Assess the potential causes and impacts of changes to the water balance within a tropical
rainforest you have studied [20 marks]
Water balance is the balance between inputs and outputs in a drainage basin. Human
activity, such as land use change and deforestation, is the primary reason for changes to the
water balance within the Amazon rainforest. However, natural factors including storm events
are also contributing to the changes to the water balance. This is having significant impacts
on vegetation growth and the ability for species to survive in the Amazon, which can have
detrimental effects on both the Amazon, and the rest of the world due to the global
importance of the rainforest.
The Amazon rainforest is located in South America, covering 7% of the Earth and producing
up to 3000mm of rainfall every year. Deforestation drives significant changes to the water
balance in the Amazon rainforest. In the past 50 years, 17% of the Amazon rainforest has
been lost due to deforestation. Where deforestation occurs, extensive positive feedback can
occur. Evapotranspiration reduces as surface runoff increases and vegetation cover
decreases. Water therefore leaves the area in rivers and is stored in the hydrosphere, rather
than recycling between the biosphere and the atmosphere. As a result, there is less water
available in the atmosphere for precipitation, less water falling into rivers and so there is a
negative water balance in the rainforest. This can result in drought in some areas of the
Amazon, reducing the ability for other species to grow and reducing biodiversity in the area.
This would be a major problem as the Amazon holds half of the world’s species. The
Amazon has been shrinking by 03% since 2000, therefore the scale of the changes to the
water balance is getting more severe. This may have regional impacts, as further
deforestation in the Amazon could result in a 20% decline in regional rainfall. As a result,
deforestation is causing changes to the water balance in the Amazon which could have
some major impacts both locally and regionally.
Land use change for farming is also a huge cause of the changes to the water balance
within the Amazon rainforest. The 80% of deforestation in the Amazon is a result of cattle
ranching, which has had destructive impacts for the rainforest. Pastoral farming compacts
soil, reducing the rate of infiltration and increasing runoff and evaporation on the land. This
means that there is a negative water balance in the area, as well as an increased likelihood
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