Environmental sustainability of small hydropower schemes in Tibet: An emergy-based comparative analysis

Exploring safe and sustainable hydropower, with regard to the size and scheme, is of particular importance to avoid unsettling the fragile ecology in Tibet. Through emergy analysis, this study aimed to assess and compare the environmental performance and sustainability of three different small hydropower (SHP) schemes that are currently in use, i.e., dam-toe, diversion and hybrid, in the Nagqu Prefecture of Tibet. The results indicate that the main difference among the three schemes is the high emergy cost associated with the sizeable dam and related sediment deposition. Correspondingly, the diversion scheme without the dam component is superior to the other two schemes with respect to environmental performance. Considering the necessity of SHP in sparsely populated Tibet, the diversion scheme is recommended more highly than the other two schemes for new SHP plants that are being planned for construction. Because of the much higher resource cost but smaller installed capacity, all three case plants in Tibet present worse performance than their counterparts in Guizhou Province. These results help to encourage China's policy makers to be conservative and proceed with caution regarding SHP development in the fragile Tibetan ecosystem, although SHP has played and will continue to play an essential role in rural electrification in this unique region.