Despite their increasing risk, wildfire hazard cascades in tropical montane regions remain poorly understood. Most existing research comes from temperate systems, where wildfires are known to amplify floods, accelerate erosion, and increase the probability of landslides and debris flows by removing vegetation, altering soil properties and increasing surface runoff (Belongia et al., 2023; Boyer et al., 2022; DeBano, 2000; Doerr et al., 2000; Guerriero et al., 2025; Jordan, 2016; Kemter et al., 2021; Rengers et al., 2020; Swain et al., 2025; Vahedifard et al., 2024; McGuire et al., 2024).

However, there are additional factors in tropical mountains that introduce a unique risk and complexity (Moazeni and Cerdà, 2024; Robinne et al., 2021). First, the fires impact upon an already diverse multi-hazard landscape with many existing hazard interactions (Arango-Carmona et al., 2025; Ometto et al., 2022; Sandwell et al., 2005). Second, many higher-altitude ecosystems within tropical mountains have no history of wildfire, such that mature climax vegetation and pristine wetlands are burned with unpredictable consequences for hydrological processes and ecosystem services (Marengo et al., 2021; Mason et al., 2026; Pivello et al., 2021; UNEP, 2022). Third, a lack of wildfire history means vulnerable populations without lived experience are exposed to new hazards (McCaffrey, 2004; Paton, 2003). Lastly, vegetation recovery at high altitudes is slow due to cold conditions and the presence of vegetation that is not adapted to fire cycles, causing prolonged impacts (Kappelle et al., 1996; Oliveras et al., 2014; Salinas et al., 2021). Given these differences, there is a need to better understand the long-term cascade of tropical montane wildfires at the process level. This is especially true for multi-hazard risk management, as identifying where hazards interact effectively highlights where those interactions can be proactively impeded (AghaKouchak et al., 2018, 2020; Vahedifard et al., 2024).

The February 2012 wildfire in Uganda's Rwenzori Mountains National Park burned 31 km² of pristine, uninhabited tropical mountain forest and wetlands (Fig. 1) during a brief meteorological drought measuring -3.5 in a 1-month Standardised Precipitation Index (Appendix A). The ecosystem was mature – the fire was the first to affect elevations exceeding 3800 m above sea level in the Rwenzori Mountains for at least 12 000 years (Mason et al., 2026).

The wildfire was followed by unprecedented debris flooding in May 2013 that displaced more than 25 000 people, caused 13 deaths and over USD 4 million in damages (Delforge et al., 2025). Local rainfall records suggested only a 6.6-year return interval (6 h duration), indicating that post-fire landscape changes drove the disaster (Jacobs et al., 2016). We present evidence that, more than a decade later, the Nyamwamba catchment continues to experience flooding, debris floods, mass movements, erosion and water pollution at an elevated level due to fire-induced environmental changes. Because the wildfire occurred in a protected area with no burn history and little subsequent intervention (Mason et al., 2026; Norville et al., 2024), it provides an unparalleled case for this study to characterise the long-term multi-hazard cascade of a tropical mountain wildfire.

The Rwenzori Mountains are an uplifted metamorphic basement block, with hard, crystalline basement geology creating steep gradients and river profiles that climb to a maximum elevation of 5109 m (UNESCO, 2012). It is the third largest glaciated region in Africa (Hinzmann et al., 2024), with abundant quaternary deposits of unconsolidated glacial and fluvial sediment in its valleys (UNESCO, 2012; Ring, 2008). The Rwenzori Mountains National Park is a UNESCO World Heritage Site dedicated to the protection of biodiverse and unique montane flora, classified into five distinct eco-zones (UNESCO, 2012): tropical mixed broadleaf montane rainforest (<2600 m altitude); bamboo forest (2600–3000 m); an ericaceous zone characterised by dense giant heather trees, giant senecios and giant Lobelia (3000–3800 m); afro-alpine moorland and bogs (3800– 4400 m); and the rock, snowfield and glacier zone (>4400 m).

Higher altitudes within the equatorial mountain range have an annual precipitation of 2500 mm, with two wet seasons (March–May and September–December) where monthly precipitation values exceed 375 mm (UNESCO, 2012). The River Nyamwamba is a major river in the southern part of the Rwenzori Mountains that transports water to its delta with Lake George within the Queen Elizabeth National Park area (Fig. 1).

This study characterizes the multi-decadal hazard cascade profile of the Nyamwamba River catchment following a 2012 wildfire that burned 31 km² of pristine tropical mountain forest and wetland in Uganda's Rwenzori Mountains National Park and interprets the implications for regional risk management and broader lessons for tropical montane environments globally. Through an integrated mixed-methods approach combining remote sensing analysis, humanitarian records, field surveys, and semi-structured interviews, we document the long-term interactions between wildfire, flooding, erosion, landslides, and pollution over a 12-year period (2012–2024). The study identifies key hazard interactions using Gill and Malamud's (2016) framework, evaluates entry points for management interventions to mitigate future hazards in fire-sensitive tropical mountain ecosystems, and derives take-aways for the governance and resilience of tropical montane regions facing emerging fire-driven risks.

Historic flood events in the Nyamwamba catchment since 2000 were compiled from multiple open sources: the Emergency Events Database (Delforge et al., 2025), the Sendai DesInventar database (DesInventar, 2025), grey literature in ReliefWeb, and a systematic keyword search (“Kasese” OR “Kilembe” AND “flood”) across Google, Google Scholar, and Google News (Google News, 2025). While recent years benefit from expanded monitoring and reporting, the inclusion of diverse sources provided confidence that all major flood events since 2000 were captured by the search.

We conducted twelve in-person semi-structured interviews during field visits in 2023 and 2024, following ethical clearance. Participants were identified through project partners in Kasese District, with snowball sampling to access other stakeholder groups. They included 2 representatives from the Ministry of Water [M – code used to reference in the results], 2 local government officials [G], 1 wildlife authority employee [W], 1 non-governmental organisation worker [N], 2 local industry workers [I], 1 farmer [F], and 3 community residents [R].

Interviews followed a lightly structured topic guide covering hazard processes and causes, changing risk, existing management, and potential alternatives, while remaining flexible to emergent themes (Creswell, 2009; Galletta, 2020; Mojtahed et al., 2014). A full guide is provided in Appendix C. Interviews lasted 30–120 min, were audio-recorded, transcribed, and coded inductively over two rounds of review, with related codes grouped into interpretive themes (Patton, 2015; Saldaña, 2021). While themes are not presented directly, this analysis informed interpretation of hazard processes, impacts, and management options.

Historic photographs of the vegetation pre- and immediately post-wildfire were taken by project partners with permission for research use. Photographs in Appendices E–J were taken by the study authors during a July 2024 site visit.

Processes identified through the above methods were integrated into a conceptual diagram of the wildfire's multi-hazard cascade (Patton, 2015), following Gill and Malamud's (2016) framework for hazard interaction types. Evidence underlying each connection is documented throughout the Results and summarised in Table D1 (Appendix D).

Remote sensing evidence shows a 30.75 km² burn area for the February 2012 wildfire (Fig. 1), with 87 % of the area burned to a moderate or high severity. The fire occurred during a meteorological drought, with <0.2 mm of precipitation in the 4-weeks preceding the fire (Jacobs et al., 2016) and a one-month Standardised Precipitation Index measuring -3.5 for January 2012 (Appendix A). The fire's cause of ignition is still unknown by the water and wildlife authorities [M1; M2; W1].

The fire burned between 3360–4400 m above sea level, burning climax “heather zone” forest, “spongy” [R1] Afroalpine moorland, and methane-rich bogs [M1] with no recorded history of wildfires (Fig. 3a; Mason et al., 2026; UNEP, 2022). Photographs from March 2012 show indicators of high burn severity (Fig. 3b), while images from July 2024, twelve years later, reveal regrowth limited to a maximum of 2.5 m, with the upper canopy still vacant (Fig. 3c). These slow growth rates and an observed scarcity of heather in the regrowth succession indicate that natural recovery will require several decades (Wesche et al., 2000).

The wildfire has unidirectional probability-increasing interactions with four secondary hazards. First, burning of soils and vegetation cover increased surface erosion and runoff to river channels, raising turbidity, carrying ash and peat, and introducing biological contaminants. Respondents recalled a strong smell “like methane” after the fire [M1; M2; R1; G1], highlighting wildfire-driven runoff pollution (#1). Second, reduced interception and infiltration capacity increased peak discharges at shorter lag times, driving a marked rise in fluvial flooding (#2; Sect. 3.2). Riverbank erosion has also accelerated due to higher discharges and loss of root cohesion (#3; Sect. 3.4), which, together with higher peak flows after the wildfire, enhanced the conditions for debris flood formation due to greater sediment supply [M1; R1] (#4, #17). These interactions (#1–4) are unidirectional because none of the secondary or tertiary hazards have resulted in further occurrence of wildfires in the catchment.

Additional relationships where the wildfire has catalysed other hazard interactions are numerous, but evidence for these cannot fully be established without intensive monitoring and field experimentation. Based on hydrological theory, some interactions catalysed by the wildfire's effects would include:

River channel erosion-triggering-landslide (#10). increased discharge after the wildfire (Moody and Martin, 2001) catalyses the generation of landslides caused by erosive undercutting from higher river erosion rates (Korup and Schlunegger, 2007).

All twelve respondents reported heightened flood risk in the Nyamwamba catchment. Five attributed this directly to changes in hydrological processes caused by the 2012 wildfire [M1; M2; G1; G2; R1], while others cited land use change [N1; W1; R3], climate change [N1; I2], or the discontinuation of dredging [I1; R2]. A government official explained that “the burning is the reason we are now having the floods annually … we know how useful wetland vegetation is in controlling floods, releasing water slowly” [G1]. Similarly, a local guide described the flood-buffering role of the alpine wetlands: “the moss was like a big 1 m thick sponge, it soaked up all the rain … 20 or 30 km² of rock that was once boulders covered in moss is now bare” [R1]. Table 2 documents ten flood events since 2012, all exceeding in intensity the two documented events during the preceding 12 years, with the 2013 and 2020 debris floods requiring international humanitarian appeals (Act Alliance, 2020; Delforge et al., 2025; Okiror, 2020).

The wildfire has increased the frequency and magnitude of fluvial flooding, but also introduced two new mechanisms of flooding, with gravity-driven debris floods and avulsion floods linked to increased mass movement (Sect. 3.3) and erosion (Sect. 3.4) in the catchment [M1; M2].

Vegetation and soil loss following the wildfire reduced interception, infiltration, and water retention capacity, amplifying the river's discharge response to rainfall. The fluvial flooding of unprecedented intensity on 5 May 2013 followed rainfall of only a 6.6-year estimated return period for a 6 h event (Jacobs et al., 2016). Two respondents emphasise that a lack of lived experience prior to this first flood created additional vulnerability among affected communities: “2013 – that was when we were all surprised. I could not believe what I saw” [I1]; “we were not prepared because we had never experienced such magnitude” [M1]. Seven years later, an industrial worker recalled the 2020 event as “an 800 cumecs flood…higher than our professional hydrologist's modelling of a 1000-year flood event” [I2].

Two floods (2013 and 2020) included debris floods, confirmed in video footage and respondent testimony [M1; R1]. A water authority described “entire mahogany trees coming down as flood load” [M1], while a resident noted “moving rocks two times the size of a minibus” [R1]. Field photos (Appendix G) confirm extensive boulder deposition on the floodplain, and the river has since shifted from a pre-wildfire meandering form with vegetated banks to a braided morphology laden with coarse crystalline sediment (Appendix K).

Elevated erosion rates and sediment deposition have heightened the risk of avulsions [M1; M2]. On 22 May 2024, for example, the Nyamwamba breached its outer bank upstream of Kasese town, inundating Kiwa hot springs and displacing 5389 people [M1] (Table 2).

High flows during fluvial and debris floods damage engineered flood defences, increasing their own probabilities of future breaches in self-perpetuating positive feedback (#7; #20; Appendix H). At the same time, their elevated velocities and turbulence generate shear stress and hydraulic action that trigger river erosion and accretion (#8; #18, #19). GIS analysis confirms that the years of greatest erosion (2013 and 2020) coincided with the largest debris flood events [M1; R1] (Sect. 3.4). Fluvial, avulsion and debris floods transport contaminants across urban and agricultural landscapes, driving runoff pollution (#6*; Appendix L). Additionally, debris floods deliver mobilized sediment directly into the river channel, promoting accretion and progressively altering channel geometry over time (#19) [M1; M2; R1] (Fig. 4).

Landslides caused by lateral river erosion undercutting riverbanks and hillslopes (Jacobs et al., 2016) have accelerated since the wildfire due to higher post-fire discharges and sediment loads [I1; M1; M2; R1]. In addition, the initial destruction and exposure of formerly stable riverbanks during the wildfire and 2013 flood has worked to further increase the probability of mass movement into the river [M1; G2]. Previously, graded banks of unconsolidated quaternary sediment were anchored by climax vegetation. Now, vertical riverbanks are exposed to direct erosion and undercutting at sites throughout the river's long profile. As one local government representative describes, “when the floodwaters come down, they remove soil and grasses to expose more boulders, and then you will have a landslide” [G2]. This process is visible in Fig. 3c, where the riverbanks on sections of the burned side are now steep, unvegetated banks of exposed and unconsolidated glacial till.

Landslides increase the probability of fluvial flooding by filling the channel with sediment and reducing the river's discharge capacity (#21). Five respondents have also witnessed a mechanism of temporary landslide damming and bursting “in the space of a few minutes” [M1] during high flow events, from which surges of sediment and discharge activate fluvial floods and debris floods [G1; M1; M2; R1; W1]. As one resident recalls: “suddenly, I heard a roar like a plane taking off at Entebbe Airport. Two landslides cut off the river and created a dam behind it, then soon after there were entire trees pole vaulting over the debris”[R1].

Five respondents describe landslides as being in a positive feedback process with erosion (through reciprocal interactions #23, #22 and #10), whereby landslides add load to the river, accelerating accretion and lateral erosion by diverting flow to the riverbanks and trigger further landslides [R1; M1; M2; I1; G2]. Landslides also trigger heavy metal pollution through the rotational slumping of solid Co-Cu tailings at Kilembe Mines into the River Nyamwamba (#24; Sect. 3.5).

The cumulative annual eroded river channel area (Fig. 4a) shows a sustained increase in the river's rate of erosion by a factor of 2.64 following the 2012 wildfire, and the average middle-lower course channel width has increased sevenfold between 2010–2021, from 16.9 to 123 m. Rapid erosion has destroyed agricultural land [M1; M2; G1; G2], residential property, and critical road infrastructure [M1].

Since the wildfire, accelerated lateral river channel erosion has shifted the river channel closer to populated areas of Kasese town and eroded debris has filled the channel via deposition, reducing its discharge capacity. Together, these erosion and accretion processes increase the probability of urban flooding in Kasese town [R1; G1; G2; M2; I2; R3] (#9). Accretion also increases the probability of avulsion flooding, as exemplified by the May and September 2024 floods, by filling the channel with sediment bars that divert flow towards riverbanks [M1] (#13), whilst directly triggering avulsion floods when it breaks through unconsolidated banks [M1; M2] (#14). Contributions of sediment to the main Nyamwamba channel also increase the probability of debris floods [M1; R1] (#17).

Erosional undercutting destabilises slopes and directly triggers landslides (#10), consistent with Jacobs et al.'s (2016) mapping of 14 bank-failure slides during the May 2013 multi-hazard event. This lateral undercutting and exposure of vertical riverbanks is also described by three respondents as putting erosion in self-perpetuating positive feedback, by increasing the probability of further erosion at exposed banks [G1, G2, M1] (#11).

Erosion and accretion are also coupled through reciprocal feedback (#15, #16). Sediment deposition narrows the active channel cross-section, increasing the flow velocity and erosive potential (#15), driving further channel erosion. The eroded material replenishes the sediment supply available for sediment deposition (#16), sustaining this cycle. Together, these dynamics place erosion and accretion in a self-reinforcing feedback loop along the river's reach.

Channel widening breached the Kilembe mine copper-cobalt tailings deposit in 2014, triggering heavy-metal pollution downstream that now presents a major risk to public health (#12; Sect. 3.5).

Immediately after the 2012 wildfire, community members reported increased turbidity and a smell “like methane” [M1] in the river. This is still reported during high discharge twelve years later, which four respondents believe to be due to runoff (non-point source) pollution through exposed bogs and organic-rich glacial sediments in the fire-affected and eroding upper catchment [M1; M2; R1; G1] (#1).

Beyond this diffuse pollution, accelerated river erosion (#12) and landslides (#24) have inputted an estimated 744 000 t of a 15 Mt Kilembe Mines Co-Cu tailings deposit directly into the River Nyamwamba (mapped in Appendix K). Satellite imagery and field photographs show erosional banks, slump scars and new channels within tailings areas, and evidence of acid mine drainage from distinctive iron oxide precipitation (Fig. 3c; Appendix E). Elevated Co, Ni, Cu, Fe, Al, S, Zn, As, Cd and Mn river contamination has previously been attributed to leaching of the Co-Cu mine (Abraham and Susan, 2017; Mwesigye et al., 2016; Mwesigye and Lawrence, 2024; Mwongyera et al., 2014).

Five respondents identified this solid waste pollution as a major concern for public health [M2; W1; G1; G2; R1]. The river is used by 38 % of its adjacent population for drinking, and by many more indirectly through crop-irrigation and groundwater abstraction (Abraham and Susan, 2017; Mukisa et al., 2020). In addition to waterborne risks, long-term contamination of arable soils by deposited mine waste raises concern for food safety [M1; M2; G1; G2]. As one Ministry of Water official noted, “in Kasese District, their teeth are turning brown with yellow patches, and we have been told that many people in this region are ailing with cancer” [M2]. Local environmental managers also expressed concern for downstream ecosystems in Queen Elizabeth National Park and Lake George, where protected flora and fauna may be affected by the pollution and vegetation dieback observed in Kasese town [G2; M1, R1, W1].

Runoff pollution from the burned area transports elevated loads of fine sediment and contaminants into the river channel (#1) [M1; M2; R1; G1]. This increased sediment supply promotes channel accretion as the excess sediment load settles into the river channel (#5).