Why can't IMD forecast extreme rainfall beyond 200 mm?

When mediapersons wanted to know the response of the Maharashtra government on Friday after massive landslides killed more than 40 people with several districts witnessing extreme rainfall and floods Chief Minister Uddhav Thackeray said that there is a need to change the definitions of the terms used by the weather departmentI have been taking stock of the situation for the last 45 days Whatever forecast that the weather department had made going by that we will need to change the definitions It said ativrishti extremely heady rainfall but there was no upper limit It is raining beyond extremely heavy rainfall This is an unexpected disaster There are landslides flood waters are increasing rivers are swelling and we are facing such extreme disasters Thackeray told mediapersons in MumbaiThe India Meteorological Department IMD uses the term Heavy Rain for 645 to 1155 mm rainfall Very Heavy Rain for 1156 to 2044 mm and Extremely Heavy Rain for all rainfall more than 2044 mmSome places such as Mahabaleshwar in Maharashtra or Agumbe in Karnataka or for that matter Cherrapunji in Meghalaya are known to have record rainfalls in the range of 40 to 60 cm 400 mm to 600 mm on a given day But for other places it is for the IMD to forecast accurately and that is where the definitions fall shortSo what is the missing factorMahesh Narvekar Director Disaster Management Brihanmumbai Municipal Corporation BMC pointed at that the need for a proper early warning for preventing loss of life or propertyAny kind of Disaster Risk Reduction DRR measures or Disaster Risk Management DRM efforts will need proper early warnings But this early warning is dependent on proper forecasting Narvekar saidThe financial capital of India faced extreme rainfall on Saturday July 17 similar to what the Konkan region and several places across the Western Ghats have been facingNarvekar cited the example from north Mumbai wherein at 1 pm the IMD issued a yellow alert heavy rainfall up to 115 mm but about 12 hours later it rained so much that it could have qualified as cloudburst Why cannot they tell us one hour before about this extreme rainfallHe said because of the heavy rainfall that night the water level in Mithi River raised from 180m to 42m At 3 am the IMD NowCast said extremely heavy rainfall But the rainfall stopped at 4 am he saidThe IMD has been constantly attacked for such misses by the local media but Thackerays remarks have put the agency in a different predicamentThackerays concern is well taken But if we look at the science it is not possible with reasonable accuracy to say that in such a particular place there will be rainfall of 30 cm or 40 cm IMDs Director General Meteorology Mrutyunjay Mohapatra told IANSThe IMD deploys Doppler radar and satellite images that give observational data which means they can tell what has happened But forecast comes from the models These models we go on improving yearwise and every year he saidEven with the stateoftheart models that are presently used by the meteorologists not just in India but across the world it is a problem to deterministically determine the centimetre rainfall such as 30 cm or 40 cm or for that matter even more Mohapatra claimedThere has been an observed increase in natural disasters like cyclones and floods in the country during recent years in many cases due to climate change The frequency of cyclones and stations reporting very heavy and extremely heavy rainfall has been increasing neccessiating the need for accurate forecastHowever the problem of flooding is not just due to accurate or inaccurate rainfall Experts said that if there is 30 cm or 50 cm rainfall for just one day there will be a flood problem but that can be managed But if such heavy rainfall continues for seven days there will be a problemThe soil is saturated and hence whatever rain happens now even if not extremely heavy the water will be standing and will cause flooding or landslidesAs claimed by the Ratnagiri district collector not all floods in Chiplun were natural as much of it was manmade illegal construction in the Vaishthi river bed and release from nearby dam caused havoc in the coastal townTherefore what is needed is prediction by the IMD of wet spells the possibility of continuous rainfall over a number of daysBut the IMD has been regularly issuing forecast for heavy to extremely heavy rainfall for the Konkan region and Western Ghats This wet spell was predicted Mohapatra addedPaying heed to IMD warnings there is a need to take preventive measures and evacuate people before disasters strikeHeeding to the states request the Centre has deployed the Army Air Force Navy Coast Guard and NDRF personnel for rescue operations since ThursdayThackeray however tweeted later in the afternoon that the administration and citizens should be taking precautionary measures over next 23 days in view of the warning issued by the weather departmentAs per IMD records rainfall recorded for various stations along the Western Ghats from 830 am of July 22 till 830 am of July 23 was 7 cm or more Mahabaleshwar 60 cm breaks alltime past rainfall record Kolhapur 40 cm Londa 38 cm Belagavi 34 cm Betul 28 cm Shivmogga 27 cm Uttar Kannada 24 cm Sanguem 21 cm Sanquelim 18 cm Kodagu 17 cm Haveri 16 cm Quepem Matheran Kolhapur Belgaum 15 cm each Ponda Hanamkonda Canacona 11 cm eachThis story has been sourced from a third party syndicated feed agencies Midday accepts no responsibility or liability for its dependability trustworthiness reliability and data of the text Midday managementmiddaycom reserves the sole right to alter delete or remove without notice the content in its absolute discretion for any reason whatsoever