Impacts of soil erosion and climate change on the built heritage of the Pambamarca Fortress Complex in northern Ecuador

The Pambamarca fortress complex in northern Ecuador is a cultural and built heritage with 18 prehispanic fortresses known as Pucaras. They are mostly located on the ridge of the Pambamarca volcano, which is severely affected by erosion. In this research, we implemented a multiscale methodology to identify sheet, rill and gully erosion in the context of climate change for the prehistoric sites. In a first phase, we coupled the Revised Universal Soil Loss Equation (RUSLE) and four CMIP6 climate models to evaluate and prioritize which Pucaras are prone to sheet and rill erosion, after comparing historical and future climate scenarios. Then, we conducted field visits to collect geophotos and soil samples for validation purposes, as well as drone flight campaigns to derive high resolution digital elevation models and identify gully erosion with the stream power index. Our erosion maps achieved an overall accuracy of 0.75 when compared with geophotos and correlated positively with soil samples sand fraction. The Pucaras evaluated with the historical climate scenario obtained erosion rates ranging between 0 and 20 ton*ha-1*yr-1. These rates also varied from -15.7% to 39.1% for four future climate change models that reported extreme conditions. In addition, after identifying and overflying six Pucaras that showed the highest erosion rates in the future climate models, we mapped their gully-prone areas that represented between 0.9% and 3.2% of their analyzed areas. The proposed methodology allowed us to observe how the design of the Pucaras and their concentric terraces have managed to reduce gully erosion, but also to notice the pressures they suffer due to their susceptibility to erosion, anthropic pressures and climate change. To address this, we suggest management strategies to guide the protection of this cultural and built heritage landscapes.