G’nY SINCE 2001 Vol. 15, ISSuE 93, 2015 `120 GEoGraphYandYou.com Droughtsin India38 India’s Weather Extremes AnD e A Development AnD WeATheR INDIA’s VA HeatWave 42 4
TheMonsoon 10 nvironment mA nvironment ColdWave 46 Tropical Cyclones 16
RIANT gA zine www.geographyandyou.com METGEEKS Programme GETTING WEATHER WISE
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Un-seasonal rain in March 2015 led to widespread crop failure, loss of life and property. It destroyed the rabi crop affecting about 182.38 million hectares as per the report of the Department of Agriculture and Cooperation in May 2015. INDIA’s VARIANT WeATheR 4 India’s Weather Extremes 58 Thunderstorm StaFF RePoRteR L S RathoRe, D R Pattanaik anD S C Bhan 10 The Monsoon INDIA ouTDooRs StaFF RePoRteR 60 The Chambal 16 Tropical Cyclones Sumit ChakRaBoRty ajit tyagi 22 The Science Behind the Tamil Nadu Floods Expert Panel j R kuLkaRni Prithvish Nag Vice Chancellor, 26 Floods MG Kashi Vidyapeeth, StaFF RePoRteR Varanasi. Y K Alagh 32 The Inevitable Yet Preventable Disaster: Chancellor, Central University The Chennai 2015 Floods of Gujarat, Professor Emeritus, SuRya PaRkaSh Ahmedabad. 38 Droughts in India B Meenakumari StaFF RePoRteR Chairman, National Biodiversity Authority, 42 Heat Wave Chennai StaFF RePoRteR Ajit Tyagi Air Vice Marshal (Retd) 46 Cold Wave Former DG, IMD, StaFF RePoRteR New Delhi. B Sengupta 52 Hailstorms Former Member Secretary, StaFF RePoRteR Central Pollution Control Board New Delhi. 56 Wettest Place in the World: Mawsynram Rasik Ravindra ajit tyagi anD P guhathakuRDa Former Director, NCAOR, Goa In brIef 2 Letters 3 Editor’s note 21 Term power Saraswati Raju 45 Term power rating Professor, CSRD, Jawaharlal Nehru IN coNVeRsATIoN University, New Delhi. Sachidanand Sinha M N RAjEEvAN Professor, CSRD, 50 Secretary, Jawaharlal Nehru Ministry of Earth University, New Delhi. Sciences, Government Dripto Mukhopadhaya of India. Director, Economic Research, Nielsen, New Delhi.
GeoGraphy and you . november - december 2015 1 ExpErt panEllist’s notE Extreme Weather Events
Extreme weather events causing natural disasters GeoGraphy and you in the current decade are occurring nearly five edIToR times as often as they were in the 1970s. The Sulagna Chattopadhyay frequency of geophysical disasters—earthquakes, GUeST edIToR tsunamis, volcanic eruptions and mass movements, K MohandaS remained broadly constant throughout this period, Ajit Tyagi LeGAL AdvISoR KriShnendu datta but a sustained rise in hydro-meteorological related Air Vice Marshal (Retd) CoveR phoToGRAph events (mainly floods and storms) pushed total Former Director General, getting CoMfortable occurrences significantly higher. Since 2000, on India Meteorological after a Sudden drop in teMperature following an average of 341 hydro-meteorological related Department, New Delhi. a thunderStorM—don, disasters were recorded per annum, up 44 per cent ChaMparan, bihar, by praSad from the 1994-2000 average and well over twice the level in 1980-1989. Of all hydro-meteorological disasters, about phoTo TeAm praSad, Vinod M. 89 per cent were due to flooding and storms. The year 2015 will be remembered as the year of IRIS pUbLICATIon pvT. LTd. extremes. The year turned out to be the warmest year; ReGISTeRed offICe record number of category 4 and 5 hurricanes formed in 111/9 K g, aruna aSaf ali Marg, new delhi -110070 the Northern hemisphere with Hurricane Patricia being the CoRReSpondenCe/ strongest till date. El Niño, the strongest in recent years, edIToRIAL offICe has been a major driver of anomalies in weather of many 1584, b-1, VaSant Kunj, parts of the world. Summer was unusually severe over new delhi-110070 south and Southeast Asia. Heat waves caused more than phone: +91-11-26122789 2000 deaths in India and about 2000 deaths in Karachi for new SubSCriptionS, and parts of Sindh state of Pakistan. The year 2015 renewalS, enquirieS became year of deficient rainfall during monsoon season pleaSe ContaCt CirCulation Manager for the second consecutive year. While many parts of the e-Mail: editor@ country are facing drought, Manipur, West Bengal, Gujarat geographyandyou.com and Tamil Nadu experienced floods. Rainfall in Chennai pleaSe ViSit our Site at www.geographyandyou.com broke a 100-year-old record. Landslides occurred in for further inforMation. Manipur, Himachal, Jammu and Kashmir and ©IRIS pUbLICATIon pvT. LTd. western Ghats. all rightS reSerVed Awareness about extreme weather phenomena helps in throughout the world. reproduCtion in any better preparedness and this issue of Geography and You Manner, part or whole, is dedicated to raising its understanding. iS prohibited. printed, publiShed and owned by Sulagna Chattopadhyay. pRInTed AT india graphiC SySteMS lEttErs to thE Editor pVt. ltd. f-23, oKhla Issues and concerns induStrial area, phaSe-i, Good ATTempT, I appreciate the effort of G’nY new delhi - 110020. The WATeRWAYS ISSUe in undertaking weather station related pUbLIShed AT issue was not only training in Miranda House, Delhi University, iriS publiCation pVt. ltd. geography and easy to understand New Delhi. Many more universities should you doeS not taKe any the complexities of also introduce initiatives like this, especially reSponSibility for managing the various Himalayan universities and not only returning unSoliCited publiCation Material. national waterways establish a automatic weather station but all diSputeS are SubjeCted to but it touched me at also get trained in how to use it —ravinDra the exCluSiVe juriSdiCtion of a personal level with PanDey, via faCebook CoMpetent CourtS and foruMS pictures that reminded in delhi/new delhi only. me of my childhood days in Allepey, The modI GoveRnmenT’S new scheme ‘Pradhan Kerala.—Cherian, new Delhi Mantri Fasal Bima Yojana’, on crop For more details log on to our website www.geographyandyou.com insurance scheme is laudable and will be
2 november - december 2015 . GeoGraphy and you Editorial India’s Variant Weather
Dear Readers, In the current decade, substantial change in the frequency and intensity of extreme events may be seen, with heat waves, floods, cyclones and more occurring in a grim cycle of climate related disasters. The pattern of precipitation too has changed, with fewer light and moderate rains being replaced by more heavy rain events. Almost every day the newspapers scream of a rarest and most extreme record being beaten by a new high or low. We know that weather anomalies are part of a normal climate cycle, yet when its frequency increases, recurrent disaster strikes with unnerving consequences. However unlike tectonic, climate disasters can be predicted with a fair amount of precision. Armed with data and an understanding of the ‘what-if’, we can not only make micro-level changes in our day to day living, but also participate holistically in the nation’s macro-level needs, such as change in cropping pattern, water conservation for drought scenarios, evacuating flood plains and more. As social scientists we recognise that personal experiences during extreme weather events play an active role in building public opinion in favour of proactive action. However, extreme events are rare and it would take decades before the political tipping point is achieved. Such events need to be recognised as plausible threats and without preparedness, developing countries such as our will continue to be beleaguered by rare to rarer climate disasters. This issue of Geography and You is dedicated to hydro- meteorological events that affect the Indian region—cyclones, floods, droughts, heat and cold waves, thunderstorm and hailstorm. The issue also covers plausible causes of Chennai floods and associated disaster management.
Sulagna Chattopadhyay
an ever-green scheme in India. I believe that it will be English both on your website. Students in rural areas are an efficient step taken by government and will increase starved for material in Hindi. —asha Tanwar, via faCebook insurance coverage to 50 per cent.—karan Joshi, via faCebook eARThqUAke pRepARedneSS. It’s only after large scale devastation following natural calamities that makes us RURAL IndIA. If you really want to bring quality information act but that also remains short lived. to rural people you should provide material in Hindi and —aMan PanDey, hyDerabaD
WRITe To editorial office: geography and you, 1584, b-1, Vasant Kunj, new delhi-110070. letters may be edited for clarity and length. include name, address and telephone. phone 011-26122789, 26892275, fAX 011-41775126, emAIL [email protected], fACebook http://goo.gl/eieah, LInkedIn http://in.linkedin.com/pub/geography-and- you/5a/b32/b24 WebSITe www.geographyandyou.com. SUbSCRIpTIonS for institutional subscriptions of print copies you may write to [email protected] To ConTRIbUTe An ARTICLe: Kindly send the abstract of your article in not more than 200 words to [email protected]. the abstract will be reviewed by our guest panelists. once selected we shall respond for the procurement of full article. the length of the final article may range from 1000 to 1500 words. please also mention if you can contribute relevant high resolution photographs. The Editorial Advisor.
GeoGraphy and you . november - december 2015 3 INDIA’s | VARIANT WeATheR
By L S RathoRe, D R Pattanaik and S C Bhan IndIa’s Weather extremes Being a land with a unique climatic regime, including two monsoon seasons, two cyclone seasons, hot and cold weather seasons, cold waves and fog, India is vulnerable to several extreme weather events. A spatio- temporal analysis of these weather extremes is extremely essential to help understand India’s vulnerability potential, and hence minimise the adverse impacts on the population.
ndia is a land with a unique climatic regime, interannual variations, can have adverse impacts, that includes, two monsoon seasons (south- such as crop failures. west and north-east); two cyclone seasons This is particularly so since India receives nearly (pre- and post-monsoon cyclone seasons); 75-90 per cent of its annual rainfall during the hot weather season characterised by severe JJAS monsoon season. Hence, any shortfall in rain thunderstorms, dust storms and heat waves; and, during this season can create drought conditions Icold weather season characterised by violent snow in the country, particularly in the drought-prone storms in the Himalayan regions, cold waves and regions—which comprise one sixth of the total area fog. Since agricultural output in India is primarily of the country. dependent on rainfall, the variability in rainfall- On the other hand, extremely heavy rainfall particularly the monsoon rainfall during June to can result in disaster at another end of the scale, September (June-July, August-September- JJAS) wherein floods can cause heavy damage to crops, that occurs over a range of temporal scales from life and property. With about 40 million hectares intra-seasonal to inter-decadal, dominated by (mha) in India prone to floods, and an average of 7.5
4 November - December 2015 . GeoGraphy aND you mha hit by floods every year—particularly in the about 89 cm with a coefficient of variability of ≈8.9 plains, the variability of monsoon rainfall within a cm (10 per cent of LPA) as shown in Fig. 1a and b. season, especially its onset, withdrawal, active and The inter-annual variation of AISMR during 1901- dry spells are very crucial indeed. 2014 is shown in Fig. 2 and Table 1. As seen from India is frequently affected by cyclones, hail- Fig. 1 the period from 1901 to 2014 witnessed many storms, cloudbursts, dust storms and severe deficient and excess monsoon years. The deficient thunderstorms on a regular basis. Of these, cyclones or excess years are identified based on the rainfall are the most significant, given the fact that India departure of ±1 coefficient of variability. has a 7516 km coastline covering ten states. On an Although there have been many studies linking average, 5 to 6 cyclones form over the Bay of Bengal deficient monsoon to the El Niño and Southern and Arabian Sea and hit the coasts every year. Oscillation, K Krishna Kumar et al., in their publi- As per the 4th Assessment Report of The Inter- cation, ‘On the weakening relationship between the governmental Panel on Climate Change (IPCC) Indian monsoon and ENSO’, Science,1999, have (AR4; IPCC, 2007) more frequent and intense suggested that the link with El Niño has weakened weather events have been projected in the 21st in the last decade, and in fact the All India Summer century. This is likely to further degrade the resil- Monsoon Rainfall (AISMR) anomaly was positive ience and coping capacities of poor and vulnerable in the recent intense warm event of 1997. communities. Thus it is all the more necessary to Many other studies have also linked various tele- undertake spatio-temporal analytical studies, and connection patterns other than ENSO to explain hence plan well in advance to reduce losses to life the observed interannual variability. In fact, even and property. in a year of excess rainfall, there may be pockets of deficient rainfall and vice-versa. This can lead to variability in weather extremes drought or flood situations, as the case may be. The southwest monsoon has a stranglehold on agri- culture, the Indian economy and consequently, the active and break cycles of the monsoon livelihoods of a vast majority of the rural populace. Analysis of seasonal monsoon rainfall shows intra An overwhelming majority of cropped area in seasonal variations with active and break phases of India (around 68 per cent) falls within the medium monsoon, which is very important for the agricul- and low rainfall ranges regions. The All India ture sector and water management. The convective Summer Monsoon Rainfall (AISMR) during JJAS activity over the monsoon trough region and that has a unique identity due to its large interannual over the equatorial south Indian ocean oscillates variability. The long period average (LPA; 1951- in sea-saw fashion with one active and the other 2000) of summer monsoon rainfall is found to be inactive and vice versa. These influence monsoon
Fig. 1a: Mean all India summer monsoon rainfall Fig. b. Mean co-efficient of variability (per cent) during June to September (1951-2003);
36N 39N 400 36N 60 33N 300 55 250 33N 30N 50 175 30N 45 27N 150 27N 40 100 24N 24N 35 90 21N 70 21N 30 60 18N 25 18N 40 20 15N 30 15N 15 10 12N 10 12N 9N
9N 6N 60E 65E 70E 75E 80E 90E 95E 100E 69E 72E 75E 78E 81E 84E 87E 90E 93E 96E 99E Map not to scale Source: L S Rathore, D R Pattanaik and S C Bhan, et al, ‘Weather extremes: A spatio-temporal perspectives’, 2016, Mausam
GeoGraphy aND you . November - December 2015 5 activity over the Indian region on an intra seasonal the country receive heavy to very heavy rainfall scale. The phenomenon of `break in monsoon’ is during the active spells of the summer monsoon. of great interest because long intense breaks are Yet, within the season, spells with heavy rainfall often associated with poor monsoon seasons. Such alternate with spells of little or no rainfall. Occa- breaks have distinct circulation characteristics sionally the rainfall is exceptionally heavy at some (heat trough type circulation) and have a large stations associated with an active monsoon trough impact on rainfed agriculture. and passage of low pressure areas and depressions. Although interruption of the monsoon rainfall is These heavy rainfall events with daily rainfall considered to be the most important feature of the of the order of 10 cm or more at some stations break monsoon, traditionally breaks have been iden- over the west coast and other parts of India cause tified on the basis of the surface pressure and wind extensive damage to life and property every year patterns over the Indian region. In K Ramamurthy’s during JJAS through landslides and flash floods. 1969 paper, ‘Monsoon of India: Some aspects of the There are many past instances of Indian stations ‘break’ in the Indian southwest monsoon during having recorded as much as half of their annual July and August’ Forecasting Manual, No. IV , India mean rainfall, and sometimes even more than their Meteorological Department, a break situation annual mean rainfall, in one single day, such as 944 is defined as one in which the surface trough (the mm over Mumbai (Santacruz) on July 26-27, 2005, ‘monsoon trough’) is located close to the foothills, which resulted in massive urban flooding. and easterly winds disappear from the sea level, Climate change studies have indicated increasing provided the break is for over two days. frequency of extreme weather events including Incidentally, the coupled convective phenom- the frequency of heavy rainfall over the globe. enon like the phase and magnitude of Madden Modelling studies indicate changes in intense Julian Oscillation (MJO) has a direct influence precipitation are more likely as global temperature on intra seasonal oscillation of monsoon rainfall increases. There have also been a few studies over over India. The excess (deficient) rainfall years are the Indian region highlighting different aspects mainly associated with more active (break) spells of mean and extreme rainfall events during the of monsoon. southwest monsoon season. Like the frequency of extreme rainfall events, the extreme rainfall and its variability contribution of extreme rainfall to the total rainfall During the southwest monsoon season (JJAS), in a season is also showing a highly significant many parts of India including the west coast of increasing trend during the JJAS monsoon on the peninsula, northeast and central region of seasonal scale and during June and July on monthly
Fig. 2: Mean All India Summer Monsoon Rainfall (AISMR) departure (per cent) during 1901 to 2014 30 25 20 15 10 5 0 -5 -10 -15 -20
Percentage of Deficient 1901-2014 Deficient of Percentage -25 -30 1911 1915 1951 1971 1975 2011 1941 1931 1981 1921 1961 1901 1991 1925 1955 1955 1995 1935 1905 1985 1945 1945 1965 2001 2005 Deficient years Excess years Normal Year
Table 1: Excess (14) and deficient (23) categories of years based on seasonal rainfall year based on the departure of 1 SD
All India Summer Excess 1914, 1916, 1917, 1933, 1942, 1955, 1956, 1959, 1961, 1970, 1975, 1983, 1988, 1994 (14 years) Monsoon Rain- 1901, 1904, 1905, 1907, 1911, 1913, 1918, 1920, 1941, 1951, 1965, 1966, 1968, 1972, 1974, 1979, 1982, 1986, Deficient fall (1901-2014) 1987, 2002, 2004, 2009, 2014 (23 Years)
Source: L S Rathore, D R Pattanaik and S C Bhan, et al, ‘Weather extremes: A spatio-temporal perspectives’, 2016, Mausam
6 November - December 2015 . GeoGraphy aND you 80 per cent stations in scale, as per the 2010 study of D R Pattanaik and M Rajeevan, titled ‘Variability of extreme rainfall peninsular India show events over India during southwest monsoon season’, published in Meteorological Applications. increasing trends in
Tropical cyclones critical extreme maximum Data for 64 years of tropical cyclones from 1951-2014, documents monthly total cyclonic temperatures during the day. disturbances; formed over the northern Indian Ocean (Fig. 3). These data sets are collected from knots; very severe cyclonic storm (VSCS) when it the storm e-atlas published by the India Meteoro- exceeds 63 knots till 119 knots; super cyclone when logical Department (IMD), and indicate that the surface wind speed exceeds 119 knots. months of October-November-December (OND) The incidence of TCs with intensity of severe produce cyclonic disturbances of severe intensity. to very severe cyclones across Tamil Nadu and The strong winds, heavy rains and large storm Andhra Pradesh is high during the northeast surges associated with cyclonic disturbances monsoon season (OND), whereas, the highest are the factors that eventually lead to loss of life annual number of CSs and SCSs occur along the and property. Rains associated with cyclones are Odisha-West Bengal coast. another source of damage. However, one does not discern much of a trend in the data sets indicating Surface air temperature the frequency of cyclones over the Bay of Bengal, The surface air temperature is an important the northern Indian Ocean and Arabian Sea. factor that affects agriculture and food security. These systems form initially as low pressure areas The surface air temperature drives crop growth (when the maximum sustained surface wind is duration; influences milk production in animals less than 7 knots) over the northern Indian Ocean and spawning in fish. Temperature in conjunc- and then intensify into depressions (DD; where tion with relative humidity can influence pest and maximum sustained surface wind is between 17 diseases incidence on crops, livestock and poultry. and 33 knots) and occasionally become tropical Surface air temperature during the pre-monsoon cyclones (TCs). These may be cyclonic storms season also influences soil moisture and hence (CS); when surface wind speed is between 34 and the performance of the ensuing monsoon. Thus, 47 knots and severe cyclonic storm (SCS) when variability of surface air temperature plays an surface wind speed is between 48 knots and 63 important role in the national economy.
Fig. 3: Cyclonic disturbances yearwise NIO (Mean = 4.7; SD = 1.7) BoB (Mean = 3.6; SD = 1.5) 9
8
7 The mean 6 cyclonic distur- 5 bance frequency over the Bay 4 of Bengal and Northern Indian 3 Cyclonic Disturbances (CDs) Disturbances Cyclonic Ocean is found
2 to be 3.4 and 4.6 respectively. 1
0 1951 1971 1975 1979 2011 1973 1977 1957 1987 1981 1997 2013 1967 1961 1959 1991 1969 1989 1953 1955 1993 1995 1999 1983 1963 1985 1965 2007 2001 2009 2003 2005 Year
Source: L S Rathore, D R Pattanaik and S C Bhan, et al, ‘Weather extremes: A spatio-temporal perspectives’, 2016, Mausam
GeoGraphy aND you . November - December 2015 7 There are some other aspects of surface air Fig. 4a: Avg Severe Heat Wave Days: temperature which have assumed significance of March-July 1961-2010 late. According to a study by D R Kothawale and 35N K Rupa Kumar., 2005, ‘On the recent changes in surface temperature trends over India’, in Geophys. 30N Res. Lett., the mean maximum temperature 4 (Tmax) over India increased during the 1901-1987 25N period. Currently, there is a significant warming 3 trend in annual mean temperature over India due 20N 2 to increasing Tmax during 1901-2003. Associated 1 with high Tmax in summer, most areas in India 15N 0 have experienced episodes of heat waves causing sunstroke, dehydration and death. Extreme heat 10N waves can also result in losses in standing crops, livestock and fisheries, affecting a majority of the population. On the other hand, cold waves and 70E 75E 80E 85E 90E 95E frost in winter can play havoc with winter crops. Fig. 4b: Avg Heat Wave Days: March- 35N July 1961-2010 heat wave and abnormal high temperature 30N Many areas of West Rajasthan, Punjab, Haryana, 8 northern parts of East Rajasthan, Madhya Pradesh, 25N Chhattisgarh, Vidarbha, western Uttaranchal, 6 East Uttar Pradesh, western parts of Jharkhand 20N 4 and Bihar, Gangetic West Bengal, northern parts 2 of Odisha, Telangana, Coastal Andhra Pradesh, 15N 0 eastern parts of Rayalaseema and north Tamil Nadu on an average have experienced ≥ 8 heat wave 10N days (Fig 4a and b).
Although the maximum number of severe heat 70E 75E 80E 85E 90E 95E wave days have always been reported in the north- Source: D S Pai et al,’Long term climatology and trends of heat waves over India during western north and eastern parts of India, heat the recent 50 years (1961-2010)’, 2013, Mausam waves in June could also occur due to the stagna- tion of movement of the monsoon. The heat wave increasing trend in the frequency of occurrence of during the middle of June in 2005 was due to such hot days and hot nights and widespread decreasing stagnation in monsoon progress over the region. trend in those of cold days and cold nights in the During the period from June 14-22, 2005 the Tmax pre-monsoon season. In their article, S K Dash and anomaly reported was of the order of 5 to 6 °C in Ashu Mamgain (2011), ‘Changes in the frequency some eastern states of India, where maximum of different temperature extremes in India’, in deaths were reported during this period. Journal of Applied Meteorological Climatology, There have been several studies that have indi- have pointed out that seven homogeneous regions cated extreme temperatures all over India. during the period 1969-2005 indicated a significant G S P Rao et al. 2005, ‘Climate change over increasing trend in the number of warm days in India as revealed by critical extreme temperature summer in the interior peninsula. On the eastern analysis,’ in Mausam, have reported that 80 per cent and western coasts, the maximum number of stations in peninsular India and 40 per cent stations warm days in summer was noticed only during in northern India showed increasing trend in 1996-2005. These results, thus, broadly suggest temperatures during the day with critical extreme warming trends in large parts of India. maximum temperature. D R Kothawale et al. (2010), in their article, ‘Recent trends in pre-monsoon cold wave, abnormal low daily temperature extremes over India’, Journal temperatures and fog of Earth Systems Science, have found widespread Cold wave conditions observed in the hilly
8 November - December 2015 . GeoGraphy aND you Rapid urbanisation has caused regions in the north of India and adjoining plains are usually influenced by western disturbances. fog occurrences to increase These systems are transient winter disturbances in the mid-latitude westerlies with weak frontal and maximum temperature to characteristics. U S De et al. (2005), ‘Heat and Cold Waves Affecting India During Recent Decades’, fall in winters. International Journal Of Meteorology, have inferred that the occurrence of cold wave conditions in the last century was at a maximum in the Jammu and Kashmir region followed by Rajasthan and Uttar Pradesh. Results of D S Pai et al. 2004, in ‘Decadal than and Haryana with 95.17, 30.57 and 22.24 lakh variation in the heat and cold waves over India hectares respectively. during 1971-2000’, Mausam, show that cold wave Also, during the first half of December, 2014 conditions were most often experienced in west unprecedented hailstorms struck several villages Madhya Pradesh in the decade 1971-80, in Jammu in Nashik district, in Maharashtra. The untimely and Kashmir in 1981-90, and in Punjab in 1991- rain caused a lot of damage to farmers. Almost 8 2000. The 2011 study by S K Dash et al, cited earlier lakh hectares of crop was damaged, particularly indicates a significant decrease in the frequency of standing crops like wheat, jowar, pulses, and occurrence of cold nights in winter months in India sunflower, as also grapes, pomegranate, and and its homogeneous regions in the north except vegetables. in the western Himalaya. Southern regions showed a drastic decrease in the frequency of cold nights cloudburst and landslides relative to 1969-75. The Western Himalayas sometimes witness cloud- As regards fog, R K Jenamani, 2007, ‘Alarming bursts under active monsoon conditions. In 2010, a rise in fog and pollution causing a fall in maximum cloudburst resulted in flash floods and mudflow in temperature over Delhi’, Current Science, has Leh and surrounding areas causing severe damage shown that due to the rapid urbanisation in cities to human lives and property. It left 196 persons like Delhi, fog occurrences have increased with the dead with 65 missing, 3,661 houses damaged and rise in pollution causing a fall in Tmax (maximum affected 27,350 hectares of crop area. temperature) in winter. Heavy rainfall events in the western Himalayas often produce landslides; nearly 30 per cent of Thunderstorm and hailstorm the world’s landslides occur in these regions. The A thunderstorm occurs when a giant cumulus cloud Himalayan mountains, which constitute the develops into a towering dark cumulonimbus giving youngest and most dominating mountain system off lightning flashes during the pre-monsoon season. in the world, comprise a series of seven curvilinear While farmers welcome thunderstorms, due to the parallel folds running along a grand arc for a total accompanying rain and other benefits, a thunder- of 3400 km. In fact, in north Sikkim and Garhwal storm that develops into a hailstorm can result regions in the Himalayas, there are an average of in severe crop losses, and cause harm to standing two landslides per square kilometre. crops. Gangetic West Bengal and Bangladesh record between 80 and 100 days of thunderstorm annually. endnote Kerala records the highest (80-100 days) thunder- Given the widespread damage that weather storm frequency over the peninsula. Udhampur extremes like extreme heavy rainfall events, cloud- observatory (132 days) in Jammu sub-division bursts, hailstorms, drought and cyclones regularly records the highest number of thunderstorms in the cause in India, it is extremely important that moni- country followed by Kumbhigram (Silchar) observa- toring and forecasting of these be undertaken on a tory (129 days) in south Assam and Hasimara (123 regular basis. This can help keeping casualties and days) in Sub Himalayan West Bengal. agricultural losses to a minimum. In 2015, hailstorm and unseasonal rain lashed India during February, March and April. A total of The authors are Director General and Directors, 182.38 lakh hectares of cropped area was affected, respectively, India Meteorological Department, New worst amongst which were Uttar Pradesh, Rajas- Delhi. [email protected]
GeoGraphy aND you . November - December 2015 9 INDIA’s | VARIANT WeATheR
Urban flooding begins with an unanticipated high rainfall event which seriously disrupts public transport, electricity and communica- tion. The frequency of urban floods has increased in the last decade with at least one major city being submerged in a year.
10 November - December 2015 . GeoGraphy aND you By STAFF REPORTER The monsoon Monsoon refers to a period of widespread rains from June to September over the Indian subcontinent. The economic discourse in the nation is much dependant on the efficacy of the monsoon.
GeoGraphy aND you . November - December 2015 11 The term monsoon is customarily used in the South Asian context to refer to a period of widespread rains during June-September, otherwise known as the ‘Indian summer monsoon’. The common reference to a ‘good’ or ‘bad’ monsoon denotes whether the rainfall is in excess or deficient over a large area like India. While the monsoon has a wider economic and socio cultural importance for South Asia, its origins have been subject to much scientific debate.
ith the development of west in winter). Hadley explained that moving air sophisticated scientific tech- is deflected as a result of rotation of the earth on niques and advancement its axis, veering towards the right in the northern in observing techniques hemisphere and forming the monsoon southwest- like satellite imageries, our erlies, and to the left in the southern hemisphere, understanding of the dynamics of the monsoon creating the monsoon northwesterlies. Whas improved significantly in the last few decades. Nevertheless, the origins and mechanics of the Monsoon variability monsoon are yet to be fully understood. While The most spectacular part of the monsoon climate empirical seasonal forecasts of the monsoon have system is the timing of the commencement of the been moderately successful for the past hundred wet season, which often involves a sudden change in years, attempts to model the basic mean structure the weather from dry hot conditions to cloudy and of monsoon have proved to be elusive. It is, however, rainy. For farmers, it is critical to know when the generally accepted that monsoon is a result of three onset will occur as this affects the timing of crops. physical processes—uneven heating of land and Prediction systems are thus central to preventing sea causing pressure differential that drives winds futile sowing and faulty harvesting. from high pressure to low pressure; the rotation of India has large rainfall variability over both space the earth forcing winds to veer towards the right in and time. Areas on the west coast and northeast the northern hemisphere and to the left in southern India receive maximum rainfall. Cherrapunji and hemisphere; and change in the state of water from Mawsynram, the two small towns of Meghalaya liquid to vapour, which determines the strength located on the southern slopes of the Khasi hills, and location of the monsoon rains. record an annual rainfall of over 1000 cm. On the Theories of the causes of monsoon in the eight- other hand, areas like western Rajasthan and Tamil eenth and nineteenth century were based on an Nadu, receive a summer rain of less than 20 cm. understanding of the effects of non uniform heating Also monsoon experiences a temporal variability of land and sea. The earliest propounder of this line both within the season and annually. A delay in the of thought, Edmund Halley, an astronomer influ- start of monsoon can be just as harmful, even if the enced by Newtonian physics, showed in his ‘sea aggregate for the year is normal. As per an estimate breeze-land breeze’ model of 1686 the tendency one bad growing season brought on by an abnormal for the northeasterly trade winds on the northern monsoon can lower the season’s agricultural output side of the equator and the southeasterly trades to by as much as 15 per cent. the south of the equator to converge towards the most strongly heated regions of the globe. This Monsoon advisories theory, refined by George Hadley, observed that Despite the known variability of the monsoon, the wind flow between land and ocean was in an government has been making concerted efforts to oblique direction (southwest in summer, north- improve the ability of scientists to predict rainfall
12 November - December 2015 . Geography and You patterns so as to anticipate and preempt crisis. towards the end of the third week helped the The cost in establishing sophisticated weather monsoon advance rapidly resulting in the entire and climate prediction systems has, however, country getting covered by June 26. dissuaded most South Asian governments. The India Meteorological Department (IMD), an Chief synoptic features and rainfall exceptional case in point, established in 1875 by The season saw 11 low pressure systems (low pres- H F Blanford, began issuing seasonal forecasts of sure areas and more intense systems) form. Out monsoon rainfall since 1884, following the Indian of these, 8 intensified into depressions, against a famine of 1877. With the advancements in Indian normal four to six depressions every season. Two space technology and research capability there has of these intensified into cyclonic storms ‘Ashobaa’ been considerable improvement in India’s capacity (7-12 June) and ‘Komen’ (26 July - 2 August), over to monitor and predict monsoon. India is now Arabian Sea and Bay of Bengal respectively and capable of predicting monsoon rains in almost all three became deep depressions with two over land scales—short range (upto 48 hours), medium range (27-30 July and 16-19 September) and one over the (3-10 days in advance), extended range (upto one Arabian Sea (22- 24 June). Of the three depressions, month) and long range (seasonal scale), with varied two formed into land depression over and around accuracies. India has acquired most sophisticated Jharkhand (10-12 July) and over east Madhya computing resources to handle simulation and Pradesh and adjoining Chhattisgarh (4 August). prediction of weather systems. Besides IMD, other The remaining formed over the Bay of Bengal (20 institutions, National Centre for Medium Range -21 June). Of the three low pressure areas, one inten- Weather Forecasting, Noida and Indian Institute sified into a well-marked low pressure area. of Tropical Meteorology, Pune, Centre for Atmos- The setting of southwest monsoon over Kerala on pheric Sciences in several premier institutions like 5th June was associated with the eastward move- IIT, Delhi and Kharagpur; and IISc, Bangalore are ment and strengthening of the Madden Julian working on advanced monsoon modelling. India is Oscillation (MJO) over the Indian Ocean. This among few countries in the world which has imple- also helped intensification of the onset vortex over mented a weather forecast based district level agro the east central Arabian Sea into cyclonic storm advisory system that provides reliable and timely ‘Ashobaa’ (7-12 June). advice on agricultural operations like sowing, The northeastward movement of the deep harvesting, irrigation, application of pesticides depression formed over Arabian Sea (22-24 June) and insecticides, and drought and flood situa- towards Gujarat brought widespread rainfall over tions. Several Indian states too have established Konkan, Goa and Maharashtra and scattered to crop weather watch groups, which monitor the isolated rainfall over Saurashtra and Kutch with behaviour of the monsoon and plan future course isolated extremely heavy rainfall for a couple of days. of action for cropping strategies and dealing with The presence of trough and cyclonic vortex in mid pest attacks. latitude westerlies caused active monsoon conditions over extreme north and western Himalayan region. Monsoon-2015 roundup Consequently, the southwest monsoon advanced Onset and Advance: In 2015 the southwest further and covered major parts of central India, monsoon set over the south Andaman Sea on northern plains and western Himalayan region by May 16—four days earlier than normal. On 24th June and the entire country by 26th June. There- May 21, the monsoon advanced further over after, the rainfall activity reduced substantially over the remaining parts of the Andaman Sea. most of south peninsular and central India, in the The southwest monsoon set in over Kerala on 5 wake of unfavourable phase of MJO, which moved June—4 days later than normal. By June 15, the eastward into the western Pacific region. monsoon was all over the central Arabian Sea, some Subsequent MJO activity in the western Pacific parts of the north Arabian Sea, the entire southern directed significant part of cross equatorial Peninsula, and most parts of central and northeast flow towards the typhoons developed over the India. The formation of a couple of intense pres- west Pacific Ocean, leading a to weak monsoon sure systems, one each over the Arabian Sea (deep circulation pattern. This caused subdued rainfall depression) and the Bay of Bengal (depression) activity over major parts of central and peninsular
Geography and You . November - December 2015 13 Fig. 1: Cumulative rainfall for the period June to September 2015
614.0 (15) 534.6
638.3 (-23) 825.3 336.3 (-32) 491.9 881.5 (-28) 295.5 (-37) 1229.1 466.3 1883.0 (-6) 1875.0 (6) Out of the total 36 mete- 439.9 (-43) 2006.2 1768.0 769.4 orological subdivisions, the 384.0 (46) 263.2 472.1 (-47) season (June-September) 1747.7 (-3) 555.6 (-10) 897.6 742.3 (-28) 1792.8 615.8 1027.6 rainfall was normal in 18 1050.3 (-30) subdivisions (55 per cent of 1496.9 745.1 (-29) 941.9 (-14) the total area of the country) 659.4 (-27) 914.5 (4) 1051.2 1091.9 1265.5 (8) and deficient in 17 subdivi- 502.5 (6) 901.0 1876.1 1167.9 473.5 1009.8 (-12) sions (39 per cent). Only one 1147.3 848.2 (-11) 1034.4 (-10) subdivision (West Rajasthan) 954.6 1149.9 constituting 6 per cent of 412.4 (-40) 682.9 the total area of the country 488 (-33) 2005.0 (-31) 729.3 600.8 (-20) received excess rainfall. Out of 2914.3 755.2 the 17 deficient subdivisions, 642.0 (10) six were from northwest India, 581.1 357.3 (-29) five from central India, two 506.0 358.3 (-10) Excess (>19 per cent) from northeast India and four 2285.0 (-26) 398.3 Normal (-19 to +19 per cent) from south Peninsula. 3083.8 607.4 (-8) 660.0 Deficent (-20 to -59 per cent) Scanty (<=-60 per cent) 285.8 (-10) 1678.5 (0) 317.2 All India area weighted rainfall 1682.5 860.8 (-14) 1514.7 (-26) 2039.6 Actual Normal %Dep. 998.5 760.6 887.5 -14 Excess: 01 Deficient: 17 Normal: 18 Scanty: 00 Map not to scale Source: IMD 2015, ‘2015 Southwest Monsoon End of Season Report’
India during the first week of July. With the India remained subdued. Towards the end of formation of a low pressure area over north Bay the July, two intense low pressure systems (deep of Bengal on 8th July and its movement northwest depressions) formed along the axis of the monsoon along the axis of the monsoon trough plus abundant trough at both the ends, one over northeast Bay of moisture present in the lower levels over the Indo- Bengal and the other, over southwest Rajasthan. Gangetic plains, aided rapid intensification into As the monsoon trough lacked the characteristic a land depression over and around Jharkhand southwards tilt with height, the rainfall associ- on 10th July. In addition, the presence of cyclonic ated with the deep depression over Rajasthan was circulation over southwest Uttar Pradesh and confined to the core area surrounding the system. adjoining areas and couple of western disturbances The deep depression over Bay of Bengal intensified led to increase in rainfall activity all along the Indo- further into a cyclonic storm ‘Komen’. As it moved Gangetic plains and northwest India during the northwestwards, it brought heavy to very heavy second week of July. rainfall with extremely heavy rainfall at isolated The third and fourth week of July witnessed places over eastern and central parts of the country. rapid movement of number of disturbances in mid Its subsequent movement inland after weakening latitude westerlies, in the form of cyclonic vortex caused vigorous to active monsoon conditions and, the active monsoon trough caused active to along the track. vigorous monsoon conditions over central India The strengthening of winds at lower levels and and western Himalayan region. Further strength- circulation features during the first week of August ening of the cross equatorial flow in the lower led to formation of a low pressure area (11-15 Aug.) troposphere led to enhanced rainfall along the west over west central and adjoining northwest Bay of coast. However, rainfall activity over peninsular Bengal off north Andhra Pradesh–south Odisha
14 November - December 2015 . GeoGraphy aND you An abnormal monsoon can lower the season’s India received normal/excess rainfall. The excess rainfall was in sub Himalayan West Bengal and agricultural output by 15 Sikkim, Assam, Meghalaya, and Arunachal Pradesh and scanty rainfall was in Saurashtra and per cent. Kutch, Gujarat and Madhya Maharashtra. In September, majority of the subdivisions from northwest India, west central India and east India received deficient/scanty rainfall. On the other coasts. This revived active monsoon conditions hand, most subdivisions from south peninsula and over major parts of the country and gave heavy to neighbouring central India, and northeast India very heavy rainfall at isolated places over eastern, received normal/excess rainfall. The excess rain- northern and central parts of India. Thereafter, fall was in subdivisions of Jammu and Kashmir, weakening of the low pressure area and subsequent Saurashtra and Kutch, Kerala and Andaman & shifting of the monsoon trough northwards to the Nicobar Islands. foot hills of Himalayas, led to a weak monsoon flow From the monthly distribution, it can be seen that pattern, thereby keeping rainfall activity confined to all subdivisions received deficient/ scantly monthly eastern and northeastern India in the second week. rainfall during at least one of four months. However, The first week of September, witnessed reduced none of the subdivisions were deficient/scanty rainfall activity over northwestern India thereby during all the four months of the season. Except in indicating favourable conditions for withdrawal June, during each of the other three months, at least of the southwest monsoon from west Rajasthan. 14 out of the 36 subdivisions had received deficient/ The change in circulation pattern in the lower scanty rainfall. During the peak rainfall months of tropospheric levels led to withdrawal of monsoon July and August, 23 subdivisions each had received from western Rajasthan on September 4. However, deficient/scanty rainfall. Saurashtra and Kutch the presence of a trough in lower tropospheric received scanty rainfall during August but received westerlies, couple of cyclonic vortex revived rainfall excess rainfall during all the other three months. activity over parts of south peninsular India. The low pressure area formed over west central and Withdrawal of southwest monsoon adjoining northwest Bay of Bengal on September 12 Rainfall activity over northwestern Rajasthan intensified into a depression over and around south remained subdued since last week of August. Odisha on September 16 and into a deep depres- A change in the lower tropospheric circulation sion over Vidarbha and south Chhattisgarh on pattern over the region from cyclonic to anti- September 17 resulting in strengthened monsoon cyclonic resulted in the withdrawal of southwest activity over northern peninsular India, thereby monsoon from the northwestern Rajasthan on delaying withdrawal. September 4. Monsoon withdrew from some more Fig. 1 shows the cumulative for the period June parts of Rajasthan and some parts of Punjab and 2015 to September 2015. In June, except for 3 subdi- Haryana on September 9. On September 29, the visions (Bihar, Nagaland, Manipur, Mizoram, monsoon withdrew from the remaining parts Tripura and Andaman and Nicobar Islands), of Rajasthan, Punjab, Haryana, Chandigarh which received deficient rainfall, all the other and Delhi, entire Jammu & Kashmir, Himachal subdivisions received normal (20 subdivisions) or Pradesh, Uttarakhand, most of western Uttar excess (13 subdivisions). In July, most subdivisions Pradesh and parts of western Madhya Pradesh, from peninsular and northern India (along the Gujarat and north Arabian Sea. On October 6, the Himalayas) received deficient or scanty rainfall. monsoon further withdrew from some more parts The scanty rainfall subdivisions were Marathwada, of Bihar; remaining parts of Madhya Pradesh; parts north interior Karnataka, Telangana and Rayala- of Jharkhand, Chhattisgarh, Vidarbha, Madhya seema. Maharashtra; some more parts of Gujarat and the In August, majority of the subdivisions from northern Arabian sea. northwest India, central India and neighbouring south Peninsula received deficient/scanty rainfall. Inputs from Sunitha Devi, Director (Weather Section) On the other hand, most subdivisions in northeast India Meteorological Department, Pune.
GeoGraphy aND you . November - December 2015 15 INDIA’s | VARIANT WeATheR
Out of 11 low pressure systems observed in 2015 monsoon, two intensified into cyclonic storms. Photo courtesy: courtesy: Photo
16 November - December 2015 . GeoGraphy aND you Tropical cyclones By Ajit tyAgi A tropical cyclone is an intense low pressure system that is classified on the basis of its wind speed. The phenomena has a definitive structure and a well-defined life cycle.
GeoGraphy aND you . November - December 2015 17 ropical cyclones (TCs) are intense Frequency low pressure systems where the wind About five to six TCs occur in a year over the NIO speed in the surface circulation system during the pre-monsoon (March-April-May) and exceeds 33 nautical miles per hour post-monsoon (October-November-December) (knots). The low-pressure systems seasons (Fig. 1). This accounts for about seven per over the northern Indian Ocean (NIO) are classi- cent of all global TCs. The ratio of formation over the fiedT (Table 1) on the basis of associated maximum Bay of Bengal (BoB) vis-à-vis the Arabian Sea (AS) sustained surface wind (MSW) at the surface level. is 4:1 (Fig. 2). Globally, the frequency is maximum Systems with the intensity of depressions and above over the northwest Pacific followed by the north are considered cyclonic disturbances. TCs occur- Atlantic Ocean. In the NIO, the frequency of TCs ring over the north Atlantic Ocean are known as is bimodal, with primary maxima in the month of hurricanes and those occurring over the Pacific November followed by secondary maxima in the are known as typhoons. A TC that has a MSW month of May. of 64 knots corresponds to a very severe cyclonic storm (VSCS) over the NIO. TCs occurring near movement the Australian continent are the willy-willies. TCs generally move in a northwesterly direc- Tropical cyclones usually do not occur over the tion. However, they may sometimes re-curve south Atlantic Ocean or SE Pacific (east of 140oW) depending upon atmospheric conditions. The mainly because of the colder sea surface tempera- BoB TCs mainly strike the Odisha-West Bengal tures (SSTs) and other unfavourable ocean and coast in October, Andhra coast in November and atmospheric conditions. the Tamil Nadu coast in December. Over 50 per
Fig. 1: Monthly frequency of cyclonic disturbances during 1961-2015 over the northern Indian Ocean
110 100 100 90 91 80 66
70 65 63 58
60 56 52 47
50 45 44 40 41 31
30 27 26 17 18 20 17 9 9 7 8 9 10
10 6 4 2 1 3 0 2 2 0 1 1 0 0 January February March April May June July August September October November December Depression and above Cyclonic storm and above Severe cyclonic storm and above Source IMD
Table 1: Type of tropical cyclones and their Fig. 2: Frequency of cyclones during 1961-2015 associated wind speeds System Associated Wind Speed (a) Tropical cyclone landfall - Bay of Bengal (Abbreviation) Knots (Kmph) (b) Tropical cyclone landfall - Arabian Sea Low Pressure Area (L) <17 (<31) Depression (D) 17 – 27 (31 – 49) 40 38 35 34
35 33 Deep Depression (DD) 28 – 33 (50 - 61) 30 Cyclonic Storm (CS) 34 – 47 (62 – 88)
25 24
Severe Cyclonic Storm (SCS) 48 – 63 (89 - 117) 21 20 Very Severe Cyclonic Storm 64 – 89 (118 - 166) 15 12 11 (VSCS) 10 10 7 Extremely Severe Cyclonic Storm 6
5 3 90 – 119 (167 - 221) 2 (ESCS) 1 0 Super Cyclonic Storm (SuCS) ≥120 (≥222) Odisha Gujarat over sea Source: www.imd.gov.in and Goa Pakistan Sri Lanka and Africaand Myanmar Weakened Weakened Iran, Arabia Tamil Nadu Maharashtra West Bengal West Bangaladesh Andhra PradeshAndhra
18 November - December 2015 . GeoGraphy aND you Undisturbed winds Tropopause Km Tropopause Tropopause 15 Steering wind flow Subsiding warm air
Out flow Out flow 12
9 T2 T2
6 T1 T1 Rain bands Rain bands
Cb
Cb Eye wall Eye wall 3 P2 P2 R R Cu Cu P1 P1 Eye 200 100 100 200 Km : Pressure Fig. 3: Vertical structure : Temperature Cb: Cumulonimbus of a mature Tropical Cu: Cumulus Cyclone
Direction of the storm Vertical structure: A TC has three distinct vertical layers—inflow, middle, and outflow. The inflow layer is where one sees a flow towards the centre of the TC from the outside. This layer extends from the surface up to about 3 kms in height. The strongest or maximum inflow of winds occurs in the frictional layer, which is layer between the surface to 1 km. This layer is also called the planetary boundary layer. The diameter of the TC remains more or less the same in the inflow layer. In the middle layer, the inflow into the centre of the TC is compensated by the outflow away from the centre. Thus, at any height, there is neither inflow nor outflow. This layer extends from 3 -7.65 km (700 to 400 hPa) above the mean sea level. The diameter of the TC here decreases rapidly with height. The outflow layer occurs above 7.65 km. One notices a predominant flow away from the centre. Maximum outflow occurs at about 12 km, which again is dependent upon the wind distribution at that level. We can also notice the cirrus outflow from TC in satellite pictures. The diameter of the vortex is small, and is about o1 lat/long at this level. At times, the cyclonic outflow is visible at this level in intense systems. A mature TC extends up to about 15 km, with the cyclonic circulation or vortex extending into the entire troposphere. The associated circulation is vertically straight and does not tilt with height. This is because the temperature gradient associated with the TC is equal in all directions, preventing a tilt. The core is warm as compared to the surrounding regions, with the difference in temperature being around 8oC. The maximum warming occurs at the height of 9.5 km. cent of the TCs in the BoB strike different parts but represent a continuous process. The period of the eastern coast of India, 30 per cent strike the from the formation of an initial disturbance or low- coasts of Bangladesh, Myanmar and Sri Lanka and pressure area, to its intensification into a depression, about 20 per cent dissipate over the sea (Fig. 2). The a deep depression, and thereon to a cyclonic storm percentage of TCs dissipating over the AS is higher and its ultimate weakening make up the life cycle of (60 per cent) as the western AS is cooler. Maximum a TC. This can be divided into four stages—forma- landfall occurs over the Gujarat coast (18 per cent tive, immature, mature and decaying. of the total cyclones in the AS) in India, followed Formative stage: Since the development of a TC is by coastal Oman. a continuous process, features associated with the earliest stages may overlap. The formative stage Life period marks the period when an initial low-pressure The life period of a TC over the NIO is 5-6 days. disturbance intensifies into a depression, a deep The VSCS with an intensity of 64 knots or more depression and finally into a TC. The pressure falls lasts for 2-3 days as against a global average of 6 gradually along with an increase in surface wind days. The vertical and horizontal structures of a speed. Clouds and rain associated with the storm tropical cyclone are described in Fig. 3 and 4. There occur in a disorganised pattern at this stage. The are several stages that comprise the life-cycle of an development of marked circular cloud masses also average TC. These stages are not discrete entities, occurs at this stage and lasts a few days.
GeoGraphy aND you . November - December 2015 19 Fig. 4: Structure of a Tropical Cyclone
sA Horizontal structure: Considering the horizontal structure, the TC consists of four parts. The first is the central part, known as the eye, characterised by calm winds, a clear sky and the lowest pressure. Abrupt precipitation is observed when the eye passes over an area. The diameter of the Eye Eye-wall eye varies from 10-50 km, which is generally circular, but could be elliptical too. It could also be a
Photo courtesy: NA courtesy: Photo diffused or have a double eye. Inside the eye, the surface temperatures are slightly higher than the surroundings, and as one moves to the upper level it turns significantly higher. Spiral cloud bands Outer storm The second part is the wall cloud region that is adjacent to the eye—the most dangerous part of a region TC. The width of the wall cloud is about 20-100 km, comprising of huge cumulonimbus clouds. The Horizontal structure of a TC as maximum pressure gradient is 0.2-0.5 hPa per km and temperatures are lower than the eye region. observed through a satellite This region is associated with the heaviest precipitation and strongest winds. In some TCs, one might notice double wall cloud regions. Herein, one wall cloud region weakens and then, another wall cloud is formed. If an existing wall cloud weakens and a double wall cloud forms, the system may be undergoing changes in intensity. Normally, in such cases, the intensity may reduce temporarily and would increase again as the two wall clouds merge leading to a single eye. The third part is the spiral band of clouds, which extends from the outer region and spirals towards the wall cloud region. This area also experiences heavy rainfall and wind speed gradually decreases outward. The fourth part is the area from the wall cloud to the outermost region of the TC—the outer storm region. The wind speed decreases as we move away from the wall cloud, accounting for rainfall of lower intensity as compared to that of the wall cloud region and spiral bands.
Immature stage: In this stage, two things occur the TC that causes weaker circulation. —rapid fall of pressure in the central region of the TC experiences a high vertical wind shear and TC, and strengthening of winds in the surface the convective heat engine moves away from the circulation. At the end of this stage, the lowest centre, preventing further development. pressure and the strongest winds associated with Formation of an outer eye wall, typically around the storm are reached. The winds, clouds, and 50-100 miles from the centre of the storm, precipitation pattern become more organised, chokes off convection within the inner eye wall. and form spiral bands directed inward. This Such weakening is generally temporary unless it stage lasts for half a day to 2-3 days. The duration meets the other conditions mentioned above. If is dependent upon the ocean basin. For BoB and the outer eye wall merges with the inner eye wall, the AS, the stage lasts up to a day while for the the TC may strengthen. Atlantic Ocean, it takes 2-3 days. Sometimes, if the TC meets mid-latitude west- mature stage: In this stage, the system reaches a erlies, it can turn into an extra-tropical cyclone. steady state. The central pressure no longer drops When passing over the sub-tropical ridge while and wind strength does not increase. However, moving north or northeastwards, cold air is the circulation expands in area and the size of the likely to favour its transformation into an extra- system expands horizontally in all directions to tropical cyclone. reach its maximum size. Strong winds extend up to 200 miles from the centre. The symmetry in circu- Intensification lation associated with the cyclone is lost and the About half the depressions formed develop into maximum wind and maximum pressure gradient TCs, and only less than a quarter intensify into are concentrated in the right forward sector of the severe TCs. However, the rate of intensification TC in the northern hemisphere. This stage lasts a differs with the seasons (Fig. 3). While it takes few days to a week depending on the basin in which about 2-4 days for a low-pressure area to develop it is formed. into a depression, intensification into severe or very Decaying stage : In this stage, the TC weakens into severe cyclones can occur in 24-48 hours. a depression, and gradually or rapidly subsides depending upon the ocean basin and atmospheric endnote conditions. Dissipation occurs when: Climatological information is crucial for effec- Landfall results in supply of moisture being tively planning hazard management during severe cutoff and surface friction increases. cyclonic conditions. The understanding can also be TC enters into an area of relatively cold waters utilised to predict the characteristics of a TC based which is below 26°C. on analogue techniques. TC remains for too long in the same area of the ocean and upper 100 feet of warmer water mixes The author is Air Vice Marshal (Retd) and Former with the colder water due to upwelling. Director General of India Meteorological Department. Entrance of colder and dry air in lower levels of [email protected]
20 November - December 2015 . GeoGraphy aND you Term Power Answers on PAge 45 ❯❯ India’s Variant Weather Here are some terms that you may unravel to lead you to a greater understanding of weather and climate in the Indian sub-continent. See page 45 to check how far you got.
1. Baroclinic water deficits, reduced groundwater change caused by variations in instability zones in or reservoir levels, and so forth. sea surface temperatures over the atmosphere c. is associated with the effects of tropical eastern Pacific Ocean, a. The Baroclinic areas in atmos- periods of precipitation (including warming much of the tropics and phere are generally found in the snowfall) shortfalls on surface or sub-tropics. mid-latitude/polar regions whereas subsurface water supply. b. is an irregularly periodical the Barotropic zones of the Earth climate change caused by are generally found in the central variations in sea surface latitudes, or tropics. 5. The Standardized temperatures over the tropical b. Baroclinic zones of the Earth Precipitation Index eastern Pacific Ocean, cooling are generally found in the central a. is a tool which was developed much of the tropics and latitudes, or tropics, whereas the primarily for defining and monitoring sub-tropics. barotropic areas are generally found drought. c. is an irregularly periodical climate in the mid-latitude/polar regions. b. is a tool which was developed change caused by variations in c. Baroclinic instability zones primarily for measuring the amount sea surface temperatures over the in atmosphere are found in of rainfall. tropical eastern Pacific Ocean, tropics only. c. is a tool which was developed warming and cooling much of the primarily for measuring landfall due tropics and sub-tropics at the same to flooding. time. 2. Madden-Julian Oscillation a. is the largest element of the 6. Dipole Mode Index 9. Western Distur- intraseasonal (30-90 day) variability a. The index is an indicator of the bances in the tropical atmosphere. east-west temperature gradient a. Occurs in India bringing sudden b. is a measure of an oscillator’s across the tropical Indian Ocean. monsoon in the north-western parts ability of maintaining constant b. The index is an indicator of the of the Indian subcontinent. voltage amplitude with variations in surface temperatures in a region b. Occurs in India bringing sudden the output signal frequency. east of South Africa and south of winter rain to the north-western c. is a measure of how closely the Madagascar. parts of the Indian subcontinent. output wave from of the oscillator c. The index is an indicator of the c. Frequently occurs in India resembles a pure sinusoidal signal. surface temperatures in the south- bringing sudden hailstorms to the eastern tropical Indian Ocean, west north-western parts of the Indian of the Indonesian island of Sumatra. subcontinent. 3. Flood a. An overflow of a large amount of water beyond its natural limits, 7. Indian Ocean especially over a normally dry land. Dipole 10. Hadley Cell b. A result of continuous rain is a. is a pressure pattern charac- a. is the average motion of air in the defined as a flood. terised by high pressure on the mid-latitudes. It is characterised by c. A result of a dam burst that regions of India, and a low pressure sinking air near 30o and rising air affects nearest villages or towns/ on the Eurasia region. farther poleward. cities—a situation known as flood. b. is an irregularity in the speed and b. is a tropical atmospheric directions of winds on the western circulation which features Indian Ocean. rising motion near the equator, 4. Hydrological c. is an irregular oscillation of poleward flow 10-15 km above the Drought sea-surface temperatures in which surface, descending motion in the a. is defined usually on the basis the western Indian Ocean becomes sub-tropics, and equator ward flow of the degree of dryness and the alternately warmer and then colder near the surface. duration of the dry period. than the eastern part of the ocean. c. They extend from between 60 b. links various characteristics of and 70o N and S, to the poles. droughts to agricultural impacts, Air in these cells sinks over the focusing on precipitation shortages, 8. El Niño Southern highest latitudes and flows out differences between actual and Oscillation towards the lower latitudes at potential evapotranspiration, soil a. is an irregularly periodical climate the surface.
GeoGraphy and you . September-october 2015 21 INDIA’s | VARIANT WeATheR
By J R KulKaRni The Science behind The Tamil nadu FloodS
Tamil Nadu experienced unprecedented floods in November- December 2015, with Chennai bearing the brunt of non-stop rains and inundation paralysing normal life. High sea surface temperatures over the Bay of Bengal, a stationary pressure trough and easterly waves caused this phenomenon. .gov Sa rvatory.na Se rthob ea Source:
22 November - December 2015 . GeoGraphy aND you he Indian state of Tamil Nadu experi- Northeast monsoon enced a series of floods this winter. The The period October to December is the Northeast city of Chennai was flooded between (NE) monsoon season over peninsular India—the November 13 and 17 and on December major period of rainfall activity over the region, 1, 2015 which persisted well into the particularly in the eastern half comprising of the second week of December. District after district meteorological subdivisions of coastal Andhra wasT inundated—Kanchieepuram on December Pradesh, Rayalaseema and Tamil Nadu-Puduch- 5; Tirunelveli on December 7; and Thanjavur, erry. For Tamil Nadu this is the primary rainy Thiruvarur and Nagapattinam on December 8. season accounting for about 48 per cent of the Cuddalore city and the district remained flooded annual rainfall. Coastal districts of the State get till December 10. More than 500 people died and nearly 60 per cent of the annual rainfall and the inte- over 18 lakh people were displaced. Damages and rior districts get about 40-50 per cent of the annual losses have been estimated of the order of 50000 rainfall. As per the IMD the climatological onset crore (US$7 billion) to 100000 crore (US$15 billion). date of NE monsoon over south India is October These floods are by far the costliest natural disaster 20. During this period (later part of October and that the world has seen in 2015. November) monsoon trough prevails around
Fig. 1: Sea Surface Temperature (SST) distribution in November 2015. SSTs higher than 27oC are seen over Indian seas.
30 60N 29
40N 28 27
20N 26 25 ED 24 23 20S 22 21 40S 20 19 60S 18 30W 0 30E 60E 90E 120S 150S 180 150W 120W 90W 60W 30W 0 Avg. Sea Surface Temperature (oC) November 4, 2015 - December 2, 2015
Source: NCEP Global Sea Surface Temperature Analyses o Figure 1: SST distribution in November 2015. SSTs higherFig. than 3: 27KalpanaCare seen satellite over pictureIndian seas.of clouds in the visible channel on 2015 El Nino effect November 16. Fig. 2: Rainfall time series from November 5- TheDecember southwest 7, 2015 summer at Chennai. monsoon 2015 was weaker than normal due to the El Nino effect.
350Weak winds associated with the weaker monsoon were favorable for generating positive SST Chennai Daily Rainfall 2015 300anomalies (deviation from climatological mean values) over BoBand AS during post monsoon
250season. Figure 2 shows SST anomalies during November 2015. These provided extra fuel for formation of low pressure systems over BoB and AS in this season. 200 Rainfall (mm) Rainfall 150
100
50
0 Dec 1 Dec 3 Dec 5 Dec 7 Nov 5 Nov 7 Nov 9 Nov 11 Nov 17 Nov 19 Nov 13 Nov 15 Nov 27 Nov 21 Nov Nov 25 Nov 23 Nov 29 Source: www.imd.gov.in
Source: www.imd.gov.in Figure 6: Kalpana satellite picture of clouds in the visible channel on 16 November.
Figure 6 shows Kalpana satellite picture on 16 November in the visible channel. The thick white GeoGraphy aND you . November - December 2015 23 cloud mass over Chennai indicates existance of a deep convection.Along with satellite cloud Figure 2: Distribution of SST anomalies (deviation frompictures, climatological deep convection mean is identified values) by theduring verical 25 distribution of vertical velocity in the November- 23 December 2015 period. atmosphere. Generally velocity is measured in units of cm or mm/sec. In meteorology, it has been found useful to measure in terms of pressure change ‘pascals/sec’. Figure 7 shows omega field over Chennai region from 16 November to 1 December. Negative values indicate upward Active NE monsoon 2015 motion. Deep upward motion extending up to 250 hPa (~ 11 km) occurred on 16-17 November, 30 November- 1 December. These caused extremely heavy rainfalls at Chennai and sorrounding Thus theNE monsoon 2015 was active with successive formationsregion resulting ofin flood. low pressure systems over AS and BoB. A low pressure systemformed over theSummerizing, AS intensified persistingrainin into Chennai depression during November-December on 7 were the results of unique combination of high BoB SSTs, (positive anomalies due to EL Nino effect) prevaling stationary pressure trough at the surface and passage of easterly waves. 2
5
Chennai’s November 2015 rainfall record of 1049 mm was lower than the 1918 November developed over BoB near Tamil Nadu coast. Under the influence of these systems, rainfall over south record of 1088 mm. peninsula in the month of November was 251.5 mm, which was 227 per cent of the long term average rainfall of this area. Chennai received continuous rainfall throughout November. Time series of Chennai rainfall from November 5 to December 7 is shown in Fig. 2. Mean NE monsoon seasonal rainfalls at 13oN latitude (Chennai 13.08°N, 80.27°E) over Nungambakkam and Minambakkam (Chennai peninsular India and Bay of Bengal (BoB). During airport) are 750 and 770 mm respectively. Chennai the southwest monsoon sea surface temperatures received 1049 mm of rainfall in November, the (SSTs) are high over Indian seas especially over highest recorded since November 1918 when 1088 BoB. Climatologically SSTs are above 27oC, which mm of rainfall was recorded. The above figure is a threshold for genesis of cyclones in this region. shows heavy rainfalls on November 13 (120 mm), BoB shows secondary peak in SSTs during north- November 17 (265 mm) November 24 (150 mm) east monsoon period. Fig. 1 shows SST distribution and December 1 (350 mm). Chennai consequently over the globe during November 2015. SSTs above witnessed floods during and after these days. 27oC are seen over BoB and Arabian Sea (AS). High SSTs associated with pressure trough at surface role of easterly waves provides favourable conditions for large scale Moderate to heavy rainfall persisted throughout upward motion for formation of clouds. It becomes November under the influence of prevailing a breeding ground for formation of low pressure surface pressure trough and anomalous SSTs. systems over these seas. These provided low level moisture convergence and upward motion. The upward motion was 2015 el Niño effect further intensified with the passage of easterly The southwest summer monsoon 2015 was weaker waves. The winds in tropics termed as ‘trade than normal due to the El Niño effect. Weak winds’ blow from the Northeast to the Southwest. winds associated with the weaker monsoon were Near to the equator their direction becomes nearly favourable for generating positive SST anomalies easterly. Occasionally these easterly winds change (deviation from climatological mean values) over their direction. They become southeasterly, south- BoB and AS during post monsoon season. These erly, northeasterly and again restoring to easterly provided extra fuel for formation of low pressure direction with height. This type of variation is systems over BoB and AS in this season. representation of presence of easterly wave. The wavelength of the wave is of order of 1000-2000 active Ne monsoon 2015 km in east west, north-south direction. The mass Thus the NE monsoon 2015 was active with succes- divergence occurs in the forward section of the sive formations of low pressure systems over AS and wave. Such divergence in the middle atmospheric BoB. A low pressure system formed over the AS levels (2-6 km) provides additional lifting of mois- which intensified into a depression on November ture for formation of deep convection. 7 and turned into the extremely severe cyclonic storm ‘Megh’ on November 8. It moved towards heavy rainfall and flooding the west and hit the Oman coast on November 10. Deep convection (cloud tops reaching 10-12 km During the same period a low pressure system was in the vertical) produced very heavy (more than developed over BoB near Tamil Nadu coast which 130 mm/day) to extremely heavy (more than 200 intensified into a depression on November 8 and mm/day) over Chennai and surrounding area had landfall north of Chennai on November 11. on November 17 and December 1 which caused On November 15, another low pressure system flooding over the region.
24 November - December 2015 . GeoGraphy aND you
Fig. 4: Omega field over Chennai region
Omega*100 (12-14 N & 79-81 E) 100
200
The Omega field over the Chennai 300 region from November 16 to December 1 indicates a high degree of upward motion which is associated 400 with heavy rainfall. Negative values indicate upward motion. Omega fields are plotted to describe vertical motion in the atmosphere. The 500 ‘Omega equation’ used in numerical weather models is determined by the amount of spin (or large scale rotation) and warm (or cold) advection 600 present in the atmosphere. On a weather forecast chart, high values of Omega (or a strong Omega field) relate to upward vertical motion 700 (UVV) in the atmosphere. If this upward vertical motion is strong enough and in a sufficiently moist airmass, precipitation results. 800
900
1000 16 Nov 21 Nov 26 Nov 1 Dec 6 Dec 11 Dec
-18 -15 -12 -9 -6 -3 -0 3 0
Source: National Centre for Environmental Prediction (NCEP) Figure 7: Omega field over Chennai region from 16 November to 1 December. Negative values indicate upward motion. Fig. 3 shows Kalpana satellite picture on km) occurred on November 16-17, November November 16 in the visible channel.Dr. S. The G. Narkhedkar, thick 30-December DR. S. B. Morwal,1. These Dr. caused B. Padma extremely Kumari heavy and Dr. R. Mahesh Kumar of IITM provided white cloud mass over Chennai indicatesdata and exist-figures forrainfalls the article. at Chennai and surrounding region ence of a deep convection. Along with satellite resulting in flood. cloud pictures, deep convection isDr. identified J. R. Kulkarni by Summarising, persistent rain in Chennai during the verical distribution of verticalExpert velocity Team in the WMRWMO November-December was the results of unique atmosphere. Generally velocity is measured in combination of high BoB SSTs (positive anomalies units of cm or mm/sec. In meteorology,Ex-Advisor it hasIITM, duePune to EL Niño effect), prevailing stationary pres- been found useful to measure in terms of pressure sure trough at the surface and passage of easterly change ‘pascals/sec’. Fig. 4 shows Omega field over waves. Chennai region from November 16 to December 1. Negative values indicate upward motion. Deep The author is Head, Expert Team, WMRWMO,6 Ex-Advisor IITM, Pune. [email protected] upward motion extending up to 250 hPa (~ 11
GeoGraphy aND you . November - December 2015 25 INDIA’s | VARIANT WeATheR Floods By Staff RepoRteR Floods refer to the overflowing of a river or water body beyond its normal confines. They may take the shape of flash floods, surface floods, rapid onset or slow onset floods, depending on the manner of their occurrence.
26 November - December 2015 . GeoGraphy aND you In July, 2010, 23,000 people were affected and 48 people died due to flash floods in Kerala, following, which the State put in place 24-hour control rooms in all districts to track floods and provide early warnings to the vulnerable population.
GeoGraphy aND you . November - December 2015 27 simplistic definition of flood may Types of floods be the overflowing of the normal Floods may be caused due to various reasons. On confines of a stream or other water the basis of their manner of occurrence, floods body. The events leading to it may be are classified into various sub types. Flash floods complex, caused by a combination occur within a very short time (2-6 hours) as a of heavy rainfall and rivers/water body dynamics, result of heavy rainfall, when a levee or dam Awhich can happen at any time of the year. has breached, or after a sudden release of water The US National Oceanic and Atmospheric by a debris or ice jam, as in glacial lake outburst Administration (NOAA) defines floods as “An phenomenon. Sometimes, intense rainfall from overflow of water onto normally dry land. The slow moving thunderclouds can also cause floods. inundation of a normally dry area caused by Flash floods are the most destructive since there rising water in an existing waterway, such as a is usually no warning, thus no preparedness, river, stream, or drainage ditch.” According to the taking people by surprise. Rapid onset floods are standard definition of floods, introduced by the similar to flash floods, but take a little more time Australian government in 2011, floods are “the to develop and last for just a day or two. The large covering of normally dry land by water that has amount of water dispersed may become difficult escaped or been released from the normal confines to manage. However, these do not surprise people of: any lake, or any river, creek or other natural the way flash floods do. Slow onset floods result watercourse, whether or not altered or modified; or when slow rise of water in channels and water any reservoir, canal, or dam. bodies lasts for days and weeks and spreads over Floods generally develop over a period of many kilometres. These generally occur in flood days, when excess rainwater above the carrying plains. Coastal floods affect coastal areas or capacity of the channel spreads over the land next areas close to the sea shore when a heavy storms, to it (‘floodplain’). However, they can also happen combined with high tides can cause sea levels to very quickly with heavy rain inundating the basin rise above the normal, forcing sea water into the in a short period. These ‘flash floods’ occur with land and hence, causing coastal flooding. Surface little or no warning and can lead to huge loss of floods also known as pluvial floods occur on dry human lives. lands when heavy rainfall creates a flood event Coastal areas are also at risk from sea flooding, independent of an overflowing water body. when storms and cyclones cause storm surges, Floods are primarily caused by rains that exceed bring in walls of seawater onto the land. The the capacity of the drainage system. Heavy rain worst cases of flooding may occur if there is a over a very short period can result in floods since combination of storms, ‘spring tides’ and low the massive amount of water cannot percolate atmospheric pressure. into the soil. At other times, moderate rain spread Floodwater can seriously disrupt public and over a long period can also result in floods. Also, personal transport by cutting off roads and railway rivers overflowing their banks when there is more lines, as well as communication links when tele- water upstream than usual, can result in floods. phone lines are damaged. Floods disrupt normal Strong winds in coastal areas can carry seawater drainage systems in cities, and sewage spills are on to coastal lands and cause flooding. The situ- common, which represents a serious health hazard, ation worsens if the winds carry rain. At times, a along with standing water and wet materials in tsunami can cause sea water to flow inland into living spaces. Bacteria, mould and viruses, cause coastal habitations. Dam or embankment breach disease, trigger allergic reactions, and continue to can cause floods when man-made blocks mounted damage materials long after a flood. to hold water, give way. At times, excess water inten- Although floods can distribute large amounts tionally released from the dam to prevent it from of water and suspended sediment over vast areas, bursting—especially during heavy monsoons, can restocking valuable soil nutrients to agricultural also cause floods. Moreover, ice that is accumulated lands; in the present scenario, with poor soil in winter remains frozen until summer after which management practices and rapid urbanisation, it suddenly melts with the rise in temperature. This floods only contribute to loss of livelihoods. It erodes snow-melt causes massive movement of water into large tracts, ruins crops, destroys agricultural land / places that are usually dry and can be termed as a buildings and drown livestock and humans. snow-melt flood.
28 November - December 2015 . Geography and You Chennai has a drainage system Pradesh. Rivers such as Jhelum, Sutlej, Beas, Ravi that isn’t functional, creeks and and Chenab are flood prone. The Central and Peninsular river basins of Narmada, Tapi, Chambal culverts that are blocked and and Mahanadi are flood prone too. Heavy floods often occur in the Godavari, Krishna, Pennar and an administration that fails to Cauvery. ensure timely desilting. analysis of flood affected states in 2015 assam: According to the Assam State Disaster Management Authority (ASDMA), over 12000 urban flooding villages in 17 districts of the State were affected by Until recently, any pre-emptive strategy always several waves of floods caused by the Brahmaputra, focussed on riverine floods and flooding of rural Jia Bharali, Dhansiri and Kopuli in early Septem- tracts. Although urban flooding has occurred ber 2015. The floods affected 12,68,770 people and in the past, it is only now that it is recognised as inundated 92,820 hectares of cropland. a phenomenon that can debilitate vast popula- One of the most flood-prone regions of India, tions and destroy infrastructure. According to Assam suffers from regular floods every year owing the National Disaster Management Authority, to its unique topographical and geographical situ- (NDMA) “urban flooding is significantly different ation. The flood prone area of the State as assessed from rural flooding as urbanisation leads to devel- by the Rastriya Barh Ayog (RBA) is 31.05 lakh oped catchments which increases the flood peaks hectares against the total area of the State which from 1.8 to 8 times and flood volumes by up to six stands at 78.523 lakh hectares. This is about 9.40 times”. Encroachments over natural watersheds, per cent of the total flood prone area of the country. and drainage channels in major Indian cities has In the post-independence period, Assam has resulted in several major floods, such as those faced major floods in 1954, 1962, 1972, 1977, 1984, in Ahmedabad in 2001, Delhi in 2002 and 2003, 1988, 1998, 2002, 2004 and 2012. Almost every Chennai in 2004, Mumbai in 2005, Surat in 2006, year three to four waves of flooding ravage Assam. Kolkata in 2007, Jamshedpur in 2008, Delhi in 2009 Average annual loss due to floods in Assam is to and Guwahati and Delhi in 2010 , besides the 2014 the tune of INR 200 crore. As the Water Resources Srinagar, and 2015 Chennai floods. Division of the Government of Assam points out, The Mumbai floods of 2005 were an eye-opener, the two major rivers of Assam—the Brahmaputra and saw NDMA release the urban flood guidelines and the Barak and the 50 tributaries that feed them, in 2008. However, failure to tackle the root cause leave the State vulnerable to floods every year. of such disasters has resulted in repeated debacles. Additionally, the Assam valley gets affected by cloudbursts and heavy rains in the upper reaches of Flood prone regions of India its rivers in Meghalaya and Arunachal Pradesh, as In India, an average of 40 million hectares or in 2004 and 2014, respectively. 12 per cent of the total land is flood prone, as per Maharashtra: Heavy rains and ensuing floods in the India Disaster Knowledge Network, of the north-eastern areas of Maharashtra left at least five SAARC Disaster Management Centre. Every year, people dead in the city of Nagpur in 2015, according about 8 million hectares in India is affected by to National Oceanic Atmospheric Administration floods—several hectares of crops lost, along with a (NOAA) reports on August 14, 2015. Roof top few hundred lives, with millions rendered home- rescue by IAF helicopters saved 1,500 people, par- less. The most flood prone region of the nation is ticularly those marooned in Pipli village. the basin of the Himalayan rivers covering parts More than two lakh hectares, about 6.5 per cent, of Punjab, Haryana, Himachal Pradesh, Delhi, of land area in Maharashtra is prone to floods and Rajasthan, Uttar Pradesh, Bihar and West Bengal Paturtaluka in Akola district has the largest flood (Fig. 1). The Kosi and the Damodar are the main prone area in the State. Nanded and Nashik are rivers causing floods here. Another flood prone frequently affected by floods in the monsoons as region is the north-western river basin covering are the basins of Tapi, Wardha and occasionally the the states of Jammu and Kashmir, parts of Punjab, Pen-Ganga. Haryana, Western Uttar Pradesh and Himachal Maharashtra has a long history of floods.
GeoGraphy aND you . November - December 2015 29 The 1996 flood in the State destroyed 2,899 lakh All major rivers in the State pass through a wide hectares of land, killing 198 people. In September, stretch of the very flat terrain before reaching 2005, the flood claimed approximately 1,200 lives the sea. These flat lowlands, where the cities of and affected 20 million people. Much of Mumbai’s Ahmedabad, Surat and Bharuch are also located, drainage system collapsed and as the flood waters are prone to flooding. subsided. There was a continued risk from water- In 2005, Gujarat flood was caused by heavy borne diseases, which had caused an estimated 150 monsoon rains in June affecting many parts of the deaths in the weeks following the flooding. State. The death toll stood at 123 while more than Manipur: More than six out of Manipur’s nine dis- 250,000 people were evacuated. tricts were flooded following heavy rainfall in the Rajasthan: Flood affected the State in late July last week of July, 2015. All 12 houses of the village of 2015, resulting in 28 deaths. The districts of Jalore, Joumul in Chandel district were buried and waters Jhalawar, Baran, Sirohi, Barmer and Dungarpur of all major rivers of the State rose to an alarming were the worst affected. World Meteorological level according to media reports. The European Organisation (WMO) reports say that Bikaner Commission’s Humanitarian aid and Civil Protec- received 363.5 mm of rain in 24 hours on August tion department (ECHO) termed the floods as the 2, 2015. worst in 200 years. Thousands of hectares of paddy Though most parts of Rajasthan receive scanty fields and a large number of fish farms were washed rainfall, the State has a history of floods and inunda- away, with the Sugnu-Serou Lamkhai road being tions, mostly along the basins of rivers like Luni and rendered unusable. Chambal. Major portions of Bharatpur districts Most flood prone areas of Manipur are those falling under the basin of River Banganga, and the where dams are built. Imphal, Thoubal, Bishnupur, basins of River Ghaggar in Sriganganagar are prone Chandel and Churachandpur are frequently to floods. Barmer district is the most affected area flooded. Almost two third population of Manipur in Rajasthan. A total of 3.26 million hectares (about is concentrated in the Manipur Valley (constituting 10 per cent) of the State is flood prone. 8.2 per cent of the State’s land), with rivers from In 1981 heavy rainfall caused flooding in Jaipur, the hills flowing into the valley, which makes it Tonk, Nagaur and Sawai Madhopur and caused even more disaster prone—leading to flash floods extensive damage to property and life. Barmer almost annually. received 720 mm of rainfall in 1990 and in 1994, In the last two decades, beginning from 600 mm rain fell over the district. In 2006, Barmer September 1997, breaches of embankments took was deluged with 750 mm of rainfall in the last place at four different places in Manipur, which week of August which is five times the district’s damaged 4965 houses. In September 1999, inces- average annual rainfall. Over 800,000 of Barmer’s sant rainfall between August and September two million people were reportedly affected due to affected southern parts of the valley, damaging the floods. 7,300 houses and 15,300 hectares of paddy fields. In Odisha: With three rivers—Subarnarekha, August 2002, severe flood occurred which caused Budhabalang and Baitarni overflowing during embankment failures at 59 places. About 10,000 July 28-30, 2015, flooding affected 240,000 people houses and 20,000 hectares of paddy fields were across 282 villages in five districts of Keonjhar, affected. Jajpur, Mayurbhanj, Balasore and Bhadrak. In Gujarat: A wave of thunderstorms hit Gujarat August, flooding was reported in seven districts on June 21, 2015 and killed dozens of people and affecting over 480,000 people across 644 villages. several Asiatic lions in Gir. Waterlogging affected The 482 km long of coastline of Odisha exposes crops in more than two lakhs hectares. Further the State to flood, cyclones and storm surges. About rains in July killed at least 72 people and over 81,000 9 per cent, or 1.40 million hectares of the State’s land cattle. The worst affected districts were Banaskan- is prone to flooding. Rivers such as the Mahanadi, tha, Patan, Rajkot and Kutch causing three deaths Subarnarekha, Brahmani, Baitarni, Rushikulya, in each district. Vansadhara and their many tributaries are prone About 1.39 million hectares of Gujarat’s land to floods. (about 7 per cent) is prone to flooding. Owing to A devastating flood in 2006 affected 18912 its geo-climatic, geological and physical features, villages and 67.39 lakh people and destroyed 4.90 Gujarat is vulnerable to all-major natural hazards. lakh hectare of crop. 105 persons lost their lives.
30 November - December 2015 . Geography and You Fig. 1: India’s flood prone areas
Jammu & Kashmir
Himachal Pradesh
Punjab Arunachal Haryana Sikkim Pradesh Chandigarh Assam Rajasthan Delhi Uttarakhand Nagaland Bihar Meghalaya Uttar Pradesh West Bengal Manipur Gujarat Jharkhand Tripura Mizoram Madhya Pradesh Chhattisgarh Maharashtra
Odisha
Goa Andhra Pradesh Karnataka
Kerala Tamil Nadu
Flood prone area Map not to scale Source: National Institute of Hydrology, Roorkee
Floods in 2007, 2008 and 2009 affected 5, 19 and 15 30,000 mud houses were destroyed. In 2007, heavy districts, respectively out of 30 districts resulting in rain from tropical depression in the Bay of Bengal heavy losses to life and property. caused flooding leading to 51 deaths and affecting West Bengal: Cyclone Komen hit West Bengal 3.2 million people. on July 30, 2015 and brought heavy rainfall and flooding across many southern districts of the Tamil Nadu: Flash floods in Virudhunagar district State. Nearly 10,000 villages in 12 districts were killed six persons in May, 2015. Another flash flood affected. Local authorities said that 200,000 hit the Sathuragiri Hills, near Watrap, about 80 people had to be evacuated and housed in 1,537 km south west of Madurai city, sweeping away relief camps. As many as 38,000 homes were eight persons who had gathered to worship at the fully damaged and over 200,000 homes were left Sundara Mahalingam Temple. But a month long partially damaged. spell of rain—the worst in a hundred years, starting Approximately 55.8 per cent of West Bengal is November 4, 2015, left Chennai totally paralysed, susceptible to floods. The State has 37,660 sq km of with several crores worth of property destroyed. flood prone area spread over 111 blocks where the From the flood hazard map of India (Fig. 1), it is total geographical area of the state is 88,752 sq km. seen that no area in Tamil Nadu’s 32 districts falls in Furthermore, major flood producing rivers beyond the risk zone. In Chennai Metropolitan Area, there the state’s jurisdictional limits, viz, Teesta, Torsa, are only few areas along the rivers and canals and Joldhaka, Kaljani etc. from Sikkim and Bhutan are low-lying areas, that are susceptible to flooding/ mainly responsible for disastrous flash floods in inundation during heavy storms. North Bengal. A total of 347 people died due to floods in Tamil In 1991, flash floods damaged 35,000 houses. Nadu in 2015 and economic losses were calculated In 2000, flash floods triggered incessant torrential at INR 200 billion. For the month of November, storms with 1262 fatalities besides dislocating Chennai reported 1,024 mm (40.31 inches) of thousands of people. rain, more than 300 per cent of the normal rain- Heavy rains in 2005 caused floods in many fall expected for the entire month. December parts of Bengal. About 3,000 coastal villages were continued this wet pattern as more than 300 mm inundated and 60,000 huts washed away. Simi- (12 inches) of rain fell in Chennai on the first day of larly, in 2006, heavy rainfall caused 50 deaths and the month.
GeoGraphy aND you . November - December 2015 31 INDIA’s | VaRIaNT Weather ://www.asiatimes.com.au/
The National Disaster Response Force (NDRF), p Army and Indian Air Force (IAF) personnel were deployed to carry out rescue and relief operations in rain-hit Chennai. Photo courtesy: httcourtesy:Photo
32 November - December 2015 . Geo graphy and You The inevitable yet preventable disaster The Chennai 2015 Floods
Geo graphy and You . November - December 2015 33 By Surya Parkash The Chennai floods in November-December 2015 are a wake-up call for us all. It is high time we stopped all unregulated unauthorised illegal encroachments and constructions over natural watercourses, creeks, estuaries, ponds, lakes and marshlands in our greed to over-exploit our natural resources under the ruse of development.
limatic conditions and processes the sedimentary and biotic deposits. change over space and time. Nearly However, a common man’s concerns about 70 per cent of the earth’s surface is atmospheric conditions and processes relate to covered by oceans. Both land and short-term weather changes over a daily, weekly oceans have different characteristics or seasonal basis. It primarily pertains to their in terms of their heating and cooling capacities, dependency on natural weather for day to day Cresulting in differences in atmospheric pressure, activities like livelihood, agriculture, fresh water temperature and relative humidity. In addition resources, and more. Extreme weather conditions to the massive ice-sheets over the Arctic and the in the form of extreme heat or cold waves, urban Antarctic, the warm and cold oceanic currents heat islands, high intensity or long duration heavy are also responsible for moderating the climate in to very heavy rainfall with uneven distribution or different latitudes, as also the El Niño Southern delayed/advanced precipitation, acid rain, deep Oscillation (ENSO). depressions resulting in high wind speeds/squalls, However, land use changes through human cyclones, rapid glacial melting and retreat brought activities have affected the natural weather systems, by critical changes in weather conditions can turn changing their characteristics as well as the rate these phenomena into hazards and disasters. of change. Changes in weather systems over long The Indian climate is dominated by a monsoon periods, whether due to natural or anthropogenic season that provides about 80 per cent of the causes, are usually termed as climate change. Gener- annual rainfall, generally extending from June ally speaking, climate is a long term phenomena, to September. The period between October and measured over a period of at least 30 years, that December is normally referred to as the north-east- describes the average weather conditions and monsoon season, which affects parts of peninsular processes in a certain region in terms of pressure, India. It is also known as the ‘post-monsoon season” temperature, precipitation (including rain, snow or ‘retreating south-west monsoon season’. The and hail-storms), relative humidity, wind speed north-east monsoon season is the major period of and direction. Environmental studies related to rainfall (40 to 60 per cent of the annual rainfall) in climate, focus on air composition including green- coastal Andhra Pradesh and Tamil Nadu. About 20 house gases, suspended particulate matter, impacts per cent of the annual rainfall in Kerala, Karnataka of sunlight and cosmic rays and the ozone hole. and Lakshadweep is also attributed to north-east While a meteorologist or climatologist carries out monsoon. It is also noted that the maximum rain- such studies for periods varying from a few years/ fall in this season occurs between late night and decades to centuries over which scientific obser- early morning spells of about 3-4 days, often being vations and instrumental data are often directly associated with a depression or cyclone. available; geologists and paleoclimatologists study The Intergovernmental Panel on Climate climate changes over longer periods of time, that Change (IPCC) in its 5th Assessment report has is, in terms of centuries and millennia, by going discussed the emergent risk and key vulnerabilities through the earth’s historical records, particularly due to climate change and proposed an approach
34 November - December 2015 . Geo graphy and You At one point of time, even a marginally heavy rainfall. Most of its drains Chennai had 650 water are clogged with silt, garbage and plastics resulting in a much lower actual carrying capacity than the bodies - now there are expected discharge. less than 30 lakes. C hronology of recent weather events, impact and response A depression over the southwest Bay of Bengal on to prevent, adapt and mitigate these risks. During the morning of November 8, 2015 intensified into the 3rd World Conference on Disaster Risk Reduc- a cyclone, ‘Rovan’ and on November 10, it crossed tion during March 14-18, 2015, UNISDR adopted the northern part of the Tamil Nadu coast between the Sendai Framework for Disaster Risk Reduc- Puducherry and Cuddalore. Heavy to very heavy tion (2015-2030) that also focussed on ecosystem rainfall resulted over many parts of Tamil Nadu, based disaster risk reduction and highlighted four Andhra Pradesh and Karnataka, with some parts priority actions with seven guiding principles. of Tamil Nadu reporting as much as 550 mm of These priority actions were, rainfall between November 9 and 16. ◆ Understanding disaster risk, On November 23, 2015, another spell of heavy ◆ Strengthening disaster risk governance to rainfall caused fresh floods in the coastal districts manage disaster risks, of Tamil Nadu, Andhra Pradesh and Puducherry. ◆ Investing in disaster risk reduction for resilience; Neyveli received 450 mm of rainfall between and 8:30 am and 5:30 pm, causing water to pool. On ◆ Enhancing disaster preparedness for effective November 28-29, another system developed and response and to ‘build back better’ in recovery, reached Tamil Nadu on November 30, bringing rehabilitation and reconstruction. additional rain and flooding. Tambaram saw 490 mm of rain in 24 hours on December 1, 2015. C limatic conditions at Chennai According to data from IMD, Chennai received Chennai, the capital city of Tamil Nadu, is located 1,522.7 mm of rain between December 1 and 4 as in the south-eastern India on the shores of the Bay against a normal of 662.6 mm (130 per cent excess), of Bengal. Together with 16 municipalities, 20 Cuddalore 1,041.5 mm against a normal of 550.1 towns and 214 village panchayats, the metropolitan mm (89 per cent excess), Kancheepuram 1,681.4 area of Chennai has about 9.19 million people. It is mm against a normal of 535.1 mm (214 per cent the biggest industrial and commercial centre in excess), Thiruvallur 1, 414 mm against a normal of south India. 496.9 mm (185 per cent excess), and Puducherry Due to it’s proximity to the sea, it has a low eleva- 1,406.1 mm against a normal of 673.5 mm (109 tion coastal zone with the Adyar and Cooum rivers per cent excess). The rains led to flooding across meandering through the city. These rivers are the entire stretch from Chennai to Cuddalore. connected through the Buckingham canal. Besides Stricken residents from Chennai, Kancheepuram the rivers, the city had about 650 small and big and Thiruvallur districts attempted to flee their water bodies at one point of time. However, most homes to safer places, with little success. Chennai of these lakes have disappeared or shrunk through airport had to be closed down, and re-opened only the years. As a result, the number of existing lakes on December 5, 2015. in Chennai stands at less than 30. The water courses Damages have been estimated at over INR of Chennai fall under the jurisdiction of Water 50,000 crore, with more than 450 deaths in Tamil Resources Division (WRD) of the Public Works Nadu, 81 deaths in Andhra Pradesh and two Department (PWD). deaths in the union territory of Puducherry. An Being close to the equator, Chennai has a hot and overnight discharge from Chembarambakkam humid climate. It receives most (about 50 per cent) of reservoir into the Adyar river became a watery its annual precipitation in October and November grave for people who were trapped. A power break- during the north-east Monsoon. The city has down during the floods killed 14 patients at a private inadequate provisions for storm water runoff with hospital. The Hindu, for the first time in its history, only 855 km storm water drains against 2,847 km could not publish a print edition on December 2, of urban roads, resulting in frequent flooding after 2015,. On December 2, 2015, Chennai was officially
Geo graphy and You . November - December 2015 35 The Chennai rainfall flooded extensive areas of the city including West Mambalam, Anna Nagar, Villivakkam, Vadapalani, Valasaravakkam, Nandamvakkam, Tambaram and Mudichur. Even the airport was affected and shut down for several days as its runway was flooded as it is built on the Adyar flood plains despite experts warning against it. I T declared a disaster area and the Coast Guard, the army, navy and air force were pressed into action
for rescue. A relief package of INR 1,940 crore was P courtesy:Photo announced by the Prime Minister even as relief camps were set up in Chennai, Kancheepuram threshold that can threaten the safety of the dam. and Thiruvallur. Insurance companies anticipate On December 1-2, it had reached its threshold claims worth at least INR 500 crore, with motor levels and was forced to release the excess water. insurance accounting for the bulk of the claims. In the wake of predictions of heavy to very heavy rainfall in Chennai by different agencies the Chem- Inevitability of this preventable disaster barambakkam reservoir could have systematically The Disaster Management Act 2005, envisages released water into the outskirts of the city so that preparation and implementation of disaster the lake could bear the load of the heavy rains management plans by the authorities at the district, during subsequent days. Similarly tanks along the state and national levels to ensure the safety of Adyar river could have also released some water life, economy and the environment. As per IMD prior to the heavy rains so that runoff could be records, rains were expected in Chennai between diverted and accommodated in them. October and December. The rains arrived on The last decade has seen Chennai embrace time. However, the unregulated and unscientific development through the building of malls, bus development over marshlands, lakes and ponds has terminals, mass rapid transit system, as also info- played havoc to the natural drainage system which tech, automobile and telecom complexes, most has either disappeared or reduced in capacity. of which are on marshlands, ponds, lakes and Hence, more run-off is expected after rains with drainage channels. This unregulated, haphazard, dysfunctional or insufficient drainage systems to unscientific development left the city vulnerable carry water. and exposed to the wrath of nature. In short, it was a Further, the Chembarambakkam reservoir level disaster waiting to happen, although preventable. was rising due to continuous rains in November. The standard operating procedures for main- The author is Associate Professor, Head of the Knowledge taining the level of water in the reservoirs require Management and Communication Division and Leader, systematic release of water from the sluice gates if World Centre of Excellence on Landslide Risk Reduction the expected rainwater is likely to cross the critical (ICL and IPL-ISDR). [email protected]
36 November - December 2015 . Geo graphy and You EVERY DAY IS EARTH DAY
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ReLeaSed In PuBLIc InTeReST on THe occaSIon of eaRTH day ceLeBRaTed on aPRIL, 22 IPPL © INDIA’s | VARIANT WeATheR
Droughts in inDia By Staff RepoRteR Drought is a deficiency in precipitation for a season or more, resulting in water shortage. Droughts may be meteorological, agricultural or hydrological. Depletion of tree cover can combine with scanty rains to increase the magnitude of a drought. Photo courtesy: courtesy: Photo
38 November - December 2015 . GeoGraphy aND you Fig. 1: Drought prone areas of India
Jammu & Kashmir
Himachal Pradesh Punjab Uttarakhand Haryana Delhi Arunachal Pradesh Sikkim Rajasthan Assam Nagaland Uttar Pradesh Bihar Meghalaya Manipur Tripura Gujarat Madhya Jharkhand Mizoram West Bengal Pradesh Chhattisgarh Maharashtra Odisha
Andhra Pradesh Karnataka Goa
Legend Source: Agro Economical Arid Research Centre Kerala Semiarid Tamil Nadu Subhumid (dry) Others Map not to scale
In 2015, 25 out of 27 districts were declared drought hit in Chhattisgarh. This was the sixth state to be declared as drought hit and the fourth to seek central aid.
GeoGraphy aND you . November - December 2015 39 rought is defined as a deficiency away into rivulets and thereon, into the sea. Under- in precipitation over an extended ground reserves, hence, fail to get recharged and period, usually a season or more, agricultural and hydrological drought follows. resulting in a water shortage causing Unlike earthquakes or cyclones, droughts can adverse impacts on vegetation, be predicted well in advance. Natural phenomena animals, and/or people. It is a normal, recurrent such as flowering of bamboo, intense flowering of Dfeature of climate that occurs in virtually all climate the Moringa tree, and the multiplying of the rodent zones, from very wet to very dry. A temporary population are indicators of drought. Besides, aberration from normal climatic conditions, a advanced instruments and technical know how drought can vary significantly from one region to can help meteorological scientists predict the another. Drought is different from aridity, which is quantity and duration of rainfall with a fair degree a permanent feature of climate in regions where low of accuracy. precipitation is the norm, as in a desert. monitoring of drought through early When is a drought declared? warning systems The Indian Meteorological Department (IMD) Since 1992, the India Meteorological Department defines a drought year as one in which the overall (IMD)’s Earth System Science Organisation (ESSO- rainfall deficiency is more than 10 per cent of the IMD) monitors the rainfall situation throughout long period average and more than 20 per cent of the year in different spatial scales (districts/states/ the agricultural area is affected. Because of the meteorological subdivisions and all India) on daily, interplay between a natural drought event and weekly/monthly/seasonal scales. Based on this various human factors, drought means different data, ESSO-IMD prepares rainfall reports for the things to different people. Drought can be of use of different state/central government agencies. various types (Fig. 2): Until 2012, ESSO-IMD was monitoring drought ◆ A meteorological drought is based on the degree using two most important drought indices viz. per of dryness (in comparison to ‘normal; or average cent deviation of rainfall from normal and aridity dryness) and the duration of the dry period. anomaly index (AAI). Since 2013, ESSO-IMD A drought generally follows a meteorological has started using the standardized precipitation drought. index (SPI) to monitor drought in various Indian ◆ An agricultural drought links various characteris- districts of India on a monthly scale, in accordance tics of a meteorological (or hydrological) drought with guidelines issued by the World Meteorological to an impact on agriculture, with precipitation Organization (WMO). shortages, soil water deficit, reduced ground Besides standard monthly and cumulative SPI, water or reservoir levels needed for irrigation, four weekly district SPI maps are computed and and so forth. prepared every week to monitor progress, starting ◆ Hydrological drought usually occurs following or ending of agricultural drought. In addition to the periods of extended precipitation shortfalls that SPI and AAI, the normalized difference vegetation impact water supply (stream flow, reservoir and index (NDVI) is also used in drought monitoring. lake levels, ground water), potentially resulting in The Central Water Commission, National Centre significant societal impacts. for Medium Range Weather Forecasting, National Remote Sensing Centre and National Rain-fed Why does it happen? Area Authority are other key agencies that provide The most common cause for drought is the failure early warning on drought. of rains. Consequently, there is not enough water Since 1967, the Drought Research Unit of the available through hand pumps, wells and other ESSO-IMD conducts studies on various aspects traditional sources that depend on underground of droughts in India, in collaboration with the reserves of water. Indian Council of Agricultural Research (ICAR), Apart from scanty rainfall, a number of other and provides medium range weather forecast based factors also adversely affect the magnitude of agro-advisories at district levels through its Agro- droughts. Depletion of green cover is one such Meteorological Field Units (AMFUs)(GoI 2010). factor. Rainwater falling over barren land is washed In addition, the National Agricultural Drought
40 November - December 2015 . GeoGraphy aND you Assessment and Monitoring System (NADAMS) Fig. 1: Flow chart illustrating the progression project provides near real-time information on of drought, and the relationship between meteorological, agricultural, and hydrological prevalence, severity level and persistence of agri- drought cultural drought at state/district/sub-district levels in 13 drought prone states. Natural Climate Variability
Precipitation deficiency High temperature, high winds, low The 2015 drought (amount, intensity, timing) relative humidity, greater sunshine, After a promising, forecast-defying start in June less cloud cover
and good rainfall in July, resulting in a better-than- Reduced infiltration, runoff, Increased evaporation Drought
deep percolation, and ground and transpiration Meteorological average sowing, the monsoon weakened end-July water recharge 2015 owing to a strong El Niño phenomenon that disrupted international weather patterns. By mid- Soil water deficiency September, the rainfall deficit had widened to as
Plant water stress, reduced Drought Agricultural much as 16 per cent, with the prolonged dry patch Time (duration) biomass and yield making it the worst monsoon in three decades, Reduced streamflow, inflow to barring the drought years of 2002 and 2009, as reservoirs, lakes, and ponds: reduced per reports in The Economic Times, September wetlands, wildlife habitat Drought Hydrological 14, 2015. The deficit was as high as 40 per cent in the agriculturally-rich northern states of Punjab, Economic Impacts Social Impacts Environmental Impacts Haryana and Uttar Pradesh, raising concerns Source: drought.unl.edu regarding soil moisture and hence, the health of the winter crops. About 700 farmers committed suicide in Telan- As per IMD data, India received 6 per cent gana amid mounting debts and poor production lower rainfall than usual, but in some areas, the of paddy, maize and cotton. With drastic reduction deficit was as high as 57 per cent. Meanwhile, the in water levels, farmer bodies pressed the panic southernmost and northeastern regions received button. Madhya Pradesh declared 35 out of 51 adequate to very heavy rains resulting in massive districts in the State as drought affected and sought floods. Thus, the country was faced with contradic- an initial central assistance of INR 2,400 crore. tory weather patterns spanning two extremes. The State also sought an additional INR 300 crore Uttar Pradesh declared 44 of its 75 districts for drinking water supply and INR 750 crore for ‘drought-hit’ and sought INR 6,000 crore as central waiving off interest payments on loans. Overall, assistance for relief, having suffered a 60 per cent the State recorded a 12 per cent rainfall deficit, deficit in rainfall. Haryana declared a drought on according to the IMD, affecting 4.4 million hectares September 2 and sought INR 4,830 crore in central of farmland, and estimated crop losses amounting assistance, since it faced an overall rain deficit of 54 to INR 13, 846 crore. per cent, with 10 out of its 21 districts being drought In Maharashtra, for the first time in a hundred hit. According to the Central Ground Water years, farmers were unable to sow the Rabi (winter) Board(CGWB), Haryana has been overexploiting crop, thanks to the region’s worst dry spell in the its groundwater reserves by over 9 per cent. Gujarat period. The Marathwada region received just a third faced a deficit ranging between 8-60 per cent except of its average rainfall until September, according to for a couple of districts in north Gujarat and one in IMD reports. Latur was the worst affected district, Saurashtra. As on September 9, 2015, water storage followed by Parbhani, Osmananabad, Jalna, Beed, stood at 16,262 million cubic meters (MCM) in 203 and Aurangabad. Odisha faced a 13 per cent deficit irrigation schemes including Sardar Sarovar, down in rainfall until August 31, 2015, with six out of its 154 MCM from corresponding levels last year. 30 districts facing a deficit as high as 40 per cent. The Andhra Pradesh government declared Bolangir, Koraput, Kandhamal, Khorad, Nayagarh 196 mandals in seven districts drought affected. and Puri were the worst-affected. Karnataka too The majority of the drought hit mandals are in was faced with a 34 per cent deficit in rainfall in 27 Rayalaseema, with some in the coastal districts out its 30 districts and demanded INR 3050 crore of Srikakulam, Prakasam and Nellore. The State in central assistance from the National Disaster suffered a 5.4 per cent deficit in rainfall in 2015. Response Fund.
GeoGraphy aND you . November - December 2015 41 INDIA’s | VARIANT WeATheR Fig. 1: Map Shows Absolute Maximum Temperature (OF) in India (May 24-20, 2015)
By Staff RepoRteR Heat Wave In the last few decades, there has been an increasing incidence of high-humidity heat waves. Human-induced climate change has been proved to be the major factor behind the increased frequency and severity of heat waves all over the world.
heat wave is generally perceived as a period of abnormally hot weather. The World Meteorological Organi- zation (WMO), however, defines a heat wave as five or more consecutive days during which the daily maximum tempera- Ature exceeds the average maximum temperature by five degrees Celsius. how a heat wave is declared in India
In India, scientists declare a heat wave when the Map not to scale temperature rises five to six degrees Celsius above normal—where normal is 40 degrees Celsius or 4.4 10 15.5 21.1 26.6 33.2 37.7 43.3 48.8 below. There are no minimum number of days Source: climate.gov for such temperatures to linger for it to qualify as a heat wave. If the temperature climbs to more than For much of May, 2015, parts of India were gripped in an seven degrees Celsius above the normal maximum intense heat wave that saw the mercury rising above 43°C. temperature, the heat wave is classified as severe. Temperatures were hot enough (over 44°C) to melt road tar in New Delhi. The heat waves was later declared as the The following are the criteria for a heat wave, worst heat event in a decade by the India Meteorological as defined by India Meteorological Department Department. (IMD) and used by the National Disaster Manage- ment Authority (NDMA) for declaring a disaster: When actual maximum temperature remains Heat wave need not be considered till maximum 45oC or more irrespective of normal maximum temperature of a station reaches atleast 40oC for temperature, heat wave should be declared. plains and atleast 30oC for hilly regions. For a heatwave, there has to be a five to six degree effects in India centigrade departure from normal. For a severe Higher daily peak temperatures and longer, heat wave, there has to be a seven degree centi- more intense heat waves are becomingly increas- grade or more departure from normal. ingly frequent globally. India too is experiencing
42 November - December 2015 . GeoGraphy aND you increased instances with a devastating impact been the unusual north-westerly winds. These on human health thereby increasing the number anomalous north-westerlies overpowered the of heat wave casualties. In the past three to four moist southerly winds that typically come off the decades, there has been an increasing trend in water and kept pre-monsoon showers offshore. high-humidity heat waves, which are characterised This deviation from normal wind trends allows by the persistence of extremely high night-time hot air from desert areas to the northwest to spread temperature. The combination of high humidity over much of the country. A meteorologist from the and high night-time temperature can make for IMD termed this phenomenon a ‘heat bomb’ from a deadly pairing, offering no relief and posing Pakistan as that is where the hot air mass had origi- a particular threat for the elderly. Extreme heat nated from. Eventually though, the north-westerly events are responsible for more deaths annually winds relaxed and turned south-westerly and the than hurricanes, lightning, tornadoes, floods, and Indian Monsoon arrived around June 5th in India’s earthquakes combined. south-western state of Kerala. Globally, extremely warm nights that used to come once in 20 years now occur every 10 years. Increasing heat waves And extremely hot summers, those with more Intergovernmental Panel on Climate Change than three standard deviations above the historic (IPCC) has warned of more frequent and intense average, are now observed in about 10 per cent of heat waves in Asia (including India) that will the global land area, compared to 0.1-0.2 per cent negatively impact vulnerable communities and for the period 1951-1980. increase mortality. In a future with high carbon These trends cannot be explained by natural emissions, it is likely that a maximum temperature variation alone. Only with the inclusion of human that occurs once every 20 years will at least double influences can computer models of the climate in frequency (to a 1-in-10-year event) by the end of reproduce the observed changes. These changes the 21st century. Decadal variation of heat waves / include an increase in the number of warm nights, severe heat waves in India is shown in Fig 2. unusually hot days, and heat waves, as well as warming of the warmest night of the year, warming 2015 heat Wave: Lessons of the coldest nights and days of the year, and Despite 2015 being the one of the worst heat wave warming of the hottest day of the year. episode, timely interventions and ensuring of In 2015, a heat wave in India claimed more than basic measures in Gujarat and Odisha kept casual- 2,300 lives according to reports from the Press Trust ties low. As against this, Telangana and Andhra of India. Most deaths occurred in the southern Pradesh with a lack of awareness about the symp- states of Andhra Pradesh and Telangana, where toms of heat-related illness and a complete lack of dehydration and heat stroke have been the biggest proactive effort by the respective state governments threats. The absolutes maximum temperature in saw thousands succumb to the heat. The number of India between May 24 and June 20 is shown in Fig 1. deaths due to heat waves / severe heat waves since 1970 is shown in Fig 3. effects of heat wave on health Gujarat issued public advisories through As the NDMA points out, the health impacts of newspapers and public broadcasting services the heat waves typically involve dehydration, heat moment the heat wave set in. Hoardings were cramps, heat exhaustion and/or heat stroke. Heat placed at various places and pamphlets were cramps cause Edema (swelling) and Syncope distributed, to boost public awareness about heat (fainting) generally accompanied by fever below stress prevention during extreme heat events. The 102oF. Heat exhaustion can result in fatigue, campaign also aimed to inform the public about weakness, dizziness, headache, nausea, vomiting, heat stress first aid. muscle cramps and sweating, while heat stroke In fact, following the unprecedented heat wave can cause body temperatures to rise above 104oF in 2010, Gujarat has been the first state to introduce accompanied with delirium, seizures or coma. a Heat Action Plan in South and South East Asia. This is a potentially fatal condition. Gujarat’s Heat Action Plan (HAP) , introduced in 2013, concentrated on three main aspects; causes ◆ building public awareness and community One of the causes of these extreme heat waves has outreach;
GeoGraphy aND you . November - December 2015 43 Fig. 2: Decadal variation of the all India (sum of all the stations) heat wave/severe heat wave days during the hot weather season (March-July) for the period 1961-2010
Decadal Variation of All India HW/SHW days 800
700 The graph alongside shows increasing 600 trend of heat waves and severe heat waves in the decadal period. Further, 500 as per the 2016 IMD report on annual climate over India for 115 years (1961- 400 2015), the linear trend per 100 years in the annual mean land surface air HW/SHW days/year HW/SHW 300 temperature anomalies averaged over o 200 India was 0.63 C.
100
0 1961-70 1971-80 1981-90 1991-00 2001-10 HW SHW Decade Source: D S Pai et al., ‘Long term climatology and trends of heat waves over India during the recent 50 years (1961-2010)’, 2013, Mausam.
Fig. 3: Number of deaths due to heat wave/severe heat wave: 1970-2015
L - La Niña E - El Niño 2400
2100 E
1800 L 1500
Number of deaths 1200 E E
900 L L L 600 L
L 300 E E E L L E L L E E E 0 1970 1974 1978 1982 1986 1990 1994 1998 2002 2006 2010 2014 2018 The data regarding deaths related to the heat wave events were collected from reports of disastrous weather events published by IMD and various media reports. Highest number (2249) of deaths related to heat wave was reported in 2015 followed by 1681 in 1998. It is seen that the recent decade (2001-2015) registered the highest number of deaths due to heat wave events compared to previous three decades. Chaudhury et al., (2000) observed mortality associated with heat wave to be more during years followed by El Niño events than El Niño years. The number of deaths related to heat waves in years following El Niño years (1983, 1988, 1995, 1998, 2003, 2005 and 2010) were more than that during the El Niño years.
◆ initiating a simple early warning system; and, Gandhi Rural Employment Guarantee Scheme ◆ capacity-building of health care professionals. during peak noon hours; water kiosks were set Odisha too has learnt from its earlier experi- up in all public places; ambulance networks ences of heat waves. Following a disastrous heat were boosted; hospitals and dispensaries were wave in 1998, the State took prompt measures to equipped with life-saving medicines for emer- limit casualties in 2015. Timings of schools and gencies, etc. The print and electronic media and colleges were changed, so that classes ended by civil society organisations were widely used to 12 noon; directives were issued so that no labour build awareness on heat-related emergencies, and work was to be undertaken under the Mahatma first aid.
44 November - December 2015 . GeoGraphy aND you Term Power raTing
India’s Variant Weather ■ 1 to 5 Correct - Informed ■ 6 to 8 Correct - Knowledge bank ■ 9 to 10 Correct - Encyclopaedia
1. Baroclinic instability zones in historic data. It can also be used to determine periods atmosphere of anomalously wet events. The SPI is not a drought Ans. b: The Baroclinic areas in atmosphere are prediction tool. generally found in the mid-latitude/polar regions whereas the Barotropic zones of the Earth are generally found in the central latitudes, or tropics. 6. Dipole Mode Index Ans. b: The Dipole Mode Index is an indicator of the east-west temperature gradient across the tropical 2. Madden-Julian Oscillation Indian Ocean, linked to the Indian Ocean Dipole or Ans. b: is the largest element of the intra-seasonal Zonal Mode. variability in the tropical atmosphere. In 1971 Roland Madden and Paul Julian stumbled upon a 40-50 day oscillation when analysing zonal wind anomalies in the 7. Indian Ocean Dipole tropical Pacific. The MJO, also referred to as the 30-60 Ans. b: The Indian Ocean Dipole, also known as the day or 40-50 day oscillation, turns out to be the main Indian Niño, is an irregular oscillation of sea-surface intra-annual fluctuation that explains weather variations temperatures in which the western Indian Ocean in the tropics. becomes alternately warmer and then colder than the eastern part of the ocean. 3. Flood Ans. b: An overflow of a large amount of water beyond 8. El Niño Southern Oscillation its natural limits, especially over a normally dry land. Ans. b: El Niño Southern Oscillation (ENSO) is an irregularly periodical climate change caused by varia- tions in sea surface temperatures over the tropical 4. Hydrological Drought eastern Pacific Ocean, affecting much of the tropics and Ans. b: Hydrological drought is associated with the sub-tropics. The warming phase is known as El Niño effects of periods of precipitation (including snowfall) and the cooling phase as La Niña. shortfalls on surface or subsurface water supply (i.e., stream flow, reservoir and lake levels, ground- water). The frequency and severity of hydrological 9. Western Disturbances drought is often defined on a watershed or river Ans. b: Western Disturbance occurs in India, Pakistan, basin scale. Although all droughts originate with a Karnataka and Nepal to describe an extra-tropical storm deficiency of precipitation, hydrologists are more originating in the Mediterranean, that brings sudden concerned with how this deficiency plays out through winter rain and to the north-western parts of the Indian the hydrologic system. subcontinent. This is a non-monsoonal precipitation pattern driven by the Westerlies. 5. The Standardized Precipitation Index 10. Hadley Cell Ans. b: The Standardized Precipitation Index (SPI) is Ans. b: The Hadley cell, named after George Hadley, a tool which was developed primarily for defining and is a tropical atmospheric circulation which features monitoring drought. It allows an analyst to determine rising motion near the equator, poleward flow 10-15 the rarity of a drought at a given time scale (temporal kilometres above the surface, descending motion in the resolution) of interest for any rainfall station with sub-tropics, and equatorward flow near the surface.
GeoGraphy and you . September-october 2015 45 INDIA’s | VaRIaNT Weather Sikkim2015
46 November - December 2015 . Geo graphy and You When minimum temperatures of a region drop substantially below the normal minimum tempera- ture, a cold wave is declared.
Cold Wave
By Staff Reporter As India braces itself for another cold wave this winter, its dynamics are explored in a brief treatise. The cloudiness, fog, precipitation and more are decoded for quick understanding and greater preparedness.
Geo graphy and You . November - December 2015 47 A significant increase in the
he year 2015 has seen a delayed winter frequency, persistency and and warm weather conditions in December all over northern and spatial coverage of cold wave eastern India, with unseasonal rains thrown in. However, a year before may be observed in the later in December 2014, a severe cold wave wreaked periods possibly indicating havocT across North India claiming 16 lives in Uttar Pradesh alone, taking the national death toll to 140. climate change. Most casualties were related to cold-related deaths and accidents due to fog.
C riteria for cold waves value of minimum temperature of 10oC is rarely Weather scientists claim that extreme weather reached. However, local people feel discomfort due events will be increasingly palpable, throwing life to wind chill factor, which reduces the minimum out of gear, more often now than ever before. Cold temperature by a few degrees depending upon the waves too fall under such extreme events, which wind speed. Here WCTn is used to declare cold can severely and fatally affect the very young, the wave or cold day. elderly and the infirm. Occurrences of extreme low temperature in association with incursion of dry Western disturbances (WD) and cold waves cold winds from north into the sub-continent are A generalised pattern of day to day changes during defined as cold waves. a WD is as follows—it starts with the build-up of Word Meteorological Organisation (WMO) has low and medium clouds making for partly cloudy determined certain criteria for declaring a cold skies; a slight warming of the air is accompanied wave, which is followed by Indian Meteorological during nights and early mornings; day tempera- Department (IMD). Although cold wave condi- tures experience a fall and the prevailing winds tions may be understood differently for varied remain southwesterlies. The following two or three geographical locations, only coastal locations days are characteristically marked by the arrival of have been meted out a separate parameter by multi-layered clouds and a nearly overcast sky, with WMO. Temperate, mountainous or coastal areas or without rains. The day temperatures fall further may have wind chill factor playing an important while night temperatures remain steady and the role in bringing down the actual minimum prevailing winds shift to southeasterlies and east- temperature. Thus, the actual minimum tempera- erlies. Day four onwards with the passage of WD ture of a station is reduced to ‘wind chill effective the cloud cover moves away leaving skies clear, with minimum temperature’ (WCTn) based on this rising day temperatures but plummeting night factor. Thus cold conditions are not measured temperatures with cold dry north westerly winds only in terms of temperature but also in terms of giving rise to cold wave conditions. human comfort level. In the plains of north India, foggy conditions C old waves (CW) and their frequency prevail during winter for several days or weeks. A cold wave or severe cold wave (SCW) spell is the The minimum temperature on these days remains duration where such conditions are continuously above normal, while maximum temperature experienced,varying from one day to several remains much below normal. This creates cold days, by a sub-division. A study by D S Pai, et conditions for a prolonged period. When maximum al., 2004, ‘Decadal variation in the heat and cold temperature is less than or equal to 16°C in plains, a waves over India during 1971-2000’, published in ‘cold day’ is declared. When declaring a cold wave, Mausam, provides insightful information about however, wind chill factor is taken into account. the prevalence and distribution of cold waves in When WCTn is 0°C or less, cold wave is declared India (Fig. 1a, b, c). irrespective of normal minimum temperature of The duration of most frequent CW/SCW spells the station. However, this criteria is not applicable in most sub-divisions is generally less than 1-2 for those stations whose normal minimum temper- days. Only a rare occasion saw a CW spell last ature is below 0°C. For coastal stations the threshold more than 10 days, and there were only two occa-
48 November - December 2015 . Geo graphy and You Fig. 1: Total number of CW (SCW) days experienced by 35 meteorological sub-divisions of India during the cold weather season (November - March) for the decades 1971-80, 1981-90 and 1991-2000. The sub- divisions that have experienced the number of CW days of ≥ 25 are shown as shaded areas
N N 35o a. 1971-1980 35o b. 1981-1990
30o 30o
25o 25o
20o 20o
15o 15o
10o 10o
70o 75o 80o 85o 90o E 70o 75o 80o 85o 90o E
In 1971-80, highest number of CW days was N experienced by West Rajasthan (58) and highest 35o c. 1991-2000 number of SCW days was experienced by East Rajasthan and Saurashtra & Kutch (17 days each). During 1981-90 and 1991-2000, the highest number 30o of CW days was experienced by Punjab (193 days) and Jammu & Kashmir (48 days) respectively. During o the same periods, the highest number of SCW days 25 were experienced by Rajasthan state (14 days) and West Rajasthan (21 days). It is seen that in the 20o last decade, the CW/SCW activity over many sub- divisions has increased significantly. Source: D S Pai et. al, Decadal variation in the heat and cold waves over India during 1971-2000, 2004 Mausam. 15o
Map not to scale
10o
Source: D S Pai et al., ‘Long term climatology and trends of heat waves over India during the recent 50 years (1961-2010)’, 2013, Mausam. 70o 75o 80o 85o 90o E
sions when a SCW lasted beyond 5 days. The data in the frequency, persistency and spatial coverage also indicates that the longest CW/SCW spells of CW/SCW may be observed during 1991-2000 in were experienced post-1989. During the 1981-90 comparison to the two earlier decades. In 1971-80, period, a 10 day cold wave spell was experienced the most frequent spells and highest number of CW/ in the Bihar plains, and the longest (7 day) SCW SCW days were experienced in western Madhya was experienced in Jharkhand. In the period Pradesh, In 1981-90 and 1991-2000, the maximum 1991-2000, Jammu and Kashmir experienced the CW activity was in Jammu and Kashmir and Punjab longest 11-day CW spell, while the longest 4 day respectively, while the maximum SCW activity was SCW spell was experienced by western Rajasthan, in Rajasthan and Punjab. It is thus noted that CW Madhya Maharashtra and Marathwada. activity in northern India showed an increase from one decade to the next. However, how this is linked E ndnote to broader issues of climate change, falls within the As D S Pai’s study points out, a significant increase ambit of further research.
Geo graphy and You . November - December 2015 49 In | conversatIon
Madhavan Nair Rajeevan, the Secretary, Ministry of Earth Sciences, spoke with Sulagna Chattopadhay from within the precincts of his new office, providing an excellent overview of a possible link between increased extreme events and climate change.
G’nY. Are the number and intensity temperatures rising, increase in can have an impact on monsoon. Even of extreme rainfall events rising in frequency of heavy rainfall events is though there are many ambiguities India? possible, due to increase in moisture in establishing a clear relationship Yes, the number and intensity of content in the atmosphere and between the global warming and the extreme rainfall events are rising in more instability of the atmosphere. Indian monsoon, increase in heavy India. Heavy rainfall events generally However, one individual event cannot rainfall events and rainstorms is likely occur over central India, northeast be attributed to global warming. An to be influenced by the global warming. India and along the west coast. For analysis of 100 years of data suggests example, frequency of heavy rainfall that there is an epochal variation which G’nY. What are the prospects of events (with 15 cm or more in 24 hours) is attributed to natural variability. climate projections at regional/local over central India is about ten events However, there is an appreciable levels and for planning mitigation and in the monsoon season. However, effect of global warming overriding the adaptation methods? frequency of heavy rainfall events natural variability. The IPCC climate models suggest that (exceeding 15 cm in 24 hours) has with the global warming, the mean increased from about 7 to 15 during the G’nY. Has Indian science garnered monsoon rainfall is likely to increase. last 50 years (that is about 80 per cent adequate strength to predict such However, rainy days (days with 2.5 and an appreciable change). events on different time scales? mm of rainfall) are likely to decrease. Rainstorms are large scale heavy Yes, to some extent. These heavy This clearly suggests that whenever it rainfall events (with area more than rainfall events are predictable at least rains, it will be heavy, a clear indication 50,000 sq km) and persisting for 2-3 days in advance. High resolution that heavy rainfall events are likely to more than two days. These events numerical models are capable of increase in future. are primarily responsible for large- predicting these events. There is a scale floods in India. An analysis of problem in exact location of heavy G’nY. What has been envisaged to rainstorms over India suggests that rainfall event. However, magnitude enhance the Ministry’s extreme event there is an increase of 100 per cent in and structure is well predicted 2-3 days prediction capability? rainstorm days over India during the in advance. There is a hope that the It is the priority of the Ministry of last 50 years (increase from about five lead time of accurate prediction can be Earth Sciences to not only predict days to ten days now). increased to 4-5 days. mean monsoon rainfall, but to predict extremes events too. This is a G’nY. If indeed there are changes in G’nY. What is the likely impact of challenging task. However, we hope to the number of extreme events, can it global warming in general and of Bay achieve the improvement of prediction be ascribed to climate change? of Bengal warming in particular and skill of these events. We are planning In general, the changes in extreme its effect on monsoons? to have the second phase of the rainfall events can be attributed Global warming in general and the monsoon mission, in which the focus to global warming. With global Indian Ocean warming in particular will be on extremes.
50 November-December 2015 . GeoGraphy aND you Extreme event prediction, a priority research
The Ministry is planning to have the second phase of the monsoon mission, in which the focus will be on extremes.
GeoGraphy aND you . November-December 015 51 INDIA’s | VARIANT WeATheR
By Staff RepoRteR Hailstorms A hailstorm is a thunderstorm that produces ice as precipitation. Hailstorms can cause serious damage to crops and property. In India, hailstorms mostly affect the northeast and western Himalayas, with the maximum strikes in March and April.
ailstorm is a severe weather 2015 India suffered an estimated loss of INR 20,453 phenomena, which causes exten- crore due to unseasonal rains and hailstorms in sive damage to crops, property and March. livestock. Hail is solid precipitation The United States gets a large share of hail made of balls or irregular lumps each year, resulting in 1 billion USD in damages. of ice, each of which is called a hailstone. Unlike Australia has a history of both small and large hail- Hgraupel or snow-ice pellets that are smaller and storms, although the 1999 hailstorm remains one translucent, hailstones consist mostly of water ice of the worst on record when around half a million and measure between 5 mm and 15 cm in diam- tonnes of hail fell from the sky during a single hail- eter. Any thunderstorm, which produces hail that storm that hit Sydney on April 14, 1999. It ripped reaches the ground, is termed a hailstorm. apart roofs of 20,000 houses, 40,000 vehicles and 25 aircrafts, resulting in whopping losses of over 1.7 hailstorm damage billion USD. Hail can cause serious damage, notably to aircraft, automobiles, glass-roofed structures, skylights, Favourable conditions for a hailstorm besides crops, people and livestock. Hailstorms Hail forms in the strong updraft region of a thun- occurring primarily in the months of March and derstorm. Atmospheric conditions favourable for April cause maximum damage to ‘rabi’ crops when the formation hail bearing thunderstorm are : it is ripening for harvest and when the mango ◆ high degree of instability, orchards are flowering. One of the most damaging ◆ high moisture content, hailstorms hit the north Indian city of Moradabad ◆ low freezing level, on April 30, 1988, and resulted in the death of 246 ◆ high vertical wind shear. people, in addition to 1,600 livestock fatalities. In Hailstorms occur mostly over mid-latitude
52 November - December 2015 . GeoGraphy aND you The annual frequency of hailstorm extends to central India and, at times, of hail is the highest in up to Telangana, Andhra Pradesh and Karnataka. Hailstorm occurrence however is maximum over extreme northeast of the the Northeast and Western Himalayas followed by Vidarbha, eastern Maharashtra, parts of Madhya Brahmaputra valley where Pradesh and Jharkhand. Southern states generally do not experience hailstorms. annual occurrence exceeds In general, most hailstorms over North, North- 15 such events. east and Central India occur from January to May with the months of March and April recording the highest number. Latitudinal and longitudinal distribution with the monthly frequency and diurnal variation of hailstorms over Northeast India is shown in Fig. 1a and b. Hailstorms, occur continental regions and decrease in frequency mostly in the afternoon and evening between 1500 towards the pole and equator and over oceans and hrs and 1900 hrs. seas with the exception of Kericho, which is located close to equator at an elevation of 7,200 ft in Kenya hail Formation process and gets an annual average of 50 days of hail. The Hail forms as super-cooled droplets, ice crystals hail at Kericho is typically small but frequent. Other and water freeze upon an embryo hailstone. regions of significant hailstorm occurrence in the Once hail forms, gravity will bring the hail to world include the Great Plains of the United States, the earth’s surface. If the updraft is stronger than Australia, China, India, Central Europe, Central the pull of gravity, the hailstone will continue to Asia and adjoining parts of Russia. grow. Once the hail reaches a size that the updraft In India the favourable hail conditions are met can no longer keep aloft, the hail stone will make by active western disturbances during winter and its way down (Fig. 2). the pre-monsoon season. Low level circulation associated with western disturbance, middle Structure of a hailstone level trough in westerly winds and presence of On cutting through a hailstone, one can see rings a jet stream at higher level provide favourable of ice. Some rings are milky white; others are clear, conditions for the formation of hail-bearing which suggests that a hailstone can grow by two thunderstorms along the line of discontinuity over different processes, wet and dry. The wet growth north and northeast India. During the passage of occurs when the hailstone is in the storm where an induced circulation, a deep westerly trough belt the air temperature is below freezing, but not super cold. When the hailstone collides with a drop of water, the water does not immediately freeze on the ice. Instead, the liquid water spreads over the hail- Fig. 1: Latitudinal and longitudinal distribution of hailstorm with their monthly and diurnal stone and slowly freezes. During this slow freezing, variations over NE India is shown in (a) air bubbles can escape, forming a layer of clear ice. latitudinal distribution of hailstorms and Dry growth of hailstones occurs when the air (b) longitudinal distribution of hailstorms temperature is well below freezing (Fig. 1). In these conditions a water droplet freezes immediately 20 upon colliding with the hailstone. Air bubbles 18 quickly freeze in place, leaving cloudy ice. Counting 22 16 20 14 the layers of clear and milky white ice gives an indi- 18 12 16 cation of how many times the hailstone travelled to 14 10 Frequency 12 8 the top of the storm. 10 6 8 4 Frequency 6 4 2 hailstone shapes 2 0 0 oN Hailstones can be as large as oranges and grape- 84 86 88 90 92 94 96 20 22 24 26 28 30 fruits. If hailstones collide with each other and Source: P Kumar et al., ‘Hailstorm-Prediction, Control and Damage Assessment’, 2010. freeze together, they can form hailstones with a
GeoGraphy aND you . November - December 2015 53 Table 1: Reporting guide to hailstorms. large variety of aerodynamical shapes. Hailstones Character Very severe cyclonic storm are commonly spherical, conical, pear-shaped, precipitation ellipsoidal or discoidal in shape. The shapes are Pea 0.25 inch/(0.62 cm circular at smaller sizes and irregular at larger sizes. The shape is used as a guide for reporting hail size Dime 0.75/1.84 cm by comparing it to objects of the same diameter for Quarter 1.00/2.45 cm simplicity in reporting (Table 1). It is considered to Golf Ball 1.75/ 4.3 cm be severe hail if the diameter is 0.75 inches/1.84 cm Tennis Ball 2.50/6.1 cm or greater. Base Ball 2.75/ 6.9 cm Giant hailstones are usually irregular in shape, Grapefruit 4.00/9.8cm exacerbated with the merging of smaller hailstone Giant 4.00+ /10 cm+ on to a bigger hailstone ending up with bulges and Source: nssl.noaa.gov irregularities. As per official US records, Vivian in South Dakota saw a hailstone of 20 cm diameter fall on 23 July 2010 which was the largest hailstone recovered in the US. There are unconfirmed reports of Gopalgunj district in Bangladesh having been hit by a one kg hailstone, the heaviest hailstone known, on April 14, 1986.
Fig. 2: How a hailstone forms
Supercooled moisture The cloud’s cold upper levels produce layers of opaque ice on the hailstone.
ColD Air 2 5 1 5 3 4 3 Frozen water 4 droplet Cumulonimbus cloud
1 A frozen water droplet is swept up by currents within a thundercloud. Supercooled moisture freezes onto the WArWArm Air 2 6 droplet’s surface forming a layer of ice. 3 As it gets heavier, gravity pulls it The cloud’s warmer downward. lower levels produce layers of clear ice. 4 Then it’s sucked back upwards by strong updrafts. Golf-ball-size hailstones need 60 mph updrafts of air to form. 5 As the process continues, thick layers of ice accumulate on the hailstone’s surface. 1. A water droplet is carried upward within a thunderstorm Eventually, gravity pulls the hail 2. Supercooled moisture freezes onto the droplet’s surface, 6 through the warm, wet cloud base and forming an ice layer and an embryo hailstone. finally to the ground. 3. As it gets heavier, gravity pulls it down. 4. The strong winds then suck it back, upwards. As the process continues, thick layers of ice accumulate on hailstone’s surface and the hail grows in size.
Source: everythinglubbock.com
54 November - December 2015 . GeoGraphy aND you Fig. 3: AMSRE estimated serve hail, all months
30 60 20 Hailstorm frequency of 10 30 occurrence estimated from 7 5 AMSR-E 36-GHz PCT, 4 3 0 2003–10. Units are storms 2 per 500 km square per year, using 2.58 grid spacing and -30 1 bilinear interpolation. .7 .5 .4 -60 .3 .2 -150 -120 -90 -60 -30 0 30 60 90 120 150 Storm per year per (500 km)-2, per 4 overpacess/day Source: journals.ametsoc.org
hailstorm observations hail suppression Hailstorm reports are based on observations of hail The need to protect crops from the damage falling on ground. Since hailstorm is a mesoscale caused by hailstorm has been a matter of interest phenomena, it occurs in a limited area—thus amongst scientists since 1896, when Alber Stinger goes unreported in remote areas. However, radar tried using a hail cannon to protect orchids is an extremely useful tool in the detection of any in Styria, Austria. However, since Vincent J hydrometeor in the atmosphere. The reflectivity Schaefer’s discovered that dry ice acts as a good of any cloud is dependent on the number, type and nucleating agent for ice crystals in atmosphere size of hydrometeors, which includes rain, snow in 1946, hail suppression programmes have been and hail. Today, dual polarmetic radars are able undertaken by 15 nations. to detect hail from differences in radar reflectivity Cloud seeding is undertaken so as to reduce accu- of rain and hail at horizontal and vertical linear mulation of large amounts of super cooled water by polarisation. This techniques hold great promise in supplying the cloud with numerous freezing nuclei improving the detection of hailstorms. capable of converting water to ice. This prevents the growth of large hailstones. Smaller hailstones are hailstorm climatology believed to inflict lesser damage. The Advanced Microwave Scanning Radiometer Of the early ambitious projects were those for Earth Observing System (AMSR-E) allows a by Russians in the Caucuses region. Russian unique, consistent comparison between regions scientists claimed a 50 per cent reduction in that cannot be otherwise compared using ground- losses through cloud seeding with silver iodide based records owing to varying standards of data nuclei. Since statistical evaluation of the Russian collection. Daniel J. Cecil and Clay B. Blankenship projects has not been possible, their claims of Earth System Science Centre, University of remain open to interpretation. The United States Alabama, have developed an eight year climatol- initiated the National Hail Research Experiment ogy of storms producing large hail estimates from (NHRE) in 1972, monitoring 30 hailstorms near satellite measurements. The Study shows that the Colorado-Nebraska border. An analysis of severe hailstorms are indicated in a broad region the NHRE in 1975 failed to support statistically of northern Argentina and southern Paraguay and significant increases in hailstorms with small a smaller region in Bangladesh and eastern India. hail or an increase in rain. Numerous hailstorms are also estimated in the Although there has been much interest in hail central and southeastern United States, northern suppression, lack of an adequate standard to Pakistan and northwestern India, central, western, determine the success or otherwise of experi- and southeastern Africa. Fewer hailstorms are ments undertaken leaves its efficacy open to doubt. estimated for other regions over land and scattered However, the research has certainly yielded a lot across subtropical oceans. (Fig. 3) more information on hail formation.
GeoGraphy aND you . November - December 2015 55 INDIA’s | VARIANT WeATheR
By Ajit tyAgi and P guhAthAkurdA Wettest Place in the World: MaWsynraM These observations will also help in understanding the Mawsynram, has currently overtakenmechanism/processes Cherrapunji of heavy as the rainfall. wettest place on earth. But both these places in Meghalaya’s East Khasi hills share a common orography, although facing different valleys.
The dry season in the world’s wettest place is worse in many ways. With no conservation effort the land is parched and inhabitants actually have problems to find water.
ecords—sports, music, cooking or northeast India. Weather observations ranging even rainfall always generates curi- from as far back as 1902, when climatic record osity. But, there is this thing about keeping began in the region, placed Cherrapunji on records—it is almost always broken top where rainfall was concerned. Climatic records by a new one. Thus, Cherrapunji’s such as the wettest place are based on ‘climatic
record as the wettest place in the world has been normals’ in relation to a given reference period. The tyAgi overturnedR with Mawsynram figuring as the first climatological normals published by the India ‘latest’ wettest place on earth. Meteorological Department (IMD) for 1901-1940 Locally known as ‘Sohra’, Cherrapunji is located showed Cherrapunji as the wettest place in India in the East Khasi Hill district of Meghalaya in with an annual rainfall of 10800.8 mm. Measure- Ajit courtesy: Photo
56 November - December 2015 . GeoGraphy aND you The possibility of some other ment of rainfall at Mawsynram, which is 16 km location receiving higher away from Cherrapunji started from June 1940. In a study by V Thapliyal and S M Kulshrestha rainfall than Mawsynram using 26 years of available rainfall data from 1941- 78, the average annual rainfall of Mawsynram needs to be explored. at 11873 mm, was found to be higher than Cher- rapunji’s 11763 mm for the same period. The Guinness book of World Records refers to the above value while declaring Mawsynram as the Wettest Place on Earth. The World Meteorological Organi- valleys and highland plateaus. Elevation in the zation’s extreme record site also shows Mawsynram plateau region ranges between 150 m (490 ft) to as the site of Asia’s greatest precipitation. 1,961 m (6,434 ft), with the central part comprising Subsequently new rainfall normals have the Khasi Hills with the highest elevations. Both been published for 1951-2000 by IMD. The Cherrapunji and Mawsynram lie in the southern monthly average and annual average rainfall for part of the East Khasi Hills overlooking narrow Mawsynram and Cherrapunji are shown in Tables north-south oriented valleys opening to the plains 1. It is seen that Mawsynram has figures higher of Bangladesh in the south. The rainfall in Cher- than that of Cherrapunji. Annual average rainfall rapunji-Mawsynram is caused by the orography of Mawsynram for the latest period (1951-2000) is favouring a monsoon wind regime. The northward 12397.3 mm as against the 11720.3 mm of Cher- moving moist winds from the Bay of Bengal rapunji. Thus, Mawsynram continues to hold on to passing over the plains of Bangladesh are forced to the ‘wettest place’ record. converge in the narrow valleys of the Khasi Hills with orography providing forced ascent that causes rainfall in the Khasi hills condensation, formation of clouds resulting in rain Both Cherrapunji (25o15ʹN, 91o44ʹE, elevation on the windward side of the slope. 1313 m) and Mawsynram (25o18ʹN, 91o35ʹE, eleva- Although both Mawsynram and Cherrapunji are tion 1401.5 m) are located on the southern slopes located on the southern slopes, they face different of the east Khasi Hills in Meghalaya. Stretching valleys. The valley separating Mawsynram and 300 km in length and about 100 km in breadth, Cherrapunji is drained by the Umiam river, while Meghalaya is a mountainous state, numerous the valley to the east of Cherrapunji is drained by the Umsohryngkew river. The elevation of Table 1: Rainfall normals (1951 -2000) Mawsynram is 88.5 m higher than that of Cher- rapunji and it is situated on the fringe of the narrow Month Mawsynram Cherrapunji valley with its mouth about 6 km wide open to Rainfall No. of No. of Rainfall No of No of the south. The 1000 m deep valley is north-south (mm) Rainy Years (mm) Rainy Years oriented, up to a distance of 9 km whereafter it Days Days January 19.1 1.4 28 21.5 1.6 46 turns northeast. Higher elevation and cyclonic February 25.5 1.8 28 53.0 2.3 45 curvature of the valley are the probable causes of March 198.8 6.7 27 276.9 7.5 46 higher rainfall at Mawsynram. April 488.4 15.3 28 729.8 14.5 43 May 1436.8 21.4 28 1447.8 21.4 43 mawsynram - the wettest? June 3161.4 25.4 28 2745.3 24.7 42 Since the unique orography of Cherrapunji- July 3295.4 27.6 28 2897.2 28.0 42 Mawsynram is primarily responsible for very high August 2335.3 25.5 28 1877.8 24.8 42 rainfall, the possibility of some other location in the September 1049.4 18.1 25 1089.3 18.6 44 region receiving higher rainfall than Mawsynram October 334.3 8.9 26 499.0 9.0 44 can not be ruled out. Therefore, there is need to map November 48.4 2.0 25 65.0 2.0 46 southern slopes of Khasi Hills by a dense network December 3.5 0.5 26 17.7 0.8 43 of rain gauges and dual pol-doppler weather radar Total 12397.3 154.6 11720.3 155.2 to locate the place of highest rainfall, which will also help in building the understanding of rainfall Source: India Meteorological Department mechanism better.
GeoGraphy aND you . November - December 2015 57 INDIA’s | VARIANT WeATheR
By Staff RepoRteR ThundersTorm Thunderstorms are localised phenomena that can cause substantial damage. These are classified into the ordinary or single-cell, long-lasting multiple-cell or violent super-cell ones. In India, the pre-monsoon season is when most thunderstorms occur.
nlike cyclonic storms, thunder- their ferocity and leave a trail of destruction in the storms are a meso-scale or localised affected areas. phenomena, generally occurring Convection is the building block of a thun- between 100 and 1000 km. However derstorm. Convection is initiated due to strong because of its large frequency and heating of the land mass during the day time, or by associated multiple hazards, cumulative damage is mixing of different types of air masses. Presence Uquite substantial. It is estimated that at any given of atmospheric instability coupled with moisture instant more than 2000 thunderstorms are taking convergence results in the formation of deep cumu- place around the world (WMO, 1953). Hailstorms, lonimbus clouds and thunderstorms. A typical tornado, lightning, cloud burst, microburst, thunderstorm cell may have a size of 1-10 km with squall are hazardous phenomena associated with life period of less than an hour (Fig. 1). Depending thunderstorms. In aviation, thunderstorms are the on the atmospheric conditions a thunderstorm most dreaded weather phenomena. It causes pres- undergoes three distinct stages i.e. cumulus, sure perturbation leading to defective altimeter mature and dissipating in its life cycle. reading, poor visibility due to heavy rain, turbu- The single cell thunderstorm: The ordinary or lence, icing, and radio static and communication single cell thunderstorm is an ephemeral burst problem. Many air accidents have been attributed of convection. Each burst creates a towering to thunderstorms. Tornadoes are notorious for cumulus or ‘cell’ of convection. When the cell gets
Fig. 1: Three stages of a hailstorm (a) Cumulus stage (b) Mature stage (b) Dissipating stage
Atmosphere 15
10 (km)
0OC 0OC 5
Surface 0 Heavy rain Light rain Source: climate.ncsu.edu
58 November - December 2015 . GeoGraphy aND you Fig. 2: Annual thunderstorm frequency Thunderstorm climatology Orography, low level moisture and favourable atmospheric conditions shape N thunderstorm climatology in India. The o 35 highest annual frequency (100-120 days) is observed over Assam and sub Himalayan West Bengal in the east and Jammu region in the north. The lowest frequency (less
30o than 5 days) is observed over Ladakh region. In the plains Gangetic West Bengal and Bangladesh record between 80 and 100 days of thunderstorm annually. Kerala records highest (80-100 days) frequency 25o of thunderstorms. Udhampur observatory (132 days) in Jammu sub-division records highest number of thunderstorms in the country followed by Kumbhigram (Silchar) observatory (129 days) in south Assam 20o and Hasimara (123 days) in Sub Himalayan West Bengal. In the plains Saurashtra and Kutch record lowest number (less than 15 days) of thunderstorm in the country (Tyagi 15o 2007). With respect to the seasonal distri- bution the winter season has the lowest number of thunderstorms. Significant increase in thunderstorm activity takes place during pre-monsoon season (March 10o N to May) over all parts of the country with significant increase over northeast India Bangladesh, West Bengal, south peninsula and Jammu region.
65oE 70o 75o 80o 85o 90o 95oE
Source: Ajit Tyagi, “Thunderstorm climatology over Indian region”, 2007, Mausam.
large (and tall) enough, it is classified as a cumulo- tornadoes are still threats. Sometimes thunder- nimbus or thunderstorm. storms form in a line which can extend laterally for The multi cell storm:As the name suggests, it hundreds of miles. These ‘squall lines’ can persist for consists of many cells that grow to form a group many hours and produce damaging winds and hail. of cells that move together as one unit. A multicell The super cell storm:This type of storm is the cluster thunderstorm results from a vigorous classic deep cumulonimbus tower (12 km and parent-daughter effect. In this case, an ordinary more height) with the anvil top and on occasion thunderstorm creates neighbouring storms via the overshooting updraft tower. These storms are the downdraft and gust front. The multicell cluster notorious for producing damaging straight-line storms last longer than ordinary or single cell winds, frequent lightning, flash floods, large hail, storms, and cover a larger area. Each cell in a multi- and violent tornadoes. This is a stand-alone entity cell cluster storm usually lasts about 20 minutes, which is so well organised that it actually support but the cluster of storms itself can persist for several itself and enhances its own growth. In order to form hours. Because of the storm-storm interaction, a supercell, three ingredients are necessary: high it is rare to get extreme weather (large hail, severe thermal instability, strong winds in the middle and tornadoes) from a multicell cluster, but heavy rain, upper troposphere, and veering of the wind with strong winds, small to medium sized hail and weak height in the lowest kilometre.
GeoGraphy aND you . November - December 2015 59 INDIA | OUTDOORS
An estimated 75 per cent of the Indian Gharial population declined between 1998 and 2006. As of 2007, only 208 are reported to survive in India.
60 November - December 2015 . GeoGraphy aND you The Chambal Story and photograph by Sumit Chakraborty The Chambal National Park is a rare, unspoilt place off the tourist circuit where you can enjoy the sight of the Indian gharial, and flocks of Indian skimmer in their natural habitat.
GeoGraphy aND you . November - December 2015 61 Indian Skimmer, a threatened bird of India which is mainly seen in National Chambal Wildlife Sanctuary is fighting for its survival after its numbers came down to 203 in 2015 from 555 in 1995.
62 November - December 2015 . GeoGraphy aND you ‘Aap Calcutta se Chakraborty sahib hai?’ I nodded in affirmation, to be issued a command ‘Chaliye, hume Bhaiji ne bheja hai,’. Before I could ascertain the whys and wherefores of this ‘Bhaiji’, the broad- shouldered young fellow hauled up my camera bag, while his assistant lugged my heavy rucksack and strode right ahead. I had no option but to trot obediently behind them to the SUV parked across the road. A perfunctory instruction to the driver for destination ‘circuit house’ was given. In 10 minutes’ time, the vehicle entered a huge compound where I was instructed to wait in the lobby, while the team proceeded to select the best room. My luggage was finally dropped in a huge suite that could easily accommodate an entire badminton court. Along- side the ceiling fan, a big handmade ‘pankha’, a legacy of the Raj, adorned the room. This earnest effort to maintain a ‘period’ flavour elicited mixed feelings within me about whether to enjoy the ambience or berate the servitude. I had left Bharatpur, Rajasthan, at break of dawn under a thick veil of fog, with the intention of clicking the gharial and Indian Skimmer in their natural habitat at the Chambal National Park, 125 kms away, but the weather made it difficult to even read my own wristwatch. Of course memories of Chambal’s notorious past made me apprehensive, my expensive camera and photographic equipment could well be in danger, I thought. I dialed an old acquaintance, a senior forest official who had once served in the Chambal, who assured me that the region was safe and informed me that unlike many other rivers in India, the Chambal continued to be relatively pollution free. Thus reassured, I decided to set out for Dholpur, a well-connected town, which would serve as my base for touring Chambal National Park, roughly 50 km away. I lay on the king sized bed in the circuit house, my mind racing back to the morning and the anxie- ties about being kidnapped, when I found my two ‘abductors’ peeping in. Once beckoned they gingerly stepped into the room and clarified that
GeoGraphy aND you . November - December 2015 63 my senior forester friend had requested one of his old acquaintances to help me on my trip. This was the ‘Bhaiji’ they were referring to! After an early lunch, I left the circuit house in a lighter mood. Amit, the person-in-charge who had received me at the Dholpur bus stand, gradually opened up as we drove. At just 26 years of age he was in charge of the administration of three poly- technics, an engineering college and five schools, all a part of his family business. He was into active politics as well and was striving to prominently place Dholpur in the tourism map with its rich historical heritage, Rajput architectural marvels and spiritual sites. In the meantime, we had crossed the Chambal (river) and entered Morena district in Madhya Pradesh. Descending from the bridge we turned left, driving carefully on a sandy track. Amit parked the car opposite the forest camp—mini- ature versions of circus tents, fastened with ropes. landscape, I imagined how it would be to face a dark As we moved towards the River for our boat safari, mustached dacoit galloping through the ravines Siyaram, the guide-cum-boatman handling our with a red ‘tilak’ besmeared on his forehead. In a 4-seater speedboat, greeted us with a happy smile. few hours, as the daylight dimmed, I headed back He informed me that there were no skimmers and tucked myself into a comfortable bed, retiring sighted in the last 3-4 days. Alongside the jetty, a for the day. gigantic pipeline was withdrawing river water for A lazy morning was followed by a post-lunch supplying to Dholpur town. A few ruddyshel ducks sojourn to the Morena Gharial breeding centre, were swimming about. They allowed us decent where I met experts who had dedicated their lives proximity, which allowed me to capture excellent to the conservation of the gharial. Moving from frames. Moving ahead, we found a baby gharial there to the jetty, we found Amit’s brother Naveen perched on its mother’s back, basking in the sun on and a few of his college mates waiting for us. This a small islet. I sighted several mixed flock of river time, we opted for a 12 seater speedboat for our lapwing, Egyptian vultures, three different varie- safari. I was anxious, as I had failed to encounter ties of kingfisher, the Asian soft shell turtle, black a single skimmer so far. Siyaram tried to cheer me, winged stilts, spoonbill, river tern, lapwings and ‘aaj dikhayenge Sir aapko Skimmer’ and added that ruddyshel ducks enjoying the morning sun and a flock of around 20 skimmers that had been seen feasting in delight. Gangetic dolphin sprung out a few minutes ago, which I had a fair chance of of water several times, both in front and behind encountering. our boat; but the leaps were so sudden that I could True to his word, I managed to get a eyeful of hardly aim my camera at them in time and manage the elusive Indian skimmer. There were 26 birds a shot. Seeing my interest in the creatures, Siyaram in the flock, enjoying an afternoon siesta. Siyaram drove the boat in a zigzag pattern and resultant switched off the engine and silently cruised as close turbulence saw the dolphins leap up at least ten as possible. As soon as the sun softened, the birds times in number, all around us. But the glimpses stirred into activity. Flapping their wings, they were momentary, and partial. I still couldn’t ‘skimmed’ the waters in their unique style, giving manage a single shot of an entire dolphin. me ample opportunity to record a great deal of bird Back to shore, we drove down to a hilltop fort activity, making my safari memorable—one that I that lent us a mesmerizing view of the Chambal would most definitely want to repeat. valley. The red, barren soil, stony hillocks eroded into undulating ravines looked unworldly under The author is freelance writer and photographer from the setting sun. As I busied myself to capturing the Kolkata. [email protected]
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