Human Impacts on the water and carbon cycle Flashcards
Water - farming practices
Ploughing breaks up the surface so more water can infiltrate.
Crops increase infiltration + interception, reducing run-off - not as effective as trees though.
Livestock trample the ground and compact it, decreasing infiltration and increasing run-of.
Water - land use
Construction of new buildings and roads creates impermeable surfaces which massively increase run-off
Houston - population has nearly doubled to 2.3m in the last 50 years. Consequently, the city has been pushed outwards. This has led to the loss of 100,000ha of wetland and the building of over 7,000 homes on floodplains. Hurricane Harvey, 2017, led to 400mm of rain in one day, without the wetlands acting as a ‘natural sponge’ and the floodplain providing space for infiltration , Houston suffered substantial flooding.
Water - deforestation
Reduces amount of water intercepted by vegetation, increasing overland flow.
Dead plant matter on the floor also holds water, when it is removed, the amount of water it holds is also reduced.
Freetown, Sierra Leone, was subject to a massive mudslide which left 1141 people dead or missing. This was due to deforestation on the hills surrounding the city leaving soil exposed and weakened as they weren’t anchored by the roots of trees.
Water - water abstraction
Reduces water stores in lakes, rivers and reservoirs, this is prevalent in dry seasons.
Carbon - fossil fuel combustion
90% of human-caused carbon released comes from combustion of fossil fuels. Vegetation and the oceans help to reabsorb 50% of this. 2013 - China - 28% of CO2 emissions, USA - 14%, India - 7%
Carbon - agriculture
10% of carbon emissions
When soil is ploughed, air is mixed in with the soil, increasing microbial activity meaning more organic matter is decomposed.
Enteric fermentation - methane (CH4) belched by livestock during digestion
Biological processes in rice paddies generate methane
Carbon - land use change: deforestation
CO2 emissions from land use change (deforestation) account for 30% of anthropogenic carbon emissions.
Roughly 13 million hectares of forest cut down each year, mostly driven by need for agricultural land, logging, building roads, urban sprawl, wildfires.
LINK TO WATER - trees return water vapour to the atmosphere, maintaining water cycle.
Carbon - land use change: urban growth
More than 50% of the world live in urban areas expected to reach 60% by 2030, 21 most polluting cities in the world release 10% of global emissions, expected to go to top 10
