CS(AR)-11/2000-2001 : Hydro-meteorological inventory of Orissa Cyclones

Abstract

A cyclone is the combination of heavy wind, rainfall, and/or high surge. The scientific understanding on the subject is not much developed due to lack of data and abnormal atmospheric conditions arising in the affected region and endangering the lives of human being. The favourable demographic nature of low-lying coastal areas facilitates settlements, industries, and agricultural activities. According to an estimate, about 60% of the total 5.5 billion population live in coastal areas and 65% of cities with population more than 2.5 million are located along the world's coast-lines. With the enhanced human interference in the nature's activities, the problems of these coastal areas are aggravating. The devastating action of cyclones in Bangladesh, India, France and other countries in the recent past forces the engineers, scientists, research scholars to focus on the problems of coastal areas for possible remedial measures.

Of late, the State of Orissa faced two severe cyclones in October 1999. The first occurred during October 17-18, 1999 and hit the Orissa coast at Gopalpur. This severe cyclone caused extensive damages to life and property in Ganjam district. The second cyclone of catastrophic category stroke on October 29-31, 1999 (named as super-cyclone `99) and hit the Orissa coast near Paradip and inflicted unprecedented damages in the districts of Kendrapara, Jagatsingpur, Cuttack, Bhubaneswar, Puri, Jajpur, Balasore, and others. The supper cyclone devastated about 3 million ha of cropped area in addition to sizeable loss of cattle (200,000+) and human lives (50000+), based on the personal inquiries with the local inhabitants.

The October-99 super cyclone of Orissa is distinguished to have far exceeded all historical cyclones occurred in India. The wind speed exceeded 260 kmph, extremely intense rainfall varied from 400-960 mm in 2-3 days, and a tidal wave of 5 to 6 m height swept across a 20 km strip of 100 km coastal stretch in Jagatsinghpur and Kendrapara district and created havoc. The maximum rainfall intensity was of the order of 40 mm/hr for 3 to 6 consecutive hours at some places and heavy winds and rain prevailed continuously for about 36 hours. The tide caused huge destruction to life and property, and submerged, severely scoured, and breached large saline embankments in the area from Astrang to Basudevpur. Deltaic areas from Mahanadi to Subernarekha were submerged up to 3 m depth by stagnation due to impeded drainage. Extremely high flood of 5,00000 Cusec was experienced in Baitarani at Akhuapada on October 30, 1999. The obstructed drainage network and high flood due to continuous intense rainfall in several sub-basins created submergence of agricultural lands up to more than a week in deltaic areas. The largest concentration of urban population of 1.5 million in Cuttack and Bhubaneswar suffered unprecedented damage from intense rainfall of 500-600 mm and cyclonic gale of 200-250 Kmph.

The above extraordinary event forces to re-look at the cyclonic phenomena of the country in general and Orissa in particular. The disturbance of the hydrologic regime of the region compels to fix the design criteria taking into account the abnormal features of the above event. To this end, there is a pressing need to revise the design considerations, viz., revision of empirical formulae used to determine design discharges accounting for the backwater effect of surges, probable maximum precipitation, instrumentation for data collection etc. The impacts of cyclonic surges on the surface water and ground water quality and soil salinity, etc. are of vital research importance, leading to specialised studies on these aspects.