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4 May 2021 | Cryosphere

Importance of glaciers for water availability in Pakistan

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Zone-wise cumulative rain, snow, and glacier melt contribution to flow derived from the Snowmelt Runoff Model using data from 2001-2012.

Snow and glacier meltwater from the Karakoram and western Himalaya provides water to 268 million people in the Indus basin for drinking and household use, hydroelectricity generation, industry, and irrigation. Climate change is increasing variability in the water cycle, reducing the predictability of flows and water availability. Water use policy and planning must therefore take an integrated approach to climate change and water management, including understanding cryosphere contributions to river flows.

 

Understanding meltwater contributions

Our experts and partners conducted recent research showing that snowmelt contributes the most to river flow in the Gilgit River basin (GRB) of Pakistan followed by glacier melt and rainfall. To understand the contribution from snow and glacier melt, and rain, they used two approaches– the Spatial Processes in Hydrology (SPHY) model, which covers the hydrological process in a large-scale area, and the Snowmelt Runoff Model (SRM) for runoff simulation in GRB for the period from 2001 to 2012.

Results from both models show promising replication of the runoff, but efficiency and accuracy of the SRM was slightly compromised due to the model deficiency in simulating glacier melt and extreme discharge particularly during July and August. During this period, contribution from glacier melt is high. SPHY performed well as it was able to differentiate glacier, snow, and rainfall contributions to runoff during the melt season. The average simulated or modelled runoff from both models revealed that snowmelt contributed to 62% of the runoff, followed by glacier melt with 28% and rainfall 10% in this basin. This differs from the findings of previous studies.

 

Climate change impacts on summer flows

The research team also carried out research on the potential impact of climate change on future flows based on two climate scenarios – Representative Concentration Pathways (RCPs) 4.5 and 8.5. Based on this assessment, our researchers project that the summer flow in GRB will increase between 5.6%–19.8% because of increased temperatures between 0.7–2.6°C during the period 2039-2070.

Each RCP is a scenario that includes time series of emissions and concentrations of the full suite of greenhouse gases (GHGs) and aerosols and chemically active gases, as well as land use/land cover change. The word “representative” signifies that each RCP provides only one of many possible scenarios that would lead to the specific radiative forcing characteristics. The term “pathway” emphasizes that it is not only the long-term concentration levels that are of interest, but also the trajectory taken over time to reach that outcome.

This increase in summer flows in the region could prove beneficial for a range of sectors, but only over the short- to medium-term. The higher melt rate also means increased risk of extreme events and disasters. If the findings and projections made by the researchers are communicated to and understood by policymakers, it can create an opportunity for economic growth, minimizing risk and encouraging investment in evidence-based policy for short, medium, and long-term water resource management.

In the long-term scenario, water resources in GRB may decline, especially meltwater from snow and glaciers, with insufficient water to address the increasing demand. Hence, this projection can be used to devise an adaptation plan and explore other alternatives to address the impending water scarcity.

Routed runoff simulated by SPHY
Routed runoff simulated by SPHY for the year 2010 at Gilgit River at Gilgit.
(a): Rain runoff (b): Snow runoff (c): Glacier runoff. All units in (m3/sec)
Coping with climate change impacts

The study finds that water management facilities in Pakistan lack the capacity to store sufficient water resources during peak-water seasons and for use during the drought/low flow periods. “The sensitivity of the water sector was recently highlighted when the storage capacity of the Tarbella, Mangla, and Chashma hydropower reservoirs was compromised due to heavy silt loads, during which dam operations ran at a much-reduced capacity,” says Sher Muhammad, our remote sensing specialist, who is from Pakistan.

To cope, the study recommends increasing the storage capacity of existing reservoirs and investing in developing new ones. Pakistan is an agrarian country, and its irrigation system is heavily reliant on the water storage capacity within the Indus basin. If climate change increases the seasonality of flows, existing infrastructure will not be capable of storing sufficient water resources for use during the low flow periods, which will result in increased vulnerability of the region to climate change. Therefore, decisions need to be made quickly.

The study also recommends improving the efficiency of the hydrological models by using field-based data collected through regular visits to the glaciers, particularly during early and late ablation periods. With improved monitoring and subsequent model efficiency, more robust findings will further help the design of improved sustainable water management policies in a changing climate.

 

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