Global Hydrological cycle

97% of global water is stored in the Ocean. Subsequently, only ~3% of the Earth's water is fresh and the majority is locked away in groundwater stores or icecaps.

Water budget is defined as the balance between physical inputs and outputs. The rate of evapo-transpiration however can be affected by deforestation and land use change.

Precipitation usually occurs when warm air is forced to rise and cool, leading to condensation; types of rainfall are: Orogaphic occurs over a mountain, Convectional causes from land heat, Frontal occurs on warm/cold air fronts

ENSO(El-Nino Southern Oscillation) affects precipitation and drought patterns. El Nino increases precipitaion in South America while La Nina increases it in Australia and SE Asia.

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Local Drainage Basins

On a global scale the Hydrological Cycle is a closed system, however in a local Drainage basin, it is open with flows and fluxes transferring water between stores depending on inputs, transfers and stores.

Physical factors: Climate variability through type, quantity and frequency of rainfall; Soil type and depth can affect water stores and infiltration/saturation levels; Geology and relief can affect percolation rates and surface run-off; vegetation affects interception and evapo-transpiration rates, the size and drainage density of the catchment area/watershed can affect rates of channel flow.

Human factors: Cloud seeding can facilitate cloud condensation through silver iodide; Dam and reservoir construction improves water storage and usage but reduces river discharge downstream; groundwater abstraction provides freshwater but can deplete stores, leading to saltwater encroachment as the water table (surface level) lowers, which contaminates supplies further.

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A drought is an extended period of average rainfall deficit. Physical causes of drought are divided into four categories: Meteorological is the most common (precipitation variation); Hydological and Agricultural refer to water stores and soil moisture deficiencies respectively. Finally, Socio-Economic occurs when demand exceeds availability leading to famine.

Human causes of drought often are accentuating the physical causes. 

Overgrazing and over-cultivation increase agricultural drought through soil erosion. The excessive growth of crops and farmland for cattle (40% more in Sahel) degrades soil quality, causing desertification such as in the Sahel region.

Over Abstraction and Dam construction increase hydrological drought by affecting water stores. Groundwater aquifers cannot be easily replenished and dams often limit river discharge downstream.

Deforestation and land use change reduce evapo-transpiration and air humidity, subsequently reducing condensation and precipitation. They have the secondary impact of creating a positive feedback loop for wildfires in the Amazon rain forest as well as reducing flood water regulation in the Pantanal Wetlands following dredging.

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Flooding is caused from a surplus of precipitation, usually during a flash flood or heavy prolonged monsoon season.

Storm Desmond (2015) in the UK is an example of high levels of impermeable surfaces and drainage systems through urbanisation reducing lag time and intensifying the flood. £500 million in damage costs.

The 2010 Pakistan flood occurred when the annual monsoon season was exacerbated by the La Nina event, producing intense rainfall. Additionally, increased sediment load and snow melt from the Himalayas overwhelmed the river Indus, causing 5.7 million to be left unemployed.

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Causes of Water Insecurity

Water insecurity is defined as the lack of a reliable source of water, in quality and quantity. In contrast, Water Scarcity is an extreme water deficit and can be categorised in two ways: Physical Scarcity is when 75% of blue water flows are being used, indicating a lack of availability; whilst Economic Scarcity is the lack of access to clean and affordable water, often due to poor storage infrastructure.

The physical causes of water insecurity are: Climate Variability is the changes to precipitation patterns; seasonality refers to the ITCZ and monsoon/ drought seasons; Geology can affect the distribution of aquifers e.g England's chalk aquifer = 70% of supply

Human Causes of water insecurity are: Over abstraction can lead to saltwater encroachment as the water table drops, e.g Tuvalu, Samoa or Marshall Islands where abstraction tripled; Contamination from industry and agriculture fertilisers (eutrophication); Population growth increases demand for water, indirectly reducing water availability and affordability (Economic Scarcity, main cause in developing countries) as well as consumption through manufacturing products (virtual water, growing middle class)

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Impacts of Water Insecurity

The price of water can vary due to a range of reasons. Often the quality of water storage infrastructure affects physical scarcity however the management of water supplies through funding to public sector or privitatisation can affect economic scarcity of freshwater.

The price of water rose in Bolivia in 1999 following the privitatisation of it's water by Agua del Tunari. The price rose by 20% and was met by young, motivated protesters as this was equal to 1/2 their income.

Similiarly, in Papau New Guinea, 60% of the population live without access to safe water. Furthermore, they spend 1/2 their daily income to meet basic needs (50 litres).

The price of water in Israel increased in 2008 to fund drainage repairs and storage improvements. This indirectly reduced the frivolous usage of water, such as in Denmark. Drip irrigation was developed to reduced water consumption by 60% and the recycling of park irrigation water saved 85%

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*Impacts of Climate Change

Climate Change has impacted the water budget trends (annual balance between precipitation, evapotranspiration and runoff) of regions locally.

A recent climate change in the Sahel region has allowed farmers to implement sustainable, "re-greening" agricultural techniques. This involves planting more vegetation and bushes to increase evapo-transpiration to encourage rainfall.

California has experienced 3x the number of wildfires in 2014-2015 due to extreme droughts. Scientists forecast that a 90% of a decade-long drought before 2050.

Singapore has implemented sustainable management by using a combination of hard and soft engineering. The Marina Bay was developed in 2013 and contained a barrage to prevent floods and saltwater encroachment, improving water security and creating a new CBD; 17 new reservoirs were also built. In terms of soft engineering, desalination and recycling plants were created to recycle irrigated water for green spaces. Additionally, rain gardens and wetlands were recreated for increased water regulation.

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*Conflicts over Water

In the 1960s there was a plan to create 11 HEP dams on the Mekong River; the electricity generated would fuel China's and Laos' economic growth. However, only 3 have been built so far due to concerns that the dams would destroy the agriculture, fishing and eco-tourism industries of downstream countries such as Cambodia and Vietnam.

China has implemented the hard engineering, "South to North" transfer project to redirect water in the Yangtze river to the Northern provinces to fuel economic growth. The project cost $62 billion, so not every country has the funds to do this, and provides 70% of the North's water. However, it has increased river contamination from industry and eutrophication in the South.


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*Conflicts over Water 2

Tensions with Egypt arose surrounding the trans-boundary Nile river. In 1929 they signed a policy empowering them to veto any construction on the river. However, they have become increasingly protective over the water supply, opposing the Cooperative Framework Agreement in 2010 which aimed to properly distribute water supplies to upstream countries e.g Kenya and Tanzania.

Ethiopia has attempted to fuel it's economic growth as the "Powerhouse of Africa" through dam construction. In 2015 the Gilgel Dam 3, greatly reduced downstream river discharge, with indigenous tribes struggling to grow crops, leading to famine and tensions. Additionally, Lake Turkana dropped by 10m, greatly affecting the fishing industry and freshwater supplies. 

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Additional Case Studies

FLOODING: The Tundra climate of the Yukon river in Alaska and Canada means river discharge is high during May-June when permafrost melts, however climate change has meant that the snow melts earlier in the year.

DROUGHT: The 2006 El- Nino event in Australia resulted in a 25% reduction in water availability. The Murray-Darling Basin which provides 75% of Australia's water was shut off, leading to the decimation of the agriculture and tourism industries; 80% tourism loss and 1% GDP loss. In response, drainage pipes were repaired and Lake Brewster was developed as an improved water store.

DROUGHTBrazil's drought in 2014-2015 was due to high pressure anticyclones blocking precipitation. However, it was greatly accentuated by excessive water usage and over abstraction. 17 reservoirs were depleted and HEP production was stopped, leading to power cuts. Additionally, water rationing for 1/2 million people was only circumvented by the creation of illegal boreholes which depleted aquifers further. 

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