Figure 1. Urban Water Cycle and Sustainability (Senn & Spuhler, 2018)
Rapid urbanization and changing climate have impacted the urban water cycle. Urban cities are under water stress and hence water-smart cities are the need of the hour. Urban floods impact the performance of smart cities and are considered to be critical in designing smart cities. Peak Flow of food occurs with high intense rainfall for short durations in core urban areas, disrupting economic activities. Urban floods become disastrous due to lack of efficient drainage systems. Urban floods also bring huge volumes of flood which could be routed for other smart utilizations. This study discusses the various strategies to manage and integrate urban floods in water smart city development. Indian scenario regarding urban flood management has been reviewed in this paper.
Rapid urbanization demands faster urban facilities and requirements, which has to cater to the exponentially growing population. Urban cities have become human centric zones, which have altered the regional climate of the urban area.
The urban development authorities have to consider the effects of microclimate changes and urban heat island (UHI) effect while preparing expansion activities.
Climate change and urban development go hand in hand but in consequential directions. The phenomenon of climate change majorly includes variation of temperature and rainfall. These variations affect the economic index of the urban city in terms of industrial production, city infrastructure and public services. Climate change is a potential challenge for planning a smart city. With the advent of technologies, a smart city has to be planned as a secure and sustainable dwelling place. The planning should mandatorily include mitigating natural disasters such as urban flooding. The preparedness of smart city to such events always stakes out the consequences.
Urban flooding is a form of climate change consequence which occurs usually at densely populated areas and causes submergence of built environment, infrastructures and arrests the urban life cycle. It is not just a natural flood phenomenon which occurs in urban areas, but aggravates due to insufficient drainage systems for prolonged duration of intense rainfall events. Urban flooding is significantly different from rural flooding as urbanization leads to developed catchments, which increases the flood peaks from 1.8 to 8 times and flood volumes by up to 6 times (National Disaster Management Authority, 2010).
Smart cities thrive with vital infrastructure and technology which requires to be secured at all instances. Hence a smart city has to be planned for natural disasters such as urban flooding.
Urban floods have been studied extensively after their occurrences in global scenario. These flash floods have become frequent since early 20th century. Urban floods are caused by meteorological, hydrological and anthropogenic factors.
The extreme variation of basic climate parameters such as temperature, rainfall, wind speed and humidity play crucial role in initiating urban floods. The urban heat island causes high heat stress attracting more convectional rainfalls. If this scenario is accompanied with storms, it would turn into a disastrous urban flood.
Large cities usually develop along river banks or coastlines and depend on specific geography and topography. Urban Water resources for urbanized cities include lakes, aquifers, dams and reservoirs. Urban flooding happens due to high intensity rainfall occurring for short span of time. The drainage systems built in cities are insufficient to cater such large volumes of surface runoff. In the 30 years between 1973 and 2002, Asia had a 40 percent share of all flood disasters, followed by America-25%, Africa-17%, Europe-14% and Oceania-4% (Ramachandraiah, 2011). World Meterological Organisation (2012) reports that absence of drainage systems act as catalysts in urban flooding.
Unscientific urbanization and unplanned expansion of cities are the main cause of urban flooding. Human induced economic development activities such as the construction of concrete buildings, pavements and roads, heavy industrial emissions of pollutants and effluent pollution work against natural systems. Urban infrastructures obstruct the flood flow and blocks the surfaces rainwater infiltration into deeper aquifers. The indiscriminate disposal of solid waste into storm water drains and canals are major impediment to water flow during the monsoon season (Gupta, 2016). Improper reservoirs maintenance of add on to urban flooding events.
Consequences of urban flooding is complex to confront and manage as climate change is a driver of concurrent hazards in an urban environment. Urban water cycle and sustainability cycle is given in Figure 1.
Figure 1. Urban Water Cycle and Sustainability (Senn & Spuhler, 2018)
Inundation of urban areas affects urban life activities during prolonged rainfall. Urban infrastructure, industries, flora and fauna and neighboring agricultural plains are vulnerable physical features. Immediate impacts would be on public transportation systems and residential communities. The continuous rainfall of 483 mm for 48 hours paralyzed Chennai city in India during November 2015. The same event turned more disastrous in December 2015. The physical impacts include threat of toxic materials and sewage water mixing with surface runoff, which could lead to casualties, injuries and water-borne epidemics.
Flood damages in the densely populated areas accompanies loss to the assets. The quantifiable economic impacts individuals are household damages, industrial loss and crop damages. At a public level, economic impacts are on failure of electric stations, water and sewerage works, damage to roads/bridges incus relief expenditures.
All natural disasters are accompanied by natural and human factors. Risk which is a probability of loss which depends on hazards, vulnerability and exposure can be expressed through a function as
Risk = f (hazard, vulnerability, exposure)
The flood risk factor affects the performance of a smart city. Urban planners assess the risk prior to planning a smart city. Flood risk assessment of construction and destruction is given in Figure 2.
Figure 2. Flood Risk Construction and Reduction ( World Meterological Organisation, 2012)
Smart cities are urban hubs which are being focused to provide sustainable, energy efficient and technology driven facilities to the urban population. The focus is due to the incorporation of resilient urban flood management plans is most suited to building new smart cities than established urban cities.
The study by MoUD (2015) under Smart Cities Mission in India has proposed a Smart City Transformation Framework (SCTF) to integrate all smart city initiatives. The strategies for urban flood management are explained.
Flood controlling structures such as dams, river dikes, and coastal sea walls can control small floods (Tingsanchalc, 2012). The study conducted on Bengaluru City (Avinash, 2016) infers that urban floods aggravate due to insufficient storm water drainages in the city. A good drainage network, based on digital elevation models using suitable software and urban water systems can cater immediate disposal of surface runoff, which can be routed to ground water recharge locations or storage tanks. The huge flood volumes, if stored could be used for various water demands in the city.
Non-Structural Flood Control measures include technology driven sensor-based early warning systems which could predict the potential damage and risk of upcoming urban flood scenario. Also study of previous urban floods and prediction of flood hazard maps, public response and participation, and immediate relief are some strategies (Tingsanchali, 2012). Training on flood management and providing institutional arrangements at administrative levels in preparing urban population to reduce the effects urban floods.
The main aim of urban flood risk management is to minimize human loss and economic damages (Tingsanchali, 2012). The strategies towards achieving this aim in smart cities are risk assessment of the urban flood, planning for smart control measures on an integrated platform, implement control measures prior to execution of development plans, evaluation and maintenance of preventive measures. Evaluation has to be converted in to suitable policies with reassessment of risk over a period of time, as the city develops.
Control of green house gas (GHG) emissions by adapting sustainable industrial methods and simplifying urban activities towards environmental friendly lifestyles can indirectly reduce impact of climate change in the region. Smart devices to monitor emissions, pollutants, reduce energy consumptions, can be installed as measure to control extensive urban development against environment.
An increasing trend in occurrence of urban flood disasters can be witnessed in India. The major events are Hyderabad in 2000, Ahmedabad in 2001, Delhi in 2002 and 2003, Chennai in 2004, Mumbai in 2005, Surat in 2006, Kolkata in 2007, Jamshedpur in 2008, Delhi in 2009 and Guwahati and Delhi in 2010. The most recent devastating ones were Srinagar in 2014 and Chennai in 2015 (Smartnet, 2017). An image depicting Chennai urban flood in December 2015 is shown in Figure 3.
Figure 3. Chennai Urban Flood – Submergence ( Seenirajan, et al., 2017)
In India is are caused by Urban floods low pressure system called western disturbances in Arabian Sea and Bay of Bengal. The microclimate and urban heat island effect also causes untimely rainfalls, for which the urban development authorities are to be prepared. The trend of urbanization in India since 1951 is as shown in Table 1.
Table 1. Trend of Urbanization (Based on Census of India – 2001)
With the establishment of smart cities, India is likely to witness more frequent urban floods as per the predication of GCM (general circulation model) type of climate models. The flood events especially during post monsoon periods depict an increasing trend. Figure 4 shows the variation in monthly rainfall trends in cities in India.
Figure 4. Variation Monthly Rainfall in mm in Major Metropolitan Cities in India (National Disaster Management Authority, 2010)
“Smart water” is one of six components that define a smart city; the others include energy, mobility, buildings, public services and integration. Water smart cities aim to make the city more sustainable, consumption of water, efficient water management and improve socio-economic wellbeing. It generally involves a holistic approach in managing water and water infrastructure systems, i.e., sourcing, treatment and delivery. This requires investment in our water infrastructure by integrating ICT products, by which real data can be stored for analyzing and planing effective sharing and avoiding any wastage of water. This will ensure measurement of significant parameters such as groundwater, usage and demand for water. A roadmap to water smart cities with six action steps is given in Figure 5. As an example, water smart cities will have predictive capabilities of flood mapping when looking at historical flood data paired with real-time and predicted weather and precipitation data. By recognizing anomalies in water consumption patterns, smart cities can optimize and eliminate water waste and water cost in delivery. The highenergy demand of a city's water treatment and delivery networks are often underestimated, meaning that improving operational efficiency through actionable data will reduce greenhouse gas emissions and cut costs simultaneously (Taddune, 2018). Figure 6 shows framework for the concept of water smart city.
Figure 5. Roadmap Towards a Water-Smart City (Hattum, et al., 2016)
Figure 6. Scenario-Based Framework for Assessing Urban (Water) Infrastructure (Löwe, et al., 2019)
This is a new endeavour for planning a smart city to ensure optimal planning using intelligent software technologies for mitigating urban floods. This is a collaborative project by Dansk Hydraulisk Institut (DHI), the Technical University of Denmark (DTU), Krüger, Ramboll, and the Danish Meteorological Institute (DMI) executed through Danish water companies (Dansk Hydraulisk Institut, 2016). The project involves development of robust model concepts for real-time simulation and real-time control of drainage systems which will be incorporated using MIKE software.
The Water Smart Cities Program was outlined in 2017 through metropolitan Water Plan for Greater Sydney in Australia. This program investigated new ways to deliver more integrated water systems in a cost-effective and sustainable way (Metropolitan Water, 2017). Some of the projects under such programs are water measurement technologies, urban water management, stormwater management, waste water management and water treatment. Water as a basic entity is integrated with smart technologies to avoid water wastage and sensible per capita usage of water in smart cities.
With the advent of intense urban development and climate change effects, there is a requirement for smart cities to be water smart. Urban smart city planners have to consider various strategies of urban flood management on a water resources integrated platform to make it resilient to flood risks. Urban flood risk depends on a combination of components comprising hazard, exposure and vulnerability. Assessment of urban flood risk and suitable strategies depend on implementation of smart technology with community participation. Policies and institutional frameworks involving real-time technologies are likely to reduce the flood vulnerability in smart cities. Provision of an efficient drainage network is considered to be one of the major solutions for many existing urban cities. Urban flooding is driven by climate change which makes the city vulnerable under extreme variation of temperature and rainfall. Smart City Transformation Framework by NDMA in India has to include water smart cities (WSC) concept and further implement more structural control measures at vulnerable areas. Advanced research is required in modeling and assessing the effect of urban development on urban flood events. It is certain that watersmart cities can be more efficient and cost effective.