MODELING AND SOCIO-ECONOMIC IMPACT ANALYSIS OF FLOODS IN COASTAL CITIES UNDER SEA LEVEL RISING SCENARIOS: A CASE STUDY OF KARACHI, PAKISTAN ABSTRACT

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1 MODELING AND SOCIO-ECONOMIC IMPACT ANALYSIS OF FLOODS IN COASTAL CITIES UNDER SEA LEVEL RISING SCENARIOS: A CASE STUDY OF KARACHI, PAKISTAN Habib-ur-Rehman 1), Rabin Bhattarai 2) 1) University of Engineering & Technology, Lahore, Pakistan 2) RNUS, School of Civil Engineering, Asian Institute of Technology,Klong Luang, Pathumthani 12120, Thailand of Corresponding author: mughalhabib@uet.edu.pk ABSTRACT The coastal zone of Pakistan is extended over a length of 1,046 km in between 62 o E to 68 o E longitudes with the average annual rainfall varying from mm. The urban population along the coast line varies from 10 to more than 7000 persons per Km 2 which is vulnerable to tropical cyclones as well as resulting floods. Such natural hazards are responsible for the loss of millions of lives and damage to the properties. According to the Reports of the International Governmental Panel on Climate Change, the global mean sea level may rise as high as 88 cm by end of the 21st Century and it may severely affect coastal regions in many parts of the World. The objective of this research was to conduct a case study in Karachi, a low lying coastal city in Pakistan, to analyze the flood characteristics under sea level rising scenarios and its socio-economic impacts. A physically based distributed hydrological model, which combines surface and river flow modules, was adopted to simulate flooding in future climate change scenarios based on the report of Inter Governmental Panel on Climate Change (IPCC). Input rainfalls and upstream boundary conditions of a worst flood period were considered based on the records of the last few decades as the baseline for modeling. Flood inundation modelling and socio economic analysis has been carried out and the results are discussed in the paper. Keywords: Sea level rising, coastal flooding, flood modeling INTRODUCTION The coastal zone of Pakistan runs over a length of 1,046 km in between 62 o E to 68 o E longitudes. The average January temperature is 18 o C, whereas it is o C in June, which is hottest month for the coastal area. The climate of the area can be classified as arid with warm summer and mild winter. The average annual rainfall over the coast line varies from mm. The monsoon rainfall varies mm, whereas the winter rainfall varies mm. The monsoon rainfall increases with the increase in longitude along the coast line, whereas, winter rainfall decreases with the increase in longitude. The urban population along the coast line varies from 10 to more than 7000 persons per Km 2. The entire length of the coast line is subjected to tropical cyclones. Though floods are common in various parts of the Pakistan particularly along the river Indus and its tributaries, most of the flood events appear in Monsoon season due to the snow melting and monsoon rainfalls. Localized and widespread floods are common in Pakistan, especially in the Indus Basin Plains. Monsoon currents originating in the Bay of Bengal and resultant depressions often cause heavy downpour in the Himalayan foothills. These are additionally affected by weather systems from the Arabian Sea (by seasonal lows) and from the Mediterranean Sea (through westerly waves), which occasionally produce destructive floods in one or more of the main rivers of the Indus system. Furthermore, exceptionally high floods have also been experienced due to the overtopping/breaching of some of the small dams, both man made (e.g. Shadi Kor dam in Pasni breached on washing away 80 people) and those resulted by the landslides and avalanches. International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand,

2 Based on a 2001 study, Intergovernmental Panel on Climate Change (IPCC) predicts that global mean sea level (msl) may rise as much as 88 cm by the end of the 21 st century. Sea level rising has many adverse impacts on coastal population and environment such as saline water intrusion, erosion of shorelines, amplified intensity and frequency of coastal flood inundation, etc. And, coastal zones are expected to be highly vulnerable to climate change in the coming years owing to the rapid urbanization and coastal zone development. The frequent extreme weather events are expected to endanger human lives as well as dampen the economy of these coastal cities. Many of the low lying coastal cities in South-East Asia, which are located at the estuary of major rivers and frequently affected by floods, are under greater threat of severe floods due to sea level rising. Many coastal cities have already been facing severe flood problems due to lower elevation and sea level rising will potentially worsen such problems. STUDY AREA For the present study, Karachi is the coastal city selected from Pakistan based on size, population and social and economic importance. Karachi is the most populous as well as a city of highest population density in Pakistan (average population density of 6666 persons/km 2 ). The total population of Karachi in 1998 was reported as million with 9.33 million urban population and million as rural population [Population Census, 2002]. The present (2005) estimated population of Karachi is 12 million with a population growth rate of about 4 %. Karachi is the largest city of Pakistan and the capital of the province of Sindh. It is the financial and commercial hub of Pakistan. The city is located on the Arabian Sea north west of the mouths of the Indus River. The geology of Karachi consists mainly of sedimentary rocks having two ranges namely Kirthar range and Pab range. The soils of Karachi city are classified into two types; the loamy sandy and gravilly soils of river valleys and alluvial cones near the coast line and shallow loamy gravelly soils and rock outcrops of plateaux. The southern part of the Karachi district has the swamps. Karachi lies in the semi arid zone and its rainfall is highly variable both in intensity and duration. Because of its location in the coastal belt, rainfall of high intensity is experienced on occasions but there is no fixed cycle for the occurrence of these occasional heavy downpours. They are dependent upon the local atmospheric disturbances in the sea which occur from time to time. The River Indus flows much away from the Karachi city, so no impacts of flooding appear on the study area due to flooding in River Indus. Floods in Karachi city are rare, and are only result of heavy rainfall over the city area. There are two main non perennial rivers crossing the thickly populated city areas before outfalling into Arabian Sea, the Malir River and Lyari River. The map of the city, depicting the layout of these two (Malir and Lyari) along with another the Hub river, is shown in Figure 1. Hub River lies on western boundary of Karachi and new settlements are now reaching this boundary due to shortage of land in the inner city. In monsoon season, Malir and Lyari River are observed flooded and there are katchi abadies settled along the banks of the rivers and some industrial units. Also due to insufficient drainage capacity of the storm sewer network water stays over the roads for few days after severe rainfalls and slightly disturbs the daily life routines and causes slight damages to the road network. The catchment of Malir river is comparatively larger and extends up to 112 km towards north of Karachi, whereas catchment area of Lyari river is very small and flood water reaches the city soon after the rain with little warning time. HISTORY OF FLOODS IN KARACHI The flood susceptibility of the Karachi city is the least among all other coastal cities selected for this study due to having relatively small annual rainfall and because Karachi is located outside of the Indus Basin, the major source of flooding in Pakistan. Having said that, the concentrated spell of rain in the catchment of Malir river and Lyari rivers, occasionally cause flash floods affecting the thickly populated areas on both sides of these rivers. Such flooding has been experienced in 1967, 1973, 1977, 1978, 1984, 1989, and in The flashy nature of the streams of Karachi is shown in Figure 2 depicting the rainfall in the catchment of Malir river and the resulting discharges at one of the river gauging station namely Super Highway Bridge with contributing catchment area of 2,240 km 2. Although rainfall in Karachi is comparatively lower than other Asian cities in this study, yet due to major economic hub, being home to nearly 10% of population of Pakistan and due to proximity to Arabian Sea, Karachi is more vulnerable to flood damages than any other city of Pakistan. 30 International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand, 2005

3 Figure 1: The map of Karachi city showing Malir River, Lyari River and Hub River. The largest damages due to floods in Karachi are caused in 1977 due to the abnormal rainfall of 30th June, 1977 (254 mm in one day). The discharges of flood waters on that day for Malir river and Lyari rivers were estimated as 6,380 and 1,420 m 3 /s, respectively. The flooding of the Karachi city results in huge losses due to synergetic effects of; absence of flood warning system, encroachment in flood plains, concentrated rain and the flashy nature of the rivers (high slopes of upper catchment). Rainfall in the upper catchment only and no rain in lower catchment (like what happened in 1977) results in a surprise flood for the inhabitants of the city in absence of proper warning system. daily rainfall (mm) Rainfall (mm) Flow (cusecs) daily discharge (cfs) time (days) Figure 2: Flash floods in Malir river at Super Highway Bridge gauging station International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand,

4 Due to these reasons the losses of life and property due to 1977 flood were quite high. Only in Karachi, about 300 persons were washed away [Iqtidar, 2005] and about 350 industrial units in Korangi including National Oil Refinery sustained damages to the extent of US$ 16.7 Million. Figure 3: DEM and Land-use map of study area Another kind of disaster is flooding due to Cyclones in Arabian Sea having potential to cause large-scale damage to the coastal areas of Sindh and Balochistan. The World Conference for Reduction of Disaster [WCDR, 2005] reports that the cyclone of 1999 in Thatta and Badin districts wiped out 73 settlements, and resulted in 168 lives lost, nearly 0.6 million people affected and killing of 11,000 cattle. It destroyed 1,800 small and big boats and partially damaged 642 boats, causing a loss of Rs 380 Million (US$1 approx equal to Pak Rs. 60). The losses to infrastructure were estimated at Rs. 750 Million. The period records 14 cyclones. 4 0 Water level (above msl) Rainfall Water level Rainfall (mm) Time (hours) Modeling flood characteristics Figure 4: Upstream boundary condition and rainfall input for the model Although entire Karachi Metropolitan covers an area of about 1800 km 2, this study is focused on the city having area of about 1000 km 2 on the basis of Karachi development Plan for the year The information on spatial variation of elevation in the study area was obtained from HYDRO1K DEM having 1 Km resolutions. The landuse map used in the study is taken from USGS ( global data set of 1 Km resolution. A local Landuse map developed by the Karachi Development Authority (KDA) was scanned and then digitized and used for verification purpose. The population distribution information for the study was obtained from Grided Population of the world (GPW) website ( for 1990 and Population information for year 2000 was obtained from Karachi development Plan, On the basis of the available population information, future projections were made for years 2025, 2050, 2075 and 2100 using Gibb s method. Similarly, building 32 International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand, 2005

5 distribution was computed on the basis of population distribution. The DEM and landuse map of the Karachi city is shown in Figure 3. Flood inundation RESULTS AND DISCUSSION The simulation has been carried out for the present and future scenarios of climate change. Under climatic change conditions the flows over the watershed plains and in the rivers is simulated based on the rise in MSL due to global warming after each quarter century. For the simulation, the observed MSL for the year 2003 was considered as present condition, and the mean sea level was increased by 14, 32, 57 and 88 cm from the present level to obtain future flood inundation condition for future years of 2025, 2050, 2075 and 2100 respectively in Karachi based on IPCC, the A1 scenario. (a) (b) (c) (d) (e) Figure 5: Flood simulation results for scenarios of (a) 2003, (b) 2025, (c) 2050, (d) 2075 and (e) 2100 International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand,

6 Institute of Industrial Sciences Distributed Hydrological Model (IISDHM, Jha et. al., Dutta et. al.) is used for flood modelling. Different spatial inputs (DEM, landuse) for the model were prepared with the collected GIS data base. The water level of Malir River at Superhighway Bridge is taken as upstream boundary condition for the simulation while tide level at the mouth of Malir River is taken as downstream boundary condition. On the basis of the collected data, the highest flow was observed in the last week of July in Malir River. So, the simulation was carried out from July 27 to 29 in year The rainfall and upstream boundary condition used for the flood simulation is shown in Figure 4. Table 1: Flood impact on population Depth of Duration of flood flood (m) < 1 day 1-2 days 3-4 days 5-7 days > 1 week No Impact No Impact No Impact No Impact No Impact Less Less Less Moderate Moderate Moderate Moderate High High High High Highest Highest Highest Highest > 3.50 Highest Highest Highest Highest Highest Table 2: Flood impact on buildings Depth of Duration of flood flood (m) < 1 day 1-2 days 3-4 days 5-7 days > 1 week No Impact No Impact No Impact No Impact No Impact Less Less Moderate Moderate High Less Less High High Highest Moderate High High Highest Highest > 3.50 High Highest Highest Highest Highest Table 3: Flood impact on road Depth of Duration of flood flood (m) < 1 day 1-2 days 3-4 days 5-7 days > 1 week No Impact No Impact No Impact No Impact No Impact No Impact Less Less Less Less Less Moderate Moderate High High Moderate High High Highest Highest > 3.50 High Highest Highest Highest Highest Table 4: Flood impact on railway Depth of Duration of flood flood (m) < 1 day 1-2 days 3-4 days 5-7 days > 1 week No Impact No Impact No Impact No Impact No Impact No Impact No Impact No Impact No Impact No Impact Less Moderate Moderate High High Moderate Highest Highest Highest Highest > 3.50 High Highest Highest Highest Highest For future scenario, the change in downstream boundary condition (sea-level rise) is considered according to IPCC report and simulation was carried out. Finally, the flood inundation maps for the study area have been developed for the years 2025, 2050, 2075 and The flood simulation result for the present scenario (year 2003) is shown in Figure 5 (a). The flood simulation results for the year 2025, 2050, 2075 and 2100 are shown in Figures 5 (b), (c), (d) and (e) respectively. Maximum flood inundation depth simulated was 4.57 m, for an increase in msl value of 88 cm compared to present maximum flood inundation depth of 2.53 m. From the Figures 5, it can be observed that low lying coastal area is more prone to flooding than the high lying area in the city. Although majority of area 34 International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand, 2005

7 is subjected to flooding in most scenarios, the flood depth in more than 50% of the area is less than 0.5 m which has negligible socio-economic impact. Socio-Economic Impacts and Vulnerability The preliminary information for assessing the socio-economic impact of the flood was obtained by conducting a questionnaire survey. The survey was aimed to develop Flood Impact Indices for various categories such as Buildings, Transportation and Population under different flood depth conditions. Tables 1, 2, 3 and 4 comprehend the indices developed from the questionnaire survey. Table 5: Flood impact on population in present and future scenarios Population affected Impact index Less impact 240, , , , ,384 Moderate impact 3,127 3,479 17,380 19,213 42,558 High Impact 6,229 3,945 4,356 4,401 28,727 Highest Impact - 2,449 2,532 3,291 6,405 Table 6: Flood impact on buildings in present and future scenarios Buildings affected Impact index Less impact 32,370 33,412 34,636 37,253 35,804 Moderate impact 828 1,231 2,096 1,585 3,815 High Impact Highest Impact - Table 7: Flood impact on road and railway in present and future scenarios Year Impact Index Less Moderate High Highest Year Impact Index Rail way Railway length Rail way Railway Railway length length length length No Impact Less Moderate High Highest With the above indices as the basis and by incorporating the flood depth values obtained as the output of the model, the Hazard classification was done for different scenarios. Tables 5, 6 and 7 depict the estimated damage for residential buildings, transportation and population categories from the present study and future scenarios. The number of residential buildings at present was approximated from the population data with the assumption that five people occupy one residential building because of the lack of building distribution International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand,

8 inventory in the city. The present road and rail network for the study area was obtained from the Global Coverage Digital Chart of the World of ESRI. For the future years, the road and rail network is retained the same and the damage caused was estimated. It is observed from the analysis that climate change scenarios affects population and road network in some extent while rail network will remain unaffected. CONCLUSIONS The presented study was focused to assess the socio-economic impacts of floods under sea level rising conditions in Karachi city. The simulated inundation results by the distributed hydrologic model show that magnitude of flood depths would increase along with the sea level rise. Subsequently the socio-economic impacts will be accelerated. The outcomes of the study are still in preliminary stage and there is a scope to enhance those by improving the input temporal and spatial datasets for the model and model calibration and verification and detailed socio-economic factors. REFERENCES Church, J.A., Gregory, J.M., Huybrechts P., Kuhun M., Lambeck K., Nhuan M.T., Qin, D., and Woodworth P.L., Changes in sea level, Intergovernmental Panel on Climate Change Third Assessment Report, Cambridge University Press, (2001), pp Dutta D., Herath S. and Musiake K., Distributed Hydrological Model For Flood Inundation Simulation, Annual Journal of Hydraulic Engineering, JSCE, Vol. 43, (1997), pp Iqtidar H. Siddiqui (2005), Park in Malir river-bed, letted.htm#3 Jha, R., Hearth S. and Musiake K., Development of IIS Distributed Hydrological Model (IISDHM) and its application in Chao Phraya River Basin, Thailand, Annual Journal of Hydraulic Engineering, JSCE, Vol. 41, (1997), pp WCDR 2005, A Review of Disaster Management Policies and Systems in Pakistan Islamabad, Pakistan ( national-reports/ Pakistan-report.pdf) accessed on International Symposium on Floods in Coastal Cities under Climate Change Conditions, Thailand, 2005