4.1.5—Human activity impacts
- Syllabus
- First assessment 2026
- Objective
- 4.1.5
- Level
- SL
Trace Land Use into a Changed Hydrograph
Land use changes interception, evapotranspiration, infiltration and drainage, which can alter peak flow, recharge and flood risk.
Deforestation can reduce canopy storage; compaction and urban surfaces reduce infiltration and speed runoff. Irrigation may raise evapotranspiration or runoff depending on soil, rate and drainage.
Replacing permeable ground with roads shortens the time to peak flow and can increase flash flooding after the same rainfall.
Impermeable surfaces reduce infiltration and groundwater recharge while faster surface run-off shortens lag time and can raise peak discharge and flash-flood risk.
One land-use change can affect several flows; do not assume every deforestation site has the same direction or size of effect.