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The South Asian Summer Monsoon: What Our Climate Projections Tell Us


The South Asian summer monsoon (SASM), the strongest component of the global monsoon system, contributes about 80% of the annual rainfall in South Asia and provides the water supply for more than a billion people. Being able to predict SASM variations on different time scales is crucial for agriculture, ecosystems, and the hydrological cycle in the region. 

A climate projection is used to simulate the climate system based on a scenario of future external forcing. It can provide information essential for decision-makers to develop effective adaptation and mitigation strategies. The climate projection is based on numerous climate simulations with specified models, external forcings, and boundary conditions. The model results encompass both the long-term climate changes which are driven by the external forcings such as anthropogenic emission and the short-term variations due to the internal variability, however, with large uncertainties. Internal variability could overshadow or even override the long-term change over a period of several decades. With growing societal demand on the near-term climate prediction, a lot of efforts have been made to improve the understanding of internal climate variability and their impacts on future climate projections

In a recently published research article in Science Advances, authors Xin Huang, Tianjun Zhou, Hongmei Li, Chao Li, Xiaolong Chen, Jingwen Lu, Jin-Song Von storch, Bo Wu, and MAPP funded PI Aiguo Dai, investigate the causes for the large projection uncertainties of SASM and found the Interdecadal Pacific Oscillation (IPO) is one of the key internal climate modes affecting the near term projection of SASM rainfall. Their study relied on a large ensemble of climate simulations by a single model and a single external forcing and quantified the internal variability using the inter-member spread. The SASM rainfall trends were found to be related to the IPO phase transitions, especially on the occurrence of an extreme wetting or drying trend. 

Interdecadal Pacific Oscillation (IPO) is one of the dominant internal modes of the climate system. It refers to a long-term oscillation of sea-surface temperatures (SST) in the Pacific Ocean that can last from 20 to 30 years. The IPO-related SST anomalies affect large-scale atmospheric circulation over the tropical Pacific Ocean/tropical Indian Ocean can further lead to a change of southwest monsoon winds. Thus, a better understanding and prediction of the decadal-multidecadal climate modes will improve the near-term projection of SASM and other regional climates.  

Read the full paper here


About MAPP

The Modeling, Analysis, Predictions, and Projections (MAPP) Program is a competitive research program in NOAA Research’s Climate Program Office. MAPP’s mission is to enhance the Nation’s and NOAA’s capability to understand, predict, and project variability and long-term changes in Earth’s system and mitigate human and economic impacts. To achieve its mission, MAPP supports foundational research, transition of research to applications, and engagement across other parts of NOAA, among partner agencies, and with the external research community. MAPP plays a crucial role in enabling national preparedness for extreme events like drought and longer-term climate changes. For more information, please visit


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