Water cycle essays - AQA

From the 2018 series

I’ve gone back to the first set of the current era of A level questions in 2018, and the first essay title. Here are three answers - two that were standardisation answers, together with my own attempt. For the former two I have added the AO1/AO2 annotations that were given at the time. I think it is fair to say that everyone was learning how to do this annotation then, so they may not be entirely correct now. More will follow on this topic in due course. The numbers in brackets at the end of each essay is the word count. I set myself a limit of 600 words for these essays. Students have approximately 30 minutes to answer.

For my new cohort of subscribers from Australia - welcome. In case you didn’t know, AQA is the largest overall exam board in the UK (out of 6), and currently has the largest number of A level Geography entries - just.

Assess the potential causes and impacts of changes to the water balance within a tropical rainforest that you have studied. (20)

Standardisation answer

The Amazon rainforest covers an area of 7.3 million km2 and contains the 6.1 million km2 drainage basin of the Amazon River which has the largest discharge of any river in the world. [AO1] However it is undergoing huge changes in the water balance which refers to the change in the volume of different stores in the water cycle which will have various impacts some of which will be assessed in this response. [AO2]

Firstly, deforestation (80% of which is down to cattle farming) [AO1] is likely to reduce rainfall [AO2]. The Amazon rainforest generates 40% of its own rainfall due to high temperatures (28C) allowing high rates of evapotranspiration from trees, the water from which rises, condenses its clouds and results in rainfall [AO1]. However, without the trees, rainfall will reduce as lower rates of evapotranspiration exist [AO1] and the bacteria on the leaves of the trees are no longer there to help bind water molecules together to form clouds. [AO2] On the other hand slash and burn usually occurs when an area of forest is removed for agriculture (to make the land more fertile) so 30-50% of the stores carbon in the trees [AO1] reduces the atmosphere with the particles released inhibiting cloud formation. [AO2]

Furthermore, river discharge of the Amazon will vary due to deforestation and will likely increase with deforestation on a watershed level as there will be reducing interception storage from trees [AO2] (rainfall can take up to 10 minutes to reach the ground in the Amazon) [AO1] and therefore increased surface runoff as the river will have a higher peak discharge and a shorter lag time. [AO2] However discharge will decrease on a continental level as there will be lower rates of precipitation and higher rates of evaporation [AO1] from the river due to less vegetation cover over the channel reducing the solar radiation reaching it meaning the river channel is losing water to the atmosphere. [AO2]

Human developments such as dams can also cause areas of rainforest to flood. [AO2] For example the Brazilian government approved the construction of Belo Monte dam on the Xingu River which will flood 400,000km2 of rainforest and reduce discharge downstream as energy demands need to be met for cities such as Manaus which has seen its population grow from 500,000 in 1970 to 2 million today. [AO1] This means that water is being removed from channel storage to the general rainforest floor. [AO2]

Finally, some inputs could be caused by physical factors [AO2] such as the ITCZ could be moving further north as the Sahel region is now experiencing more rainfall according to a 2015 study [AO1]. Therefore, the Amazon could be losing rainfall as the expense of the semi-arid regions.

To conclude, generally the water balance of the Amazon is changing such that water is being lost from the system mainly due to human factors. Increased population has led to increased demand for resources putting a strain on our natural planet mostly felt by fragile environments such as the rainforest. [AO2] (486) [Awarded 20 marks]

Second standardisation answer

Tropical rainforests are somewhat in potential danger due to changing climate and global warming. However, things can be done to reduce these impacts. The water cycle and balance can be impacted by certain aspects in the area. [AO2]

The Amazon rainforest is a large factor and has great importance on our planet. The humid climate and greatly occurring rainfall [AO1] contributes large amount of water every single day. Factors that may affect the water balance are deforestation. The cutting down of trees will create less interception and evapotranspiration [AO1]. This creates more ground water [AO1] as the canopy is less full so there is a greater risk of flooding in the area [AO2]. This is also a problem as trees are growing quicker but also dying young. This proves to be a problem as the Amazon rainforest plays an important role in the grand scheme of things so changing it can be a large problem. [AO2]

Climate change is also a contributing factor to the potential impacts to the water balance [AO2]. As temperatures are rising there is less rain and moist conditions for the animals and plant species living there. The prolonged dry conditions can lead to severe droughts (like in 2005 and 2010) [AO1]. This makes the animals and trees suffer and some species may die out due to these conditions they have adapted to. This also reduces rainfall and can negatively affect and damage the water balance. [AO2]

Although these potential impacts can be reduced, laws have been put into place to stop logging in unsustainably managed areas. There are also things set up like CACC in Brazil, 2003 [AO1] to help sustain biodiversity and allow people to maintain their land use so that at least 50-80% of their land is still forestry. This helps the water balance continue as normal to allow for growth and infiltration and to keep all the animals for as long as possible [AO2]. Selective logging is also put in place so that only fewer older trees are cut down to keep the canopy structure to allow the water balance to remain sustained and as usual. [AO2]

More trees are replanted, and the same varieties kept as the same species must be replanted in its place. This also keeps soil rich with nutrients as the soil is still held together with the roots. If the soil is damaged with heavy downpours, then the nutrients that aid the trees’ growth are washed away. This still allows the water balance and cycle to be kept [AO2] the same with its usual surface runoff and infiltration.

In conclusion, the potential causing, and impacts will make a large difference to the water balance in the Amazon. However, with the laws and plans put in place the Amazon can be sustained and the impacts that change the water balance can be reduced. [AO2] (463)

[Mid Level 3 awarded]

My answer

Human activities affect the water cycle in tropical rainforests because of the many human influences on the rainforest. These activities include agricultural practices that cause compaction of the soil increasing run-off, deforestation which reduces evapotranspiration and mining which causes the total clearance of vegetation and that all that brings with it. In the longer term, climate change will also have an impact

Tropical rainforests are one of the most important ecosystems on the planet. The Amazon is an example. The water cycle in this rainforest is very active as there is so much water together with high levels of energy provided by the sun, which is very intense all year and means that the temperature is high, usually above 25°C. The high temperatures mean that there is a lot of evaporation every day from any water on the surface. This means there is a huge amount of water vapour going into the atmosphere above the rainforest, which means that clouds can form, and heavy rainfall occurs.

Soil compaction by heavy machinery across the forest will lead to lower rates of infiltration and an increased likelihood of flooding. The rains in the wet seasons in the Amazon rainforest can be very intense, and if they take place on wet ground from previous rainfall that is compacted, then water will flow across the surface and increase the size of rivers. As more and more forest is cleared, then the amount of compaction will increase.

In rainforest areas, such as in the Brazilian states of Para, Acre and Rondônia, widespread deforestation has drastically reduced interception, increased surface runoff and flood risk, and reduced evapotranspiration, potentially reducing cloud cover and hence precipitation. The culprits are cattle ranching, palm oil cultivation, commercial logging and developments such as HEP reservoirs.

Not all human activity has this impact. Traditional, small-scale shifting cultivation had a much more limited impact because areas were farmed for only a few years and vegetation and the local water cycle recovered quickly. The advent of commercial rainforest exploitation in the twentieth century has made changes to the water cycle permanent and significant. Furthermore, in some areas there are many eco-tourists. Some parts of Peru and Brazil for example (such as along the Aripuana River) have conserved the forests to protect this vital income stream. Appropriate use of the forest, such as replanting after any harvesting of crops, and re-afforestation can have a minimal impact on the water cycle in the forest.

Climate change is happening all over the world. As human activities produce more greenhouse gases (carbon dioxide and methane), more of the sun’s energy is being kept in the atmosphere and so global warming is taking place. This means that more evaporation can happen, and this affects the water cycle. This might mean that there is more rainfall but because the air is warmer, it may not rain as much. Scientists suggest that climate change might result in the rainforest becoming less wet as the pattern of rainfall changes.

In summary, deforestation is causing the most impact on the Amazon rainforest in the short term, whereas in the longer term it is likely that climate change will have the greatest impact. Climate change could in fact result in the decrease of the forest through a drier climate, so the two main causes are interrelated. (552)