image: Ensemble mean forecast anomalies averaged over forecast years 2 to 9 for summer precipitation over the Inner Tibetan Plateau. Red line: retrospectives; Blue line: near real-time predictions; Black line: observations. Shadows represent uncertainty.
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Credit: HU Shuai

Summer precipitation on the Tibetan Plateau is highly predictable over multi-year timescales in large ensemble forecasts, according to a research team led by ZHOU Tianjun of the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences.

The study, published in Scientists progress June 9, shows that the predictable summer rainfall signal in the Tibetan Plateau hinterland is significantly underestimated in advanced decadal forecast models.

The predictable signal is so weak that it can be masked by unpredictable noise. “The predictable signal that is too weak comes from the low signal-to-noise ratios in the models compared to the real world,” said ZHOU, corresponding author of the study. “This phenomenon is kind of a deficiency in climate models, but it also prompts us to once again recognize the decadal predictability of prediction models.”

ZHOU is Principal Investigator at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics at IAP. He is also a professor at the University of the Chinese Academy of Sciences.

ZHOU and his team used large assemblies from the Sixth Coupled Model Intercomparison Project (CMIP6) of the Decadal Climate Prediction Project (DCPP), an archive of comprehensive decadal prediction experiments based on various climate models, to eliminate stochastic noise. unpredictable and extract the predictable signal. summer rainfall in the Tibetan plateau.

The researchers produced realistic predictions through a post-processing variance adjustment procedure, indicating that the Tibetan Plateau’s summer precipitation is highly predictable over ten-year time scales.

The Tibetan Plateau has the most glaciers outside of the Arctic and Antarctic. Melt water supplies more than 10 major rivers, including the Yangtze River, the Yellow River and the Ganges. “Our results mean a lot for the management of water resources for about 40% of the world’s population,” ZHOU said.

Based on real-time forecasts, the researchers revealed that the Tibetan Plateau hinterland will become wetter, with a 12.8% increase in rainfall for the period 2020-2027 compared to 1986-2005.

“The government and scientists have recognized the urgent need for effective short-term climate information (2021-2040), but there are large uncertainties in traditional short-term climate projections based on summer rainfall scenarios on the Tibetan Plateau. due to internal variability. in the climate system, ”ZHOU said. “Our results demonstrate that decadal climate prediction systems can be a valuable tool in overcoming the shortcoming of traditional projection uncertainties based on short-term climate change scenarios on the Tibetan Plateau.”

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