水电是一种清洁、可再生，且对环境友好的能源。全球每年的水力发电量达到3930 TW·h，占全球总发电量的16 %，同时占可再生能源发电量的78 % (2015年)。水电和气候变化具有双重的关系。一方面，水电作为一种重要的可再生能源，对于避免温室气体排放和减缓全球变暖贡献显著；另一方面，气候变化会改变河道流量，进而影响水资源可用量和水力发电。水电对于减少温室气体排放和保障能源供应至关重要。与常规燃煤电厂相比，水电每年可避免3×109 t CO₂ 的排放，占全球年CO2 排放量的9 %。除了对电力行业的贡献，水电项目还可作为多功能水库的融资工具，以及水资源应对气候变化影响的一项适应性措施，这是因为水库的蓄水可作为气候变化的缓冲器，有大水库调节的流域更能适应水资源变化，而不容易受到气候变化的影响。从全球层面来看，预期气候变化对现有全球水力发电的整体影响较小，甚至可能产生一些积极影响。然而，世界不同地区甚至各个国家内部可能存在巨大差异。总之，对水电的解读为：水电是一种廉价、成熟的技术，对减缓气候变化有重大贡献，且可以在水资源适应气候变化中发挥重要作用。有必要关注并减轻巨大的环境压力和社会成本，预计未来几十年内可新增水电装机容量1 000 GW。

Hydropower is a clean, renewable, and environmentally friendly source of energy. It produces 3930?(TW•h)•a^–1, and yields 16% of the world's generated electricity and about 78% of renewable electricity generation (in 2015). Hydropower and climate change show a double relationship. On the one hand, as an important renewable energy resource, hydropower contributes significantly to the avoidance of greenhouse gas (GHG) emissions and to the mitigation of global warming. On the other hand, climate change is likely to alter river discharge, impacting water availability and hydropower generation. Hydropower contributes significantly to the reduction of GHG emissions and to energy supply security. Compared with conventional coal power plants, hydropower prevents the emission of about 3?GT CO₂ per year, which represents about 9% of global annual CO₂ emissions. Hydropower projects may also have an enabling role beyond the electricity sector, as a financing instrument for multipurpose reservoirs and as an adaptive measure regarding the impacts of climate change on water resources, because regulated basins with large reservoir capacities are more resilient to water resource changes, less vulnerable to climate change, and act as a storage buffer against climate change. At the global level, the overall impact of climate change on existing hydropower generation may be expected to be small, or even slightly positive. However, there is the possibility of substantial variations across regions and even within countries. In conclusion, the general verdict on hydropower is that it is a cheap and mature technology that contributes significantly to climate change mitigation, and could play an important role in the climate change adaptation of water resource availability. However, careful attention is necessary to mitigate the substantial environmental and social costs. Roughly more than a terawatt of capacity could be added in upcoming decades.