Increased sea surface temperature affecting Indian monsoon: Study
The climate across the world is changing in many ways, triggered by different global warming phenomena that have resulted in a change in the monsoon onset time and pattern. The process is affecting the agricultural yield. Any excess or little rainfall is, therefore, detrimental to these crops.
A new study on variability in the Mascarene High (MH) during global warming hiatus (GWH) revealed that the region experienced significantly increased sea surface temperature (SST) during this period (1998-2016).
The Mascarene High (MH) is a semi-permanent subtropical high-pressure zone in the South Indian Ocean. Apart from its large influence on African and Australian weather patterns, it also helps in driving the inter-hemispheric circulation between the Indian Ocean in the south and subcontinental landmass in the north.
A global warming hiatus is referred to a global warming pause, or a global warming slowdown, which is a period of relatively little change in globally averaged surface temperatures. The hiatus, however, can result in an increase in the SST.
This warming in SST, according to the study, resulted in a decrease in the pressure gradient between the MH and the Indian landmass, which in turn suppressed the intensity of low-level cross-equatorial winds over the western Indian Ocean affecting the onset of the monsoon over the Indian subcontinent and rainfall over East Asia.
The Mascarene Islands is a group of islands in the Indian Ocean east of Madagascar from where the cross equatorial winds blow to India. It is also called the Indian Ocean subtropical high, which is a high-pressure area located between 20° to 35° South latitude and 40° to 90° East longitude.
The southwest monsoon caused by this high pressure area is the strongest component of the Indian subcontinent monsoon that contributes about more than 80 per cent of the annual rainfall in entire East Asia.
It is also the principal water supply source for more than a billion people in this region. Many climate modes / factors modulate the monsoon; one of the factors is Mascarene high influence.
The findings are alarming for a country whose food production and economy depend heavily on monsoon rainfall. According to National Centre for Polar and Ocean Research (NCPOR) scientists, the weakening of the MH in the southern Indian Ocean during GWH may affect the strength of the upwelling along the coast of Somalia and Oman and thus, influence the Arabian Sea ecosystem.
During the study, it was found that increased sea level and heat content in the MH region during the GWH (1998-2016) suppressed the intensity of low-level cross-equatorial winds.
NCPOR scientists have also investigated the recent warming trends in MH during GWH period and found a significant positive trend in SST, sea surface height (SSH) and oceanic heat content (OHC).
Out of which, SST impacted more on the monsoon with rainfall during the last 18 years. Scientists, therefore, called for urgent steps to reduce greenhouse gas emission to avert the associated risk of climate change effect, including killer heatwave and stop flooding from snow and glacier melting caused by rising temperatures.
Led by Vidya PJ, the research team comprised of Ravichandran, M Subeesh MP, Chatterjee S, and Nuncio M of NCPOR, Goa, Ministry of Earth Sciences. The research paper was published in Nature.