If a river has a very large catchment area, its discharge will be more affected by what?

Correct answer: Rainfall, snowmelt and tributaries of that area

The direct answer is A, rainfall, snowmelt and tributaries of that area. A catchment area is the entire land area from which water drains into a particular river and its tributaries. If this area is very large, many different sources can contribute to the river’s discharge, meaning the volume of water flowing through the river at a given time. First, rainfall adds surface runoff and groundwater recharge. Second, melting snow or ice adds water, especially in mountain regions. Third, tributaries collect water from their own smaller catchments and bring it into the main river. Thus a large catchment makes discharge strongly dependent on the region’s rainfall, snowmelt and tributary network. Option A is correct because it lists real water sources. Option B, the colour of the sea, is irrelevant to the amount of river discharge. Option C, the language of cities, has no physical effect on water flow. Option D, mountain names, are labels and do not themselves supply water; the relevant factors are precipitation, melting and drainage. The reasoning is: larger catchment means more land collecting water, more collecting sources mean potentially greater and more variable discharge. A useful memory trick is “catchment catches water.” Do not confuse catchment area with the river channel: the catchment is the whole contributing region, while the channel is the path through which the collected water flows.