A2 - How physical and human factors exacerbate and mitigate flood risk for different places

Storm hydrograph

A graph showing how river discharge changes after a storm event

Lag time

Time delay between peak rainfall and peak river discharge

Peak discharge

The highest amount of water flowing in a river during a storm event

Base flow

Normal level of river flow sustained by groundwater input

Geology (hydrographs)

Permeable rock increases infiltration and longer lag time, impermeable rock increases runoff and short lag time

Seasonality

Changes in river discharge due to seasons, with higher flows in wet seasons and lower flows in dry seasons

Natural flood risk factors

Physical conditions like rainfall intensity, soil type, geology, and vegetation that affect flooding

Urbanisation (flood risk)

Increases impermeable surfaces, reducing infiltration and increasing surface runoff

Urbanisation effect on hydrograph

Shorter lag time and higher peak discharge, increasing flood risk

Deforestation (flood risk)

Reduces interception and increases surface runoff, increasing river discharge

Channel modification (flood risk)

Straightening and deepening rivers increases flow speed and can move flood risk downstream

Flood frequency

How often flooding occurs in an area

Flood magnitude

The size and severity of a flood event

Flood distribution

Where floods occur across a drainage basin or region

Human vs physical factors

Human factors often increase flood risk, but physical factors determine baseline vulnerability

Weather forecasting

Use of satellites and radar to predict rainfall and potential flooding

Flood prediction technology

Includes radar, river gauges, satellites, and computer models to track rainfall and river levels

Climate models

Computer simulations that predict future climate patterns but include uncertainty due to complex variables

Uncertainty in prediction

Errors in forecasts caused by unpredictable weather patterns and limitations in data

Effectiveness of flood prediction

Early warning systems reduce damage and save lives, but extreme events can still be difficult to predict accurately

10-second summary + evaluation

Physical factors = control how fast rivers respond
Human factors = often increase flood risk
Prediction = improves safety but is not perfect