Explain how climate change affects the water cycle. Illustrate with examples.
Climate change - caused mainly by rising global temperatures due to excess greenhouse gases - disrupts and intensifies several stages of the water cycle:
1. Increased evaporation: A warmer atmosphere causes more water to evaporate from oceans, lakes, rivers, and soil. A warmer atmosphere can also hold more water vapour (roughly 7% more for every 1 °C rise in temperature), loading the atmosphere with extra moisture.
2. Heavier and more uneven precipitation: Extra atmospheric moisture leads to more intense rainfall in some regions. For example, India experiences more intense monsoon events due to the warmer Arabian Sea supplying more moisture. However, other regions see less rainfall and more droughts - making the water cycle more extreme and uneven.
3. Melting glaciers: Rising temperatures melt glaciers and polar ice caps. Himalayan glaciers that supply water to rivers like the Ganga and Brahmaputra will initially cause flooding but will eventually shrink, reducing long-term river flow and threatening millions who depend on these rivers. Globally, melting polar ice raises sea levels, threatening coastal cities like Mumbai and Chennai.
4. Reduced groundwater recharge: Heavy bursts of rainfall cause rapid surface run-off rather than slow infiltration into the ground. This reduces groundwater recharge, making it harder to maintain water supply during dry months.
5. Soil erosion: Intense rainfall on deforested land washes away topsoil, reducing the land's ability to absorb water and further disrupting the local water cycle.
In summary, climate change makes the water cycle more extreme - wetter in some places, drier in others - and disrupts the balance between the cryosphere, hydrosphere, atmosphere, and biosphere.