Escalating Risk of Disaster in the Coffee Landscape: Lessons from the Gayo Highland
- Asep S Adhikerana
- Jun 1
- 5 min read
Introduction
Central Aceh Regency, located in the Bukit Barisan plateau in Sumatra, Indonesia, and referred to as the Gayo Highland, is a critical upstream ecosystem that regulates the hydrological processes for downstream areas. Highland catchment areas such as Central Aceh play a disproportionate role in controlling runoff, sediment transport, and water availability, making their ecological integrity important for regional resilience (Bruijnzeel, 2004; FAO, 2015). By the end of November 2025, the region experienced severe compound disasters involving landslides and flash floods, with a multi-stage impact that extends into early 2026. Rather than a single catastrophic event, these disasters reflect the interaction of extreme climate, geological fragility, hydrological processes, and land-use pressures.
This brief paper examines disasters through an integrated systems perspective, showing how natural vulnerabilities combined with anthropogenic drivers produce systemic failures.
Regional Settings
Geographical and ecological context.— Central Aceh is characterized by altitudes ranging from about 200 to 2,600 meters above sea level, steep mountainous terrain, and its proximity to Laut Tawar Lake, a freshwater body that serves as a hydrological buffer. As an upstream water catchment area, this region regulates downstream hydrology through gradual infiltration, storage, and release of water. Disturbances to vegetation cover or soil structure in such systems can significantly increase runoff, erosion, and flood risk (Bonell & Bruijnzeel, 2005).
Geological characteristics.— The geology of Central Aceh is dominated by volcanic formations associated with the Bukit Barisan mountains, including tuff (consolidated volcanic ash) and highly weathered volcanic soils. These materials show: (a) High porosity and permeability; (b) Low shear ability when saturated; and (c) Vulnerability to rapid loss of cohesion. Volcanic soils are widely recognized to be susceptible to landslides under heavy rainfall due to their metastable structure (Sidle & Ochiai, 2006). Once saturated, pore-water pressure increases and reduces effective stress, triggering slope failure.
Climate and rainfall patterns.— Central Aceh has a humid tropical climate with high annual rainfall. During the November 2025 event, the intensity of rainfall was reported to have reached extreme levels (about ~400 mm/day) for about three consecutive days. Such rainfall can only be held by soils with a saturated profile, and will increase the water pressure of the pores, as well as accelerate surface runoff and subsurface flow. Extreme rainfall events in Southeast Asia are increasingly linked to climate variability and change, which reinforces the frequency of hydrometeorological hazards (IPCC, 2021).
3. Overview of Disaster Events
The events of late November 2025 were characterized by several interacting hazards:
(a) Widespread landslides on steep slopes;
(b) Flash floods that affect several sub-districts; and
(c) River blockages caused by debris (logs, sediment, soil).
The impacts include damage to settlements, roads, and bridges, as well as massive losses to farmland and local livelihoods. It was recorded that there were 4,221 units of damaged community houses (1958 units severely damaged, 500 units moderately damaged and 1763 units lightly damaged). Four national roads and dozens of roads from district, provincial and national levels were affected, where 93 roads and 74 bridges were damaged or washed away, worsening logistics and evacuation distribution. In addition, there were 2,765 hectares of rice fields, 13,064 hectares of plantation land, and 4,328 hectares of horticulture (chili) damaged and failed to harvest. Around 11,105.38 hectares of Arabica Coffee plantation was destroyed very significantly, with a value of damage reaching Rp 310.95 billion. Critically, these events represent a cascading hazard system, where landslides contribute debris to river systems, forming temporary dams that then fail and produce destructive flood waves (Cutter, 2018).
Causal Analysis
Direct trigger: extreme rainfall.— The main trigger is high-intensity and prolonged rainfall. This causes:
(a) Soil saturation;
(b) Increased water pressure of the pores; and
(c) Reduce soil cohesion and shear strength. Landslides caused by rainfall are one of the most common natural hazards in mountainous tropics (Guzzetti et al., 2008).
Geological amplification.— Geological conditions reinforce the danger:
(a) The tuff layer weakens significantly after saturation;
(b) Weathered volcanic soil loses structural integrity;
(c) The slope fails under gravitational pressure. This results in mass movements, including landslides and debris flows. The interaction between rainfall and weak lithology is a driver of well-established slope instability (Sidle & Ochiai, 2006).
Hydrological processes.— Hydrological dynamics intensify the impact of disasters through several mechanisms:
(a) Steep terrain accelerates runoff concentrations;
(b) Landslide debris enters the river channel; and
(c) Temporary natural dams are formed. The sudden failure of this dam triggered flash floods, greatly increasing the destructive force. Such processes are typical in mountainous catchment areas that experience debris flow activity (Jakob & Hungr, 2005).
(a) the conversion of forests to agricultural land;
(b) cultivation on steep slopes; and
(c) increased exposure to the ground surface.
These changes result:
(a) reduced root reinforcement;
(b) increased erosion; and
(c) higher runoff coefficients. Deforestation and agricultural expansion are widely recognized as the main drivers of increased risk of landslides and floods in the tropical highlands (Geist & Lambin, 2002; Bradshaw et al., 2007).
Pre-existing land instability.— Evidence suggests that parts of the landscape were already unstable prior to the event, including: long-term slope movements, subsurface weakening, and cavity formation. This indicates that the system is in a critical threshold state, where external triggers (precipitation) can quickly lead to failure. Such preconditioning is common in landslide-prone terrain (Crozier, 2010).
Policy Gap and Spatial Planning
The disaster highlighted the mismatch between spatial planning frameworks and actual land use. Regional land use planning (RTRW) emphasizes:
(a) steep slope protection;
(b) conservation of upstream forest areas;
(c) restrictions on development in hazard-prone zones.
However, the observed conditions include:
(a) expansion of agriculture into protected or non-suitable areas;
(b) settlements in high-risk zones; and
(c) weak enforcement of land-use regulations. These gaps reflect broader governance challenges, including limited law enforcement capacity, economic dependence on land-based livelihoods, and inadequate integration of disaster risk reduction into spatial planning (UNDRR, 2019).
Systemic Risk Perspective
The Central Aceh disaster can be understood as a compound and systemic risk event, arising from the interaction between:
(a) natural drivers (rainfall, geology, topography), and
(b) human drivers (land use changes, policy gaps).
These interactions create reinforcing feedback loops, such as:
(a) land degradation leads to increased hazards leading to greater damage and then leads to further degradation; and
(b) reactive disaster response leads to limited prevention and then leads to recurrent risks. These dynamics are in line with the concept of risk accumulation, where vulnerability increases over time due to unsustainable land management and inadequate governance (IPCC, 2022).
Key Lessons Learned
a. Upstream area as a critical control point.
Highland ecosystems regulate downstream hydrology; their degradation reinforces the risk of regional disasters.
b. Land use as a central risk driver.
Unsustainable land use can turn a natural disaster into a disaster.
c. Policy implementation issues. Spatial planning instruments (RTRW) require effective law enforcement, incentives, and community involvement to be meaningful.
d. The need for an integrated approach.
Effective disaster risk reduction should be combined: Spatial planning, watershed management, and ecosystem restoration (e.g., agroforestry systems).
Conclusion
Landslides and floods in Central Aceh are not isolated natural events but a form of systemic risk. Extreme rainfall acts as a trigger, geological fragility allows slope failure, and land-use changes amplify their impacts. Reducing risk in the future requires a transition to: (a) risk-based spatial planning, (b) sustainable land management practices, and (c) stronger institutional coordination and enforcement. Restoring the ecological integrity of upstream systems like Central Aceh is critical to increasing resilience and protecting downstream communities.
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