Experts from the Indian Institute of Tropical Meteorology in Pune and Assam University have been examining the rapid dessication occurring in Northeast India over the past 30 years. The Northeast, notoriously known as one of the wettest regions on Earth, has logged a notable drop in precipitation. Areas that previously received a staggering 3,000 mm of rain during monsoon season now face a reduction of nearly 25-30%.
The Role of Monsoons and The Pacific Decadal Oscillation
Research indicates that the region’s rainfall is largely influenced by monsoon patterns and the long-reaching effects of the Pacific Decadal Oscillation (PDO). Occurrences of PDO, a long-term ocean fluctuation of the Pacific Ocean, have a noticeable impact on rainfall in the Northeast. The PDO typically ebbs and flows over a duration of 20 to 30 years, much like the El Nino/La Nina phenomena in the tropical Pacific. However, the PDO leaves a more prolonged imprint on sea surface temperatures and its interaction with atmospheric conditions, which brings about changes in the Northeast Indian summer monsoon.
Comparing PDO and ENSO Time Scales
Although similar in nature, the PDO differs from The El Nino-Southern Oscillation (ENSO) in its time scale. While ENSO cycles generally last for 6 to 18 months, PDO phases can persist for 20 to 30 years. Both consist of warm and cool phases which modify upper-level atmospheric winds.
| Phenomenon | Duration |
|---|---|
| PDO | 20 – 30 years |
| ENSO | 6 – 18 months |
Implications of PDO Shifts
Shifts in the PDO phase can have far-reaching consequences for the global climate. They can influence Atlantic and Pacific hurricane activity, cause droughts and flooding around the Pacific basin, affect marine ecosystem productivity, and alter global land temperature patterns.
The PDO’s Impact on ENSO
Interesting interplays can be observed between PDO and ENSO, where the phase of the PDO can either intensify or mitigate the effects of ENSO. If both phenomena are in the same phase, it is postulated that El Niño/La Nina impacts may be amplified. Conversely, if ENSO and PDO are not in sync, they may counterbalance each other, preventing “true” ENSO impacts from manifesting. Such complex interactions and their potential effects are key elements in understanding the increasingly dry conditions in Northeast India.