FIGURE 1.2 Global map of water-stressed basins. The water stress indicator is the ratio of total water withdrawals to calculated in-stream flow requirements. Many basins in the HKH region have “high” levels of water stress. SOURCE: Smakhtin (2008).
and agricultural water availability as well as for the various in-stream ecological uses.
In addition, in the context of incomplete science and unresolved uncertainties, there are other important questions about regional water security that need to be addressed. From the beginning the Committee was mindful that it would need to sort out these confusions and resolve any resultant misunderstandings in order to successfully address the statement of task (Box 1.1). Included among the questions examined by the Committee in the course of addressing their charge are the following:
• What are the rates of retreat of the Himalayan glaciers over the last decades and how do they compare with the rates of retreat of glaciers elsewhere in the world?
• Are the rates of glacial retreat in the study region accelerating, decelerating, or remaining static?
• What proportion of the seasonal flows of the Indus and Ganges/Brahmaputra rivers are accounted for by glacier melt?
• What has been the impact of recent climate change on both glacial wastage and streamflow in the region?
• Has the relative contribution of glacier meltwater to dry-season or wet-season flows increased, decreased, or remained static?
• Would the deglaciation of the HKH region imply that the area is headed toward water scarcity within the next few decades?
• Over the next several decades,2 how will these high-altitude changes in climate and hydrology compare, and interact with, other economic, social, and demographic impacts on regional water supply and demand?
• Does the retreat or accelerated retreat of HKH glaciers increase the likelihood of natural disasters such as outburst floods from moraine dammed lakes or seasonal flooding?
Available science does offer some important information that leads to conclusions that are relevant to these questions.
This report was prepared by the Committee on Himalayan Glaciers, Hydrology, Climate Change,
2 Wherever possible, the Committee has attempted to limit its projections to the order of three to four decades at most. However, in some cases this was not possible. For example, decadal-scale climate projections are currently an area of active research, and the climate modeling community has more skill in projecting climate over longer timescales.