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. 2021 May 4;118(18):e2101174118.
doi: 10.1073/pnas.2101174118.

COVID-19 lockdowns show reduced pollution on snow and ice in the Indus River Basin

Edward Bair  1 , Timbo Stillinger  2 , Karl Rittger  3 , McKenzie Skiles  4
Affiliations

COVID-19 lockdowns show reduced pollution on snow and ice in the Indus River Basin

Edward Bair et al. Proc Natl Acad Sci U S A. .

Abstract

Melting snow and ice supply water for nearly 2 billion people [J. S. Mankin, D. Viviroli, D. Singh, A. Y. Hoekstra, N. S. Diffenbaugh, Environ. Res. Lett. 10, 114016 (2015)]. The Indus River in South Asia alone supplies water for over 300 million people [S. I. Khan, T. E. Adams, "Introduction of Indus River Basin: Water security and sustainability" in Indus River Basin, pp. 3-16 (2019)]. When light-absorbing particles (LAP) darken the snow/ice surfaces, melt is accelerated, affecting the timing of runoff. In the Indus, dust and black carbon degrade the snow/ice albedos [S. M. Skiles, M. Flanner, J. M. Cook, M. Dumont, T. H. Painter, Nat. Clim. Chang. 8, 964-971 (2018)]. During the COVID-19 lockdowns of 2020, air quality visibly improved across cities worldwide, for example, Delhi, India, potentially reducing deposition of dark aerosols on snow and ice. Mean values from two remotely sensed approaches show 2020 as having one of the cleanest snow/ice surfaces on record in the past two decades. A 30% LAP reduction in the spring and summer of 2020 affected the timing of 6.6 km3 of melt water. It remains to be seen whether there will be significant reductions in pollution post-COVID-19, but these results offer a glimpse of the link between pollution and the timing of water supply for billions of people. By causing more solar radiation to be reflected, cleaner snow/ice could mitigate climate change effects by delaying melt onset and extending snow cover duration.

Keywords: COVID-19; Indus; light-absorbing particles; remote sensing; snow.

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Conflict of interest statement

The authors declare no competing interest.

Figures

Fig. 1.
Fig. 1.
Decrease in melt from an energy balance model using observed snow/ice cover in 2020 compared to the same snow/ice cover with 20-y mean levels of LAP. Shown is the mean difference using approaches 1 and 2 (see Materials and Methods).
Fig. 2.
Fig. 2.
Results from approach 1: (A) fractional snow-covered area (fsca) over the Indus; (B) snow grain radius, in micrometers; (C) equivalent dust concentration (equiv. dust), in ppmw; and (D) visible (vis.) to near-infrared (nIR) snow albedo. For the red and black lines, line width represents uncertainty. The timescale shown is the melt season, with times after July not shown, due to cloud obfuscation of the snowpack from the monsoon.
Fig. 3.
Fig. 3.
Results from approach 2. A−D are the same as in Fig. 2.
See this image and copyright information in PMC

References

    1. Mankin J. S., Viviroli D., Singh D., Hoekstra A. Y., Diffenbaugh N. S., The potential for snow to supply human water demand in the present and future. Environ. Res. Lett. 10, 114016 (2015).
    1. Khan S. I., Adams T. E., “Introduction of Indus River Basin: Water security and sustainability” in Indus River Basin, Khan S. I., Adams T. E., Eds. (Elsevier, 2019), pp. 3–16.
    1. Sarangi C., et al. ., Dust dominates high-altitude snow darkening and melt over high-mountain Asia. Nat. Clim. Chang. 10, 1045–1051 (2020).
    1. Skiles S. M., Flanner M., Cook J. M., Dumont M., Painter T. H., Radiative forcing by light-absorbing particles in snow. Nat. Clim. Chang. 8, 964–971 (2018).
    1. Patel K., et al. ., “Image of the day for April 21, 2020: Airborne particle levels plummet in northern India” (NASA Earth Observatory, 2020). https://earthobservatory.nasa.gov/images/146596/airborne-particle-levels.... Accessed 5 April 2021.

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