Impact of Monsoon Variability on the Northern Hemisphere Terrestrial Carbon Cycle on an Interannual Time Scale

A monsoon climate covers a large portion of the global land and exhibits notable interannual variations. However, the effect of monsoon variability on the terrestrial carbon cycle has been investigated less due to the gap between physical and biogeochemical climate research communities. Here, using the FLUXCOM dataset, we show that the Northern Hemisphere land monsoon (NHLM) regions account for 40.24% (+/- 3.40%) [+/- one standard deviation (SD)] of the climatological summer mean net ecosystem production (NEP) over the NH land from 1981 to 2010 and contribute 21.35% (+/- 7.57%) to the interannual variability (IAV) in NH NEP. Using singular value decomposition (SVD), we fi nd that the leading modes of NEP anomalies are associated with El Ni & ntilde;o development and decay phases. During the El Ni & ntilde;o-developing summer, a higher sea surface temperature in the tropical central-eastern Pacific fi c results in reduced photosynthetic productivity and weaker carbon uptake because of the reduced precipitation associated with monsoon circulation changes. Precipitation is the predominant driver of NEP anomalies relative to temperature and radiation, contributing 65.20% in the NHLM regions. During the El Ni & ntilde;o-decaying summer, abundant rainfall along the Yangtze River valley in China results in increased photosynthetic productivity and ecosystem respiration, leading to less change in carbon uptake. In other monsoon regions, photosynthesis anomalies are driven by higher temperatures, and respiration anomalies are driven by enhanced precipitation. Both of these conditions are favorable for the release of CO2 2 into the atmosphere. Our study highlights the impact of monsoon variability on the carbon cycle in monsoon regions during different phases of El Ni & ntilde;o-Southern Oscillation (ENSO) evolution.