Tamil Nadu’s rainfall picture changes dramatically in 27 days; 18 deficit districts move into normal or excess categories

Image used for representation | Photo Credit: C. Venkatachalapathy In a striking shift in Tamil Nadu’s rainfall position, 18 of the 23 districts that were rainfall-deficient at the close of the Southwest monsoon have moved out of the deficit category in the 27 days since October began, Commissioner of Revenue Administration B. Chandra Mohan said on Thursday (October 29, 2026). By October 27, only five districts continued to record deficient cumulative rainfall, while several others had moved into the normal or excess categories.The change is reflected in the State’s cumulative rainfall figures, he said. “At the end of the Southwest monsoon on September 30, Tamil Nadu had recorded a 16% rainfall deficit. By October 27, the cumulative shortfall had narrowed to less than 1%, bringing the State’s overall rainfall close to its normal level for the period. The shift has been driven by substantial rainfall during the opening weeks of the Northeast monsoon.”Between October 1 and 27, Tamil Nadu recorded an average of 217.2 mm against the period’s normal of 144.2 mm – a surplus of 51%. All 38 districts received rainfall within the normal, excess or large excess categories during this period, with none recording deficient rainfall during October. The most significant change was evident in districts that had ended September with substantial rainfall shortfalls.Nagapattinam’s cumulative rainfall departure improved from −54% to −8%, while Karur moved from −53% to −6%. Kallakurichi shifted from −29% to +2% and Erode from −32% to +6%. Mayiladuthurai’s departure narrowed from −28% to −6%, while Tiruchirappalli improved from −39% to −7%. The cumulative rainfall position also improved in the Nilgiris, from −32% to −13%; Namakkal, from −42% to −8%; and Tiruppur, from −40% to +13%.“These changes illustrate the scale of the shift in just 27 days. Districts that had entered October with marked shortfalls are now recording cumulative rainfall closer to, or above, their respective normals. The improvement is not uniform, however, and some districts continue to carry substantial deficits from earlier months,” Dr. Chandra Mohan said.Northeast monsoon effectThe first 27 days of the Northeast monsoon have substantially changed Tamil Nadu’s cumulative rainfall position, with most districts that entered October in deficit now recording rainfall within the normal or excess categories, he said. The Statewide cumulative rainfall deficit has narrowed to less than 1%, reflecting the scale of the improvement so far. With November and December still ahead, the season remains in progress.“Continued monitoring will be important, particularly in districts where deficits persist and in catchments where rainfall distribution remains uneven. The present figures mark a significant change in the State’s rainfall position, rather than the conclusion of the season’s rainfall needs,” the officer said.HEAVY OCTOBER RAINFALL DRIVES THE SHIFTSeveral districts recorded rainfall well above their normal for October 1 to 27Coimbatore received 313.4 mm against a normal of 137.4 mm, a surplus of 128%Tirunelveli recorded 258.2 mm against 123.0 mm (+110%)Dindigul received 328.0 mm against 166.4 mm (+97%)Kallakurichi recorded 261.6 mm against 136.2 mm (+92%)Tiruvannamalai received 281.8 mm against 149.1 mm (+89%)FIVE DISTRICTS CONTINUE TO RECORD CUMULATIVE DEFICITSDespite the broad improvement, Chengalpattu, Thanjavur, Kancheepuram, Vellore, and Thoothukudi continued to record deficient cumulative rainfall as of October 27. Their departures stood at −38%, −30%, −24%, −22%, and −20%, respectively.Thoothukudi’s shortfall has narrowed considerably from the 65% deficit recorded at the close of the Southwest monsoon. Although rainfall during October has been close to normal in the district, the earlier shortfall continues to weigh on its cumulative total.District averages also mask local differences in rainfall distribution. Rainfall received across a district may vary considerably, including in reservoir catchments. A narrowing rainfall deficit, therefore, does not, by itself, establish a corresponding improvement in groundwater levels or stored water. Published - October 29, 2026 04:46 pm IST