Changes in the water cycle over time to include natural variation…

The idea

The water cycle experiences dynamic changes over time through natural variations and human impacts. Natural variations include seasonal changes, where summer evapotranspiration exceeds precipitation causing soil moisture deficits, and storm events that generate rapid surface runoff and spikes in river discharge. Human impacts significantly alter these pathways. Farming practices, such as overgrazing, compact soils and reduce infiltration. Land use changes, particularly urbanisation, replace permeable soils with impermeable surfaces, accelerating runoff. Furthermore, water abstraction for agriculture depletes groundwater stores and lowers the water table, fundamentally disrupting the natural balance of the drainage basin system.

What earns the marks

• Explain how seasonal changes affect the water balance, such as winter soil moisture surplus and summer deficit.
• Assess how intense storm events exceed infiltration capacities, leading to rapid overland flow and increased flood risk.
• Describe how farming practices like pastoral overgrazing or arable ploughing alter soil structure and infiltration rates.
• Analyse the impact of land use change, specifically how urbanisation increases impermeable surfaces and reduces interception.
• Evaluate the consequences of water abstraction on aquifer depletion and reduced baseflow in rivers.

Common mistakes and how to put them right

• Treating land use change and farming practices as identical.

  Put it right: Land use change often refers to urbanisation or deforestation, whereas farming practices refer to specific agricultural methods like ploughing.

• Stating that water abstraction only affects surface water.

  Put it right: Abstraction frequently targets groundwater aquifers, leading to a lowered water table and reduced river baseflow.

• Assuming seasonal changes only relate to temperature.

  Put it right: Seasonal changes also dictate precipitation types and vegetation growth, which heavily influence interception and evapotranspiration.

Exam tips

• Use the water balance equation to structure answers about seasonal changes in the water cycle.
• When discussing human impacts, explicitly trace the effect through the hydrological cycle, for example explaining how abstraction reduces groundwater, which in turn lowers baseflow.
• Provide specific examples of farming practices, such as contour ploughing or the use of heavy machinery, to demonstrate detailed knowledge.