The seasonal variation in the volume of water in a river is known as its

The seasonal variation in the volume of water in a river is known as its regime. A river's regime can vary depending on the climate and topography of the region it flows through. In areas with distinct wet and dry seasons, the river's flow will be higher during the rainy season and lower during the dry season. This can be due to increased rainfall and runoff during the wet season or reduced groundwater recharge during the dry season. Understanding a river's regime is important for managing water resources, as it can impact activities such as irrigation, hydropower generation, and transportation. Therefore, the correct option is: regime.