Human Impacts on Hydrological Cycle

GY262

Deforestation

• Trees intercept + slow runoff

• Roots help water infiltrate soil + recharge groundwater

• Trees provide transpiration

• Deforestation reduces infiltration + increases runoff

• Causes floods, soil erosion, + reduced groundwater levels

Deforestation- Amazon Rainforest

• Large-scale deforestation has reduced evapotranspiration

• Led to lower rainfall and longer dry seasons

• River flow has become irregular, increasing flood + drought risk

Agriculture + Irrigation

• Uses about 70% of the world’s freshwater

• Increases evaporation + reduces water downstream

• Over-irrigation causes waterlogging + increased soil salinity

• Natural river flow patterns are redistributed

Agriculture + Irrigation- Aral Sea

• Rivers feeding the Aral Sea were diverted for cotton irrigation

• The sea shrank drastically, increasing evaporation losses

• Local climate became drier and ecosystems collapsed

Agricultural Pollution

• Fertilisers and pesticides enter rivers + groundwater through farm runoff

• Pollutes water + affects natural water quality

• Eutrophication in rivers + lakes caused by nutrient pollution

• Aquatic life damaged + drinking water deemed unsafe

Urbanisation

• Urban areas are covered with concrete + asphalt, preventing infiltration

• Runoff rapidly increases, causing flooding

• Groundwater recharge decreases

• Urban heat islands increase evaporation

Urbanisation- 2005 Mumbai Floods

• Heavy rainfall combined with impermeable surfaces caused severe flooding

• Natural drainage and infiltration were blocked by urban development

Groundwater Extraction

• Groundwater is pumped for farming, industry, + cities

• Over-extraction lowers the water table

• Rivers + wetlands receive less baseflow

• Land subsidence may occur

• Coastal areas face saltwater intrusion

Groundwater Extraction- Punjab + Haryana, India

• Excessive amounts of groundwater pumped for irrigation

• Falling water tables + drying wells

• Long-term groundwater depletion

Climate Change

• Human-induced global warming intensifies the water cycle

• Higher temperatures increase evaporation

• Rainfall becomes more intense but irregular

• Some regions experience floods, while others face drought

• Melting glaciers reduce long-term water storage

Climate Change- Himalayan Glaciers

• Rapid glacier melting increases short-term river flow

• Long-term water supply for rivers like the Ganga is threatened