Observational/forecasting aspects of the meteorological event that caused a record highest rainfall in Mumbai

The Santacruz observatory at Mumbai airport exper i-enced unprecedented rainfall of 94.4 cm on 26 and 27 July 2005, an all -time highest record over the city. The country’s commercial capital came to a co m plete sta ndstill due to severe flooding/deluge. It also caused severe damage to life and property . In the present a rticle, we have brought out the characteristics of this unique rainfall event, compared it with past in tense rainfall events in I n dia and other places in the world, and also analysed various data to find possible causes of occu r-rence of this event. Technology available for predic-tion of such events is also briefly touched upon. Keywords: Isohyet analysis, synoptic scale feature, scale interaction, thunde rstorm. Mumbai (lat. 18.50°N, long. 72.52°E), formerly called Bombay, situated on the west coast of India, is the com-mercial and financial capital of the country. It generates about 5% of India’s GDP and contributes over one -third of the country’s tax revenues. It is among the few port cities of the world having major industrial and economic activities. The influx of labour and other work force over the last two decades has resulted in the total population of the metropolitan and the surrounding suburbs to increase from 9.9 million in 1981 to 13.0 million in 1991 and 17.7 million in 2001. Mumbai is not only the most populated city in India, but also the fourth most populated city in the wor ld after Tokyo (36.0 million), New York (22.0 mi llion ), and Seoul (21.7 million). If only the population of the metropolitan city, excluding its surrounding suburbs is considered, Mumbai is the se cond most populated city in the world, after Shanghai. Such densely populated cities with highly developed infrastructure are always vulnerable to natural disasters. The economic losses are also e xpected to increase over time, as people move into more vulner-able areas because of shortage of free space. Parts of Mumbai experienced an unprecedented rai nstorm on 26 and 27 July 2005. The 24 h rainfall ending at 0830 h IST of 27 July was 94.4 cm as per the meteorological o b-servatory at Santacruz airport, Mumbai. C olaba, the other meteorological observatory, which is roughly 27 km away, recorded only 7.4 cm rain during the same period. Very heavy rains also lashed other parts of Maharashtra on subsequent days and completely di srupted normal life across the state, with Mumbai being the most severely hit . On the subsequent two days, though rainfall over Mumbai reduced to 1.9 cm per day, it again i ncreased to 20 cm on 1 August 2005; further worsening the situation over the already deluged city. Mumbai was totally cut -off from the remaining parts of the world almos t for a week. Mumbai airport was closed for two days on 26 and 27 July as the runway was waterlogged, the terminal building flooded and crucial navigation and landing aids dam aged, thus forcing all international and domestic flights to be diverted or cance lled. Normal operations could resume only on 4 August 2005. Train services to and from Mum bai were also cancelled for more than a week. Local trains which are Mumbai’s life line – running every 3 min and ferr ying 4.5 million passengers daily – were totally thrown off gear as railway tracks were not only submerged, but also damaged. Follo w ing were the initial damage assessments due to this severe rainfall spell and flooding in the state, as reported by F inancial Times and Economic Times on 4 August 2005. • The number of dead in the Maharashtra floods could well be above 1000, with Mumbai alone accounting for over 409. • Around Rs 5000 crores estimated loss in the state, with Mumbai accounting for half the amount. • No electricity in certain areas of Mumbai city for up to five days. • One million people rendered homeless. • About 1100 flights cancelled and airport closed for two days. • Five million mobile and land lines crashed. In addition to the two observatories at Colaba and Sa nta-cruz, Mumbai of India Meteorologic al Department (IM D), the Maharashtra government and the Mumbai Municipal Corporation have a separate network of rain gauges, which also captured this intense rainfall event. The gauge at Vihar Lake, located around 15 km northeast of Santacruz, recorded 104 . 9 cm of rain on 27 July 2005. The measur e-ment of rainfall at Santacruz is of importance, particu-larly in the field of national and international avi ation.