Climate change (CC) is one of the global challenges in the 21 st century, requiring countries around the world to develop specific programs and action plans to respond promptly and effectively to its impacts. As announced at the COP 15 conference on climate change in Copenhagen with a geographical position, diverse topography and climatic features, Vietnam will be severely affected by climate change; especially through extreme weather events related to water such as extreme tide, sea level rise, storms, floods, urban inundation, drought, etc. Therefore, it is necessary to have a flexible, creative and effective initiatives responding to uncertainty of climate change and natural disasters in urban and infrastructure development in Vietnam.
As a country with many river systems, Vietnamese cities are formed and developed in association with “river and water” in order to utilize the advantages related to water factors to serve economic and social development. However, these cities are always faced with natural hazards related to water influence factors (such as flooding, inundation, saline intrusion, high tides, etc.). With geographic locations situated at the end of river basins, many cities are not proactive in distribution and control of water sources and signficantly affected by upstream water sources related actions. In the context of change, extreme climatic phenomena are increasingly abnormal and have caused increasingly severe consequences. Urban flooding has been occurring in many urban areas throughout territories with increasing levels, scope and frequency. Meanwhile, the adaptive capacity of cities is currently not appropriate, leading to the risks and losses of water in urban areas more serious.
In addition to the inherent reasons due to the harsh climate causes, the impact of unreasonable urbanization in the climate change context is an issue that urban planners, designers and managers need to consider. The impact of urbanization and climate change on urban flooding are two resonant factors. The combined impacts of climate change with increasing rainfall and sea level rise along with urban expansion, surface concretization will change the flooding intensity and frequency in the future.
Currently, drainage design and planning is shifting from the conventional approach of fastest drainage to the main drainage systems to the slow drainage approach in which includes a temporary storage of water in households, neighborhoods, small basins that then slowly reasing the water to the main drainage basins. This reduces the load on the main urban drainage system and creates additional economic, social and environmental benefits (e.g. creating more green spaces combined with drainage, complementing groundwater, etc. ). Especially in the climate change context, the conventional drainage systems sometimes do not solve the drainage issue when extreme weather events such as rain and storms occur abnormally and are harder to forecast, leading to inundation and causing more serious damage to infrastructure, society and economy.
Recently,there has been a focus on the construction of drainage systems in urban areas in Vietnam. However, due to inadequate, inconsistent and inadequate planning, drainage capability is not ensured. Although the drainage system in urban areas is dredged, the flow is constantly cleared, and thus the flooding still occurs. This depends on many reasons such as: drainage channels that are blocked due to the construction process, illegal construction or not following urban plans. Also, many lakes and ponds have been filled to build houses and roads, reducing storage and drainage capacity of rain-water; high densities impervious surface, rapid increase in rainfall, loss of green space; uncontrolled waste discharge also causes the drainage system blocked, etc. Lack of water storage space and green infrastructure in urban areas is not only the cause of flooding when extreme climatic events occurs (heavy rain, high tides, storms surges, etc.) but also leads to the groundwater degradation, land subsidence, increased urban heat island, causing ecological imbalance and pollution, etc.
Detailed contents following attached file:
Guidebook (Sustainable urban drainage system and urban farming)_EN
Guidebook (Sustainable urban drainage system and urban farming)_VN