A recent study has found that Northeast India, one of the wettest places on the Earth has been experiencing rapid drying, especially in the last 30 years. The decreasing monsoon rainfall in Northeast India is associated with natural changes in the subtropical Pacific Ocean.
The study was conducted by researchers from Indian Institute of Tropical Meteorology (IITM), Pune, and Assam University. It was published in JGR-Atmospheres. Researchers observed rainfall and sea surface temperature data for period 1901-2014.
Key Findings of Study
- Northeast India has been experiencing rapid drying, especially in the last 30 years. Some places in this region which used to get as high as 3,000 mm of rain during monsoon season are now seeing drop of about 25-30% in monsoon rainfall.
- Reasons for decline in rainfall: The reduction in rainfall during major part of last 114 years may be associated with global man-made factors.
- The decline in trend during the last 36 years is associated with natural phenomena or natural changes in Pacific decadal oscillation (PDO).
- Its impact on the sea surface temperatures and its interaction with the atmosphere affects the northeast Indian summer monsoon.
Pacific decadal oscillation (PDO)
- It is spatial avaerage of monthly global sea surface temperature (SST) anamoly of Pacific Ocean north of 20 degrees. It is long-lived El Niño-like pattern of Pacific climate variability.
- It is highly correlated with temperature in California current, thus affecting coastal sea and continental surface air temperatures from Alaska to California coast.
- During warmor positive PDO phase, west Pacific becomes cooler and part of eastern ocean warms. During "cool" or "negative" phase, opposite pattern occurs.