The northeast monsoon season – it runs officially from October to December – is in its last month now. The season is an important source of rain for five peninsular states: Tamil Nadu, Kerala, Karnataka, Andhra Pradesh, and Telangana. How has the season been for these states this year? Very rainy in all states except Telangana if one is looking at summary numbers. However, this summary masks the fact that a big reason for the surplus rain in the season
The northeast monsoon season – it runs officially from October to December – is in its last month now. The season is an important source of rain for five peninsular states: Tamil Nadu, Kerala, Karnataka, Andhra Pradesh, and Telangana. How has the season been for these states this year? Very rainy in all states except Telangana if one is looking at summary numbers. However, this summary masks the fact that a big reason for the surplus rain in the season is the surplus recorded in December because of Cyclone Fengal.
Before unpacking the trends of the northeast monsoon summarised above, it is useful to underline its importance in different states. This is because it has different degrees of importance in the five states listed above. For example, the season accounts for 49% of the annual rain in Tamil Nadu but only 13% of the annual rain in Telangana, according to the 1971-2020 average (considered the Long Period Average or the LPA) for the October-December period. Therefore, Tamil Nadu has much more to lose from poor rain in this season than Telangana or Karnataka.
To be sure, while the season may not be very important for states like Karnataka overall, it is for their interior parts. The reason for this is the driver of the season. An important driver of the northeast monsoon is the northeasterly trade wind (blowing from the northeast), as opposed to the southwesterly trade winds that drive the summer monsoon, which is also known as the southwest monsoon. Because of the western ghats, the former affects only the interior or non-coastal parts of the states on the west coast while Tamil Nadu on the east coast is a rain shadow region for the southwest monsoon.
So what is the rain performance in the northeast season so far? Compared to the LPA, Telangana has a big 29.4% deficit. None of the other four states have a deficit, but the degree of surplus varies across states. Andhra Pradesh has just a 3.1% surplus, for example, while both Tamil Nadu and Karnataka have a surplus of over 30%.
The overall trends for the season so far described above suggest that this is largely a rainy northeast monsoon. However, this masks how the season’s performance changed over time. Without the rain brought by Cyclone Fengal in early December (which was followed by a low-pressure area in the second week), all states except Karnataka would have a deficit. All the five states had a surplus of over 200% in December, which helped them clear the deficit accumulated in a drier than usual November.
These trends read together mean that the overall performance of rain in the northeast monsoon season so far is good perhaps only for rain’s accumulation in natural and manmade reservoirs. Otherwise, the season is made up of the twin disasters of a dry November and a rainy December.
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