No abstract

Potential evapotranspiration can be directly calculated by the Penman-Monteith equation, known as the one-step method. The approach requires data on the land cover and related-vegetation parameters based on AVHRR and LDAS information, which are available in recent years. The Nong Son basin, a sub-catchment of the Vu Gia-Thu Bon basin in the Central Vietnam, is selected for this study. To this end, NAM model was used; the results obtained show that the NAM model has the potential to reproduce the effects of potential evapotranspiration on hydrological response. This is seemingly manifested in the good agreement between model simulation of discharge and the observed at the stream gauge.

Saline intrusion is a hot issue and has always been of concern in the VMD (Vietnamese Mekong Delta), especially in the context of many changes of impact factors such as upstream flows and SLR (Sea Levels Rise). Vulnerability to changes in the upstream flows and SLR ismust-have reasons for updated and interpreted information. This information is used for exploiting of soil and water resources. MIKE 11 model was successfully applied to assess the saline intrusion. The study provided the picture of the saline intrusion in the dry season from January to May in the VMD in the existing situation (2015 and 2016) and the future (2030 and 2050) under the impact of flow at Kratie in various frequencies of 18%, 50% and 85% based on the time series of 2001-2016, and SLR according to RCP (Representative Concentration Pathway) 4.5 scenario of MONRE (Ministry of Natural Resources and Environment) of Vietnam issued in 2016. The results show that in the year 2015 the ASI (Saline Intrusion Area) in the VMD was relatively low due to moderate tidal level and high Kratie discharge (P = 18%). The scenario like the situation in 2016 and in the future ASI increased significantly compared to the 2015 baseline scenario which shows that the VMD is very vulnerable to saline intrusion. Based on multivariate regression analysis, the study also presented the formulas for the relationship between the ASI of 0.25 g/L, 2.5 g/L and 4.0 g/L thresholds and the impact factors such as the average discharge at Kratie and the maximum daily tidal level in East Coast during the dry season from January to May. With an adjusted R 2 at 0.913-0.974, these formulas are believed to be reliable for predicting ASIs based on the Kratie flow and the East Coast tidal level.