Rainfall thresholds triggering mass movements in the central Paute River basin

Mass movements are a primary process in the evolution of landforms in the Paute River basin in southern Ecuador, where lithological, structural, and topographical factors drive terrain instability. Rainfall is a significant triggering factor due to its direct influence on increasing interstitial pressure and reducing material resistance, particularly on slopes previously modified by anthropogenic activities, such as the mega-landslide La Josefina, which occurred in 1993 (Bonnard, 2011). This research aims to establish precipitation thresholds to enhance understanding of the activation and reactivation of mass movements in the central Paute River basin, with a focus on events that impact infrastructure and human settlements (Torres Ramírez, 2021). The methodology involves collecting and refining rainfall records from manual stations operated by the National Institute of Meteorology and Hydrology (INAMHI) and comparing these with the Integrated Multi-satellite Retrievals for GPM (IMERG) satellite products to address data discontinuities and improve spatial rainfall coverage. Statistical analyses were conducted to identify critical precipitation thresholds associated with the initiation of mass movement processes, based on correlations between event occurrence and antecedent and accumulated precipitation conditions (Iza-Wong et al., 2025; WMO, 2017)​. Preliminary findings indicate that precipitation thresholds vary across the study area by season (Marco Molina et al., 2000; Zaragozí et al., 2025). During the rainy months of March, April, and May, rainfall is more concentrated in the southwestern region, with precipitation ranging from the 95th percentile value of 6 mm/day up to 14 mm/day. In contrast, during September, October, and November, higher rainfall is observed in the northeastern region. This spatial heterogeneity underscores the influence of geology, soil texture, and land-use changes on mass-movement processes; in addition, the evaluation of precipitation patterns further distinguishes the types of events that trigger landslides in the area. These conclusions offer a technical foundation for enhancing preparedness, monitoring, and early warning systems for climate risk management in the Paute River basin.

Keywords: Hydrogeomorphology, mass movements, precipitation, rainfall thresholds, climate risk, Paute River basin

References

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Iza-Wong, A., Moldovan, G., Ben-Bouallègue, Z., Hemingway, R., Chantry, M., & Lavers, D. (2025). Evaluation of precipitation observations across Ecuador. Atmospheric Science Letters.

Marco Molina, J.A.; Matarredona Coll, E.; Padilla Blanco, A. (2000) La dimensión espacial de los riesgos geomorfológicos. Boletín de la Asociación de Geógrafos Españoles. Available online: https://dialnet.unirioja.es/servlet/articulo?codigo=1122897

Torres Ramírez, R. (2021). Análisis espacio-temporal de los eventos ocurridos (movimientos en masa), en el período 2012-2020, en la zona centro de la cuenca del río Paute-Ecuador. http://rua.ua.es/dspace/handle/10045/114795

 WMO. (2017). Guide to the Global Observing System. WMO-No. 488. https://community.wmo.int/en/wmo-no-488-guide-global-observing-system

Zaragozí, B., Font, P., Cano-Aladid, J., & Marco Molina, J. (2025). A Small Landslide as a Big Lesson: Drones and GIS for Monitoring and Teaching Slope Instability. Geosciences, 15, 375. https://doi.org/10.3390/geosciences15100375