What is the issue?
- There is an increase in occurrence of extreme rainfall events in the central Indian region in recent years.
- Reports suggest that an increased supply of moisture from Arabian Sea could be the reason.
What are the observations?
- There is a trend of weakening summer monsoon winds between 1950 and 2015.
- Resultantly, there has been an average 10% decline in overall summer monsoon rainfall over central India.
- However, the frequency and intensity of extreme rainfall events during the same period in this region has been on the rise.
- There has been a three-fold increase in the number of widespread extreme events in this region since 1950s.
- Importantly, the northern Arabian Sea gets 1-2°C warmer, 2-3 weeks prior to extreme events.
- As a result, there is 20-40% more evaporation and increased moisture levels over the Arabian Sea before an extreme event.
- Notably, Arabian Sea supplies more moisture to the extreme rainfall events than the Bay of Bengal and the central Indian Ocean combined.
What are the causes?
- For Weakening monsoon - Studies have observed that central Indian Ocean had considerably warmed over the years.
- On the other hand, the Indian peninsular region had not warmed up compared to other regions in the tropics.
- This is leading to a phenomena of reduced land-sea temperature difference.
- This reduced temperature difference and possibly the cooling caused by aerosol are causes behind weakening of the monsoon winds.
- For increased moisture - At the same time, the northern Arabian Sea is becoming increasingly warm.
- This is leading to increased moist air over it.
- Also, the warm temperatures result in large fluctuations in the monsoon winds leading to occasional surges.
- Consequently, there is an increased moisture transport during such surges.
- As monsoon winds blow northeastwards from Arabian Sea into India, this increased moisture causes extreme rainfall events in central India.
Source: The Hindu
