Preprints
https://doi.org/10.5194/hess-2024-226
https://doi.org/10.5194/hess-2024-226
31 Jul 2024
 | 31 Jul 2024
Status: this preprint is currently under review for the journal HESS.

Revealing joint evolutions and causal interactions in complex eco-hydrological systems by a network-based framework

Lu Wang, Yue-Ping Xu, Haiting Gu, Li Liu, Xiao Liang, and Siwei Chen

Abstract. Climate change and human activities have evidence to change eco-hydrological systems, yet the complex relationships among ecological (normalized difference vegetation index, gross primary productivity, and water use efficiency) and hydrological variables (runoff, soil water storage, groundwater storage, etc.) remain understudied. This study develops a novel framework based on network analysis alongside satellite data and in-situ observations to delineate the joint evolutions (phenomena) and causal interactions (mechanisms) in complex systems. The former employs correlations and the latter uses physically constrained causality analysis to construct network relationships. This framework is applied to the Yellow River basin, a region undergoing profound eco-hydrological variations. Results suggest that joint evolutions are controlled by compound drivers and direct causality. Different types of network relationships are found, namely, joint evolution with weak causality, joint evolution with high causality, and asynchronous evolution with high causality. The upstream alpine subregions, for example, where the ecological subsystem is more influenced by temperature while the hydrological one is more driven by precipitation, show relatively high synchronization but with weak and lagged causality between two subsystems. On the other hand, eco-hydrological causality can be masked by intensive human activities (revegetation, water withdrawals, and reservoir regulation), leading to distinct evolution trends. Other mechanisms can also be deduced. Reductions in growing season water use efficiency are directly caused by the control of evapotranspiration, and the strength of control decreases with the greening land surface in some subregions. Overall, the proposed framework provides insight into the complex interactions within the eco-hydrological systems for the Yellow River basin and has applicability to broader geographical contexts.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Lu Wang, Yue-Ping Xu, Haiting Gu, Li Liu, Xiao Liang, and Siwei Chen

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2024-226', Anonymous Referee #1, 26 Aug 2024
    • AC1: 'Reply on RC1', Lu Wang, 20 Sep 2024
  • RC2: 'Comment on hess-2024-226', Anonymous Referee #2, 26 Aug 2024
    • AC2: 'Reply on RC2', Lu Wang, 06 Oct 2024
Lu Wang, Yue-Ping Xu, Haiting Gu, Li Liu, Xiao Liang, and Siwei Chen
Lu Wang, Yue-Ping Xu, Haiting Gu, Li Liu, Xiao Liang, and Siwei Chen

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Short summary
To understand how eco-hydrological variables evolve jointly and why, this study develops a framework using correlation and causality to construct complex relationships between variables at the system level. Causality provides more detailed information that the compound causes of evolutions regarding any variable can be traced. Joint evolution is controlled by the combination of external drivers and direct causality. Overall, the study facilitates the comprehension of eco-hydrological processes.