Monsoon margins, often located in semi-arid zones, are ecologically fragile areas highly sensitive to climate change and socio-economic activities. However, the response of monsoon margins to global warming remains unclear, primarily due to limited understanding of the competing effects between monsoon weakening and the Hadley circulation widening. We propose a monsoon margin index as the precipitation isoline bounded areas with both high summer precipitation ratio and close links with monsoon dynamics, which effectively characterizes the Northern Hemisphere Monsoon Margin (NHMM) and Southern Hemisphere Monsoon Margin (SHMM). Co-variability between the NHMM and SHMM strengthens when the NHMM leads by six months, reflecting their respective responses to the developing and peak phases of the El Niño-Southern Oscillation (ENSO). Our findings reveal an intensifying co-variability between NHMM and SHMM under an increasing ENSO variability. Expansion of both NHMM and SHMM is primarily driven by the widening Hadley circulation rather than by a weakening of the monsoon systems. Under future warming scenarios, monsoon margins are projected to expand further, coinciding with intensified ENSO variability and continued Hadley circulation expansion.
Fang et al. (Wed,) studied this question.