Urbanization and climate change impacts on future urban flooding in Can Tho city, Vietnam

Abstract

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.

Has dyke development in the Vietnamese Mekong Delta shifted flood hazard downstream?

“…This is expected to exacerbate urban flooding in Can Tho with its very low topography and poor drainage system as reported in Apel et al (2016) and Huong and Pathirana (2013). In Can Tho the total inundation area is not affected by the high-dyke construction; however, 6 % of the city area is converted from shallow inundation with depths below 1 m to deep inundation above 1 m (Table S2).…”

Sea-Level Rise and Land Subsidence: Impacts on Flood Projections for the Mekong Delta’s Largest City

“…Time-series data from monitoring wells indicates that the average rate of hydraulic head decline is 0.3 m·yr −1 , which indicates land subsidence at an average rate of 16 mm·yr −1 [14]. However, because of the lack of data, the question remains as to exactly how much of the subsidence in the delta is due to groundwater extraction [15,16].…”

Delimiting Urban Growth Boundary through Combining Land Suitability Evaluation and Cellular Automata

“…The mean fuzzy similarity started from 35% in the window size of 30 m, and stopped to 87% in a window size of 330 m. A mean fuzzy similarity exceeded 50% at a spatial resolution of about 60 m (Figure 10). Through comparing the accuracies or similarities of urban growth models in other studies [53][54][55][56][57], we thought this CA model was able to simulate future urban growth. …”