ANR China Trend Stream

Overview

The overall objective of the “China-Trend-Stream” project is to quantify and understand the processes that have caused the observed historical trends in the Yangtze and Yellow River discharges and to project future trends until 2050. To do this, we propose a 3-year project based on a novel and ambitious, synergetic approach, combining satellite observations, national surveys, in situ measurements and improved modeling.

Meetings

The second annual meeting of the CTS project was successfully held in Beijing on 18-19 Sept 2017. First, P. Ciais reviewed the project progress in the last year and pointed out current challenges. Then the meeting was continued by presentations from different working packages (WP). In WP1 (ecosystem modeling), X. Wang presented the improvement of the new Chinese PFT map. The simulation results with the new PFT map and the new crop+irrigation module was shown by Z. Yin. In the section of hydrological modeling (WP2), S. Wang analyzed the trend of observed streamflows in different regions of the Yellow River basin and Z. Yin compared the simulated streamflows with observations at different gauging stations in the Yangtze and Yellow river basins. To integrate human activities in hydrological processes, P. Dumas introduced the framework of a hydro-economic model ODDYCCEIA and implementation of ODDYCCEIA-ORCHIDEE integration. X. Zhou presented the new reservoir module in ORCHIDEE (including dam regulation) and its application to Huai and Wu river. In WP3 (trend attribution and extreme events), Y. Xi and F. Zhou showed the natural and social impacts on Chinese river streamflows, respectively. X. Feng presented how to characterize drought by precipitation-runoff relations in the Loess Plateau. On the second day, Y. Li presented weak hydrological feedbacks from afforestation and vegetation greening in China for WP4 and L. Li gave a talk about climate change scenarios for the CTS project in WP5. Several special talks were given by X. Li, Y. Qin and P. Shi. Three crucial issues were well discussed: 1) Improvement of the new irrigation scheme; 2) How to integrate human processed in hydrological modeling; 3)Is there any factor missed in explaining the trend of streamflows? Finally, P. Ciais summarised the results of the meeting and updated the plan for next step and publications.

The first annual meeting of the project was held in Beijing on 24–25th Oct 2016 with 25 participants. Simulation results using ORCHIDEE with 0.5° and 0.1° climate forcing were presented by Z. Yin and S. Peng, with and without land use change drivers and for different CO₂ concentration levels. Analysis of river discharge trends at 0.1° will be performed when the routing scheme of the model will be soon adapted to this high spatial resolution. J. Polcher presented the influence of routing resolution on simulated discharge for basins in Europe. A test case for the Tarim river discharge by X. Zhou showed the importance of glacial runoff for this basin, for matching observed hydrographs. A new dataset with streamflow from 400 streams over the last 30 years has been presented by F. Zhou and is being analyzed. Regional changes over the Loess Plateau are being analyzed by X. Feng. Coupled LMDZ ORCHIDEE runs were shown by Y. Li and L. Li for different climate scenarios with SST being prescribed and climate change in China simulated with 0.5° resolution for the period 2000-2100. Last, developments of the crop module of ORCHIDEE were detailed by X. Wang. Most of the discussion revolved around the incorporation of water demand for irrigated crops into withdrawals of water from streams, to be propagated through reservoirs using ORCHIDEE and ODDYCCEIA.

Workplan

• Improve the simulation of managed ecosystems in China, specifically the effect of management on soil moisture and runoff. Forest plantations, and crop management practice including irrigation will be incorporated into the ORCHIDEE land surface model currently used both by French and Chinese partners.

• Improve the simulation of river flow by accounting for reservoirs, floodplains and wetlands This will require new developments in the water routing scheme of ORCHIDEE, combined with the use of SPHY, a detailed catchment model. A unique set of dam management data and river discharge observations will be used for model evaluation.

• Attribute past, present and future changes in the water budgets of the Yangtze and Yellow River and their sub-basins, using ORCHIDEE and separate the effects of temperature and rainfall, plants’ response to rising CO2, land-use change and water management change (damming, irrigation). Once evaluated for the past 25 years, future projections of the discharge of both rivers, separating the above-listed driving factors, will be performed until 2050.

• Quantify the atmospheric feedbacks affecting Yangtze and Yellow River discharge changes. For this, the ORCHIDEE land surface model will be run “online” coupled to the LMDZ-ZASIA climate model for an ensemble of past and future simulations. The results will allow us to assess for the first time how regional rainfall changes resulting from atmospheric feedbacks modify soil moisture and in turn river discharge trends.

The results acquired during the project have been synthesized into a blueprint for an advanced decadal-scale forecasting system for water resources in China, available to policymakers and other stakeholders. The project has been conducted by complementary French and Chinese teams, who have already collaborated for many years through joint PhD and post-doctorate exchanges. The record of this consortium guaranteed the success of the project and the achievement of the project objective of attributing river discharge changes to anthropogenic and climatic drivers.

Consortium

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