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12 Nov 2020 | Cryosphere

A more accurate picture of snow cover change in the Karakoram

Improved MODIS snow products resolve uncertainties in glacio-hydrological models

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River sub-basins in the research site in the Karakoram region, where the new MODIs product was used to analyse snow cover change.

Accurate Earth observation is crucial for large-scale cryosphere monitoring. Although remote-sensing data offer higher spatial coverage than field-based monitoring data, there are limitations to how accurately remote-sensing techniques can monitor changes. It is therefore crucial to regularly improve and update remote-sensing tools.

Our improved Moderate Resolution Imaging Spectroradiometer (MODIS) product MOYDGL06* reduces errors in snow cover data compared with data acquired through original MODIS products. The improved product reduces snow cover estimation errors due to clouds and shadows. This provides a more accurate picture of how the region’s cryosphere is changing and how we can mitigate downstream impacts with regards to water supply, agriculture, disasters, hydropower, and livelihoods, among other sectors.

Improved data from the Karakoram

While glaciers across the world are retreating, the Karakoram is one of the most densely glacierized and snow-covered regions in the world and has been experiencing stable glacier health, with only slight mass loss. To accurately monitor this, we need to comprehensively assess the present status of other components of its cryosphere (particularly snow cover). We conducted a study on snow cover change in the Karakoram region from 2003 to 2018 using both the original and our improved MODIS product.

Snow cover, snowline altitude, and variability

The original MODIS shows large uncertainty resulting from persistent cloud cover (underestimation) and sensor error (overestimation). The improved snow product removes previous over- and underestimates in snow cover area for the Karakoram region.

With MOYDGL06*, we found that the snow cover area and snowline altitude show both intra-annual and inter-annual variability in the region. We confirmed increasing snowline towards higher elevations (which will need to be further studied through field-based monitoring), and these accurate estimates can inform water resource planning, vital for the lives and livelihoods downstream.

Resolving uncertainties in glacio-hydrological modelling

We highlighted the uncertainty in the original MODIS snow cover product, which is likely to influence results when used in glacio-hydrological application and which shows the importance of improved products over original ones. Our improved snow products for runoff, snowmelt runoff simulation, forecast and calibration, and validation of glacio-hydrological models, among others, can be particularly useful for improved water-related policy making and downstream water availability assessment. Our research shows that while Earth observation provides immense opportunities to improve understanding of spatio-temporal variability of Earth features, there are limitations that need to be improved and calibrated.

 

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