What part do the cyclones play in the season of advancing southwest monsoon ? Under what conditions can the northern plains get a fair amount of rainfall ? When do they receive floods ?

The cyclones are formed at the head of the Bay of Bengal and then enter into the main land. These pass along the axis of the monsoon trough or I.T.C.Z. of the low pressure. Northern plains would get a fair amount of rainfall only when the monsoon trough lie in the plains. We know that the monsoon trough and its axis keep on moving northward or southward. Its movement towards south determines the quantum of good rainfall over the plains.

However, when the monsoon trough shifts closer to the Himalayas there are longer, dry spells in the plains while widespread rains occur in the mountainous catchment areas of the Himalayan rivers. This condition causes devastating floods spreading damage to life and property in the plains. The frequency and intensity of tropical depressions too determine, the amount and duration of monsoon rains.