Influence of Weather and Climate on Rivers

Weather changes flow; climate shapes the longer-term pattern

A river landscape is continually adjusted by erosion, transport and deposition. Erosion removes material from the bed and banks; transport moves it downstream; deposition occurs when the river can no longer carry it.

Weather affects these processes over short periods. A storm can change a channel within hours, while a drought can reduce flow for weeks or months. Climate is the long-term pattern of weather: it influences how often rivers experience high or low flows and how much weathered material is available to move.

The important connection is discharge: the volume of water passing a point each second. Greater discharge generally gives a river more potential to erode and transport sediment, although the actual effect also depends on its slope, channel and geology.

Storms can rapidly reshape a river channel

Heavy rainfall supplies more water to a drainage basin—the area drained by a river and its tributaries. Water reaching the channel increases discharge. Where rainfall cannot soak into the ground quickly enough, surface run-off carries water towards the river rapidly.

Higher flows can strengthen hydraulic action, in which moving water forces against the bed and banks. They can also increase abrasion as transported sediment scrapes against the channel. Material that normally remains on the bed may be moved, increasing the river’s sediment load.

The landscape consequences can include eroded banks and wider or deeper channels. If the river overflows its banks, flooding affects the surrounding valley floor. Storms in February 2022 caused significant flooding along the River Ouse and River Severn, illustrating how short-term weather can affect UK river landscapes.

A storm does not mean erosion everywhere. As water slows, or discharge falls after the storm, the river loses some of its ability to carry sediment and deposition becomes more likely. One event can therefore remove material in one place and leave it elsewhere.

Drought has different effects during and after the dry period

During a drought, little rainfall replenishes the river. Hot conditions can increase evaporation, further reducing the water available. Discharge falls, so the river generally transports less sediment and erosion is reduced. Material previously being carried may be deposited as flow weakens.

However, the first heavy rainfall after a drought can produce a different response. Prolonged hot, dry conditions can harden the soil surface and reduce infiltration. Where this happens, more rain flows over the surface and reaches the channel quickly, increasing discharge and potentially causing renewed erosion or flooding.

This is a conditional effect: dry soil is not always completely impermeable. The response depends on the soil and the intensity of the rainfall. The key distinction is between low flow during the drought and a possible rapid increase in flow afterwards.

The UK’s climate creates regional contrasts

The UK has a temperate climate, but rainfall and temperature vary across the country. The north and west generally receive more rainfall, while the south and east are generally drier.

Other factors being similar, wetter areas tend to have higher river discharge. Rivers can transport more bedload and erode their channels more strongly, helping create wider and deeper channels over time. In drier areas, lower discharge generally means less erosion and sediment transport, with deposition more likely when flow becomes too weak to carry the available material.

Temperature matters too. Warmer conditions increase evaporation, which can reduce discharge. Colder areas, including Scotland and northern uplands, offer more opportunities for freeze–thaw weathering where temperatures repeatedly cross freezing point. Water freezes and expands in rock cracks; repeated cycles loosen fragments. This supplies sediment that can later enter the river and be transported or used in abrasion. Weathering breaks rock down in place; river erosion removes it.

Judging the overall influence

Weather and climate are important because they affect both the water available to do work and the sediment available to move. Storms may cause sudden change, whereas repeated wet, dry or freezing conditions influence landscapes over longer periods.

They do not act alone. Permeable rocks allow more water to soak into the ground, while steep slopes encourage rapid run-off. Rock resistance also affects how readily a channel erodes. A sound judgement is therefore that weather and climate strongly influence the timing and intensity of river processes, but geology and the shape of the drainage basin help determine the resulting landscape change.