Rivers originating in the Tibetan Plateau provide freshwater to downstream populations, yet runoff projections from warming are unclear due to precipitation uncertainties. Here, we use a historical atmospheric circulation–precipitation relationship to constrain future modelled wet-season precipitation over the Tibetan Plateau. Our constraint reduces precipitation increases to half of those from the unconstrained ensemble and reduces spread by around a factor of three. This constrained precipitation is used with estimated glacier melt contributions to constrain future runoff for seven rivers. We estimate runoff increases of 1.0–7.2% at the end of the twenty-first century for global mean warming of 1.5–4 °C above pre-industrial levels. Because population projections diverge across basins, this runoff increase will reduce the population fraction living under water scarcity conditions in the Yangtze and Yellow basins but not in the Indus and Ganges basins, necessitating improved water security through climate change adaptation policies in these regions at higher risk.
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The data that support the findings of this study are publicly available. The observational grid precipitations are available from https://www.dwd.de/EN/ourservices/gpcc/gpcc.html, http://www.cru.uea.ac.uk/data and https://www.esrl.noaa.gov/psd/data/gridded/data.UDel_AirT_Precip.html. The SLP dataset is available from https://www.esrl.noaa.gov/psd/gcos_wgsp/Gridded/data.hadslp2.html. The CMIP output is available from the Earth System Grid Federation at https://esgf-node.llnl.gov/projects/cmip5/, https://esgf-node.llnl.gov/search/cmip6/. The population data are available from https://sedac.ciesin.columbia.edu/data/set/popdynamics-1-km-downscaled-pop-base-year-projection-ssp-2000-2100-rev01. The glacier runoff data were extracted from https://www.nature.com/articles/s41558-017-0049-x#Sec14. The GLDAS Noah product is available from https://ldas.gsfc.nasa.gov/gldas/model-output. The Japanese 55-year reanalysis data are available from http://jra.kishou.go.jp/.
The codes used to perform the calculation and produce all figures are available from GitHub at https://github.com/zhaoyutong/.
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This study was supported by the Second Tibetan Plateau Scientific Expedition and Research Programme (2019QZKK0208), the NSFC project Basic Science Centre for Tibetan Plateau Earth System (41988101-04), Key Research and Development Programmes for Global Change and Adaptation (2017YFA0603604) and the National Natural Science Foundation of China (41922004 and 41871104). We acknowledge the support of Kathmandu Centre for Research and Education, Chinese Academy of Sciences–Tribhuvan University.
The authors declare no competing interests.
Peer review information Nature Climate Change thanks Daniel Farinotti, Santosh Nepal and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended Data Fig. 1 Simulated wet-season temperature change over the upper river basins sourced from the Tibetan Plateau at different warming levels.
The multimodel ensemble mean temperature difference between pre-industrial period (1850–1900) and future periods (2070–2099) at different warming levels over the upper Indus (a), Ganges (b), Brahmaputra (c), Salween and Mekong (d), Yangtze (e) and Yellow river basins (f). The dark grey region denotes the geographical location of each river basin. Blue, yellow and red represent the 1.5, 2 and 4 °C, respectively. Error bars indicate one standard deviation of intermodel spread. The number of CMIP5 and CMIP6 ESMs used to calculate projected temperature change is 6 and 4 for 1.5 °C of global warming (13 and 4 for 2 °C, and 6 and 5 for 4 °C). The wet season here is defined as the period from June to September.
Extended Data Fig. 2 Partitioning of intermodel uncertainty in projected wet-season runoff change over upper river basins sourced from the Tibetan Plateau at the three warming levels.
The multi-circular bar shows the intermodel uncertainty in projected runoff changes that can be partitioned into the individual components of projected changes in precipitation (blue), evapotranspiration (green) and the residual term (for example snow and soil water storage). Contributions are calculated as a percentage (%), estimated by means of analysis of variance. Dark grey, white, orange and light blue represent the Tibetan Plateau, the glaciered region, the upper river basin and ocean, respectively. The wet season here is defined as the period from June to September. The number of CMIP5 and CMIP6 ESMs used to calculate projected temperature change is 6 and 4 for 1.5 °C of global warming (13 and 4 for 2 °C, and 6 and 5 for 4 °C).
Extended Data Fig. 3 Same as Extended Data Fig. 2, except that the uncertainty partitioning is performed using the period from January to September in upper Indus basin.
The multi-circular bar shows the intermodel uncertainty in projected runoff changes that can be partitioned into the individual components of projected changes in precipitation (blue), evapotranspiration (green) and the residual term (for example snow and soil water storage). Contributions are calculated as a percentage (%), estimated by means of analysis of variance.
Extended Data Fig. 4 The coefficient of determination between interannual variabilities of precipitation and atmospheric moisture flux components over the Tibetan Plateau from 1960 to 2005 for JRA-55 and ESMs.
−∇ ⋅ Q, Dyn and Thermo represent the moisture flux convergence, the dynamic component and the thermodynamic component of moisture flux convergence, respectively. JRA-55 indicates the Japanese 55-year reanalysis data, and ESM indicates the Earth System Model from CMIP5 and CMIP6. The number of models from CMIP5 and CMIP6 historical experiments are 18 and 11, respectively.
Extended Data Fig. 5 Simulated and statistical-predicted precipitation over Tibetan Plateau under 1.5 °C.
Wet season (June to September) precipitation averaged over the Tibetan Plateau, simulated by CMIP ESMs (black line) and statistically predicted (red) from 1960 to 2099. All time series are smoothed with a 21-yr running mean filter. R indicates the correlation coefficient between simulated and statistical-predicted precipitation.
Extended Data Fig. 6 Simulated and constrained projections of wet-season precipitation changes over the Tibetan Plateau at different warming levels using the historical observations ensemble mean precipitation (GPCC, CRU and UDEL) and SLP relationship as a constraint on model projections of future precipitation changes.
The multimodel ensemble mean precipitation difference (in percentage) is calculated between historical period (1960–2005) and future periods (2070–2099) from CMIP original (a, c, and e) and constrained model projections (b, d and f) at different temperature levels. SLP is sea-level pressure. Dots indicates grids where all models agree on the sign of change. The bars indicate the frequency of distribution of the precipitation change. The wet season here is defined as the period from June to September. The number of CMIP5 and CMIP6 ESMs is 6 and 4 for 1.5 °C of global warming (13 and 4 for 2 °C, and 6 and 5 for 4 °C).
Extended Data Fig. 7 Same as Fig. 4, but for projected changes in percentage of population living above chronic water scarcity level (>1000 m3 per person per year) at the three warming levels.
The bars denote the percentage of the population living in the highly dependent area that could be satisfied by wet-season upstream runoff for a full year at the chronic water scarcity level (1000 m3 per person per year), and brown points represent the population (in millions) integrated over the highly dependent area.
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Wang, T., Zhao, Y., Xu, C. et al. Atmospheric dynamic constraints on Tibetan Plateau freshwater under Paris climate targets. Nat. Clim. Chang. 11, 219–225 (2021). https://doi.org/10.1038/s41558-020-00974-8