Area of study 3: Physical Systems and Sustainability Topic 5: The Water Cycle and Water Insecurity EQ1: What are the processes operating within the hydrological cycle from global to local scale EQ2: what factors influence the hydrological system over short- and long-term timescales? EQ3: How does water insecurity occur and why is it becoming such a global issue for the 21st century?

Today we are learning this content: 5.1 (a, b and c)

Present new information

The Hydrological Cycle Present new information The hydrological cycle is a closed system because all the water is continually circulated through the stores and there is a constant amount of water in the system. The system does not change because there are no gains or losses to other systems. What does solar energy have to do with the water cycle? Heated by the sun, the water on the earth’s surface evaporates into the atmosphere, while water is also drawn from the soil by plants and evaporated from leaves and stems by the process of evapotranspiration. What does gravitational potential energy have to do with the water cycle? This energy is converted into kinetic energy as the water moves through the system by plant interception or over land as surface runoff. Water also flows through the soil by the processes of infiltration and throughflow

The Hydrological Cycle on a global scale Present new information The easiest way to understand the Hydrological Cycle is to view it as a system which has key components. These are key to understanding how movement within the system occurs: STORES: these are stocks of water, places where the water is held. For example, the oceans. FLUXES: this is the measurement of the rate of flow between the stores. PROCESSES (Flows): the physical factors which drive the fluxes of water between stores.

Major Fluxes Present new information The major fluxes are shown by the numbers, driven by key processes such as precipitation, evaporation. These fluxes have been quantified – the most important being evaporation from the oceans. Use page 6 and 7 of the SUG (or page 2 and 3 of Hodder)to complete sheet a) in your booklet – (two pages)

The Hydrological Cycle facts Present new information The water is held in different states (liquid, gas and solid) and stores which vary for both human and physical reasons. In the last Ice Age more water was held within the cryosphere in a solid form as snow and ice. Fixed amount of water on the planet that is constantly recycled NO EXTERNAL INPUTS OR OUTPUTS – this is crucial for your understanding There are inputs and outputs WITHIN THE SYSTEM itself. The water exists in various forms Solid – ICE Liquid – WATER Gas – VAPOUR For example in the last Ice Age more water was held in solid form Recent years has seen more liquid water in the system Water is held in STORES Oceans Cryosphere - Ice Land – rivers, streams and lakes Vapour in atmosphere – in clouds There are FLOWS which are driven by processes such as precipitation and evaporation. High flows as per diagram on page 3 can be seen e.g evaporation. Recent climate warming is reversing this with major losses of ice in Greenland and Antarctica. Humans have built water storage reservoirs (on a smaller scale) which has increased the security of their water supply.

Main global water stores Construct new meaning Which is the world’s largest water store and what percentage of the world’s water is contained in it? The atmosphere is the smallest store of water, why might this be? Look at the residence time column. What does that tell you about the different stores of water?

Answers Construct new meaning Which is the world’s largest water store and what percentage of the world’s water is contained in it? Oceans -96.9% The atmosphere is the smallest store of water, why might this be? It soon evaporates, condenses and falls to Earth as precipitation. Look at the residence time column. What does that tell you about the different stores of water? The largest stores have the longest residence time/longest time spent in that store.

Fossil Water Present new information This is water that is found very deep and out of reach from humans and is not renewable Examples: Ancient water under Sahara Desert which stored there after wet periods in that area 5000 years ago when there were active river systems Major ice sheets such as Greenland and Antarctica store water as ice for very long periods of time. Ice core dating from Antarctica has suggested residence time of 800,000yrs!

Present new information Atmosphere Ocean-atmosphere flux - More water is evaporated from the oceans than falls on to them as precipitation Present new information Land – Ocean Flux - The balance (30) is made up by river runoff(arrow going from land to ocean). If the precipitation and evaporation budget did not work in this way, the land masses would progressively dry up, and oceans would progressively gain all of the world's water. Less evaporation from the land as stores in soil, blue water and groundwater. 370,000 Atmosphere-land flux - More water falls as precipitation on to the land masses than is evaporated 90,000 400,000 60,000 Ocean Land 30,000

Annual Fluxes Apply to demonstrate The following important points emerge from this Table: (1) More water is evaporated from the oceans than falls on to them as precipitation, and more water falls as precipitation on to the land masses than is evaporated. The balance is made up by river runoff. If the precipitation and evaporation budget did not work in this way, the land masses would progressively dry up, and oceans would progressively gain all of the world's water. (2) The annual flux of water through the atmosphere is about 460,000 cubic kilometres per year, about 35 times larger than the amount held in the atmosphere at any one time. This means that the average residence time of water in the atmosphere is very short. In contrast, the size of the ocean reservoir is over 3,000 times larger than the annual flux to the atmosphere or from the atmosphere and land masses, so the average residence time of water in the oceans is very long. Complete Sheet 5.1b) in your booklet using the SUG and the previous slides. Comment on this table using the information from the flux diagram in your booklet.

The following points emerge from this table.. Review (1) More water is evaporated from the oceans than falls on to them as precipitation, and more water falls as precipitation on to the land masses than is evaporated. The balance is made up by river runoff. If the precipitation and evaporation budget did not work in this way, the land masses would progressively dry up, and oceans would progressively gain all of the world's water. (2) The annual flux of water through the atmosphere is about 460,000 cubic kilometres per year(400 ocean + 60 land). The average residence time of water in the atmosphere is very short 10 days. In contrast, the size of the ocean reservoir is much larger than the annual flux to the atmosphere(460km3) or from the atmosphere(460km3) and land masses(60km3), so the average residence time of water in the oceans is very long.

Residence Times Present new information The table shows residence times. These are the average times a water molecule with spend in the reservoir or store. Residence times impact on turnover within the water cycle system. Some ancient groundwater, such as that found deep below the Sahara Desert – the result of former pluvial (wetter) periods – is termed fossil water and is not renewable or reachable for human use. Major ice sheets store water as ice for very long periods, so the data shows an average. Ice core dating has suggested that the residence time of some water in Antarctic ice in over 800,000 years.

Residence Times Present new information Conversely, some very accessible stores, such as soil moisture, and small lakes and rivers, have much shorter residence times. Water stored in the soil, for example, remains there very briefly as it spread very thinly across the Earth. Because of its accessibility it is easily lost of other stores by evaporation, transportation, groundwater flow or recharge. Atmospheric water has the shortest residence time (around 10 days); as it soon evaporates, condenses and falls to the Earth as rain. There is a strong link between residence times and levels of water pollution: stores with a slower turnover tend to be more easily polluted as the water is in situ for a longer length of time.

Lakes (natural and artificial) – 52% Present new information Apply to demonstrate Lakes (natural and artificial) – 52% Soil moisture – 38% Atmosphere – 8% Rivers – 1% Living things – 1% Notes: This is fresh water supply. About 69% is locked up in snowflakes, ice sheets and ice caps/glaciers. This is largely inaccessible for human use but mountain streams as snow melt from these areas are used for drinking water. Another 30% is groundwater which is very deep seated known as fossil water and cannot be accessed. That leaves only 1% of fresh water is easily accessed for human use. Technology is very important and figure 1.2 d shows current levels with current technology. Rivers are a main source of surface water 0.0007% . Its not surprising that there are so many concerns regards the usage of this tiny amount available. Its an unequal world in terms of access – technology, climate, wealth, government power…… Technology is being used to extend the availability e.g desalination plants.

Where is the Earth’s Water? Present new information Construct new meaning

Check on Learning Write out five terms/facts or figures from today’s lesson to quiz the person next to you. Homework – learn the content from today’s lesson.