Heavy rain has filled southern Taiwan's Wushantou Reservoir to the brim — good news for Tainan's water supply, but a flood warning for towns downstream.

• Days of heavy rain from a strong southwest air flow pushed the reservoir to 100% full, and it began spilling over naturally on Wednesday evening.
• Rainfall in the catchment area topped 100mm two days running, lifting the water level past the official full mark.
• Downstream areas including Guantian, Houbi, Dongshan and Liuying are under alert as water is released.
• Nearby Zengwen Reservoir also jumped from about 85% to over 90% full, holding more than 400 million cubic meters.
• Several other reservoirs and ponds in the region are releasing water at the same time.

Outlook: More rain would keep the spillover going and raise flood risk downstream, but Tainan's water worries for the season look largely settled.