The findings matter because flash floods in Indonesia have become more frequent and destructive in recent years. Understanding the combined role of land-use change and climate variability is essential for designing effective disaster mitigation strategies, especially in densely populated river basins like Jeneberang.
Environmental Pressure Builds in the Upstream Region
Over the past two decades, the upstream area of the Jeneberang watershed has undergone rapid land-use transformation. Forest cover has declined sharply, replaced by mixed agriculture and shrubland. This shift reduces the land’s natural ability to absorb rainfall.
Forests act as hydrological buffers, slowing down water flow and increasing soil infiltration. When they are removed, rainwater moves quickly across the surface, increasing runoff into rivers. The study shows that this process has intensified flood dynamics in the watershed.
At the same time, climate patterns are shifting. Extreme rainfall events—short bursts of very heavy rain are becoming more frequent. When these events occur over degraded land, the risk of sudden flooding rises dramatically.
Data-Driven Analysis of Two Decades
The research is based on a quantitative analysis of environmental and climate data collected between 2003 and 2023. The study integrates multiple data sources:
- Satellite imagery to track land-use and forest cover changes
- Daily rainfall records from meteorological stations
- Historical flood event data
- Population data for downstream areas
Geographic Information Systems (GIS) were used to map spatial changes, while statistical trend analysis identified shifts in rainfall intensity. The study also calculated hydrological indicators such as runoff coefficients and peak river discharge to measure how the watershed responds to rainfall.
This combined approach allows for a comprehensive understanding of how environmental and climatic factors interact over time.
Key Findings: Flood Risk Rising on Multiple Fronts
The study identifies several critical trends:
- Forest cover decreased by 17.8% between 2003 and 2023
- Runoff coefficient increased by 19%, indicating more surface water flow
- Peak river discharge during extreme rainfall rose by 24%
- Extreme daily rainfall events showed a statistically significant upward trend
- High-risk flood zones expanded by 29%, particularly in populated downstream areas
These findings confirm a strong link between upstream land degradation and downstream flood risk. The increase in runoff and river discharge means that more water reaches downstream areas faster, raising the likelihood of flash floods.
Climate Change Intensifies the Threat
The study also highlights a crucial shift in rainfall patterns. While total annual rainfall has not changed significantly, the intensity of rainfall events has increased. Heavy rainfall exceeding 100 mm per day is now more common.
This change has important implications. Flood risk is no longer driven by how much rain falls over a year, but by how much falls in a short period. Intense rainfall events overwhelm the watershed’s capacity, especially when upstream vegetation is reduced.
The combination of deforestation and extreme weather creates a compounding effect, significantly increasing flood hazards.
Downstream Communities Face Greater Exposure
The expansion of high-risk flood zones is most evident in downstream areas, where population density is higher. The study shows that flood-prone areas increased from 4,860 hectares to 6,269 hectares over the study period.
This means more people, homes, and infrastructure are exposed to flood risks. The research emphasizes that disaster risk is not only a function of natural hazards but also of human vulnerability and exposure.
Urban growth and settlement patterns in flood-prone areas further amplify the potential impact of flash floods.
Restoration Offers a Measurable Solution
The study goes beyond identifying problems by testing a restoration scenario. Increasing upstream forest cover by just 10% produces measurable benefits:
- Runoff coefficient decreases by 8%
- Peak river discharge drops by 8%
- High-risk flood areas shrink by 10%
These results demonstrate that reforestation and watershed restoration can significantly reduce flood risk. Environmental rehabilitation is not only an ecological priority but also a practical disaster mitigation strategy.
As Asikin Muchtar of Universitas Indonesia Timur explains, the findings provide strong scientific evidence that “integrated watershed management and upstream forest restoration are essential to reducing flash flood risk under changing climate conditions.”
Implications for Policy and Practice
The study offers clear guidance for policymakers, planners, and disaster management authorities:
- Prioritize reforestation and conservation in upstream areas
- Regulate land conversion, especially on steep slopes
- Integrate watershed management into spatial planning policies
- Strengthen early warning systems in downstream communities
- Promote sustainable land-use practices among local populations
These measures align environmental protection with disaster risk reduction, creating a more resilient landscape.
For Indonesia and other tropical regions facing similar challenges, the research underscores the need for coordinated action across environmental, climate, and urban planning sectors.
Author Profile
Asikin Muchtar, S.T., M.T. is a researcher at Universitas Indonesia Timur specializing in hydrology, spatial analysis, and disaster risk management. His work focuses on the interaction between land-use change, watershed dynamics, and climate variability in tropical environments.
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