Extreme precipitation events play a pivotal role in shaping Earth’s surface through their influences on hillslope processes and sediment transport in rivers. In this study, we focus on understanding the implications of such events on sediment transport, using Réunion Island as a natural laboratory due to its intense tropical rainfall regime. Through photogrammetric techniques and subsequent sediment volume estimates spanning decades as well as cosmogenic 3He measurements, we assessed the spatio-temporal evolution of the canyon bed of the ephemeral Rivière des Remparts and the drainage of products from major landslides and/or rock avalanches between 1950 and 2011. Results show that 39.6 Mm3 of sediment was transported out of the watershed in 62 years. Furthermore, we modeled the flow dates of this ephemeral river and show that such an export of material actually happened during only 391 days over the 62 years, at an average rate of 0.1 Mm3/day. Our investigation confirms that sediment transport coincides with officially recorded extreme meteorological events such as cyclones. Moreover, our findings reveal that sediment transport predominantly occurs on days corresponding to high-percentile rank precipitation events, demonstrating that all transport is concentrated during these intense rainfall periods. Finally, this study underscores the extremely fast conveyance of material from slopes to deep-sea fans, facilitated in Réunion by the absence of a coastal platform. This rapid transfer has implications for CO2 consumption, as it should enhance the transport and burial of organic matter particles, potentially contributing significantly to the island’s overall CO2 consumption efficiency.

On the seasonal time scale, for accessible locations and when manpower is available, direct observations and field survey are the most useful and standard approaches. However very limited studies have been conducted on direct observation at the decennial to century time-scale due to observational constrains. Here, we present an open and reproducible pipeline based on historical aerial images (up to 70 yrs time span) that includes sensor calibration, dense matching and elevation reconstruction over two areas of interest that represent pristine examples for tropical and alpine environments. The Remparts Canyon and Langevin River in Reunion Island, and the Bossons glacier in the French Alps share a limited accessibility (in time and space) that can be overcome only from remote-sensing. We reach a metric to sub-metric resolution close to the nominal images spatial sampling. This provides elevation time series with a better resolution to most recent satellite images such as Pleiades over decennial time period.

Mountainous landscape evolution under tropical and alpine environments is mainly dictated by climatic forcing which influences underlying mechanisms of geomorphic transport (e.g., soil formation, river dynamics, slope stability and mass wasting). The time scale over which this influence acts ranges from seasonal to decennial time span. On the seasonal time scale, for accessible locations and when manpower is available, direct observations and field survey are the most useful and standard approaches. While very limited studies have been focused on the the decennial and century scale due to observational constrains. Here, we present an open and reproducible pipeline based on historical aerial images (up to 70yrs time span) that includes sensor calibration, dense matching and elevation reconstruction over two areas of interest that represent pristine examples for tropical and alpine environments: The Rempart Canyon in Reunion Island, and the Bossons glacier in the French Alps share a limited accessibility (in time and space) that can be overcome only from remote-sensing. We reach unprecedented resolution: the aero-triangulation falls at sub-metric scale based on ground truth, which is comparable to the initial images spatial sampling. This provides elevation time series with a better resolution to most recent satellite images such as Pleiades. In the case of the Rempart Canyon, we identified and quantified the results of 2 landslides that occurred in 1965 and 2001, and characterized the landslides dynamics. As for the alpine case, we highlight the effect of the temperature plateau occurred during 1939-1970 in Europe before the well known accelerated retreat during the post-industrial period. In both cases, we emphasize the strong effect of extreme events over multi-decennial to century time-scales.