Water resource impacts of Afghan glacier recession

PhD candidate Jamal Shokory (Boursier of the Swiss Confederation)

Supervised by Prof. Stuart Lane

About one sixth of the world’s population live in river basins fed by significant melt of snow and/or ice including the major mountain ranges of the Himalaya, Hindukush, Andes and Rockies and European Alps. They are highly vulnerable to climate change as small changes in temperature can rapidly change whether water is solid or frozen, and this impacts both the accumulation and the melt of snow and ice. Researchers have suggested that basins whose glacial contribution to runoff is significant need particular attention in water resource terms.

Glacier recession is thought to lead to a situation of transience. Accelerated ice melt leads to a “glacial subsidy” (Collins, 2008), with a temporary increase in summer runoff over a limited time period. This is followed by declining runoff when glaciers become too small to sustain summer river flow, and hence passage through a state of “peak water”. In water resource terms, glaciers then provide an “insurance policy”: in years with lower snow cover following winter, snow line recession will be more rapid, and ice melt will start sooner and be more intense, such that the reduced runoff due to less winter snow accumulation is compensated for by increased (glacier) ice melt. This policy exists no more when glaciers retreat to a certain critical size, and runoff becomes directly dependent on interannual winter snowfall variability.

Current data confirm that peak annual runoff in basins with glaciers is increasing and shifting to periods when glacial melt is dominant (see the figure below). If we invert this situation, the runoff measured at any one time in a mountain stream is not only a product of temperature and/or precipitation in the hours, perhaps days, before; it is also a function of the history of storage of water as snow (at the annual scale) and ice (at longer time-scales). Thus, we hypothesise that current runoff analyses are likely to be dominated by glacial subsidy as a result of historical ice accumulation and so mask the relationship between current climate and runoff.

Afghanistan is a part of the Himalayan region, but being in its far West it differs from central and eastern regions in terms of climate influences. This matters as the sensitivity of glacier and snow to climate change will depend on climate influences albeit to an extent which remains unclear. Therefore, this project attempts to assess and to evaluate in detail how glaciers are and will influence runoff, of crucial importance for Afghan water resources.

The research is addressing the following questions

R1: How can remote sensing techniques be used for glacier monitoring in Afghanistan, notably capturing the negative feedback effects of glacier recession on runoff through increasing debris cover?

R2: How has and how will climate change influences future glacier runoff regime in Afghanistan?

R3: What are the impacts of long-term climate change on snow and glacier melt rate and changing frequencies of extreme flows?

R4: How should the result be used in water resource management decision-making?

This study will use remote sensing data to track the clean ice and ice covered by debris. Where debris cover develops, it may insulate ice from solar radiation and diurnal temperature rises, and this will also reduce melt. Thus, in water resource terms, it may be the transition from clean ice through dirty ice to substantial debris cover that matters, and this is likely to be readily identified through remote sensing methods. Field measurement and mass balance analysis of benchmarked glaciers will also be an important part of this study.