Peninsular rivers are seasonal as they are rain-fed rivers i.e. they are filled up only by rain water. they do not have a water source which can provide them water like the rivers of the northern plains which are fed by the glaciers of Himalayas. the rivers of the peninsular region have to depend on rain water, if rainfall is good then water is available for all. if it is more, it causes flood and if it is less, it causes droughts and famine in the surrounding areas.
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Because, mainly they need rains. If there are no rains then, the rivers will be dry.

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