Caring for the upstream to save the downstream

Rain falling for several hours should no longer be capable of paralysing a major city. Yet climate change is making weather patterns increasingly difficult to predict. In the midst of what should have been the dry season, the city of Surabaya, East Java, was drenched by high-intensity rain for several days at the end of June 2026. Water inundated a number of roads, residents’ activities were disrupted, traffic ground to a halt, and familiar questions resurfaced. Why does flooding still occur in a city that for years has been known for its serious approach to building a flood control system? The question cannot be answered simply. Inundation in Surabaya is no longer solely a matter of insufficient drainage channels, but rather an increasingly complex issue of urban water governance. The city is growing, built-up areas are expanding, absorption surfaces are shrinking, whilst rainfall is becoming more extreme due to climate change. On the other hand, the Surabaya City Government has demonstrated that flood control work is ongoing. Since mapping was conducted in 2020, a total of 1,015 inundation points have been identified. By 2025, around 440 points had been addressed, with approximately 120 more points targeted for completion throughout 2026 through drainage construction, channel connectivity, normalisation, pump houses, and the construction of retention basins. This achievement shows that tackling inundation is not a task that stops within a single budget period. It is a long-term investment requiring phased planning, as well as the ability to adapt to changing city conditions. Interestingly, the biggest challenge lies outside the small channels in residential areas. The main problem is the relationship between tertiary channels, primary channels, rivers, and estuaries. As long as this chain does not function as a single system, inundation will continue to appear, even if local drainage has been improved. The upstream node. All this time, the public has often viewed flooding only from the point where water collects. Yet the real problem is often far downstream. Sedimentation occurring in the Surabaya River, Kalimas, and Kali Jagir reduces water flow capacity. This shallowing causes water to flow more slowly towards the sea. The situation becomes even more severe when sea tides coincide with heavy rain, creating a backwater phenomenon. In such a situation, pump houses work harder because the water that has been pumped cannot fully flow out to sea. This is why urban drainage construction is insufficient if river normalisation does not proceed simultaneously. Water always follows the law of gravity. If downstream channels are blocked, then building new channels in residential areas merely shifts the problem from one location to another.