India: Lingering disruptions likely following flooding in Mumbai, Sept. 26

Lingering weather-related disruptions are expected in Mumbai on Sept. 26. Heavy rainfall on Sept. 25 amid the ongoing monsoon season triggered flooding in the city, causing casualties and disruptions to both ground and air transport. More than 20 cm (8 inches) of rainfall in five hours was recorded in parts of the city late Sept. 25. Authorities have reported at least four flood-related fatalities as of Sept. 26. Many roads were made impassable due to floodwaters and train and bus services in the city were heavily disrupted. At least 14 flights were diverted from Chhatrapati Shivaji Maharaj International Airport (BOM) on Sept. 25. Services are largely starting to resume normal operations as of Sept. 26; however, lingering disruptions are likely in the coming hours. Schools remain closed across Mumbai as of Sept. 26.

Further adverse weather is forecast across the region over the coming days. The India Meteorological Department is maintaining orange heavy rainfall, thunderstorm, and lightning warnings (the middle level on a three-tier scale) across Mumbai on Sept. 26, and yellow warnings are in place on Sept. 27. Authorities will likely issue new alerts or update/rescind existing advisories as weather conditions change over the coming days.

Further sustained heavy rainfall could trigger additional flooding in low-lying communities near rivers, streams, and creeks. Urban flooding is also possible in developed areas with easily overwhelmed stormwater drainage systems. Sites located downstream from large reservoirs or rivers may be subject to flash flooding after relatively short periods of intense rainfall. Landslides are possible in hilly or mountainous areas, especially where the soil has become saturated by heavy rainfall.

Authorities could issue mandatory evacuation orders for flood-prone communities over the coming days. Disruptions to electricity and telecommunications services are possible where significant flooding or landslides impact utility networks.

Floodwaters and debris flows may render some bridges, rail networks, or roadways impassable, impacting overland travel in and around affected areas. Ponding on road surfaces could cause hazardous driving conditions on regional highways. Authorities could temporarily close some low-lying routes that become inundated by floodwaters. Flooding could block regional rail lines; freight and passenger train delays and cancellations are likely in areas that see heavy rainfall and potential track inundation. Severe weather could also trigger flight delays and cancellations at airports in the region.

Localized business disruptions may occur in low-lying areas; some businesses might not operate at full capacity because of flood damage to facilities, possible evacuations, and some employees' inability to reach work sites.

Flooding could heighten the threat of disease outbreaks. Backflow from drains mixed with floodwaters can become trapped in open areas when inundations recede. These stagnant pools often become a breeding ground for mosquitoes and bacteria, increasing the incidence of insect- and water-borne diseases. Exposure to contaminated water from inundated industrial sites, sewer systems, and septic tanks also poses a significant health threat.