Editing IPCC:AR6/SROCC/Chapter-2 (section)

===== 2.3.1.3.1 Hydropower =====

Hydropower comprises about 16% of electricity generation globally but close to 100%, in many mountainous countries (Hamududu and Killingtveit, 2012 <sup>[[#fn:r316|316]]</sup> ; IHA, 2018). It represents a significant source of revenue for mountainous regions (Gaudard et al., 2016 <sup>[[#fn:r317|317]]</sup> ). Due to the dependence on water resources as key input, hydropower operations are expected to be affected by changes in runoff from glaciers and snow cover (Section 2.3.1.1, FAQ 2.1). Both increases and decreases in annual and/or seasonal water input to hydropower facilities have been recorded in several high mountain regions, for example, in Switzerland (Hänggi and Weingartner, 2012 <sup>[[#fn:r318|318]]</sup> ; Schaefli et al., 2019 <sup>[[#fn:r319|319]]</sup> ), Canada (Jost et al., 2012 <sup>[[#fn:r320|320]]</sup> ; Jost and Weber, 2013 <sup>[[#fn:r321|321]]</sup> ), Iceland (Einarsson and Jónsson, 2010 <sup>[[#fn:r322|322]]</sup> ) and High Mountain Asia (Ali et al., 2018 <sup>[[#fn:r323|323]]</sup> ). However, there is only ''limited evidence'' ( ''medium agreement'' ) that changes in runoff have led to changes in hydropower plant operation. For example, in Iceland, the National Power Company observed in 2005 that flows into their energy system were greater than historical flows. By incorporating the most recent runoff data into strategies for reservoir management it was possible to increase production capacity (Braun and Fournier, 2016 <sup>[[#fn:r324|324]]</sup> ).

There is ''robust evidence (medium agreement'' ) that water input to hydropower facilities will change in the future due to cryosphere-related impacts on runoff (Section 2.3.1.1). For example, in the Skagit river basin in British Columbia and Northern Washington (Lee et al., 2016 <sup>[[#fn:r325|325]]</sup> ) and in California (Madani and Lund, 2010 <sup>[[#fn:r326|326]]</sup> ) projections (SRES A1B) show more runoff in winter and less in summer. In India, snow and glacier runoff to hydropower plants is projected to decline in several basins (Ali et al., 2018 <sup>[[#fn:r327|327]]</sup> ). In some cases, catchments that are close together are projected to evolve in contrasting directions in terms of runoff, for example in the European Alps (Gaudard et al., 2013 <sup>[[#fn:r328|328]]</sup> ; Gaudard et al., 2014 <sup>[[#fn:r329|329]]</sup> ). Increased runoff due to changes in the cryosphere will increase the risk of overflows (non-productive discharge), particularly during winter and spring melt, with the greatest impacts on run-of-river power plants (e.g., in Canada; Minville et al., 2010 <sup>[[#fn:r330|330]]</sup> ; Warren and Lemmen, 2014 <sup>[[#fn:r331|331]]</sup> ) ( ''medium confidence'' ).

There is ''medium evidence'' ( ''high agreement'' ) that changes in glacier- and moraine-dammed lakes, and changes in sediment supply will affect hydropower generation (Colonia et al., 2017 <sup>[[#fn:r332|332]]</sup> ; Hauer et al., 2018 <sup>[[#fn:r333|333]]</sup> ). Many glacier lakes have increased in volume, and can damage hydropower infrastructure when they empty suddenly (Engeset et al., 2005 <sup>[[#fn:r334|334]]</sup> ; Jackson and Ragulina, 2014 <sup>[[#fn:r335|335]]</sup> ; Carrivick and Tweed, 2016 <sup>[[#fn:r336|336]]</sup> ) (Section 2.3.2). If large enough, hydropower reservoirs can reduce the downstream negative impacts of changes in the cryosphere by storing and providing freshwater during hot, dry periods or by alleviating the effects of glacier floods (Jackson and Ragulina, 2014 <sup>[[#fn:r337|337]]</sup> ; Colonia et al., 2017 <sup>[[#fn:r338|338]]</sup> ). In mountain rivers, sediment volume and type depend on connectivity between hillslopes and the valley floor (Carrivick et al., 2013 <sup>[[#fn:r339|339]]</sup> ), glacier activity (Lane et al., 2017 <sup>[[#fn:r340|340]]</sup> ) and on water runoff regime feedbacks with river channel dynamics (Schmidt and Morche, 2006 <sup>[[#fn:r341|341]]</sup> ). An increase in suspended sediment loading under current reservoir operating policies is projected for some hydropower facilities, for example, in British Columbia and Northern Washington (Lee et al., 2016 <sup>[[#fn:r342|342]]</sup> ).

Only a few studies have addressed the economic effects on hydropower due directly to changes in the cryosphere. For example in Peru, Vergara et al. (2007) studied the effect of both reduced glacier runoff and runoff with no glacier input once the glaciers have completely melted for the Cañón del Pato hydropower plant in Peru, and found an economic cost of between 5 – 20 million USD yr -1 , with the lower figure for the cost of energy paid to the producer and the higher figure the society cost. Costs calculated for all of Peru, where ~80% of electricity comes from hydropower range from 60 – 212 million USD yr -1 . If the cost of rationing energy is considered, the national cost is estimated as 1,500 million USD yr -1 .

Other factors than changes in the cryosphere, such as market policies and regulation, may have greater significance for socioeconomic development of hydropower in the future (Section 2.3.1.4, Gaudard et al., 2016). Hence, despite the efforts of hydropower agencies and regulatory bodies to quantify changes or to develop possible adaptation strategies (IHA, 2018), only a few organisations are incorporating current knowledge of climate change into their investment planning. The World Bank uses a decision tree approach to identify potential vulnerabilities in a hydropower project incurred from key uncertain factors and their combinations (Bonzanigo et al., 2015 <sup>[[#fn:r343|343]]</sup> ).

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