Factors affecting river discharge

Weather

Rainfall (volume) 

A lot of rain causes higher river levels, whereas less rainfall or prolonged dry periods will result in lower river levels due to both the volume of rain and the fact that it will take longer for the rainwater to reach the river. 

Rainfall (type)

The type of rainfall can also have an influence as long periods of heavy rain can saturate the soil and underlying rock, meaning further rainfall will flow as surface run off towards the river. Light rain or drizzle has time to infiltrate the soil freeing up space for more rain. 

Temperature

When the temperature is higher, river levels go down due to evaporation (water lost from the surface) and transpiration (water lost from pores in vegetation). Freezing temperatures can lead to frozen ground so water cannot soak in. 

Physical Factors

Relief

Steep slopes encourage fast run off as the water spills rapidly downwards due to gravity. On gentle slopes, absorption into the land reduces the volume of water reaching the river. 

Rock Type

Important in determining how much water infiltrates and how much stays on the surface. 
Impermeable rock, e.g granite and clay have more surface river water cannot infiltrate so it reaches rivers more quickly than permeable rock, e.g chalk and sandy soils which absorb the water. 

Land Use

Farming

The ploughing of fields can create channels assisting rainwater to reach the rivers during wet periods, increasing the water levels. However, farmers extract water from rivers during dry periods which can reduce the water levels.