Gully distribution at the local scale in high-mountain, tropical environment: a case study of Cordillera Villcanota, Andes, Peru

As climatic changes impact environmental conditions worldwide, the intensity and spatial distribution of geomorphic processes will be seriously modified in the foreseeable future. Mountain areas are particularly vulnerable to climate change as the general temperature and precipitation alteration trends are being amplified due to local variations in elevation and aspect. Many mountain areas are also under increasing human pressure, which is related to food production, settlement, mining, and other direct earth-moving activities. As a response to such external drives, the increase in frequency and magnitude of geomorphic processes has been observed in many mountain areas around the world, including tropical mountains of South America. This study aims to better understand the development of gullies in tropical mountains. The main objectives are: (1) To document the spatial distribution of gullies within three selected areas in Cordillera Vilcanota, Andes, Peru, and (2) To investigate the relationship between the distribution of geohazard sites and landscape topographic properties.

The study area is located in Cordillera Vilcanota in the Andes of Peru. Our research focuses on three areas (ranging from 25 to 80 km²) located along valley corridors in which several villages, roads and agricultural infrastructures are located. A relatively dense population (considering the remote mountain location) means that gully erosion constitutes serious problems for human life and infrastructure. The distribution of gullies was mapped based on high-resolution satellite data (resolution better than 1.0 m). We used satellite images from 2002, 2014, and 2020 captured by Ikonos, WorldView and Pleiades. The remote mapping was subsequently verified during the fieldworks in 2017, 2018, and 2019.

We mapped almost four thousand individual gullies and gully complexes. Their length varied from 10 to 2000 m; however, most were small (mean length 103 m, median length 60 m). Most of the gullies were located close to the roads and in the valleys' middle parts, between 4000 and 5000 m a.s.l. Gully erosion, settlements and infrastructures, and cultivated land in the studied mountain areas represent a coupled mechanism. Gully erosion transforms the landscape, impacting human activity by (1) directly damaging properties and infrastructure, (2) forcing the population to change and adapt to new landscape characteristics, and (3) limiting land available for cultivation. However, human activities are not only threatened by gully erosion but also belong to one of the principal factors enhancing the erosion and mass movements, e.g. by the construction of undercut roads, changes in drainage systems (blocking surface water flow), and changes in land cover (removal of native vegetation) promoting rapid gully erosion. To further consider the impact of gully erosion, more research is needed to evaluate the impact on land production and promote solutions which can limit negative consequences.

The research was funded by the Polish National Science Centre, Poland (Project number 2015/19/D/ST10/00251)