Even when the entire Northeast India has been experiencing heavy to very heavy rainfall for the last few days, the spatial variability due to various reasons has meant that Meghalaya has received ‘large excess’ rainfall while Tripura has received ‘deficient’ and Mizoram ‘large deficient’ rainfall since March 1 till April 23.
The India Meteorological Department (IMD) data has shown that for the period between March 1 and April 23, the quantum of rainfall received by Meghalaya is 473.8 mm, which is 99 per cent more than the normal rainfall 237.5 mm for this duration; Tripura received 98.8 mm rainfall, minus 58 per cent of 234.1 mm normal for the duration and Mizoram received 64.4 mm rainfall, minus 66 per cent of 187.3 mm normal for the duration.
In IMD parlance, 60 per cent or more rainfall is termed as large excess; 20 per cent to 59 per cent is excess; rainfall that is between minus 19 per cent to plus 19 per cent is normal; minus 20 per cent to minus 59 per cent is deficient while minus 60 till minus 99 is termed as large deficient.
Other states in the North East received normal or excess rainfall. For the same duration of March 1-April 23, Manipur received 150.4 mm (against the normal of 149.4 mm); Nagaland received 137.8 (against the normal of 148.6 mm) and Arunachal Pradesh received 420.9 mm (against 403.5 mm normal) while two states, Sikkim with 417.4 mm against 276.0 mm normal (51 per cent more) and Assam with 321.1 mm against 202.3 mm normal (59 per cent more) received excess rainfall.
Explaining the phenomenon, senior scientist from IMD, K S Hosalikar, said the orography of the region and wind direction played a major role. “The windward orography of Meghalaya and the hilly terrain further north is a major factor. Plus, this time round, the wind direction is from southwest to northeast direction. Therefore, there was more rain in the northern part of the NE region while Tripura and Mizoram in the southern parts remained dry.”
Hosalikar also pointed out the lack of favourable low pressure system in the northern Bay of Bengal in this season for the missing heavy rainfall over Tripura and Mizoram.
Incidentally, Mizoram has recovered lost ground this week and showed normal rainfall while Tripura went from deficient to large deficient. For the duration between April 14-20, Tripura received 20.4 mm rainfall against the normal of 55.3 mm normal (minus 63 per cent) while Mizoram received 29.5 mm rainfall against the normal of 31.5 mm (minus six per cent).
The IMD has further predicted widespread rainfall and thunderstorms over the region for next few days under the influence of strong southwesterly winds from Bay of Bengal to northeastern states at lower tropospheric levels.