Horana sits in Sri Lanka’s southwestern wet zone, where the southwest monsoon from May through September brings the island’s heaviest rainfall, supplemented by a second wet spell during the October-to-December inter-monsoon period.
Inland in Kalutara district, the city’s rivers can rise quickly during the wet zone’s heaviest monsoon downpours. The catastrophic May 2017 floods and landslides, triggered by an intense burst of southwest monsoon rain, remain the reference event for how quickly this densely populated region can flood, and Sri Lanka’s Department of Meteorology relies heavily on radar to track incoming monsoon rain bands. Learn more: Flash Flood Warning Signs on Radar · Open the full Rain Map