The paper argues that there is a poor understanding of the processes affecting the Himalayan glaciers in the context of the diversity of climatic conditions and the extremes of topographical relief within the region, making projections speculative, which can have a significant impact on the future of water resources in the area. It is thus important to have more information on the status of the glaciers in the Himalayan region.

The paper reviews the state of knowledge about key characteristics, current extent, and changes of H-K glaciers since the mid-19th century. The paper also sheds light on projections of possible future changes, summarises important implications for water resources and natural hazards, and ends by sketching a framework for integrated cryosphere research needed to fill the most critical gaps.

The paper informs that most glaciers in H-K have retreated and lost mass since the mid-19th century. Loss rates have probably accelerated in recent decades, but the observed tendencies are not regionally uniform. For example, in the Karakoram and parts of the northwestern Himalayas, many of the observed large glaciers have oscillated or surged since the beginning of the last century, with indications of positive mass balances for the 1990s and the beginning of the 21st century. This Karakoram anomaly stands out as a phenomenon that deserves further investigation to clarify the relation between climate forcing and glacier responses in the region, taking due account of the distinctive behavior of its many surge-type and dynamically variable glaciers.

The leading uncertainties about the state and fate of H-K glaciers relate to:

• The contribution of glaciers to runoff
• The projection of glacier changes
• The variability of glacier changes within the region
• The influence of debris cover on glacier melt
• The role of ice and snow avalanches in the glacier mass budget
• The magnitude of past glacier changes as revealed from comparisons with maps

The paper informs that these uncertainties can be mainly attributed to deficient information, lack of measurements; both of climatic forcing agents and of the glaciers themselves (mass budgets and length changes) and the use of unsuitable or uncertain data, such as imagery with extensive seasonal snow or maps drawn from such imagery. Non publication of existing data makes these problems worse. The paper argues that, to close the knowledge gaps, the most useful steps would be:

• To release a regionally complete, upto- date, and accurate glacier inventory conforming to international standards and including the most important topographic parameters
• To continue to develop and refine remote-sensing methods for the estimation of glacier changes, including length, area, and volume changes, as well as gravimetric measurement of mass changes
• To fill critical gaps in the climatic and hydrologic station network and establish transects from the lowlands in the south to the Tibetan Plateau, similar to that already established north and south of Mount Everest
• To continue existing mass-budget measurements on reference glaciers and to establish new programs to cover more climate zones and glacier types in a more representative way, particularly in the Karakoram
• To measure the thickness of selected glaciers as a basis for calibrating recently developed methods for modeling of subglacial topography and hence glacier volume
• To strengthen modeling efforts, in particular for climate projections, future glacier evolution, GLOFs, and glacier runoff. Field and remote-sensing–based investigations should consider the needs of these models when designing and performing investigations
• The continuation and extension of coordinated transboundary research on climate, cryosphere, and their impacts, including the exchange of all relevant data

 The entire paper can be accessed at this link