Bappa won’t, but you may stay dry: IMD warns of weaker rain in Mumbai ahead

In light of the India Meteorological Departmentrsquos IMD warning of below normal rainfall this monsoon season under the effect of ElNino Regional Meteorological Centrersquos IMD Mumbai head scientist Bikram Singh spoke to Sunday midday about rainfall patterns noticed in Mumbai and Maharashtra in July the weak monsoon start to the month of August and how the effect of ElNino is likely to affect the latter half of the monsoon season mdash mid August to September he also talked about IMDrsquos impact based forecast and reasons why IMD gives its red and orange alertsWhile 65 per cent of the decision is driven by the quantum of rainfall alerts are issued for administrative preparedness Singh said ldquoA lot of thought goes into sounding a red or yellow or orange warningrdquoSpeaking about what the alerts mean Singh indicated that they are meant to not just alert citizens but also alert authorities on ldquoassociated impactrdquo mdash a red alert can be issued on a day that follows several high rainfall days Singh said these alerts also account for wind speed landslide waterlogging thunderstorms or flash floodsOn what basis does IMD give alertsWhile 65 per cent of the decision is driven by the quantum of rainfall alerts are issued for administrative preparedness A lot of thought goes into sounding a red or yellow or orange warning because we are answerable to authorities that take response and preparedness decisions based on our warningsWe also give impact based alerts by gauging situations which can have an lsquoassociated impactrsquo in addition to the quantum of rainfall as per our predictionsFor instance if IMD issued a red alert for five consecutive days on the sixth day we would have already noticed that the rainfall activity is going to reduce However we will still issue a red alert despite the expectation of low quantum of rainfall to ensure everyone is prepared to handle the aftermath of a past heavy spell even during a light spell day because the impact persists even if the rain subsidesWe are also exceptionally careful about the red alerts in the ghats section If you will notice we give red alerts more leniently during the month of August because due to June and Julyrsquos rainfall the soil is already saturated The possibility of a landslide becomes highest in August and September so we immediately issue a red alertRegarding amount of rainfall expected IMD has a clear formulaVery Light 01 to 24 mmLight 25155 mmModerate 156644 mmHeavy 6451155 mmVery Heavy 11562044 mmExtremely Heavy ge 2045 mmExceptionally HeavyWhen the amount is a value near about the highest recorded rainfall at or near the station for the month or season However this term will be used only when the actual rainfall amount exceeds 12 cmWhat do the alerts meangtRed alert means there is a warning and a need to take actiongtOrange alert means there is a need to be prepared to take actiongtYellow alert means there is a need to be watchful and awaregt Green alert means no action is requiredgtIdeally a green alert indicates light to moderate rainfall as is expected during the monsoon seasongtA yellow alert is meant to tell citizens to be aware of rain carry an umbrella plan a commute etcgtAn orange alert informs citizens that they can stay at home if possible be vigilant watch news and communication from local authorities Authorities are alerted to watch lowlying areas issue warnings for those living on river banks assign dewatering pumps etcgt A red alert indicates extremely heavy rainfall It also helps local authorities decide if schools need to be given a holiday and how the emergency situation needs to be monitored from that point forward to prevent mishaps or untoward incidentsPiciStockCan you cite any examplesFor example Mumbai had a red alert on July 4 and 5 2026 Immediately before that it was an orange alert So the red alert was also issued considering that under an orange alert the city has already received a lot of rain our systems are already operating at full response capacity mdash you can say on fire fighting modeGiven this a consecutive spell of rain qualifies for a red alert because we have to consider the fact that the soil has already saturated with its water absorption capacityExample Similarly two years ago Matheran had two days of intense rain and a red alert was issued considering the amount of rainfall that was expectedanticipated However on the third day despite low rainfall we continued the red alert Because Matheran has lost red soil It had already reached its saturation capacity Even little subsequent rainfall can now lead to a landslideFor this single purpose we have also started to give additional information or warnings at the bottom of all our daily forecast that predict the associated impact or an orange or a red alert such asImpact ExpectedgtLocalised inundationflooding of lowlying areas and urban areasgtPossible uprooting of weak trees and collapse of old and unmaintained structuresgtPossibility of flash floodsgt Disruption to road rail air and ferry transportgt Local disruption of municipal services Water electricity etcgt Flow of water over lowlying roads and bridgesgt Damage to horticulture and standing crops due to water inundationgt Squally weather expected over coastal districts of Konkangt Rough sea conditions along the coastgt It may lead to riverine flooding in some river catchments for riverine flooding please visit the Central Water Commission webpagegt LandslideMudslides and rock falls in vulnerable areasgt Strong wind may damage plantations horticulture and standing cropsgt Minor damage to kutcha houseswalls and hutsgt Possibility of cloud to ground lightning during thunderstorm eventsAugust so far did not receive much rainfall in comparison to July Is it expected that August will receive weak rainfallSo far the condition is We have managed to match the seasonal rainfall expectation due to Julyrsquos rainfall If we examine the entire seasonrsquos rainfall Mumbai is not in deficit There are some districts of Maharashtra that indicate a deficit in annual average rainfall but overall the state has received good rainfall this season so far El Nino factor is likely to intensify during the later part of the monsoon season towards the end of August and in September We can expect weak rainfall during this period due to El Nino We should be prepared for less rainfall going forward for the remainder of the monsoon seasonAt present 10 districts of Maharashtra have deficient rainfall Nandurbar Amravati Nagpur Akola Chandrapur Jalna Hingoli Beed Solapur and Sindhudurg Only Nashik has a large excess rainfall and Chhatrapati Sambhaji Nagar Pune Palghar and Mumbai suburbs have excess rainfallIMD had predicted a weak monsoon below normal monsoon owing to ElNino How has this affected the monsoon seasonThe lack of sustained rainfall short periods of heavy rainfall or sudden intense rain spell followed by a considerable dry spell are all signatures of ElNinoWe have already noticed this during the intense rainfall spell of the first week of July followed by a considerable dry spell The whole of Maharashtra did not have any rainfall during JuneWe must consider temporal variation mdash if we examine the week to week rainfall pattern mdash the ElNino effect becomes evident Temporal variation in rainfall is how the amount frequency and intensity of precipitation change over time at a specific placeIf we examine the rainfall received by the entire country the El Nino effect becomes more visible There are some states that have received very little rain and are in deficit some states have received normal rainfall Even within states some districts are in deficitIntermittent dry spells also impact other factors such as a rise in temperatures with much higher maximum temperatures that do not align with the monsoon trend All of this is attributed to the impact of ElNinoWhat is considered normal below normal and above normal rainfallIMD considers average rainfall of 10 years to determine the variation expected during any particular monsoon season We categorise the variation into 5 broad bracketsLarge excess 60 OR MOREExcess 20 to 59Normal 19 to 19Deficient 20 to 59Large Deficient 60 to 99