Impact of Extreme Weather Events in Relation to Floods Over Maharashtra in Recent Years D
Total Page：16
File Type：pdf, Size：1020Kb
Vayu Mandal 43(2), 2017 Impact of Extreme Weather Events in relation to Floods over Maharashtra in Recent Years D. M. Rase, P. S. Narayanan and K. N. Mohan India Meteorological Department, Pune Email: [email protected] ABSTRACT About 400 million hectares of land in India are susceptible to floods of which about 30.8 million hectares have been protected by undertaking both structural and non-structural methods of flood control. On an average, in a year, about 8 million hectares are liable to flood. In India, about 1500 human lives are lost annually due to floods and heavy rains. On an average, about 10 million hectares of crop land is devastated in each year due to impact of flood. We cannot avoid natural hazards (like flood) and disasters, but can minimize their impact on environment by preparedness & planning. Study of extreme rainfall is essential for designing the water related structure, in Agriculture planning, in weather modification, water management, also in monitoring climate changes. Moreover, knowledge of spatial and temporal variability of extreme rainfall event is very much useful for the design of Dam and hydrological planning. In view of the above, to find the impact of extreme / heavy rainfall in Maharashtra, rainfall data for the period 1951 to 2015 for three subdivisions of Maharashtra viz. Madhya Maharashtra, Marathwada and Vidarbha have been utilized for the study. Trends in number of incidences of excess rainfall have been determined by using standard statistical methods and the results discussed. Casualties due to extreme rainfall have also been discussed. Incidences of natural hazards reports prepared by India Met. Deptt., for the period 1981-2015 have been used in the study. Only those cases have been included for the study, which caused human fatalities and significant economic losses. The consecutive years of excess/deficient rainfall and their relation with El Nino/La Nina years have also been worked out and discussed as they have significant impact on hydrological area. The cases of excess/deficient rainfall are almost same over Madhya Maharashtra (17/17) & Marathwada (17/19), over Vidarbha it is less (11/13) as compared to other two sub divisions in study period. The probability of excess rainfall in Marathwada is 16% followed by Madhya Maharashtra (15 %) and in Vidarbha (13%). The coefficient of variability for Vidarbha(19.9%) is least as compared to Madhya Maharashtra (23.3 %) &Marathwada (28.6 %). In Madhya Maharashtra region there were chances of 12%, in Marathwada 24% and in Vidarbha 25% of excess rainfall years in relation with La-Nina and 6 %,21% & 33% of chances with El- Nino being correlated with deficient years. Keywords: Natural hazards, extreme events, trends, El Nino and La Nina etc. 1. Introduction expected to occur. A study by Sinha Ray and Srivastava (2000) showed a decreasing trend The plain region of India is affected by floods almost every year during the monsoon season in the frequency of heavy rainfall (rainfall ≥ 65 associated with heavy rainfall. Thus, the inter- mm in 24 hrs) during the winter season at most annual fluctuations in the summer monsoon of the stations in India. During the summer rainfall over India are sufficiently large to monsoon season (June- September) they found cause devastating floods or serious droughts. an increasing trend in heavy rainfall in a Chowdhury and Mhasawade (1991) found number of stations on the west coast. flood to be frequent phenomenon over India. However, a few stations in Marathwada, Mega cities often encounter natural disasters Telangana, Rayalseema and Tamilnadu did not caused by adverse weather phenomena show any significant trend. These heavy rains particularly heavy rainfall. From the and associated flooding in and around urban meteorological point of view, a flood is centres bring untold miseries on the local defined as a quantum of rainfall received over population and is the main cause of increasing an area in excess of its long period average deaths in the area affected. over that area during the period when it is 73 Rase et al. Floods can threaten human life and property Vidarbha have been utilized for the study. The and it is estimated that about 1.5 billion people rainfall departures are used as per IMD criteria were affected in the world during the last i.e. Excess (≥20% of the normal); Normal decade of the twentieth century [Khole & De (lying between -19% and + 19% of the (2001)]. Floods are a major disaster in India in normal); Deficient (lying between -20% and - term of occurrences (41% of total disaster) as 59% of the normal). Trends in number of well as in casualties (De et al 2002). De et al incidences of excess rainfall have been (2005) presented a factual and brief review of determined using standard statistical methods extreme weather events that occurred in India and the results discussed. Casualties due to during last 100 years (1901-2004), discussed heavy/extreme rainfall have been discussed. specially the major rainstorm causing sever Incidences of natural hazards reports prepared flood situations. Recent studies have by India Met Department for the period 1981- confirmed an increasing trend in extreme 2015 have been used in the study. Synoptic rainfall events around the world. Floods in situations responsible for heavy/very heavy many parts of the India, particularly in urban rainfall have also been discussed. Only those areas are often devastating. Urban flooding has cases have been included for the study, which become a major source of socio-economic can cause human fatalities and significant threat to cities. Last few decades have seen economic losses. The consecutive years of rise in the damage caused by natural hazards. excess/deficient rainfall and their relation with On 26/27th July 2005, Mumbai (Santacruz) El Nino/La Nina years have also been experienced heaviest rainfall recorded with an worked out and discussed as they have accumulated total of 944 mm with huge losses significant impact on hydrological area. to life and property (De et al 2006). Extreme 3. Results and Discussion weather events over the last decade have shown that flooding is becoming more The summer monsoon season in India is extreme, more frequent and more wide-spread characterized by incidences of heavy to very [Tongdi Jamir et al. (2008)] heavy rainfalls over most parts. They generally occur in association with certain favorable During monsoon season very heavy rain often synoptic situations such as depressions, lead to street flooding, disruption of traffic and cyclonic storms, low-pressure episodes etc. telecommunication channels in the Such rainfall episodes often lead to street metropolitan cities like Delhi, Kolkata and flooding, disruption of traffic and Mumbai. Heavy rains also results in landslides telecommunication lines. These heavy and collapse of buildings in the slums located rainfall events, occurring over certain area for in the cities (De et al 2013). Singh et al (2015), a number of days continuously, often give rise observed from their study that urban flooding to floods and cause various types of human results mainly from two causes in India; firstly hardship in general and threaten the safety of because of prolonged heavy rainfall and hydraulic structure in particular like dams, secondly, urban areas which are situated close reservoirs, hydroelectric power set- up etc. It is to the flood plain of rivers. They also found observed from Table 1, that heavy rains results that by and large though there is no significant in landslides, collapse of buildings/ houses, trend, location specific heavy to very rainfalls extensively damages to property and are matter of concern for sustainable urban disruption of traffic. From Fig.1 it is observed growth. The purpose of the study is to analyze that during the period for which the data has and determine trends in the occurrence of been analyzed, the deaths over Maharashtra heavy rainfall over subdivisions of due to heavy rainfall during monsoon season Maharashtra in India. Fatal causalities and having decreasing trend, though it is not economic loss due to heavy rainfall and statistically significant. This may be due to associated floods have also been determine increase in awareness regarding government and discussed. warnings about disaster amongst the people. It 2. Data and Methodology is observed from Fig.2 (a,b,c) that the trend in excess rainfall for all the three subdivisions is The monthly rainfall data for the period 1951 increasing though it is not statistically to 2015 for three subdivisions of Maharashtra significant. Economic losses in terms of viz. Madhya Maharashtra, Marathwada and Indian currency were not available for urban 74 Vayu Mandal 43(2), 2017 flooding at regional levels and hence could not two consecutive years (1992-1993) once in be discussed. Madhya Maharashtra. In this region there are chances of 12% of excess rainfall years in The mean rainfall for the study period over relation with La-Nina and 6 % of chances with Vidarbha is highest (918.7mm) followed by El-Nino in relation with deficient years. There Marathwada (705.5 mm) and Madhya were three consecutive years twice (1988, 89, Maharashtra (696.1 mm). From Fig.3 (a,b,c), 90 & 2005, 06, 07) in excess rainfall and two it is seen that the cases of excess rainfall are consecutive years have occurred once (1958, highest in Madhya Maharashtra (17) 1959) in deficient rainfall years. Whereas there &Marathwada (17) as compared with were two consecutive years have occurred Vidarbha (11). The ratios of excess/deficient thrice (1951-52, 1971-72 & 2014-2015) and rainfall are almost same over Madhya three consecutive once (1984, 85, 86) in Maharashtra (17/17) & Marathwada (17/19), deficient rainfall in Marathwada. In this over Vidarbha, it is less (11/13) as compared region there are chances of 24% of excess to other two sub divisions in study period.