Flood Studies in Asia by
Remote Sensing M.A.H. Pramanik, S.Murai,
Y. Honda, A.S.Herath, H. kakiuchi and M. Takagi Institute of Industrial Science University of Tokyo Abstract Satellite Remote Sensing technology provides an authentic source of information for surveying, identifying, classifying, mapping and monitoring of natural resources, environment and disasters. Multiband, multidate and multistage satellite imagery has been extensively used in Asian countries for water resources studies, monitoring and management including flood investigation. The metereorological satellite imagery/data (1000m resolution), Landsat / Spot imagery/data (30m & 10m) have wide global applications for flood forecasting, monitoring, damage assessment, construction, rehabilitation, etc. In the present paper an attempt has been made to highlight the application of satellite Remote Sensing technology for flood studies in the Asian countries particularly Bangladesh and China. The unprecedented and devastating flood of 1987 and 1988 in Bangladesh and 1991 in China (Tai-Hu lake area) have been studied using satellite Remote Sensing technology. The mapping of the flood damage area has been completed and other socio-economic consequences due to flooding have been described using conventional as well as integrated RS-GIS (Remote Sensing and Geographical Information System) information/data. Asian countries with majority (about 3 billion) of world population (more than 5 billion) are facing frequent disasters like floods, windstorms (typhoons/cyclones/tornadoes), droughts, earthquake, volcanic eruptions, environmental degradations, etc. Satellite Remote Sensing technology could play a vital role in disaster monitoring, mitigation, damage assessment, preparedness, prevention, training, information exchange, regional and international cooperation. A network mechanism and possible cooperative approach has been explained in this paper. 1.0 Introduction The space age was dawned on 4 October 1957 with the launching of the Russian satellite Sputnik I as a part of the International Geophysical Year (1957-58) activities. The launching of the meteorological satellite in 1960, earth resources satellites -- ERTS / LANDSAT I 1972 and SPOT IN 1986 has made global applications of satellite Remote Sensing technology for inventorying and management of natural resources, monitoring of environment disasters. In the present paper an attempt has been made to highlight the applications of satellite Remote Sensing technology for flood studies in the Asian Countries particularly Bangladesh and China. The unprecedented and devastating floods of 1987 and 988 in Bangladesh and 1991 in China (Tai-Hu lake area) have been studied using satellite Remote Sensing technology. The mapping of the flood damage area has been completed and other socio-economic consequences due to flooding have been described using conventional as well as integrated RS-GIS (Remote Sensing and Geographic Information System) information/data. A network mechanism and possible cooperative approach -- regional and international has also been explained in the paper. 2.0 Floods in Asian Countries Disasters have global impact. Most of the Asian countries are disaster-prone. The physiography, morphology and other natural conditions have made them vulnerable to disasters and environmental hazards. The major universal disasters include. : floods, droughts, windstorms, earthquakes, volcanic eruptions, environmental degradation etc. These disasters occurs frequently and regularly all over the globe but the Asian countries suffer most because of their less preparedness and less preventive measures available in the countries. Recent floods in the Asian countries have caused havoc in terms of physical damages in property and infrastructural facilities in addition to the loss of human life and life stocks. Satellite Remote Sensing technology have been used for flood monitoring, damage assessment, reconstruction, rehabilitation activities. In the present paper an in-depth study of floods using Remote Sensing and conventional information/data for Bangladesh and China have been made. 2.1 Floods in Bangladesh Floods frequently and regularly occur in Bangladesh. Through monsoon rains are the major causes of flooding but there are various other factors like rapid runoff, the effect of the confluences of the major rivers, the flat topography of the delta and surges in the Bay of Bengal. Types of flooding in Bangladesh are :
The 1987 flood commenced in the third week of June and lasted until the end of September. The earliest flood hit the northern parts of Bangladesh. The Brahmaputra, the Ganges, and the Meghna reached their respective bankful stages in the last week of July and beginning of August. One of the unique features of the 1987 flood was that the northwestern districts of Bangladesh, which remain normally flood –free, experienced prolonged flooding from the tributaries of the Brahmaputra and the Ganges. In the northwestern region, the Ganges and the Brahmaputra and many of their tributaries exceeded their record water levels, causing extensive over bank inundation (Miah 1988). In the central region, extensive flooding was reported along the lower reaches of the Brahmaputra, Ganges and Meghna rivers. Reports also confirmed deep flooding along the tributaries of the Meghna in the northeastern region. The official estimate of the maximum extent of flooding in 1987 was 57, 300 km2 (40% of Bangladesh)(BWBD 1987). However, the accuracy of this estimate could not be verified through satellite imagery alone since it was based on varied sources of information. More than one-third of Bangladesh population was affected during this flood. 1988 Flood : The 1988 flood was the most catastrophic flood of this century. The flood commenced in early July, but the record high water levels were achieved relatively late in the summer by rapid synchronization of peak flows in eh Brahmaputra (99,500 m3/sec), and the Meghna (>19,000 m3/sec) within a period of 72 hr between 30 August and 2 September (Matin and Hussain 1988). The combined peak flow of the three rivers (190,800 m3/sec)seceded the 1987 record – highly flow by a significant margin and, thus, set a new 100 – years record. The flood also set another 100 – year record by inundating an estimated area of 82,000 km2 (57% of Bangladesh), which surpassed the previous records of the extent of 1955 and 1987 flooding 36% and 40%, respectively) by a wide margin. The flood area delineation from an AVHRR image by using visual interpretation and the computed flood areas on different dates varied significantly during the recession period, indicating the dynamic nature of the flood event. These data suggest that the flood started receding slowly through a period of secondary peaks (such as that of 15 September). By 24 September, the extent of flooding was considerably less than of 10 September, although large areas were still under water. More than fifty – percent of Bangladesh population was affected by this flood. 2.2 Floods in China A legendary flood occurred in China in 2297 BC due to extremely intensive and extended heavy rains. The Huang Ho (Yellow river) and Yangtze rivers overflowed their banks and submerged almost the entire north China. Historical records show that during the period 206 BC to 1960 AD China has experienced more than 1030 major floods. Extensive flooding also occurred in the Yangtze basin in 1870, 1896, 1911, 1931, 1949 and 1954. The catastrophic flooding of 1931 and 1954 was treated as national disasters. The Huang Ho has been called “china’s sorrow” and “The Ungovernable” but now the basin has been turned into “China’s rice granary” and productive watercourse by controlling the flood. The worth-mentioning flooding happened in the Huang Ho valley in the year 1887, 1889, 1921, 1933, 1938, 1949 and 1959. 1991 Flood Taihu lake area of China (situated between Nanjing and Shanghai) was inundated due to flooding of July 1991. Satellite imagery of March, May, June and July 1991 were used to study the effects of flooding. More than 40 percent of the surrounding lake area was inundated in July 1991 by flooding causing huge loss go agricultural crops and much sufferings of the people in the area. 3.0 Network Mechanism and International Cooperation It is very much essential to establish a network mechanism between disasters related institutes in different countries for exchange of information/data and experiences. UN and other international agencies could play a vital role in coordinating these efforts. Within the framework of IDNDR (International Decade for Natural Disaster Reduction 19990-2000 AD) these efforts could be strengthened. A flow-diagram (Appendix A) in this respect is suggested. The salient features of the flow-diagram are as follows:
In synchronization with the IDNDR objectives and strategies, the following geographical levels of action area needed :
5.0 Conclusions The present paper has dealt with various aspects of Remote Sensing and its applications in flood studies in Asian countries particularly Bangladesh and China. Appropriate steps through both structural and non-structural means without causing environmental degradation and ecological imbalance should be taken for disaster – mitigation. An all-out effort should be made at every stage of design, implementation and monitoring projects to take care of above aspects. Satellite Remote Sensing technology could provide information / data for the purpose. Acknowledgements The authors are grateful to HS / University of Tokyo for giving permission to present the paper and providing financial support for participation in the conference/ the authors are also thankful to Prof. T. Katayama, Director, INCEDE for valuable suggestions in the preparation stage of the paper. References
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