Ancient settlements of the Ganga plain: West Bengal and Bihar Dilip K Chakrabarti
Weather in relation to the floods in Bihar, Bengal and ...metnet.imd.gov.in/mausamdocs/5544.pdf ·...
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r· 551.5i9 .4 : 551.509.6(51) Weather in relation to the floods in Bihar, Bengal and Assam during July and August 1954 K. PART HASAHATHY .11cleo Tological Office, Ncw Delhi (Recei"' ,d 28 (tctober If/54) The recent floods in the rivers Gaudnk, K"osi and Brahmaput ra and their tribu t ar ies durin g Jul y and August lH5·1 have received serious coneiderntion in Gove m ment circl es as well 118 from t he pu blic. According to the sta tements in the press, these Hoods in Bihar, Bengal lind Assam had taken II toll of i lives. ,I A tot al area of 25,650 square miles an d nearly !)!} lakhs of people have hceu affected and n large number of ca tt le-hea ds huv e perished. Ser ious dam age to crops, roads. railways and bridges bas al80 occurred on a sca le IH'Y('f experienced before ". According to newspaper reports the floods of this year arc unparalleled within Jiving memory, TIl(' severe flood ill the Kosi wit hin li\'ing nU'lIlcry oc eurred in 1927. The maximum disdlfirge during t hat flood hns heeu ostimuted het wr-en (;00,000 nnd i OO,OOO cusecs (C "'INC , 1950), Bllt. this year , the est imat ed dischnrgs of Kosi on 26 Jul y wa s (i25 ,OOO l'lHH'C R, near ly the sumo as in the fl ood ; ill the last week of August also a discharge of the same order was recorded. Curiously enough, while north Bihar, nort h Bengal and were writ hin g und er t he impact of Hoot Is, the so uthern districts of D. P., south ltihar and Orissa were having a partial drought. These floods have, there- fore, been ent iroly due to tho ra in:'! ill toe Himalayan cat c hment s of t.lIf ' rivers concern- ed. One is led to WOII(]('I' what has been the character of the rains ill the Himalavan region which were responsible for the of such st upen dous magn it ude and what special meteorological featu res were prevalent during Jul y and August of this year which caused t he intense rains in t he Eastern Himalayas. t_ Regarding thefirst question, 1: ;: ., theactual intensity am] distribution of min in t he various JiiJI catchments in the Himalayas, unfortunat ely, d efinit e an swers cannot be found, as most of these catchments do not have An)'" rain recording stations in them. The catchments concerned are those of the Gandak, t he Kosi and th e B ra hma p utra su d their tribut ar ies. Of these, only in the Kosi catchment in Nepal; rain recording stations have heen funerioning for the last few years ; for th e oth ers, IlO rainfall data are availab le.• Fig. 1 shows th e network of observator ies in th e Kosi catchment. The analysis of the da ta from the station. in the Kosi catchm ent for the year. 1948-52, togethe r with the associa ted synoptic situa- tion has 8 110wn, among other things, that hcavv ra infa ll in the catchment is almost ulwavs associated with ' break ' conditions in th e "mo nsoon, d uring the period Ju ne to Soptemher (ThID, 1954). This conclusion can also be taken to app ly to t he other . catchments in the Eastern Himalayas, Southwest monsoon seasen and • brea ks ' In the monsoon The norma l isobaric and wind conditions 0\'('1' India during the southwest monsoon, t hough well known, are briefly described here. A elceed • low ' pressure area lies over th e region Baluchistan, Sind and neigh- hourhood ami an elongated trough ext ends fr.nu there to the northwest angle of the Bay of Bengal, The axis of the tro ugh on a day of normal monsoon run s approximately from Gangnnagar to Sandheads through Agra and Daltonganj. Sout h of the axis, the wind. are westerly and no rt h of it, ill the Gangetic basin t hey are easterlies. In the hjgher •
Transcript of Weather in relation to the floods in Bihar, Bengal and ...metnet.imd.gov.in/mausamdocs/5544.pdf ·...
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551.5i9 .4 : 551.509 .6(5 1)
Weather in relation to the floods in Bihar, Bengal andAssam during July and August 1954
K. PART HASAHATHY
.11cleoTological Office, Ncw Delhi
(Recei"',d 28 (tctober If/54)
The recent floods in t he rivers Gaudnk,K"osi and Brah maputra and t heir tributariesduring July and Augu st lH5·1 hav e receivedserious con eiderntion in Govem ment circlesas well 118 from t he pu blic. According to t hestatements in the press, t hese Hoods in Bihar ,Bengal lind Assam had taken II toll of ~.j ilives. ,I A total area of 25,650 square milesan d nearly !)!} lakhs of people ha ve hceuaffected and n large number of ca tt le-hea dshuv e peri shed. Ser ious damage to crops ,roads. rai lways and bridges bas al80 occurredon a sca le IH'Y('f experienced before " .According to newspaper report s th e floods oft his yea r arc unparall eled within Jivingmemory, TIl(' 1Il 0~t severe flood ill the Kosiwit hin li\' ing nU'lIlc ry oc eurred in 1927.The ma ximu m disdlfirge during t hat floodhns heeu ostimuted het wr-en (;00,000 nndi OO,OOO cusecs (C"'INC , 1950), Bllt. t hisyear, t he est imat ed dischnrgs of Kosi on26 July wa s (i25,OOO l'lHH'C R, nearly the sumoas in t he 19~7 flood ; ill the last week ofAugust also a d ischarge of the same orde rwas recorded.
Curiously enough, while north Bihar, nort hBengal and A I"~am were writ hing und er t heimpact of Hoot Is, th e southern district s ofD.P., south ltihar and Orissa were having apartial drought. These floods have , th erefore, been en t iroly due to tho ra in:'! ill toeH imalayan catchments of t.lIf' rivers concerned. One is led to WOII(]('I' what has beent he character of t he rains ill th e Himalavanregion which were responsible for t he ffdod~of such st upen dous magn itude and whatspecial meteorological features were prevalentduring July and August of th is year whichcaused t he intense rains in t he EasternHi malayas.
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Regarding the first quest ion, 1:;: ., the ac tua lintensity am] distribution of min in t hevarious JiiJI catchments in the Hi malayas ,unfortunately, definit e answers cannot befound, as most of these catchments do nothave An)'" rain recording stations in th em.The catchments concerned are those of th eGand ak, t he Kosi and th e B rahmaputra su dt heir tribu taries. Of th ese, only in the Kosicatchment in Nepal; rain recording stat ionshave heen funerioning for t he last few years ;for th e others, IlO rainfall data are availab le.•Fig. 1 shows the net work of observatories inthe Kosi catchment.
The analysis of t he data from the stat ion.in th e Kosi ca tchm ent for the yea r. 1948-52,together with t he associated synopt ic situation has 8110wn, among ot her things, t hathca vv ra infa ll in t he cat chment is almostulwavs associated with ' break ' cond it ions inth e "monsoon, during the period June toSoptemher (ThID, 1954). This conclusioncan also be taken to apply to t he ot her .catchments in t he Eastern Himalayas,
Southwest monsoon seasen and • breaks ' In themonsoon
The norma l isoba ric and wind conditions0\'('1' India du ring t he southwest monsoon,t hough well known, are briefly descr ibedhere. A elceed • low ' pressure area lies overth e region Baluchistan, Sind and neighhourhood ami an elonga ted trough extendsfr.nu there to the northwest angle of th e Bayof Bengal , The axis of t he trough on a dayof normal monsoon run s approximately fromGangnnagar to Sandheads through Agra andDalt onganj . Sout h of the axi s, the wind.are weste rly and north of it, ill the Ganget icbasin t hey are easterlies. In the hjgher
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