Topographic and Seismic Constraints on the Vulnerability of Himalayan Hydropower

We compiled damages to hydropower projects (HPPs) in the wake of Nepal's 2015 Gorkha earthquake and its main aftershock. Based on 41 records of HPP losses, we identify the main mechanisms determining the degree of loss. We show that, among these mechanisms, earthquake-triggered landslides had the largest share. Landslides clustered where peak ground acceleration and river steepness M, a metric frequently used in tectonic geomorphology, attain high values. A Bayesian logistic regression reveals that both metrics are credible predictors for HPP damage states. Our study underscores the vulnerability of Himalayan hydropower to landsliding. We estimate that similar to 25% of existing, currently constructed, and planned HPPs and >10% of potential HPP sites along Himalayan rivers have high probabilities of moderate to severe damage during future earthquake. Our study highlights that HPP hazard assessments need to consider both seismic and the geomorphic setting of HPP sites conjunctively. Plain Language Summary The 2015 Gorkha earthquake in Nepal caused severe losses in the hydropower sector. The country temporarily lost similar to 20% of its hydropower capacity, and >30 hydropower projects were damaged. The projects hit hardest were those that were affected by earthquake-triggered landslides. We show that these projects are located along very steep rivers with towering sidewalls that are prone to become unstable during strong seismic ground shaking. A statistical classification based on a topographic metric that expresses river steepness and earthquake ground acceleration is able to approximately predict hydropower damage during future earthquakes, based on successful testing of past cases. Thus, our model enables us to estimate earthquake damages to hydropower projects in other parts of the Himalayas. We find that >10% of the Himalayan drainage network may be unsuitable for hydropower infrastructure given high probabilities of high earthquake damages.