Deforestation is one human factor that links the water and carbon cycle. In the past 50 years 10% of the amazon rainforest has permanently disappeared. In the short term this effects the water cycle as it reduces interception which means soils will saturate quicker and surface runoff will increase. However, in the long term, once the water has left the area via rivers, the water cycle will be permanently disrupted. This means that there will be less rainfall, and the formations of Badlands. Deforestation also effects the carbon cycle as forest clearance reduces the size of the carbon store. Furthermore, if the cleared forest is burned, there is a rapid flow of carbon from the biosphere to the atmosphere. 13 million hectares of forest are cleared every year and between 1990 to 2005 3% of all forests were lost. This means in 100 years rainforests could disappear if we continue cutting down forests at a rate of 200km² a day. Both these changes occur at the same time and are closely linked. As the rainforest water cycle is interrupted, this coincides with the warming temperatures to form Badlands.
Urbanisation is another human factor which links the water and carbon cycle. The construction of new buildings and roads creates impermeable surfaces. This effects the water cycle as these surfaces prevent infiltration which massively increases runoff and the risk of a flood. These causes problems for towns and cities situated on flood plains. For example, Carlisle which often suffers from flooding during storms such as storm Desmond in 2015. Urbanisation also effects the carbon cycle due to increases in urban populations. Every week urban areas grow by roughly 1.3 million people and are home to more than 50% of the world’s population. In 2012, cities were responsible for 47% of carbon emissions. The emissions come from increased energy consumption, less photosynthesis taking place due to the switch from natural vegetation to urban surfaces and cement manufacture for urban dwelling. This results in more carbon being put into the atmosphere. Both these changes occur at the same time and are closely linked. Urban areas are seeing an increasing risk of flood due to impermeable surfaces combined with more intense storms as a result of climate change.
A third human factor that links the water and carbon cycle is farming practises. The water cycle is affected as infiltration can be affected by farming practices. Soil drainage is common in areas with high precipitation levels. Using pipes, soils are drained to improve growing conditions and almost double productivity. However, it can also increase throughflow rates, potentially leading to increased flooding in adjacent areas that are not drained. Farming practices also impact the carbon cycle. Animals release CO2 when they respire and digest food. In addition to this ploughing can also release CO2 as microbial activity in the soil layers inverted by ploughing, results in increased respiration. The growing of rice paddies releases a lot of methane too. Farming practices result in an increase of atmospheric carbon stores. This will only increase further as the world's population increases and so will food production which will increase carbon emissions. Both changes occur at the same time and are closely linked. As farmers seek to improve productivity to feed growing populations, the impact on the environment becomes more significant. It could result in warmer climates and an increased flood risk.
A natural factor which links the water and carbon cycle is the glacial and interglacial cycles. Every 100,000 years, the earth alternates between glacial and interglacial periods. At the peak of the last glacial period, one third of the earths surface was covered by glaciers and ice sheets. This effected the water cycle as water was locked up as snow and ice, so fresh water ice stores increased massively. Sea levels were 100m lower than current levels. However, during warmer periods in the past, ocean levels were 50m higher than current levels. This shows how relationships between the oceanic and cryosphere water stores vary greatly over large time scales. Glacial and interglacial cycles also affect the carbon cycle. Over the last 2.6 million years, global climates have fluctuated considerably between warm and cold periods. These are triggered by Milankovitch cycles when every 100,000 years the earth's orbit becomes more elliptical. Lower temperatures are associated with lower CO2 levels and vice versa. For example, during cold periods carbon stored as biomass would have become incorporated into permafrost resulting in less atmospheric CO2. Also, during cold periods oceans are more saline. This means they take in greater amounts of CO2 via the oceanic pump, atmospheric carbon stores are reduced. However, in cold periods there is more chemical weathering. So as a result, more CO2 is taken in from the atmosphere. Both these changes occur at the same time and are closely linked. As deglaciation occurs, sea levels rise and result in a corresponding growth in the size of the atmospheric carbon stores.
To conclude, both cycles are linked closely. The changes to the water cycle, often caused by human activity, result in significant changes to the carbon cycle. As human activity continues to cause these changes, it can be expected that the continued growth of the atmospheric carbon store continues beyond 400ppm, continuing the changes to the carbon cycle discussed in this essay.