the Tibetan Plateau is called Tsangpo, while the Brahmaputra is the proper name of the river once it enters India. To avoid confusion, the river is referred to as the Brahmaputra throughout this report. In this report, when discussing issues on a watershed basis, the Ganges and Brahmaputra are grouped as a single watershed because they eventually merge before draining into the Bay of Bengal. However, when discussing hydrological issues—for example, river hydrographs6—the Ganges and Brahmaputra are treated separately. The tributaries of the Indus and the Ganges/Brahmaputra Rivers are depicted in Figure 1.3b.

The HKH region is geographically vast and complex both climatologically and hydrologically and this complexity is dynamic and possibly changing. This means that it is very difficult to generalize observations and findings over the entire region because spatial variability is large. The story that emerges in this report is also characterized by the fact that there remain many open science questions that cannot be answered in the absence of additional data and research. Although global temperatures are increasing generally, and these increases have been more rapid in recent decades, spatial variability and lack of local research data mean that the specific manifestations of climate change are unclear in the HKH region. This includes how quickly and regionally glaciers might retreat, and what the subsequent impacts on the hydrological system of the HKH region might be. In recognition of the complexities of these issues, NRC formed the Committee on Himalayan Glaciers, Hydrology, Climate Change, and Implications for Water Security to begin to address some of these important questions.

STUDY APPROACH AND METHODOLOGY

The Committee was formed in summer 2011 and completed its work over the course of the next 12 months. It held four meetings during which it reviewed relevant literature and other information. To inform its analysis, the Committee organized an interdisciplinary workshop, using both invited presentations and discussion to explore the issues that may affect regional streamflow and water supplies in the face of a changing climate. The workshop, which was held in fall 2011 in Washington, D.C., was organized around four broad themes: (1) regional climate and meteorology; (2) regional hydrology and water supply, use, and management; (3) regional demography and security; and (4) risk factors and vulnerabilities. The workshop agenda and participants are included in Appendix A, and workshop presentation summaries are included in Appendix B. Workshop participants identified key concepts about the HKH region. Starting from those concepts, the Committee used its expert judgment, reviews of the literature, and deliberation to develop conclusions about the physical geography, human geography and water resources, and environmental risk and security in the HKH region. These conclusions are listed at the end of each chapter.

ORGANIZATION OF THE REPORT

This report covers three broad areas of knowledge about the Himalayan region: (1) physical geography, (2) human geography and water resources, and (3) environmental risk and security. Chapter 2, Physical Geography, provides an overview of glaciers, followed by a summary of the climate and meteorology of the region within the context of paleoclimate patterns, and descriptions of the regional hydrology and physical hazards. Chapter 3, Human Geography and Water Resources, covers population distribution, poverty and migration, and key natural resource issues of water use, access to water, water scarcity, and water management. Chapter 4, Environmental Risk and Security, presents the Committee’s further analyses of the linkages between physical and human systems, with an emphasis on those that may pose potential instabilities for the region. Chapter 5 presents the Committee’s synthesis of the range of physical and social changes facing the region, a summary of research questions and data needs, and options for adapting to the changes facing the region.

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6 A hydrograph is a record and graphical representation of river or stream discharge as a function of time at a specific location (AMS, 2000).



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