Irsyan Hasyim, Jakarta – The massive flood that struck Bali on September 10, 2025, was not just a natural disaster. According to the Indonesian Forum for the Environment (Walhi), the tragedy was closely tied to unchecked land use changes driven by rapid development.

Environmental groups warn that the Island of the Gods has exceeded its water and land carrying capacity, leaving it increasingly prone to extreme floods. Here's what you need to know.

What triggered the floods?

Walhi Bali Executive Director Made Krisna Dinata said the large-scale conversion of paddy fields into buildings and other infrastructure has altered the natural landscape, reducing the land's ability to absorb and regulate water.

Between 2018 and 2023, four regencies (Denpasar, Badung, Gianyar, and Tabanan saw significant farmland loss. These areas make up the Sarbagita region, Bali's urban and tourism hub.

Denpasar lost 784.67 hectares of paddy fields, equivalent to 6.23 percent of its area. In Badung, the reduction reached 1,099.67 hectares, while Gianyar lost 1,276.97 hectares. The largest decline occurred in Tabanan, which saw 2,676.61 hectares of farmland converted.

Why is paddy land so important?

Paddy fields are more than just farmland. They play a vital role in Bali's traditional Subak irrigation system, which regulates water flow across the island. Krisna explained that one hectare of paddy fields can hold up to 3,000 tons of water when the water level is seven centimeters.

When farmland is paved over for buildings, this natural water storage capacity disappears. The result is excess rainwater flowing directly into rivers and low-lying areas, fueling floods.

How tourism and urbanization made it worse

A decade-long study of Badung Regency, which sits in the upstream and midstream of the Badung River Basin, revealed rapid urbanization between 2010 and 2020. Built-up areas expanded quickly due to tourism infrastructure and housing projects supporting Denpasar.

At the same time, paddy fields and mixed gardens shrank, reducing the land's ability to absorb rainwater.

This shift has led to higher water overflow during storms, faster and stronger peak discharges in rivers, and declining infiltration as concrete and asphalt surfaces replaced permeable soil. As population density increases, Krisna warned, the risk of sudden downstream flooding grows even more severe.

Walhi also noted that development projects are increasingly built along river borders, areas that should be protected. This not only worsens flooding but also raises the risk of casualties when rivers overflow.

Bali's floods are a stark reminder of the island's fragile balance between nature and development. As agricultural land continues to vanish under concrete, the natural systems that once protected communities are breaking down, leaving the island more exposed to disaster.

Source: https://en.tempo.co/read/2049649/walhi-explains-the-causes-behind-balis-worst-flood-in-a-decad