changes in flow speed and distribution. As a result Pass-A-Loutre becomes a main River channel.

Salinity intrusion in a river may have an adverse effect on the quality of life and can be perceived as a modern-day curse. Therefore, it is important to find technical ways to monitor and forecast salinity intrusion. In this paper, we designed a forecasting model using Simple Exponential Smoothing method (SES) which performs weekly salinity intrusion forecast in Ham Luong river (HLR), Ben Tre province based on historical data obtained from the Center for Hydro-meteorological forecasting of Ben Tre province. The results showed that the SES method provides an adequate predictive model for forecast of salinity intrusion in An Thuan, Son Doc, and Phu Khanh. However, the SES in My Hoa, An Hiep, and Vam Mon could be improved upon by another forecasting technique. This study suggests that the SES model is an easy-to-use modeling tool for water resource managers to obtain a quick preliminary assessment of salinity intrusion. / Xâm nhập mặn có thể gây tác động xấu đến đời sống con người, tuy nhiên nó hoàn toàn có thể dự báo được. Cho nên, một điều quan trọng là tìm được phương pháp kỹ thuật phù hợp để dự báo và giám sát xâm nhập mặn trên sông. Trong bài báo này, chúng tôi sử dụng phương pháp Simple Exponential Smoothing để dự báo xâm nhập mặn trên sông Hàm Luông, tỉnh Bến Tre. Kết quả cho thấy mô hình dự báo phù hợp cho các vị trí An Thuận, Sơn Đốc, và Phú Khánh. Tuy nhiên, các vị trí Mỹ Hóa, An Hiệp, và Vàm Mơn có thể tìm các phương pháp khác phù hợp hơn. Phương pháp Simple Exponential Smoothing rất dễ ứng dụng trong quản lý nguồn nước dựa vào việc cảnh báo xâm nhập mặn.

Das übergeordnete Ziel dieser Studie ist es, die Auswirkungen des Eindringens von Salzwasser auf den Reisanbau bei unterschiedlichen Salzgehalten zu analysieren und zu untersuchen, wie Veränderungen in den Reissortenoptionen innerhalb der nördlichen zentralen Küstenregion Vietnams dazu beitragen können, diese Auswirkungen zu reduzieren. Auf Böden mit hohem Salzgehalt, die für den Reisanbau nicht mehr geeignet sind, werden geeignetere Anpassungsstrategien gefordert, indem die Präferenz der Landwirte für verschiedene Anbaufolgen und die Faktoren, die ihre Präferenzen im Zusammenspiel mit verschiedenen Salzgehaltsstufen beeinflussen, untersucht werden. Die Studie untersuchte die Auswirkungen des Salzgehalts auf den Mittelwert und die Variabilität der Reiserträge in vier Gemeinden der Provinz und untersuchte mögliche Änderungen im Portfolio der Reissorten, die Erträge zu steigern und gleichzeitig die Ertragsvariabilität zu verringern. Außerdem wurden die Auswirkungen des Salzwassereinbruchs auf die Produktivität und die technische Effizienz der Reisfarmen im Untersuchungsgebiet bewertet. Im Gegensatz zu bestehenden Studien wurden in dieser Untersuchung die Auswirkungen der Bodenversalzung analysiert. Salztolerante Reissorten können die Erträge sichern, solange der Salzgehalt moderat ist, sind aber ungeeignet, sobald der Salzgehalt hoch ist. Dies führte zur Durchführung eines dritten methodischen Ansatzes, der mit Hilfe eines Choice-Experiments Informationen über die Präferenzen und Motivationen der Reisbauern für die Wahl zwischen dem Portfolio der lokal möglichen adaptiven und transformativen Optionen generierte. Die Adoptionsergebnisse der Befragten bei verschiedenen Versalzungsgraden wurden ebenfalls simuliert. Die Ergebnisse zeigen, dass sich der Salzgehalt negativ auf die Reiserträge auswirkt, zu einer Erhöhung der Variabilität der Erträge beiträgt und die technische Effizienz von Reis in Abhängigkeit von den Reissorten verringert. / The overall objective of this study is to analyze the impact of saltwater intrusion on rice cultivation at different salinity levels and it also explores how changes in the rice cultivar options within the north central coastal region of Vietnam can help to reduce these impacts. In soils with high salinity levels which are no longer suitable for rice cultivation, more suitable adaptation strategies are called upon through examining farmers’ preference for different crop sequences and the factors affecting their preferences in the interaction with various levels of salinity. The study investigated impacts of salinity on mean and variability of rice yields in four communes of Thua Thien Hue Province and looked at possible changes in the portfolio of rice cultivars, which would offer farmers the potential to increase yields and decrease yield variability simultaneously. I also evaluated the impact of saltwater intrusion on the productivity and technical efficiency of rice farms in the study area. Contrasting to existing studies, this research analyzed season-differentiated impact of soil salinity. Salt tolerant rice varieties can secure yields as long as salinity levels are moderate but are inappropriate once salinity becomes severe. This led to the conduct of third methodological approach that generated information about rice farmers’ preferences and motivations for choosing among the portfolio of locally feasible adaptive and transformative options using a choice experiment. The respondents’ adoption outcomes at different salinity levels were also simulated. The results showed that salinity has negative impact on rice yields, contributes to an increase in variability of yields and reduces rice technical efficiency depending on rice varieties.