Asia’s glaciers are a regionally important buffer against drought

Journal name:
Nature
Volume:
545,
Pages:
169–174
Date published:
DOI:
doi:10.1038/nature22062
Received
Accepted
Published online

Abstract

The high mountains of Asia—encompassing the Himalayas, the Hindu Kush, Karakoram, Pamir Alai, Kunlun Shan, and Tian Shan mountains—have the highest concentration of glaciers globally, and 800 million people depend in part on meltwater from them. Water stress makes this region vulnerable economically and socially to drought, but glaciers are a uniquely drought-resilient source of water. Here I show that these glaciers provide summer meltwater to rivers and aquifers that is sufficient for the basic needs of 136 million people, or most of the annual municipal and industrial needs of Pakistan, Tajikistan, Turkmenistan, Uzbekistan and Kyrgyzstan. During drought summers, meltwater dominates water inputs to the upper Indus and Aral river basins. Uncertainties in mountain precipitation are poorly known, but, given the magnitude of this water supply, predicted glacier loss would add considerably to drought-related water stress. Such additional water stress increases the risk of social instability, conflict and sudden, uncontrolled population migrations triggered by water scarcity, which is already associated with the large and rapidly growing populations and hydro-economies of these basins.

At a glance

Figures

  1. Existing and planned dams in high-mountain Asia.
    Figure 1: Existing and planned dams in high-mountain Asia.

    Circles indicate existing irrigation and water supply barrages (dark blue), existing hydroelectric dams (orange)18, and planned hydroelectric dams or those under construction (light blue; which constitute a 121-GW increase in capacity)1. The background shading shows the 4-km-gridded 2015 population19 (above 3,000 people per cell) and the distribution of glaciers11.

  2. Annual and mean river-basin precipitation.
    Figure 2: Annual and mean river-basin precipitation.

    Shown are time series of total precipitation for the study basins for the period 1951–200710.

  3. Glacier temperature, water inputs and seasonally delayed melt.
    Figure 3: Glacier temperature, water inputs and seasonally delayed melt.

    ag, Monthly mean temperature (at the area-weighted mean glacier front elevation; blue line and data), area-averaged on-glacier adjusted precipitation (including avalanching and so on15; grey histograms) and net monthly ablation (orange histograms) for glaciers in the the Aral (a), Indus (b), Ganges (c), Brahmaputra (d), Tarim (e), Issyk-Kul (f) and Balkhash (g) basins. Zero net ablation implies net accumulation for that month.

  4. Precipitation and glacial melt inputs in an average year.
    Figure 4: Precipitation and glacial melt inputs in an average year.

    Mean monthly gross precipitation (background colours; refs 10,15) and NMF for dam catchments (pie charts) are indicated for an average year. The size of each pie chart shows the net water volume inputs (in km3) per catchment, with inputs from melt and precipitation indicated by the dark and light blue sectors, respectively. Geographic locations of dams are shown in Fig. 1.

  5. Precipitation and glacial melt inputs in a drought year.
    Figure 5: Precipitation and glacial melt inputs in a drought year.

    As Fig. 4, but for the summer month with the largest NMF in the driest year on record for each river basin.

  6. The demographic and political context of the contribution of glacial melt.
    Figure 6: The demographic and political context of the contribution of glacial melt.

    Drought-year NMFs for dam catchments are shown relative to population19 and geographic distribution: “ethnically fractionalized” countries9 are shaded red and disputed boundaries (http://www.naturalearthdata.com; accessed 2015) are highlighted in red; the dashed red line approximately represents the Line of Control in Jammu and Kashmir agreed on by India and Pakistan. The final status of Jammu and Kashmir has not yet been agreed on by the parties. IAK refers to Indian-administered Kashmir, PAK to Pakistan-administered Kashmir.

  7. Water stress.
    Extended Data Fig. 1: Water stress.

    Baseline water stress (total annual water withdrawals (municipal, industrial, and agricultural) as a percentage of the total annual available blue water) for the major HMA river basins in 201545. The dashed line represents the Line of Control in Jammu and Kashmir agreed on by India and Pakistan. The final status of Jammu and Kashmir has not yet been agreed on by the parties. IAK refers to Indian-administered Kashmir, PAK to Pakistan-administered Kashmir.

  8. Inter-annual precipitation variability.
    Extended Data Fig. 2: Inter-annual precipitation variability.

    Annual relative precipitation variability (coefficient of variation normalized by mean, 1961–199025; colour scale) for the Aral (1), Indus (2), Brahmaputra (3), Ganges (4), Tarim (5), Issyk-Kul (6) and Balkhash (7) basins in the global context.

  9. Relative inter-annual precipitation variability by basin.
    Extended Data Fig. 3: Relative inter-annual precipitation variability by basin.

    ag, Precipitation is shown relative to the mean (blue); ±1 coefficient of variation is indicated by the dashed grey lines. Relative interannual variability is lowest in the Brahmaputra (d) and Ganges basins (c), intermediate in the Indus (b) and highest in the four northern basins (a, eg).

  10. Datasets and processing flow used in this study.
    Extended Data Fig. 4: Datasets and processing flow used in this study.

    Processing scheme to derive NMFs for each catchment. See Methods section ‘Data available’ for references.

  11. Average- and drought-year monthly precipitation.
    Extended Data Fig. 5: Average- and drought-year monthly precipitation.

    ag, Monthly basin precipitation for an average year (green) and the driest year on record (blue) for the Aral (a), Indus (b), Ganges (c), Brahmaputra (d), Tarim (e), Issyk-Kul (f) and Balkhash (g) basins.

  12. Definition of zones.
    Extended Data Fig. 6: Definition of zones.

    River-basin hypsometric zones 2–4 are defined12 as covering the area above the area-weighted mean glacier terminus height for each basin, plus the upper 75%, 50% or 25%, respectively, of the remaining basin area.

  13. Cumulative population distribution by zone within each river basin.
    Extended Data Fig. 7: Cumulative population distribution by zone within each river basin.

Tables

  1. Correlation coefficients of precipitation
    Extended Data Table 1: Correlation coefficients of precipitation
  2. Drought-year precipitation amount and drought severity
    Extended Data Table 2: Drought-year precipitation amount and drought severity
  3. Basin and glacier gross inputs and losses
    Extended Data Table 3: Basin and glacier gross inputs and losses

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Author information

Affiliations

  1. British Antarctic Survey, Madingley Road, Cambridge CB3 0ET, UK

    • Hamish D. Pritchard

Competing financial interests

The author declares no competing financial interests.

Corresponding author

Correspondence to:

Reviewer Information Nature thanks A. Sakai, J. Arnold and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: Water stress. (726 KB)

    Baseline water stress (total annual water withdrawals (municipal, industrial, and agricultural) as a percentage of the total annual available blue water) for the major HMA river basins in 201545. The dashed line represents the Line of Control in Jammu and Kashmir agreed on by India and Pakistan. The final status of Jammu and Kashmir has not yet been agreed on by the parties. IAK refers to Indian-administered Kashmir, PAK to Pakistan-administered Kashmir.

  2. Extended Data Figure 2: Inter-annual precipitation variability. (209 KB)

    Annual relative precipitation variability (coefficient of variation normalized by mean, 1961–199025; colour scale) for the Aral (1), Indus (2), Brahmaputra (3), Ganges (4), Tarim (5), Issyk-Kul (6) and Balkhash (7) basins in the global context.

  3. Extended Data Figure 3: Relative inter-annual precipitation variability by basin. (420 KB)

    ag, Precipitation is shown relative to the mean (blue); ±1 coefficient of variation is indicated by the dashed grey lines. Relative interannual variability is lowest in the Brahmaputra (d) and Ganges basins (c), intermediate in the Indus (b) and highest in the four northern basins (a, eg).

  4. Extended Data Figure 4: Datasets and processing flow used in this study. (270 KB)

    Processing scheme to derive NMFs for each catchment. See Methods section ‘Data available’ for references.

  5. Extended Data Figure 5: Average- and drought-year monthly precipitation. (321 KB)

    ag, Monthly basin precipitation for an average year (green) and the driest year on record (blue) for the Aral (a), Indus (b), Ganges (c), Brahmaputra (d), Tarim (e), Issyk-Kul (f) and Balkhash (g) basins.

  6. Extended Data Figure 6: Definition of zones. (539 KB)

    River-basin hypsometric zones 2–4 are defined12 as covering the area above the area-weighted mean glacier terminus height for each basin, plus the upper 75%, 50% or 25%, respectively, of the remaining basin area.

  7. Extended Data Figure 7: Cumulative population distribution by zone within each river basin. (178 KB)

Extended Data Tables

  1. Extended Data Table 1: Correlation coefficients of precipitation (63 KB)
  2. Extended Data Table 2: Drought-year precipitation amount and drought severity (103 KB)
  3. Extended Data Table 3: Basin and glacier gross inputs and losses (82 KB)

Additional data