influences on the water cycle

drought

• when an suffers from a water deficit

• meteoological

• agricultural

• hydrological

• socio economic

meteological

this type of drought presents a degree of dryness compared to what is considered to be normal precipitation levels for that area, climate and season.

agricultural

when there is insufficient water for crops, leading to wilting or loss of crops without irrigation

hydrological

when the drainage basin suffers shortfalls such as reduced streamflow or an increase of river flow into the reservoirs

socioeconomic

when there is a demand for water to be used for social and economic purposes such as crop irrigation or when HEP exceeds water availability

el nino

• happen every 3-5 years, where winds weaken across the South Pacific Ocean and reverse direction.

• Warm water moves to the South American coastline, where lower air pressure causes large increases in rainfall, promoting the potential for flooding.

la nina

low air pressure descends on Southeast Asia and Australia leading to increased rainfall and risk of flooding.

short term precipitation

• There can be a short-term precipitation deficit in places when the cycle that creates clouds is interrupted

• A water deficit may be experienced in areas that are used to low air pressure systems and have a change of weather front to experience a high air pressure system. The cool sinking air in high air pressure systems does not have the ability to form clouds and produce precipitation.

overabstraction leading drought

• by withdrawing water from sources at a faster rate than they can be replenished by rainfall

ecosystem functioning

the biological, chemical and physical processes that take place in an ecosystem

ecosystem resilience

how capable the ecosystem is of surviving changing water levels

• Deserts and semi-arid areas are the most resilient to drought

removal of vegetation on flooding (human)

• The ground cover decreases, meaning that interception from the plants and their leaves is reduced. This water will now just reach the ground.

• The removal of plants reduces infiltration. With less infiltration and interception, there is an increase in surface runoff.

agriculture on flooding (human)

• As demand for food increases, so does demand for agricultural land. Increasingly farms are made on deforestation sites, for example in the Amazon.

• Agricultural practices increase surface runoff and the amount of soil exposed - leading to soil erosion. Sediment from the erosion is transported to the river.

• The river's water capacity is reduced by the sediment, increasing the likelihood that the river will burst its banks.

urbanisation on flooding (human)

• Urbanisation leads to the removal of vegetation resulting in an increase in surface runoff.

• An increase in impermeable man-made surfaces - i.e. concrete, tarmac and tiles - lead to no infiltration and so all rainfall experiences runoff.

• Runoff enters the drainage system which quickly takes the water to rivers and waterways. This significantly reduces the lag time and promotes reaching a high peak discharge.

floodplain drainage on flooding (human)

• Floodplain land is flat and fertile, making it desirable agricultural land but a target for floods.

• In many countries, this land is drained to provide this. But the process of drying out the wetlands destroys habitats.

• The drying out process leads to the area shrinking and lowering, which can actually increase the likelihood of the areas being subject to floods

meterological causes of flooding

• prolonged and heavy rainfall

• extreme monsoon rainfall

• snowmelt

• la nina

flash flooding

• Flash floods happen quickly and frequently without warning.

• Low air pressure systems can create intense tropical storms and thunderstorms that produce heavy rainfall

prolonged and heavy rainfall

• Can be caused by mid-latitude depressions (low air pressure systems that produce a lot of rain).

• A depression happens when two air masses meet, one hot and one cold. The cold air pushes the hot air up, leading to its cooling, condensing and forming rain.

• Heavy rains can lead to saturated soil, which stops infiltration and increases surface runoff. Water reaches the channel quicker and causes flooding

extreme monsoon rainfall

• A monsoon is a seasonal change in the direction of the prevailing winds as the ITCZ (Inter Tropical Convergence Zone) moves northwards.

• The change results in wet and dry seasons in subtropical areas that are close to oceans. Because of this, India and South East Asia are at particular risk

snowmelt

• When temperatures increase after winter, snow and ice in higher latitudes or altitudes will begin to melt.

• Snowmelt is particularly evident in mountain environments and the increase in water results in increased surface runoff and consequential flash floods

la nina

The La Nina years bring warm water and low air pressure to Australasia so the rainfall increases, as does the risk of flooding.

soil impacts of flooding

• When flooding takes place, sediment from places such as the banks and beds of the river are eroded.

• This sediment can block sections of a river - for example, underground waterworks.

• Flooding can also lead to soil erosion of fertile soil in places such as the Amazon.

ecosystems impact of flooding

• Flooding can destroy plants so they are damaged beyond use or are uprooted and broken into pieces in the river channel.

• When agricultural land is flooded, a farmer's harvest may be destroyed and they will need to completely restart.

• If plants, agriculture or habitats are damaged by flooding, the animals that are dependent on them for food and shelter are at risk. Animals have to compete for limited resources or migrate to other ecosystems, resulting in a decline in some species.

impact of flooding on economic activity

• Many businesses close while transport and infrastructures such as roads and bridges can be damaged.

• Business owners lose productivity and income when workers can't get into work

impact of flooding on infrastructure

Floods can lead to the long-term or temporary inability to use infrastructures such as roads, railways and bridges. The 2015 Cumbria floods damaged 100 bridges with a huge impact on communities

climate change

a change in global or regional weather patterns

climate change on precipitation

• Climate change leads to changes that include increased precipitation in some regions, which results in flooding or change in ecosystems.

• The likelihood of tropical storms increases, as sea levels rise and sea surface temperatures increase. The higher levels of rainfall mean that tropical regions near coastline are at risk of higher precipitation rates and flood risk.

• Climate change can also reduce precipitation in regions that are used to having high rainfall.

climate change on evaporation

• Areas that see an increase in temperature from climate change can lead to evaporation happening with greater ease.

• In contrast, areas that see a decrease in temperature may see a reduction in evaporation.

• If temperatures decrease to below freezing, water may remain frozen and so be stored as ice

climate change on snow and glaciers

• Climate change has lead to an increase in average global temperatures, leading to a reduction in ice-forming seasons.

• Early 2018 saw the smallest amount of winter Arctic ice since the 1960s.

• Sea ice is not forming to the same extent and current sea ice is breaking off into large icebergs

increased uncertainty

• Climate change increases the uncertainty with weather patterns across the world, resulting in higher or lower precipitation that leads to either drought and floods.

• Sea level rise and warmer sea surface temperatures increase the chance of tropical storms and the floods associated with them

drought projections

• Areas that are at risk for future drought are the USA, Central America and the Mediterranean. These regions, all around similar latitude, could see a reduction in rainwater.

• The Southern Mediterranean countries (i.e. Spain and Greece) are particularly at risk from drought because of their relatively high populations and reliance on the tourism industry.

• Countries seeing a reduction in drought risk include northern Alaska, Asian countries and countries surrounding the Indian Ocean

flood risk projections

• South East Asia (i.e. India and Bangladesh) is seeing an increase in the likelihood of flooding.

• 70% of Bangladesh is on a floodplain and the majority of the nation is only 1 m above sea level.

• Climate change is likely to cause Himalayan glacial meltwater to increase and flood the rivers. Sea level rise and the increased likelihood of tropical storms (referred to as Cyclones here) means Bangladesh is increasingly at risk from flooding