1.4

• What is a water budget, and what factors affect it?

  A water budget is the balance between water inputs and outputs in a drainage basin over time. Inputs include precipitation, surface and groundwater inflow, and diversions into the area. Outputs include evaporation, surface and groundwater outflow, runoff, and water used by people and industry.
• What is the equation for the water balance, and what does it represent?

  The water balance equation is P = Q + E ± S, where P is precipitation, Q is runoff or river discharge, E is potential evapotranspiration, and S is changes in soil moisture and groundwater storage. It represents how water moves through and is stored in the landscape.
• How do seasonal changes affect rainfall effectiveness and water availability?

  In summer, potential evapotranspiration often exceeds precipitation, causing reduced river and lake levels and lower soil moisture. In the UK, the water year begins in October when rainfall typically exceeds evaporation, recharging soil and groundwater. A water surplus can lead to flooding, while summer deficits cause dry soils and reduced availability.
• What is field capacity, and how does it relate to hydrological processes?

  Field capacity is the maximum amount of moisture soil can hold after excess water has drained. When precipitation exceeds this, soils become saturated, creating surface runoff and potentially flash floods. Water deficit, when evapotranspiration exceeds rainfall, reduces this capacity and limits water availability.
• What determines the discharge or flow of a river throughout the year?

  River flow is shaped by drainage basin characteristics (like shape, geology, soil, and vegetation), climate (rainfall and temperature), human activity (damming, irrigation), and seasonal inputs and outputs. The overall yearly pattern is called a river’s regime.
• What is the difference between a simple and complex river regime?

  A simple regime features a regular seasonal pattern of high and low flow, often due to snowmelt or monsoons (e.g., the Rhône). A complex regime occurs when a river crosses various climate and relief zones and is affected by different weather systems and human interventions like dams and irrigation (e.g., the Ganges).
• What does a storm hydrograph show, and why is it important?

  A storm hydrograph displays how river discharge changes during and after a storm. It highlights the lag time between rainfall and peak discharge, showing how quickly water reaches the river. This is important for flood prediction and management.
• How do planners and stakeholders influence the hydrological cycle in the UK?

  UK planners assess whether developments increase flood risk by changing water flow. They must balance environmental needs, such as maintaining river health, with economic growth. Tools like Sustainable Drainage Systems (SuDS) help manage this by reducing runoff using methods like green roofs, infiltration basins, permeable pavements, rainwater harvesting, and wetlands.