A diagnostic study of some flood producing rainfall events in Bangladesh with a limited area analysis-forecast system

Abstract

Lkkj & bl ’kks/k&Ik= esa nf{k.kh if’peh ekulwu dh vof/k ds nkSjku caxykns’k esa Hkkjh o"kkZ ds dkj.k vkus okyh ck<+ dk uSnkfud v/;;u fd;k x;k gSA bl v/;;u dk eq[; mn~ns’; caxykns’k ds unh csfluksa ds m/oZ izokg okys Hkkxksa esa yxkrkj gksus okyh Hkkjh o"kkZ dh flukWfIVd fLFkfr;ksa dk irk yxkuk gS A o"kZ 1987 vkSj 1998 ds nkSjku gqbZ lcls vf/kd o"kkZ vkSj lcls vf/kd ck<+ okys nks o"kksZa dk Hkkjh o"kkZ okys rwQku ds laca/k esa v/;;u fd;k x;k gSA bZ- lh- ,e- MCY;w- ,Q-  bZ- vkj- ,-&40 ls muds fQi lkbV ls MkmuyksM fd, x, uSnkfud fo’ys"k.k ds fy, ekSle laca/kh ekufp= rS;kj fd, x, gSaA y?kq vof/k esa o"kkZ dk izfr:i.k djus ds fy, ¶yksfjMk jkT; fo’ofo|ky; ds lhfer {ks= iwokZuqeku fun’kZ dk mi;ksx fd;k x;k gS A bl fun’kZ dks {kSfrt fxzM ij vk/kk fMxzh v{kka’k@ns’kkraj vkSj Å/okZ/kj esa 16 flxek Lrjksa ij O;kogkfjd cukus ds fy, iz;qDr fd;k x;k gSA v/;;u okys bu o"kksZa esa ck<+ ykus okys o"kkZ&rwQkuksa ds fy, mRrjnk;h lkekU; flukWfIVd fLFkfr] bu mRrjh caxykns’k esa mRrjkfHkeq[kh v{kka’k ij ekSleh ekulwu nzks.kh ds v{k dh vofLFkfr vkSj cM+s iSekus ij ifjlapj.k dh folaxfr;ksa ds izHkkoLo:Ik mi;qZDr fLFkfr;ksa esa fLFkj ikbZ xbZ gSA lhfer {ks= fun’kZ ls o"kkZ ds iwokZuqeku 24 ?kaVksa vkSj 48 ?kaVksa dh iwokZuqeku vof/k;ksa esa izkIr gq, gS tks izsf{kr o"kkZ forj.k ds laca/k esa lqlaxr ik, x, gSaA 

A diagnostic study of flood producing heavy rainfall in Bangladesh during the southwest monsoon period has been carried out.  The study focuses on identifying the synoptic situations leading to persistent heavy rainfall within Bangladesh and in the upstream portions of the river basins of Bangladesh.  Case studies are carried out in respect of heavy rainstorms in the two most outstanding excess rainfall and flood years 1987 and 1998.  The weather maps for diagnostic analysis are prepared from ECMWF ERA-40 Reanalysis data sets downloaded from their ftp site.  A limited area forecast model based on Florida State University has been used for simulating the precipitation in short range.  The model has been customized to run on half degree Lat./Long. horizontal grid and 16 sigma levels in the vertical.  The common synoptic situation responsible for flood producing rainstorms in the years examined is the positioning of the axis of seasonal monsoon trough in a northerly latitude over north Bangladesh and persistence of the above conditions under the influence of large scale circulation anomalies. The limited area model produced precipitation forecasts in 24h and 48h forecast ranges, which were reasonably well placed with reference to the observed rainfall distribution.