Vulnerability of Surat, Gujarat to Flooding from Tapi River: a Climate Change Impact Assessment
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Vayu Mandal 43(2), 2017 Vulnerability of Surat, Gujarat to Flooding from Tapi River: A Climate Change Impact Assessment Kirit Parikh, Jyoti Parikh and Mohit Kumar Integrated Research and Action for Development, New Delhi Email: [email protected] ABSTRACT The impact of climate change on urban areas can be serious. We need to take adaptive measures to strengthen resilience of our cities. This is particularly important as our urban population is expected to increase by hundreds of millions in the coming decades. Due to vagaries of climate, increased anthropogenic activities and encroachments, and unmindful constructions along the river-banks, impact of floods on cities often become disastrous leading to loss of livelihoods, infrastructure and property damage in affected areas, and hardship for vulnerable communities. At the same time, the rapid growth of urbanization offers an opportunity to take proactive measures to adapt urban growth to make our cities more resilient to climate change. Urban climate resilience needs to rely on scientific data and sound analytical framework encompassing urban planning and socio-economic analysis. In this study, we have attempted to identify and analyze the immediate and medium-term impacts of flooding events in a rapidly growing urban system of Surat city (Gujarat, India). We have used HEC-RAS model to analyze inundation scenario in Surat. Two scenarios have been developed. In scenario-1, water discharge corresponding to the flood of 2006 has been modeled whereas in scenario-2 the water inflow considered is 1.5 times the volume of 2006. We have considered 50% increase in the inflow of Tapi river as the probable impact of future climate change. In addition to measuring the physical impacts of floods, we have studied the socio-economic impacts also to provide policy implications for developing adaptation capacity and city resilience plans. The analysis shows that west zone and north zone of the city are highly flood prone while south zone is least. Topographically, west zone is the lowest zone and hence it has more chances to get flooded severely. The results are particularly useful for the preparation of city development plans with a view to make cities resilient to climate change, minimize the damages and informing citizens about the risk of specific areas in the city to avoid construction there. Keywords: Climate change, Flood plains, City resilience and Inundation. 1. Introduction They found that the entire system of flood control is based on: The impact of extreme weather and climate events on exposed and vulnerable human and • Prediction of daily inflow from Central natural systems manifests in the form of Water Commission disasters (IPCC, 2012). Such weather and • Processing of data and decision making by climate related disasters have social as well as Govt. of Gujarat. physical dimensions. There has been an • Rules for operation of reservoir to meet increase observed in the frequency and specified objectives magnitude of extreme weather- and climate- events in the past decades (IPCC, 2012), They concluded that the present system of which has exacerbated the disaster risks on flood management does not take into growing human population and associated consideration changes in environment, flood infrastructure. The risks associated with plain, drainage (due to urbanization), weather- and climate-related disasters can be economic analysis of overall public loss mitigated by adopting appropriate policy against benefits and hardships to 3 million measures in advance based on modeling the people for a month. Singh and Sharma (2009) potential consequences of extreme events. studied the flood of 2006 in Surat using high resolution remote sensing images and prepared Various researchers have studied flooding in urban flood hazard maps employing statistical Surat city as well as district. Desai and Tailor probabilities of flood frequency, maximum (2007) analyzed the present management discharge carrying capacity at river cross- approach of flood moderation in Tapi basin. section, mapping of inhabited areas based on high-resolution images and terrain mapping 120 Parikh et al. using GPS (Global Positioning System). Patel the water released from the Ukai dam exceeds and Dholakia (2010) assessed the flood 1.5 times the volume released in 2006 and potential of Varekhadi watershed group by assesses the vulnerability of schools, hospitals, application of Soil and Water Assessment Tool slums and industries. (SWAT) model, using Remote Sensing (RS) Flooding causes serious impact on people and and Geographical Information System (GIS). property. The European Union (EU) Floods They also suggested feasible structural and Directive (Directive 2007/60/EC Chapter 1 non-structural measures in order to minimize Article2. eur-lex.europa.eu. Retrieved on the effect of flood, in and around Surat city. 14/12/2015) defines a flood as a covering by Joshi and Patel (2010) studied morphological water of land not normally covered by water. processes in Tapi River Basin. They developed This definition includes floods from rivers, an “optimization process” for minimizing the mountain torrents and floods from the sea in impacts of floods. Timbadiya et al. (2011) coastal areas. used HEC-RAS (Hydrologic Engineering Centre-River Analysis System) model for “Vulnerability” is the level of exposure of studying the flood in the lower reaches of Tapi persons and property to hazards. Timmerman river. They carried out topographic assessment (1981) reviewed vulnerability at the society of river bed features (characterized as channel or community scale and defined it as the roughness using Manning’s roughness degree to which a system, or part of a coefficient) for simulating the floods of 1998 system, may react adversely to the and 2003. Agnihotri and Patel (2011) carried occurrence of a hazardous event. Physical out a critical study of the flood in Surat city vulnerability is related to the physical that wrought heavy devastation during August location of the people and elements at risk, 5-9, 2006. Ninety percent area of Surat was and their physical proximity to the hazard. flooded because of heavy rains and sudden Socio-economic vulnerability indicates the releases from the Ukai dam which is situated degree to which a population is affected by a at a distance of around 100 km from Surat. calamity such as disruption in services like Their study of city topography confirmed that schools, hospitals etc. It will not be strictly the depth of water induced by the flood varied confined to the physical components but also in different parts of the city. Their analysis depends on the prevailing social and revealed that the flood was due to the economic conditions. Settlements or excessive outflow of 25711 m3/s (9.08 lakh buildings which are near to the river are cusecs) from Ukai dam. They suggested more prone to flooding due to overflow of preventive remedial measures such as river embankment at the time of flooding reservoir operation policy, warning system event. from upstream, water release from the dam Climate change is likely to aggravate floods. etc. Goswami et al. (2015) studied water IPCC (2007) also noted “The most surface elevation of the nearly 110 km stretch vulnerable industries, settlements and of lower Tapi Basin using HEC-RAS model. societies are generally those in coastal and All these studies are primarily focused on the river flood plains, those whose economies past events of floods. In the changing climatic are closely linked with climate-sensitive conditions, it is also important to map all the resources, and those in areas prone to vulnerable locations and public facilities extreme weather events, especially where where a large section of vulnerable population rapid urbanization is occurring”. Poor may congregate. For example, schools where communities can be especially vulnerable, in children and hospitals where patients go in particular those concentrated in high-risk large number and evacuation may be difficult. areas. They tend to have more limited And if the probability of extreme events and adaptive capacities, and are more dependent its magnitude is greater than normal by current on climate-sensitive resources such as local standards, then additional adaptation actions water and food supplies. With an estimated might have to be planned proactively. In this 14% of population living within 100 km of context, the present work assumes significance the coast in India, the damage due to floods as it provides a glimpse of potential inundation in coastal cities in our country could not be in Surat in a modeled future situation in which overemphasized. The cities have high 121 Vayu Mandal 43(2), 2017 density of population, expensive properties Annual precipitation ranges from 1000 to 1200 and high economic activities. It is therefore mm. 90% of this rainfall occurs between June necessary to understand the ramifications of and September. The Tapi River, which meets natural hazards like floods on urban areas to the sea at a distance of 16 km from the city evolve appropriate policies to strengthen the centre. The city is located at the mouth of Gulf resilience of our coastal cities. Against this of Khambhat and experiences a tidal range of backdrop, this paper attempts to identify and 5-6 m. High tides often inundate the western analyze the immediate and medium-term part of the city. The city is governed by three impacts of flooding in the city of Surat, bodies: Surat Municipal Corporation (SMC), which is a rapidly growing coastal city on Surat Urban Development Agency (SUDA) the banks of river Tapi on the west coast of and the Hazira Development Authority India. (HDA). HDA governs the port and industrial hub located downstream from Surat city. Broadly the objectives of this study are to assess the vulnerability of the Surat city to Much of the city is located <10 m above mean flooding from Tapi river taking the scenario of sea level. The city has a history of flooding 2006 flood and to model the inundation in with the earliest record of floods being that of Surat city assuming a 50 % increase of water 1869 (Bhat et al., 2013).