4. Changes in the Local + Global Water Cycle over time

How has deforestation impacted the water cycle locally? LOCAL

• less interception by trees so more surface runoff

• the soil is no longer held together by roots to soil water storage decreases

• fewer plants so transpiration decreases

How do storm events impact the water cycle? LOCAL

• large amounts of rainfall falling quickly cause the ground to be saturated the reach its field capacity.

• No more water can infiltrate and the soil water store takes longer to recharge increasing runoff

• This doesn’t recharge water stores because the water falls to fast to allow for infiltration

Describe how seasonal changes can affect the water cycle? LOCAL

1. Spring - more vegetation growth so more interception by vegetation

2. Summer - less rain in summer so ground might be harder and more impermeable encouraging surface runoff. Any water in plants will be lost to evapotranspiration

3. Autumn - less vegetation growth so less interception and more rainfall

4. Winter - frozen ground might be impermeable causing runoff however snow discourages runoff as it takes time to melt

How does agriculture impact the water cycle? LOCAL

1. Pastoral farming - trample and compact the ground so it will infiltrate less water

2. Arable farming - ploughing increases infiltration by creating looser soil. However drainage ditches increase surface runoff and streamflow by concentrating and collecting water into 1 single channel

3. Irrigation - often found in Spain in Almeria causes groundwater depletion as water is moved through tunnels

How does urbanisation affect the water cycle? LOCAL

1. Roads/buildings - have impermeable surfaces which reduce infiltration and increase surface runoff

2. Green roofs/SUD's - use grass + soil to reduce the amount of impermeable surfaces

How does topography affect the water cycle? LOCAL

• steep slopes means faster runoff and less infiltration because of the lack of time to infiltrate

What is abstraction and why do people do it? LOCAL

Water abstraction is the process of removing water from natural sources (rivers, lakes, aquifers) for human use, such as:

-Agriculture (irrigation)

-Industry

-Domestic consumption

-Public water supply

What are the impacts of abstraction on the local water cycle? LOCAL

1. Abstraction from groundwater aquifers can cause lowered water tables or groundwater depletion

2. Abstracting from rivers and lakes can reduce channel flow so reduce surface runoff

3. Abstraction faster than recharge rates leads to over-abstraction. Groundwater stores are not replenished, leading to long-term degradation of the aquifer

4. Lower evapotranspiration rates

How does tectonic activity affect the local water cycle? LOCAL

Can create uplift in land or mountain ranges which affect local wind/rainfall patterns

• relief rainfall/rain shadow

• Also may change topography over 100’s of years

How does El Niño impact the water cycle? GLOBAL

• el nino is every 2-7years and causes warm temperatures in an predictable way

• will be more common with climate change

• can cause droughts

How does El Niña impact the water cycle?

• el nina is every 2-7years and causes cold temperatures in an predictable way

• can cause flooding

How can cryospheric processes alter the water cycle? GLOBAL

Many of the world’s glaciers are shrinking causing sea levels to rise and CO2 to be released. If all the glaciers melted the sea levels could rise by 60m.

How do cold ocean currents affect the water cycle? GLOBAL

They cause less precipitation because air is less likely to evaporate, rise, cool, condense and form clouds. E.g.: California Current

How does the prevailing wind affect the water cycle? GLOBAL

Areas far from the sea or water will receive less water from the prevailing wind

This is because the air loses its vapor as it travels inland dropping rain over coastal or mountainous areas first and possibly creating a rain shadow over inland area

How does the earth's tilt affect the water cycle? GLOBAL

Causes different parts of Earth to receive different amount of solar energy through the year so in the summer the northern hemisphere is tilted towards the sun.

This means more water will evaporate and those areas will experience less precipitation

How can huge land use changes alter the water cycle? GLOBAL

Deforestation reduces interception and evaporation as there are less trees.

• Lowers rainfall locally and downwind (forests help “recycle” moisture)

• Increases surface runoff → more floods, less groundwater recharge

• Can shift regional and even continental rainfall patterns (e.g., Amazon)

How can water abstraction change global water cycles? GLOBAL

Water abstraction increases in dry seasons. The damand is often greater than the inputs to the aquifers leading to a decline in global long-term water stores.