The water cycle over the Tibetan Plateau (TP), as known as "Asian Water Tower", is vital to the regional and downstream climate and ecosystem. A new study found that the interannual variability of the summer precipitation recycle ratio over the TP is influenced by the El Nino events in preceding winters. The study was published in Journal of Geophysical Research: Atmospheres and conducted by researchers from the Institute of Atmospheric Physics at the Chinese Academy of Sciences.

The precipitation recycle ratio is the contribution rate of the local evaporation to the total precipitation. "It's an important indicator of the water cycle process in the atmosphere. However, previous studies about precipitation recycle ratio over the TP remain inconclusive," said Dr. ZHOU Tianjun, the corresponding author of the study. "The key point is the reasonable consideration of the atmospheric water vapor mixture processes."

Using the advanced reanalysis data ERA5 of the high resolution and a bulk model method, the team analyzed the interannual variability of the precipitation recycle ratio over the TP.

"The results show the impact of ENSO, the most significant variability of the climate system at interannual timescale," said Dr. ZHOU. "In the El Nino decaying summers, the large-scale anomalous anticyclone spans over the Indo-Northwest Pacific and the westerly anomalies along the north flank of the anticyclone transport more moisture into the TP. The increased external inflow and decreased local evaporation lead to a decrease in the precipitation recycle ratio over the TP."

The schematic diagram of the atmospheric water cycle and its changes with ENSO events over the TP in summer. The black fonts represent the climatic mean value and interannual variability. The red (blue) fonts represent the average value in El Nino (La Nina) decaying summers. Italic fonts denote that changes are significant at the level of 0.1. (Image by ZHAO Yin)

"The change in the recycle ratio induced by the preceding El Nino events explains 60% of its interannual variability, but the response of precipitation recycle ratio over the TP in summer to the preceding El Nino and La Nina events is asymmetric," said Dr. ZHOU. "We hope this study is useful to reach the consensus on the climatic precipitation recycle ratio over the TP and advance our knowledge about its interannual variability mechanism."

This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No. XDA20060102 and National Natural Science Foundation of China under Grant Nos. 41988101 and 41775091, as well as the Second Tibetan Plateau Scientific Expedition and Research (STEP) program (Grant No. 2019QZKK0102).

Citation:
Zhao, Y., & Zhou, T. (2021). Interannual variability of precipitation recycle ratio over the Tibetan Plateau. Journal of Geophysical Research: Atmospheres,126,e2020JD033733. https://doi.org/10.1029/2020JD033733

Media contact: Ms. LIN Zheng, jennylin@mail.iap.ac.cn