WATER CYCLE 1 : system concepts Mass balance Inputs Outputs Stores Flows We are grateful to Hodder for their permission to use the diagrams in this resource. WJEC Focus Box 3.1.1 Eduqas Focus Box 2.1.1

Water Cycle 1 System components Stores are natural reservoirs of water, such as the ocean, lakes or ice caps A water flow entering a store is called an input: for example a river entering the ocean Flows leaving stores are called outputs: for example, evaporation of ocean water Flows are movements (or transfers or fluxes) between stores in a system Inquiry question: What are the main elements of a system? Students discuss the concepts, such as stores and flows, using prior knowledge from KS3/4 Students discuss open systems (with flows across its boundary e.g. an ecosystem) and closed systems (global water cycle) Class activity What is the difference between an open system and a closed system? What examples are there of each?

Water Cycle 1 The global water cycle The global water cycle is shown as a ‘black box’ model What are the strengths and weaknesses of viewing water stores and flows in this way? Inquiry question: What are the main elements of the global water cycle? Class activity What systems have you studied in other Geography topics? What are their similarities and differences? (c) Hodder Education [OCR A-level Geography (Raw)]

Water Cycle 1 Another view of the water cycle Inquiry question: What are the main elements of the global water cycle? Students discuss the usefulness of different system diagrams, and system theory Class activity Which illustration of the water cycle do you prefer, and why? (c) Hodder Education [Edexcel A-level Geography Book 2 (Dunn)]

Water Cycle 1 The concept of mass balance At a global scale, mass balance means that the total amount of water is always conserved At the global scale, there is a fixed amount of water in the Earth-atmosphere system (about 1385 million cubic kilometres of water) Transfers can occur; changes occur in where water is stored without affecting the mass balance. For instance, water vapour in the atmosphere is precipitated on to the land as rain or snow after condensation occurs: although it has changed state, all water still remains in the system Inquiry question: What is meant by mass balance of a system? Class activity What other water transfer processes are there? Why don’t they affect the system’s mass balance?

Water Cycle 1 Global water stores Volume (cubic km) Per cent of total water Distribution and characteristics Oceans 1,335,000 97 Oceans cover two-thirds of the Earth Cryosphere 26,000 2 Ice and snow stores found at high latitudes (poles) and high altitudes Groundwater 15,000 1 Can remain stored for 10,000 years River and lakes 178 0.01 Uneven distribution due to climate Soil moisture 122 Permafrost in Russia and North America Atmosphere 13 <0.01 There is sufficient moisture for ten days of rain in the atmosphere Biosphere 0.6 Distributed unevenly because of climate Inquiry question: How do different global water stores compare in terms of their size, distribution and characteristics ? Discussion of students’ prior knowledge (where applicable) of water stores, including the cryosphere and groundwater stores. Discussion can focus on how local geological factors affect groundwater storage; climate affects biomass size and water storage. Develop quantitative skills by comparing the importance of the different stores in the table. Class activity (1) Compare the size of the different stores (2) What local factors affect water storage in different places?

Water Cycle 1 Investigating the cryosphere These are areas of the Earth where water is present as snow or ice This includes ice sheets, ice caps, alpine glaciers, sea ice and permafrost Inquiry question: How do different global water stores compare in terms of their size, distribution and characteristics ? Discussion of students’ prior knowledge (where applicable) of the cryosphere e.g. glacial landscapes; cold environments; tundra ecosystems Class activity Which other Geography topics require you to have knowledge of the cryosphere? (c) Hodder Education [AQA A-level Geography (Skinner)]

Water Cycle 1 Water store changes Global hydrological stores change in size over time (seasonal or longer-term) Both physical and human factors can play a role For instance, water stored in the Aral Sea has declined markedly since the 1990s Inquiry question: How and why have water stores changed in the past, or are changing now? Discussion of students’ prior knowledge of possible reasons for the Aral Sea shrinking e.g. over-use by agriculture and industry; increasing aridity (possibly linked with climate change). NB introduce the Aral Sea using a map if students have no prior knowledge. Class activity What factors could explain the changing size of the Aral Sea? (c) Hodder Education [Edexcel A-level Geography Book 2 (Dunn)]

Water Cycle 1 Ice accumulation and ablation Accumulation is the build-up of snow and ice which takes place within the cryosphere Ablation is the change from solid ice to liquid or water vapour when temperature rises above 0°C. This wastage of surface snow or ice is achieved by melting and evaporation (the change from ice to vapour is called sublimation) Inquiry question: How and why have water stores changed in the past, or are changing now? Discussion of students’ prior knowledge of accumulation and ablation (if they studied glacial landscapes in Year 12) Class activity Use the RGS-IBG interactive resource to explore system changes involving ice accumulation and ablation: http://www.rgs.org/webcasts/activities/glaciation/glaciation.html

Water Cycle 1 Changes over time in the cryosphere Seasonal variations in ice accumulation and ablation bring cyclical fluctuations in water flows and storage in glaciated regions such as the Tibetan plateau Many cryospheric waters stores are expected to undergo a permanent reduction in size on account of anthropogenic (human-induced) climate change Longer-lasting changes have occurred naturally in the distant past, including the arrival and departure of glacial and inter-glacial epochs There are periods in Earth’s past when the planet is believed to have been entirely ice-free Inquiry question: How and why have water stores changed in the past, or are changing now? Discussion of students’ prior knowledge (where applicable) of past glacial epochs. Most A-level Geography textbooks will give a sound account of this. Alternatively, use: https://www.youtube.com/watch?v=yNiMhjPHPu0 A starting point for further independent research into changing water and ice storage: https://www.youtube.com/watch?v=1nSIj9tvhbY If time allows, the ‘snowball earth’ film: https://www.youtube.com/watch?v=NgpQci6iWx0 Class activity Research (1) Snowball Earth Cryogenian ice ages and (2) Hothouse Earth conditions when the poles were ice-free

Water Cycle 1 Rapid and local transfer processes A monsoon is an especially wet season In Mangalore in southwest India, more than two-thirds of the year’s rainfall falls in three months During the monsoon, rapid water transfers from the atmosphere to the land can take place in just hours or minutes Inquiry question: How is an appreciation of time and scale important for the study of water flows and transfers? Group/pair research work reviewing personal experiences of high rainfall; or looking online for recorded maxima. Class activity What is the greatest intensity of rainfall you have ever seen? How much rain can fall in an hour?

Water Cycle 1 Slower global transfer processes Long-term anthropogenic climate change is projected to impact on water transfer processes globally Major water transfers from land to the ocean - and accompanying sea level rise - would follow if the Greenland and Antarctic ice sheets were to melt Together, they contain more than 99 per cent of the freshwater ice on Earth. If the Antarctic Ice Sheet melts, sea level will rise by a further 60 metres However, this would take thousands of years Inquiry question: How is an appreciation of time and scale important for the study of water flows and transfers? Students discuss prior knowledge of sea-level rise e.g. thermal expansion Class activity What is the current rate of global sea-level rise and why is it happening?

Flows in and out of stores are called inputs and outputs Water Cycle 1 Plenary The global water cycle is a closed system in which all water is conserved over time (mass balance) Flows in and out of stores are called inputs and outputs Lakes, oceans, the atmosphere, vegetation, soil and groundwater are water stores, along with the cryosphere (the largest global store of fresh water) The relative size of ocean and cryosphere storage has altered considerably in the past Anthropogenic climate change may lead to further changes Rapid water transfers and storage changes can occur over shorter time scales too, for example the monsoon