Abstract. 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 urbandrainage/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.

Urban development increases flood risk in cities due to local changes in hydrological and hydrometeorological conditions that increase flood hazard, and also to urban concentrations that increase the vulnerability. The relationship between the increasing urban runoff and flooding due to increased imperviousness 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) climate change-driven sea-level rise and tidal effect, (ii) increase river runoff due to climate change, (iii) increased urban runoff driven by imperviousness, and (iv) enhancement of extreme rainfall due to urban growth-driven micro-climatic change (urban heat islands). A set of model simulations were used to assess the future impact of the combination of 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 risk resulting from the changes. The results show that, if the city develops as predicted, the maximum of inundation depth and area in Can Tho will increase by about 20%. The impact of climate change on inundation is more serious than that of urbanization. The worse case may occur if the sea level rises 100 cm and the flow from upstream happen in the high-development scenarios. The relative contribution of causes of flooding are significantly different at various locations; therefore, detailed research on adaptation are necessary for the future investments to be effective

In many cities in Vietnam, wastewater generated in slaughterhouses is normally discharged directly into surface waters without treatment. Management of slaughterhouse wastewater (SHWW) is difficult due to the lack of infrastructure for conveyance to centralized facilities. On-site treatment presents one cost-effective way of managing SHWW compared to mass improvement of infrastructure. This study evaluates the application of an airlift membrane bioreactor (AL-MBR) for on-site treatment of SHWW. The concentrations of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN) and NH-N in the simulated SHWW were 1,697 ± 317 mg/L, 891 ± 137 mg/L, 246 ± 65 mg/L and 171 ± 4.2 mg/L, respectively. The mixed-liquor volatile suspended solids in the aerobic and anoxic tanks were maintained at 5,000-6,000 mg/L. Air flow rate and cross flow velocity were maintained at 0.2 L/min and 0.8 m/s, respectively, to keep the trans-membrane pressure (TMP) stable at 0.8 bar and the membrane flux at 15-18 L/m h bar (LMH/bar). The removal efficiencies of COD and TN were 95 ± 1.9% and 70 ± 3.3%, respectively, at a hydraulic retention time (HRT) of 2.5 days. This study shows that GL-MBR is a promising on-site solution for SHWW treatment.

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