Collapsing Glaciers Threaten Asia's Water Supplies

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The Tsho Rolpa valley in Nepal, where increased meltwater from glaciers in the Himalayas puts local communities at risk. Collapsing glaciers threaten Asia’s water supplies Tracking moisture, snow and meltwater across the ‘third pole’ will help communities to plan for climate change, argue Jing Gao and colleagues.

he ‘third pole’ is the planet’s largest one-fifth of the world’s population depends1. they did 30 years ago5. And weather patterns reservoir of ice and snow after the Climate change threatens this vast frozen are shifting. A weaker Indian monsoon is Arctic and Antarctic. It encompasses reservoir (see ‘Third pole warming’). For the reducing precipitation in the Himalayas6 and Tthe Himalaya–Hindu Kush mountain ranges past 50 years, glaciers in the Himalayas and southern Tibetan Plateau; snow and rain are and the Tibetan Plateau. The region hosts Tibetan Plateau have been shrinking2. Those increasing in the northwestern Tibetan Pla- the world’s 14 highest mountains and about in the Tian Shan mountains to the north teau and Pamir Mountains2. 100,000 square kilometres of glaciers (an area have lost one-quarter of their mass, and Researchers still don’t understand why the size of Iceland). Meltwater feeds ten great might lose as much as half by mid-century3. these changes vary so much across the rivers, including the Indus, Brahmaputra, Their meltwater is expanding lakes4. River region, or how they will pan out. Some riv- Ganges, Yellow and Yangtze, on which almost flows at the start of summer peak earlier than ers in central Asia, such as those feeding

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the Aral Sea, are projected to gradually But there is more to be done. Researchers Physical processes that affect glaciers are dry up7. Others — such as the upper Ganges, need a better understanding of the relation- poorly understood, including the impacts Brahmaputra, Salween and Mekong — are ships between the third pole’s complex ter- of aerosols and surface debris on ice accu- likely to swell, at least until 2050 (ref. 7). rain and the weather patterns and processes mulation and melting. We cannot predict Already, Tibetan communities are dealing that affect precipitation and ice-melting. The how much meltwater will descend into lakes with the impacts of collapsing glaciers. In water cycle must be traced in three dimen- and rivers, nor how wet soils might increase October 2018, debris dammed the Yarlung sions — as liquid water, ice and water vapour, local precipitation. The region’s complex and Tsangpo River, which forms the headwater on the ground and in the air — and changes varied topography is another confounding of the Brahmaputra, threatening areas as far monitored. Computer models also need to factor. afield as Bangladesh with flooding. be tailored to provide accurate projections Then there is climate change. The west- Communities need information to help for the region. erly jet stream in East Asia has strengthened them manage risks and water supplies. in winter for the past few decades9, yet the They need to know which glaciers are melt- NEED TO KNOW Indian summer monsoon is weakening. ing fastest, and how changing snowfall and Two weather patterns — the Indian monsoon Both trends affect the distribution of snow- a warmer climate are affecting the accu- and prevailing westerly winds — drive most fall and thus the reflectivity (or albedo), mulation and disappearance of ice and the of the moisture flow towards the third pole. energy budget (the balance of all the energy volumes of rivers and lakes. As the Indian continent heats up in spring that enters and leaves the Earth system) and and summer, convec- the water budget of the land’s surfaces. MONITORING NETWORK tion draws moisture “Satellite Global climate models are designed to The water cycle is hard to monitor in this northwards from the images and simulate large-scale features of atmospheric vast, high and remote region. Satellite images Bay of Bengal, Arabian circulation, and so struggle to reproduce and climate models are too coarse to resolve Sea and Indian Ocean; climate weather patterns in the third pole. New local changes. this falls as precipita- models are models and data will be needed to improve A network of monitoring stations is tion in the Himalayas too coarse to them. Only 0.1% of glaciers and lakes in the needed across the region. It must track clas- and beyond8. In the resolve local region have monitoring stations. Few areas sical meteorological variables, such as air north and west of the changes.” higher than 5,000 metres above sea level have temperature, humidity, air pressure, precip- region, strong west- weather stations, let alone water-isotope itation and winds. And it needs to expand erly winds bring moisture from the Mediter- detectors. data on the water cycle, by measuring the ranean. Across the whole region, water also stable isotopes of hydrogen and oxygen in evaporates from the soil and is given off by NEXT STEPS water vapour. This provides crucial insights plants through transpiration. The first priority must be to extend the into the origin of atmospheric moisture and We know these patterns thanks to observa- network of weather and isotope-monitoring the processes it has gone through, such as tions of stable isotopes in water. In the verti- stations. There are already plans to install evaporation and condensation. cal dimension, such data are revealing how 20 additional stations across a wider area of As a first step, an international scientific moisture mixes in air masses and through the third pole later this year; others can be programme called the Third Pole Environ- processes at the atmospheric boundary layer. added as learning progresses. The instal- ment (TPE; led by T.Y.) has set up 11 ground That information also records how mois- lation is part of China’s Pan-TPE research stations and tethered balloons since 2014, ture is released daily from glaciers, as their programme, involving scientists from working with the Institute of Tibetan Plateau surfaces and the air heat and cool. Norway to Nepal. It has a budget of 1.48 bil- Research, Chinese Academy of Sciences, in We still lack a quantitative understand- lion yuan (US$215 million) for 5 years to Beijing. This monitoring network is already ing of the role of each process in the overall study environmental changes in the third larger than similar efforts in Antarctica and water budget. Nor is it clear how much pole, Iranian Plateau, Caucasus Mountains the Arctic, and almost doubles the number water passes between solid, liquid and and Carpathian Mountains. Another pro- of such stations around the world. vapour phases, affecting regional hydrology. gramme — the Second Tibetan Plateau Scien- tific Expedition and Research (STEP) project — will receive 4.35 billion yuan over 5 years from 2019 to study environmental change in FEI LI the Tibetan Plateau. Throughout this 10-year programme, the cost of instruments, staff and maintenance is likely to rise from 8 million yuan a year to about 150 million yuan. Most of the monitoring stations will be set up along two axes. A south–north line of 15 stations at 100–500-kilometre intervals, stretching from the tropical Indian Ocean, across Bangladesh and Nepal to the Tian Shan Mountains, will monitor processes linked to the monsoon. An east–west transect, stretching from the Iranian Plateau to China’s Loess Plateau, and comprising 12 stations 200–500 kilometres apart, will examine the impacts of the westerlies. Snow and rainfall, glacier melt and lake and river discharge will be observed in river basins, along with levels of glacial debris, permafrost and groundwater. The interplay between elevation, atmos- Researchers set up instruments to measure stable isotopes in atmospheric water vapour near Everest. pheric circulation and water vapour will be

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THIRD POLE WARMING Climate change is altering precipitation across the Himalayan Hourly monitoring at mountain ranges and the Tibetan Plateau. a few high-altitude sites will reveal how TEMPERATURES INCREASING KAZAKHSTAN mountains a ect air 1.5 and moisture ows. C)

1 MONGOLIA

0.5 Qiyi 0

–0.5 Average regional Average Pamir Xiaodongkemadi –1 temperature di erence ( ° di erence temperature Westerly winds Tibetan 1970 1985 2000 2015 Plateau CHINA SNOW COVER FALLING Iranian Plateau Himalayas 3 A 4% decrease 2 Hengduan each decade. Mountains 1 INDIA Kangwure East Asian 0 monsoon Mean from mean) from –1 Indian (standard deviations (standard Change in snow area Change in snow area Ocean –2 1997 1999 2001 2003 2005 2007 2009 2011 Indian monsoon TIBETAN GLACIERS SHRINKING

2 0 –2 –4 Qiyi –6 FOLLOW THE WATER Monitoring stations: Current Planned Xiaodongkemadi A network of stations will track the movement of Major river Glacier –8 Kangwure water using its stable isotopes. Monsoons, westerly winds and evaporation and transpiration from soils Intensive topographic study site

Cumulative mass balance –10

(metres of water equivalent) of water (metres and plants are the main sources of precipitation. 1975 1980 1985 1990 1995 2000 2005 2010

tracked through hourly measurements at They should also quantify changes in river a professor at the Institute of Tibetan Plateau three hotspots: the Pamir Mountains (domi- run-off and water quality. Such models Research, CAS, Beijing; and at the CAS nated by westerlies), the Himalayas (affected would guide regional strategies for adapt- Center for Excellence in Tibetan Plateau by the Indian monsoon) and the Hengduan ing to climate change, for preserving and Earth Sciences, Beijing, China. Valérie Mountains (where the East Asian monsoon restoring ecosystems and their services, and Masson-Delmotte is a senior scientist at prevails). Each site will host 10 stations at for conserving biodiversity. the Laboratory for Sciences of Climate and 200-metre intervals in altitude. Scientists around the world in multiple dis- Environment (CEA-CNRS-UVSQ/IPSL), Installing and maintaining this network ciplines, from climatology to social science, Gif-sur-Yvette, France. Hans Christian will be challenging. Devices must be robust must work together. And local people’s needs Steen-Larsen is a senior researcher at the and equipped with the latest technologies, must be central. Researchers should help Geophysical Institute, University of Bergen; such as fast, laser-based spectroscopic iso- communities to understand what is happen- and at the Bjerknes Centre for Climate tope measurements and high-resolution ing to their climate and environment, and Research, Bergen, Norway. Weicai Wang light detection and ranging (lidar) systems. enable them to craft strategies for managing is an associate professor at the Institute of Instruments must be regularly calibrated. risks and adaptation. For example, scientists’ Tibetan Plateau Research, Chinese Academy More than 200 professional staff members assessments of major ice collapses of the Aru of Sciences (CAS), Beijing; and at the CAS must be trained to run them. glaciers in western Tibet in 2016 enabled Center for Excellence in Tibetan Plateau

, 445−453 (2015); GLACIERS: REF. 2; MAP: J. GAO, T. YAO & W. WANG. & W. WANG. YAO T. 2; MAP: J. GAO, REF. 120 , 445−453 (2015); GLACIERS: The second priority is for data to be shared the local government to establish a hazard- Earth Sciences, Beijing, China. and fed into global and regional climate warning system and to relocate threatened e-mail: [email protected] models. A new generation of Earth-system communities. 1. Immerzeel, W. W., van Beek, L. P. H. & models should be developed for the third As the impacts of global warming rever- Bierkens, M. F. P. Science 328, 1382–1385 (2010). pole, representing its atmosphere, cryo- berate around the third pole, science must 2. Yao, T. et al. Nature Clim. Change 2, 663–667 sphere, hydrosphere and biosphere. Models be at the fore. ■ (2012). . APPL. CLIMATOL THEOR. 3. Farinotti, D. et al. Nature Geosci. 8, 716–715 (2015). should include interactions at very high reso- 4. Zhang, G. et al. Geophys. Res. Lett. 44, 252–260 lution and encompass water’s stable isotopes, Jing Gao is an associate professor at the (2017). as well as aerosols and biogeochemical cycles. Institute of Tibetan Plateau Research, 5. Huss, M. & Hock, R. Nature Clim. Change 8, 135–140 (2018). These models should explore the regional Chinese Academy of Sciences (CAS), Beijing; 6. Roxy, M. K. et al. Nature Commun. 6, 7423 (2015). implications of different scenarios of human and at the CAS Center for Excellence in 7. Lutz, A. F., Immerzeel, W. W., Shrestha, A. B. & ET AL. SHEN ET S. P. COVER: SNOW SOC . (IN THE PRESS); AL. BULL. AM. METEOROL. ET YAO T. TEMPERATURES: SOURCES: activities and climate-mitigation strate- Tibetan Plateau Earth Sciences, Beijing, Bierkens, M. F. P. Nature Clim. Change 4, 587–592 (2014). gies (greenhouse-gas emissions, aerosols, China. Tandong Yao is a member of 8. Yao, T. et al. Rev. Geophys. 51, 525–548 (2013). land-use changes, water management). the Chinese Academy of Sciences (CAS); 9. Li, W. Nature Commun. 9, 4243 (2018).