The peak water myth

The peak water concept has emerged to represent the trajectory of future water resources from glacierised basins, and has been widely adopted by the glaciology community. This is based on the notion that runoff from glaciers will increase up to a point in the near future and then decrease, because the melt rates of glaciers per unit area increase due to higher temperatures, while glaciers shrink. There is a point in the future that the glacier area becomes so small that the increase in melt rate per unit area cannot compensate for the area loss, and the absolute amount of glacier melt water starts to decrease. This peak water concept has been featured by several prominent papers and by the IPCC. However, we hypothesize that this peak water concept is an oversimplification of reality and can mask the real trajectory of changes in water resources from mountain catchments. It is only a valid concept for a single glacier, and the effect largely disappears when a mountainous catchment consists of multiple glaciers with different size, thickness, and mass balance sensitivity as result of extensive debris cover, for example. Moreover, and more importantly, it ignores climate change impacts on the non-glacierised part of the mountainous catchment, such as the buffering by snow and groundwater storages and the role of vegetation, and shifts in the partitioning between “green” (evapotranspiration) and “blue” (river runoff) water in particular. In this talk, we show a few examples of such oversimplifications, and argue for a broader and holistic perspective on the impacts of climate change on mountain water resources.