Unlocking the Mysteries of Water Dynamics on the Tibetan Plateau

The Tibetan Plateau (TP), often referred to as the "Asian Water Tower," plays a pivotal role in the global water cycle, influencing ecosystems and livelihoods across Asia through its extensive river network. In the face of global change, the TP stands as a potential tipping point in the Earth system, exerting significant regional and global influences. Runoff and evapotranspiration (ET) are fundamental components of the water cycle, profoundly influencing the exchange of water, energy, and carbon among the terrestrial biosphere, hydrosphere, and atmosphere. Therefore, a thorough understanding of runoff and ET dynamics on the TP is crucial. These processes not only sustain the plateau's delicate ecosystems but also support millions downstream who depend on its water resources.

Challenges in Hydrological Research on the Tibetan Plateau

Despite its critical importance, generating reliable runoff and ET datasets for high-altitude river basins across the TP has been challenging. The scarcity of quality-controlled observational data poses a significant hurdle, exacerbated by harsh environmental conditions, infrastructural limitations, and restrictive data-sharing policies, especially for transboundary river basins. Furthermore, existing gridded runoff and ET products across the TP often fail to adequately incorporate cryosphere-hydrological processes, thus inaccurately capturing detailed variations in runoff and ET, particularly within montane river valleys.

The Development of TPRED

To address these challenges, our team has developed TPRED, a high-quality monthly gridded dataset at 5-km spatial resolution depicting runoff and ET dynamics for the headwaters of seven major rivers across the TP from 1998 to 2017. TPRED was generated using the advanced cryosphere-hydrology model, WEB-DHM, which is constrained by the observed discharge data from the outlets of each headwater. The WEB-DHM model is well-regarded for its ability to describe cryospheric-hydrological processes accurately and assess the hydrological impacts of climate-induced changes in glaciers, snow, and permafrost.

Key Features of the WEB-DHM Model

The Water and Energy Budget-based Distributed Hydrological Model (WEB-DHM) combines a biosphere land surface model (SiB2) with a geomorphology-based hydrological model (GBHM). This integrated approach enables comprehensive consideration of water, energy, and CO₂ fluxes within soil-vegetation-atmosphere transfer systems at the grid scale. The model not only ensures energy conservation in land surface processes but also provides detailed representations of hydrophysical phenomena at high spatial resolutions. Additionally, the WEB-DHM model has demonstrated its efficacy in elucidating the impacts of cryosphere changes on hydrological processes through consistent enthalpy-based cryosphere processes.

(i) Snow Simulation: Utilizing an enthalpy-based snow model to accurately simulate snowpack dynamics, including phase transitions and albedo variations.

(ii) Glacier Module: Incorporating an energy balance-oriented module for clean and debris-covered glaciers, which enhances the model's ability to simulate glacier contributions to runoff.

(iii) Frozen Ground Parameterization: Employing a hydrothermal transfer approach to simulate freeze-thaw cycles and basin-scale hydrological processes, thereby enhancing model stability and accuracy.

Applications of TPRED

TPRED may contribute significantly to various research fields. For example,

(i) Hydrometeorology: TPRED enhances understanding of hydrological and climatic patterns. For instance, analysis of runoff to precipitation (R/P) and evapotranspiration to precipitation (ET/P) ratios reveals distinctive water-cycle characteristics across the TP (Figure 1).

(ii) Carbon Transport: Beyond hydrometeorology, TPRED provides critical insights into carbon transport dynamics originating from the TP's alpine headwaters, crucial for global carbon cycling^1–4 (Figure 2).

(iii) Water Resources Management: TPRED supports effective water allocation strategies and policy-making, essential for achieving United Nations Sustainable Development Goal 6 (SDG6) on water resources management^5,6.

Future Directions

Moving forward, TPRED will serve as a benchmark dataset for validating and improving hydrological models and forecasting tools⁷. Integration with advanced machine learning algorithms holds promise for enhancing future projections of water resources dynamics in the TP under changing climate scenarios⁸.

Conclusion

In conclusion, TPRED represents a significant advancement in hydrological research on the Tibetan Plateau, offering a comprehensive dataset that addresses critical gaps in understanding runoff and ET dynamics. By facilitating enhanced modeling capabilities and supporting sustainable water resources management, TPRED contributes to broader efforts in climate resilience and ecological sustainability in high-altitude regions globally.

Article link

Fan, X., Wang, L., Liu, H. et al. Tibetan Plateau Runoff and Evapotranspiration Dataset by an observation-constrained cryosphere-hydrology model. Sci Data 11, 773 (2024). https://doi.org/10.1038/s41597-024-03623-3

Figure 1. Hydrometeorological patterns across major headwater regions of TP during 1998-2017. (a-b) The ratio of R/P and its trend. (c-d) The ratio of ET/P and its trend. The shadow denotes that the trend has undergone statistical significance testing. The two ratios were derived from both the new TPRED and TPFMD precipitation data⁹.

Figure 2. Carbon transport patterns across major headwater regions of TP during 1998-2017. (a-b) The F_DOC and its trend. (c-d) The WUE and its trend. The meaning of shadow is similar to Fig.1. We calculated F_DOC and WUE using the TPRED, combined with the NIRv GPP dataset¹⁰ and watershed slope data (from the model input). The respective formulae applied were F_DOC = 0.004×runoff + 0.095×GPP – 8.76×slope¹⁰² and WUE = GPP/ET¹⁰⁴.  

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