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May - June 1999
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Natural Hazard Map and Vulnerability Atlas of India: A review
GIS Development Staff
Hazard maps are essential for the comprehensive understanding of spatial and temporal occurances of natural calamities. We bring to the notice of our readers, the efforts of two well-known organisations in the form of Natural Hazard Map of India by NATMO, and Vulnerability Atlas of India by BMTPC.
When an area is exposed to hazards, a map helps the planning team to analyse it for vulnerability and risk. By facilitating the interpretation of hazard information, it increases the likelihood that the information will be used in the decision-making process. The hazard maps play a vital role in planning of new development projects as well as in incorporation of hazard reduction technique into existing developments.
Due to its geographical location, geological and climatic conditions, India is one of the most disaster prone country in the world. India is also under such a diversified climatic conditions that the same area is subjected to different types of disasters in the successive years. In this background, it is necessary to prepare maps for the comprehensive understanding of spatial and temporal occurrences of these natural calamities. In this regard, the effort of two well-known organisations have been come in the form of ‘Natural Hazard Map of India’ by National Atlas and Thematic Organisation (NATMO) and ‘Vulnerability Atlas of India’ by Building Materials & Technology Promotion Council (BMTPC). An attempt has been made to review the maps prepared by these organisations.
NATMO’s effort
As the name implies the main task of the NATMO, Department of Science & Technology, Government of India, is the preparation of National Atlas and Thematic maps of India. The research and development involved in this organisation through decades have been of very high standard and useful in the planning phases of the country. NATMO came out in 1991 with"India- Natural Hazards Map". The map was published at 1:6M scale in 1991 and now the second edition of the same at 1:4M scale is under final printing.
The map on natural hazards, although not comprehensive on all counts yet focuses on certain issues related to drought and flood prone areas, desert areas, and cyclonic pathways indicating periods of occurrence and affected zones. The map identifies important epicentres of earthquake and related magnitudes. However, the various sources from where the data for the natural hazard map has been derived are not mentioned by NATMO in its map.
BMTPC’s effort
In the wake of the World Conference on Natural Disaster Reduction in 1994, the Ministry of Urban Development of the Government of India decided to prepare "Vulnerability Atlas of India", providing the State-wise hazard maps taking into account three natural hazards – earthquakes, cyclones and floods which are most common and frequently severe in India. The first edition of the atlas was published in 1997.
The zoning maps on macro-level for three natural hazards – earthquake, cyclones and floods are currently available on small scales for the country as a whole. However, for the easy identification of the areas by the planners, administrators and disaster managers, the maps are on larger scale, state-wise, showing all the administrative units, namely, the district boundaries. And a presentation of several hazards in an atlas form provides greater opportunity for discussions, recommendations and references.
Comparison of NATMO and BMTPC atlas
A comparative study of NATMO map and BMTPC atlas shows that the mode of approach differs from one another. NATMO prepared the Natural Hazard Map for the country as a whole on 1:6 M scale which is smaller than the scale used by BMTPC for preparing districtwise ‘Vulnerability Atlas’ (1:2.5 M scale). In addition Vulnerability atlas has single theme maps as against Natural Hazard map in which all the themes are covered by a single map. The single map presentation by NATMO of all the natural hazards would be have better and easily understandable as the different hazards have been displayed in different maps.
Earthquake/Seismic Hazard Map
In NATMO map, the epicentres of important earthquakes are shown according to their magnitudes measured on the Richter scale. Some earthquakes of higher magnitudes are shown with the zones of occurrence. Whereas in BMTPC atlas, seismic zones are shown as per the Seismic Zoning Map of India contained in IS: 1893-1984 Fourth Revision. All earthquakes of 5.0 magnitude on Richter scale have been plotted along with the seismic intensity zones. The catalogue of earthquake prepared by Indian Meteorological Department has been utilised for the purpose. The damage vulnerability of the various building types in MSK intensity scale, seismic intensities have also been given in BMTPC’s maps.
Cyclones/Cyclone and Wind Hazard Maps
The NATMO map not only shows the area hit by cyclones but also explains the direction and path of various cyclonic storms in different months (1931-1970). The cyclonic storms originating from the Arabian Sea are also shown in a similar way. In addition, coast exposed to tsunamis (strong high velocity sea waves) has also been worked out by NATMO in the map. In the Cyclone and Wind Hazard maps in BMTPC atlas, the wind speeds have been worked out for 50 years return period with probability of excedence of 63%, based on the upto-date wind data of 43 Dine Pressure Tube (DPT) anemograph stations. The wind speed zones have been based on the IS: 875 (Part 3) –1987 titled "Indian Standard Code of Practice for Design Loads (other than earthquakes) for Buildings and Structures, Part 3 Wind Loads". The map and related recommendations have been provided in the Code with the cooperation of Indian Meteorological Department (IMD). The Wind Velocity Map previously prepared by the Bureau of Indian Standard (BIS) Committees on Earthquake Engineering and Wind Engineering has been used to prepare 1:2.5 M scale maps superimposing the above available data on Survey of India map of same scale as the base map. IMD has also estimated the probable maximum heights of storm surge in various sections of the seacoast. These are shown in the relevant state’s ‘wind hazard maps’ in BMTPC atlas.
Flood Hazard Map
NATMO has been given the flood prone area as per the National Flood Commission statistics. The flood hazard maps in BMTPC atlas are based on the " Flood Atlas of India" brought out by Central Water Commission (CWC), with the addition of district boundaries and the location of district towns along with the rivers, making districtwise identification of vulnerable areas easy. Besides, regarding the problem of flooding in the river plains, it is found that heavy intensity rains cause local flooding in certain areas where the drainage is either naturally poor or are choked. Much of the flooding problems in towns and cities occur due to such causes. Indian Meteorological Department has compiled statistics on probable maximum precipitation (PMP) over the country considering the point rainfall over a time period of 24 hrs. The districtwise PMP values are also shown on the BMTPC maps for ready reference.
Drought and Deserts
The NATMO map of India shows 91 districts covered under the Drought–Prone Area Programme (DPAP). The 21 districts are under the Desert Development Programme (DDP) out of which 4 districts belong to hot desert zone and the other 4 inherit the cold desert characteristics. This aspect is not covered by the BMTPC atlas.
Housing Vulnerability Tables
One of the important aspects of the vulnerability atlas is ‘housing vulnerability tables’. It is for the first time in India that a systematic study for the whole country has been taken up by BMTPC in the form of tables.
The primary effort towards vulnerability assessment of buildings under seismic and cyclone intensities has been made by the Department of Earthquake Engineering, University of Roorkee and Structural Engineering Research Centre, Chennai respectively but not done systematically and for the country as a whole. Taking guidance from this work, the types of housing, as existing in each district has been taken from the Census of India, 1991 and categorised from vulnerability consideration.
The vulnerability atlas has tabular details of the house types, risk of damage to house types, damage risk levels for earthquakes, windstorm and floods. The housing infrastructure and its vulnerability to hazard have been categorically analysed in this atlas. Hence given the intensity of hazard one can analyse the effect of the same on housing infrastructure for any given district of India.
Though beyond the purview of the ‘Expert Group’ constituted to prepare the Vulnerability Atlas, it could have been more conclusive with some information on the communication and transportation infrastructure overlaid on the hazard prone area and the damage to these infrastructure for a given intensity of disaster. The print and paper quality is excellent but some of the maps lack cartographic and thematic quality.
As a whole the Atlas can be used to identify areas in each district of the country, which are prone to high risk from more than one hazard. Its information will be useful in establishing the need of developing housing designs to resist the combination of such hazards.
If these maps are entered into GIS, combining with the tables then it may be easy to identify the protected or hazard prone areas for future planning.
Conclusions
Some of the aspects of these maps need more attention. One such issue is the use of latest data. For example, NATMO has used 1931–1970 statistics, BMTPC has given 1984 earthquake figures and 1987 data for cyclone map. Now the question is what’s the use of so obsolete figures for the planners and other users? Associated issue is the updating of the map. For updation, GIS may be a useful tool. NATMO and BPMTC should consider the updating of these maps at least in every five years.
The other important aspect is that how much user-friendly are these maps? On one hand, NATMO tried to cover up all the hazards in one sheet, on the other hand, vulnerability atlas is of almost 500 pages (482 tables and total 76 maps) and weighs around 3 kgs. Carrying such a weight doesn’t seem to be very tempting.
The efforts by NATMO and BMTPC towards preparation of multiple hazard maps is appreciable. But if they prepare them in a layer form with single theme and enter it into GIS then the user can prepare different overlays for his own requirement. They can provide these maps in digital form on CD or they can create website. In this way GIS techniques make easy handling of maps. The importance of GIS does not end with the ability to Zoom In and Zoom Out the digital map. It enables the person to select the layer he desires to work on rather than have the entire layer on one paper map and decipher his relevant layer of work. Once selected a layer, one has the flexibility to add or remove any feature from the map. The non-spatial data attributes of the maps become an integral part of the GIS making the maps more meaningful.
For details, contact:
India-Natural Hazards Map
Published in 1991 by NATMO
Price Rs. 20
Dr. Prithvish Nag, Director,
National Atlas & Thematic Mapping Organisation,
Department of Science & Technology,
C.G.O. Complex, 7th Floor,
D.F.Block, Salt Lake,
Calcutta – 700064.
Telephones: 334-3699, 334-6459
334-6331, 334-6585
334-5006, 337-8413
Fax :91-033-334-6460
Vulnerability Atlas of India
Published in 1997 by BMTPC,
Price Rs. 3000 / US$150
Mr. Sharad Gupta,
Building Materials & Technology Promotion Council, Ministry of Urban Development,
Government of India, New Delhi.
Phone: 91-11-3792006, 3019367, Fax: 91-11-3010145 E-Mail: bmtpc@del2.vsnl.net.in
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