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Hoan Kiem District, Vietnam

Hung C.V.,Hanoi University of Science | Cam B.D.,Hanoi University of Science | Mai P.T.N.,Hanoi University of Science | Dzung B.Q.,Vietnam Institute of Meteorology
Environmental Geochemistry and Health | Year: 2014

Concentrations of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in sludge from Kim Nguu River, Hanoi, Vietnam, were analyzed to understand the contamination levels, distribution and accumulation pattern of municipal sludge from a highly urbanized area that receive direct discharge of wastewater. High concentrations of heavy metals such as As, Cd, Pb, Cu and Zn were observed in sludge, which were exceeded the Vietnamese regulation threshold values. In general, contamination status of heavy metals in sludge was in the similar range or slightly lower than those previously reported in sludge from the same area. The mean concentrations of As, Cd, Cr, Cu, Ni, Pb and Zn were 24.3, 2.65, 105, 166, 60.8, 73.7 and 569 mg/kg dry wt., respectively. Our result also indicates increased levels of PAHs, which are among the first data on PAHs accumulation in municipal sludge from metropolitan area in Vietnam. PAH concentrations ranged from 218 to 751 mg/kg dry wt. (mean: 456 mg/kg dry wt.), which were greater than those reported in sewage sludge from other countries as well as in sediments and soils collected from the same area. Accumulation pattern revealed the predominant of higher-ringed PAH compounds. Indicator ratios suggest the sources of PAHs were probably derived from biomass (wood and coal) and fossil fuel combustion and petroleum emissions. Most of the sludge samples contain PAHs concentrations exceeding various international guidelines values for sludge and sediment, such as probable effect levels, suggesting the possible risk for adverse biological effects in the study area and in the landfill sites where dredged sludge was dumped. © 2014, Springer Science+Business Media Dordrecht.

Huong H.T.L.,Vietnam Institute of Meteorology | Pathirana A.,UNESCO-IHE Institute for Water Education
Hydrology and Earth System Sciences | Year: 2013

Urban development increases flood risk in cities due to local changes in hydrological and hydrometeorological conditions that increase flood hazard, as well as to urban concentrations that increase the vulnerability. The relationship between the increasing urban runoff and flooding due to increased imperviousness is better perceived than that between the cyclic impact of urban growth and the urban rainfall via microclimatic changes. The large-scale, global impacts due to climate variability and change could compound these risks. We present the case of a typical third world city - Can Tho (the biggest city in Mekong River Delta, Vietnam) - faced with multiple future challenges, namely: (i) the likely effect of climate change-driven sea level rise, (ii) an expected increase of river runoff due to climate change as estimated by the Vietnamese government, (iii) increased urban runoff driven by imperviousness, and (iv) enhancement of extreme rainfall due to urban growth-driven, microclimatic change (urban heat islands). A set of model simulations were used to construct future scenarios, combining these influences. Urban growth of the city was projected up to year 2100 based on historical growth patterns, using a land use simulation model (Dinamica EGO). A dynamic limited-area atmospheric model (WRF), coupled with a detailed land surface model with vegetation parameterization (Noah LSM), was employed in controlled numerical experiments to estimate the anticipated changes in extreme rainfall patterns due to urban heat island effect. Finally, a 1-D/2-D coupled urban-drainage/flooding model (SWMM-Brezo) was used to simulate storm-sewer surcharge and surface inundation to establish the increase in the flood hazard resulting from the changes. The results show that under the combined scenario of significant change in river level (due to climate-driven sea level rise and increase of flow in the Mekong) and "business as usual" urbanization, the flooding of Can Tho could increase significantly. The worst case may occur if a sea level rise of 100 cm and the flow from upstream happen together with high-development scenarios. The relative contribution of causes of flooding are significantly different at various locations; therefore, detailed research on adaptation are necessary for future investments to be effective. © Author(s) 2013.

Gobin A.,Flemish Institute for Technological Research | Nguyen H.T.,Center for Meteorology Hydrology and Environment Science and Technology Hanoi Vietnam | Pham V.Q.,Vietnam Academy of Science and Technology | Pham H.T.T.,Vietnam Institute of Meteorology
International Journal of Climatology | Year: 2015

Heavy rainfall months of more than 450mm occur in all 56 meteorological stations in eight climatic zones of Vietnam during the rainy season from April to September in the north (>20°N), from August to December in the centre and from May to November in the south (<12°N). The severity of an El Niño Southern Oscillation (ENSO) episode, expressed as the integral of sea surface temperature anomaly (SSTA) in the central tropical Pacific over the duration, shows a 4.6-fold (2.3-fold) increase in number of heavy rainfall months during La Niña (El Niño) per unit change in severity during the 1960-2009 period, suggesting a twin peak occurrence with both ENSO extremes. A heavy rainfall index (HRI) links heavy rainfall months to the rainy season duration, and allows evaluation of the rainfall severity per station, climatic zone and ENSO cycle. For the deltas and central climatic zones, seasonal rainfall and number of heavy rainfall months are significantly higher at the p<0.05 level during La Niña than during El Niño episodes. Interpolated seasonal rainfall shows distinct differences between regions, with location having a larger effect than ENSO cycles on monthly rainfall amounts. Twenty-year return monthly rainfall derived from generalized Pareto distributions for peak over thresholds range from 475mm in the central highlands to 2185mm in the central coast. The spatial and temporal patterns of heavy monthly rainfall help explain flooding and paddy inundation which occur at least twice as frequent during La Niña as compared to El Niño conditions, particularly in Central Vietnam. The relation of HRI with both 20-year return levels and ENSO cycles offers opportunities for fast screening of impacts in a wider region of Southeast Asia. Because ENSO cycles have an impact on flooding and paddy inundation, it provides prospects for early warning, differentiated for different zones and rainfall regimes. © 2015 Royal Meteorological Society.

Hitzl D.E.,University of Hawaii at Manoa | Chen Y.-L.,University of Hawaii at Manoa | Nguyen H.V.,University of Hawaii at Manoa | Nguyen H.V.,Vietnam Institute of Meteorology
Monthly Weather Review | Year: 2014

During the summer, sustained winds in the -Alenuihāhā Channel, Hawaii, may exceed 20ms-1 with higher gusts. The Advanced Research Weather Research and Forecasting model is used to diagnose airflow in the Hawaiian coastal waters. High-resolution (2 km) runs are performed for July 2005 covering the -Alenuihāhā Channel and nested in a 6-km state domain. Under normal trade wind conditions (7-8ms-1), winds at the channel entrance are 1-2ms-1 faster than upstream due to the convergence of the deflected airflows by the islands of Maui and Hawaii, and accelerate through the channel due to along-gap pressure gradients and lower pressure in the wakes of both islands. The acceleration is accompanied by descending airflow (>9 cms-1) in the exit region with lowering of the trade wind inversion. Deceleration occurs downstream of the channel exit with a rapid change from sinking motion to rising motion (>3 cms-1). Under normal or strong trade wind conditions, the flow is subcritical [Froude number (Fr)< 1] upstream of the channel, supercritical (Fr>1) in the exit region, and subcritical again (Fr<1) downstream with a weak hydraulic jump. The localized sinking motion on the lee side of bordering ridgelines (>1ms-1) is most significant in the afternoon hours and results in warming and lowering of surface pressure on the lee side, into the channel, and farther downstream. As a result, the channel winds and the wind speed maximum along the southeastern coast of Maui exhibit an afternoon maximum. © 2014 American Meteorological Society.

Vinh V.D.,Institute of Marine Environment and Resources | Ouillon S.,Toulouse 1 University Capitole | Ouillon S.,Hanoi University of Science and Technology | Thanh T.D.,Institute of Marine Environment and Resources | Chu L.V.,Vietnam Institute of Meteorology
Hydrology and Earth System Sciences | Year: 2014

The Hoa Binh dam (HBD), located on a tributary of the Red River in Vietnam, has a capacity of 9.45 × 109 m3 and was commissioned in December 1988. Although it is important for flood prevention, electricity production and irrigation in northern Vietnam, the Hoa Binh dam has also highly influenced the suspended sediment distribution in the lower Red River basin, in the delta and in the coastal zone. Its impact was analysed from a 50-year data set of water discharge and suspended sediment concentration (1960-2010), and the distribution of water and sediment across the nine mouths of the delta was simulated using the MIKE11 numerical model before and after the dam settlement. Although water discharge at the delta inlet decreased by only 9%, the yearly suspended sediment flux dropped, on average, by 61% at Son Tay near Hanoi (from 119 to 46 × 106 t yr-1). Along the coast, reduced sedimentation rates are coincident with the lower sediment delivery observed since the impoundment of the Hoa Binh dam. Water regulation has led to decreased water discharge in the wet season (-14% in the Red River at Son Tay) and increased water discharge in the dry season (+12% at the same station). The ratios of water and suspended sediment flows, as compared to the total flows in the nine mouths, increased in the northern and southern estuaries and decreased in the central, main Ba Lat mouth. The increasing volume of dredged sediments in the Haiphong harbour is evidence of the silting up of the northern estuary of Cam-Bach Dang. The effect of tidal pumping on enhanced flow occurring in the dry season and resulting from changed water regulation is discussed as a possible cause of the enhanced siltation of the estuary after Hoa Binh dam impoundment. © 2014 Author(s).

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