Rainwater is considered a promising alternative water source for coastal areas where freshwater resources are increasingly under pressure. This study evaluates rain regime characteristics that influence the ability to exploit rainwater in the coastal provinces of the Vietnamese Mekong Delta (VMD). In particular, it considers the impact of climate change and El Niño–Southern Oscillation (ENSO) processes. We analyzed rainfall data from 102 monitoring stations across the VMD from 1989 to 2017. Using statistical methods, we explored (1) characteristics of the rainy season, including the dates of onset and cessation and season length; (2) average rainfall volumes; and (3) the maximum number of consecutive nonrainy days during the rainy season and over the year. We also analyzed changes in these characteristics over time, in parallel with ENSO processes and climate change. Trend lines were determined using nonparametric methods, utilizing Sen’s slope estimation and the Mann–Kendall test. Results showed a tendency for the rainy season to start earlier and end later in the western coastal zone of the study area, with season length gradually decreasing towards the East Sea and inland. The shortest rainy season was found in the estuary zone (in the northeast of the VMD). Rainfall was abundant on the west coast, again diminishing gradually towards the East Sea and inland. Rain was also quite plentiful during four dry season observation months in the study area, but it lacked the predictability needed for effective exploitation. The number of consecutive days without rain averaged 96 annually, with a difference of 29 days between the largest and smallest observations. The difference between the provinces with the longest and shortest periods without rain averaged 41 days. Although the impact of climate change on the rain regime is complex, we can say that the rainy season now tends to start earlier, end later, and be lengthier, though without exhibiting clear trends. ENSO processes significantly impacted rainfall regime characteristics, especially the dates of onset and cessation, and season length.

This paper focuses on quantifying the uncertainty in climate change and its impacts on hydrology in the Srepok watershed in the Central Highlands of Vietnam. The uncertainty associated with the general circulation model (GCM) structure from a subset of CMIP3 (CCCMA CGCM3.1, CSIRO Mk3.0, IPSL CM4, MPI ECHAM5, NCAR CCSM30, UKMO HadGEM1, and UKMO HadCM3), SRES emission scenarios (A1B, A2, B1, and B2), and prescribed increases in global mean temperature (0.5-6°C) using the soil and water assessment tool (SWAT) was investigated. For prescribed warming scenarios using HadCM3, linear decreases in mean annual streamflow ranged from 2.0 to 9.8 %. Differences in projected annual streamflow between SRES emission scenarios using HadCM3 were small (−3.8 to −3.3 %). Under the A1B scenario and 2°C increase in global mean temperature using seven GCMs, there was substantial disparity, of −3.7 to 21.0 % and −6.0 to 16.1 %, respectively. It was concluded that, in the case of the Srepok watershed, the most important source of uncertainty comes from the GCM structure rather than from the emission scenarios and climate sensitivity.

Characteristics of typhoon activity in the coastal area of North center Region, Vietnam in the period 1960-2013 Typhoon data during period 1960-2013 at JMA ((Japan Meteorological Agency) was used for analysis the typhoon activity characteristics in the coastal area of Northern Center Region Vietnam. The result showed that, there were about 1,5 typhoons have passed or strong affected to the study area annually. The typhoon season is from July to October, and the frequency was highest in September (Avg. 0,6 typhoon/y) and secondly in October (Avg. 0,4 typhoon/y). The trend of typhoon occurrence was reducing during period 1960-2013. During ENSO's years, the number of typhoon in La Nina years were twice higher than in La Niño years. The decade 80' was reached highest number of typhoon, and also the highest number of strong typhoon among 5 recent decades.

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The wastewater treatment plant (WWTP) in Ca Mau city, which is being planned for construction, will be responsible for treating domestic wastewater with a capacity of 8,000 m3/day. After being treated by the physic-biological method, the plant’s wastewater will be discharged into the Thong Nhat canal and the Tac Thu river. As a result, this article applies the MIKE21 model to calculate the range, the distance, and the concentration of typical pollutants for domestic wastewater, including TSS, BOD5, NH4+, and total Coliforms in the dry season, to provide evidence for water resource management following the plant’s construction. Two scenarios were established; in scenario 1 (S1), the WWTP is being operated inefficiently, and the wastewater has not been treated up to standards. Maximum calculation in case the processing performance = 0; in scenario 2 (S2), the WWTP is being operated efficiently. The concentration of 4 components in wastewater is lower than the critical value of QCVN 14:2008/BTNMT (column B, K = 1). The results show that the waste source will highly affect the water in the Thong Nhat canal both downstream and upstream due to the irregular semi-diurnal tide regime in case of the plant experiences problems (S1). In the case of the stable operation plant (S2), the pollutant concentrations at all positions will be lower than the critical value of QCVN 08-MT:2015/BTNMT (column B1) except for the TSS. Concentration variation is evident over time and distance: after about 1 hour and about 1 km from the source, the concentration of pollutants reaches the maximum value, then gradually decreases and ends at about 4 km after 7 hours.