The Water Cycle and Water InsecurityNew topic…

The Water Cycle and Water InsecurityNew topic…

The Global Hydrological CycleToday’s title… Recap on the hydrological cycle

Key idea 5.1: The global hydrological cycle is of enormousimportance to life on earth

Lesson Objectives:

Understand how water moves within a closed cycle

The water budget limits the water available for human consumption

Key words:Stores= Reservoirs where water is held, such as the oceans. Flux= The flow or flowing of a liquid.Processes= The physical mechanisms that drive the fluxes of water between the stores. Closed system= Where inputs and outputs are balanced. As in reference to the hydrological cycle, the system has inputs and outputs, linked by stores and flows.Cryosphere= Areas of the Earth where water is frozen into snow or ice. Solar energy= Energy from the sun, heating water and causing evaporation/ transpiration. Gravitational potential energy= ways in which water accelerates under gravity, thus transporting it to rivers and eventually to the sea. Global water budget= the amount of water transferred and stored in the Earth’s hydrological cycle each year, including fluxes, and the volume of water stores. Blue water= water stored in lakes, rivers, streams and groundwater in liquid form (the visible part of the hydrological cycle).Green water= water stored in the soil and vegetation, (the invisible part of the hydrological cycle).

Where does our water come from? Task: In pairs or small groups, discuss the following:

Name three: stores of water, flows of water above the ground and three flows of water below the ground.

In terms of global supply of water, what is the % of fresh water?

How much of all freshwater is readily accessible for human use?

What powers the hydrological cycle?

Extension: Explain three things in the water cycle that would be affected by a change in climate and how this would affect the global water budget.

Where is all the water?

1) Discuss- where the world’s water is found?

2) The challenges this may bring as the population continues to exponentially rise?

As you can see from above, water can exist in different states within this closed system- liquid, vapour and solid. This may change when climates warm or cool e.g. In the last Holocene more water was held within the cryosphere in a solid form of snow and ice.Recent climate warming has been reversing this process- with major losses to the ice sheets.

Where is all the water?

Accessible water for human life: approx. 96-97% of water is saline (stored in the oceans) . Only around 2.5% is fresh drinking water. -69% of this fresh water is stored in glaciers and ice caps-30% occurs as groundwater, which is at times very deep and inaccessible (fossil water). -This leaves only around 1% of freshwater accessible for humans.

The hydrological cycle as a system- recap

• The hydrological cycle is a closed system because water is continuously recycled and circulated through all stores.

• It is driven by SOLAR ENERGY- as 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. When humid air rises, condensation occurs, forming clouds, and this eventually leads to precipitation and water is returned back to the Earth’s surface.

• GRAVITATIONAL POTENTIAL ENERGY turns into kinetic energy to allow the water to move on the SURFACE system in a sequence, of: inputs, outputs, stores and flows.

The hydrological cycle as a system

Q – Is water a renewable source?

Water is technically considered a renewable resource because it can be used over and over again and it has a rain cycle. However, it is only in the short-term that water can be thought of as a renewable resource and the sustainability of this renewable resource is questionable.

Q-What are non-renewable water sources?

1. Cryosphere losses

2. Fossil water: ancient, deep groundwater from former pluvial (wetter) periods. There is fossil water deep below the Sahara Desert but it is not reachable for human use.

The global hydrological cycle, with estimates of the main water stores (white type) and fluxes (black type)

Task: 1) Discuss the variation in

figures for stores and fluxes. Is this what you

would expect to see and why? How much will these figures vary by and why?

2) Which are most likely to be the long and short term

stores? 3) Add cryospheric processes

onto your diagram- arrows going both ways.

The global hydrological cycle, with estimates of the main water stores (white type) and fluxes (black type)

The major fluxes are shown, driven by key processes such as: precipitation, evaporation, cryospheric exchange and runoff (surface and ground water) The major stores RECAP: ------

Plenary

Explain why the global hydrological cycle is an example of a closed system. [6 marks]

Guidance:

-Define the term ‘closed system’

-Use named processes and stores to show why the water cycle is closed.

Plenary help if needed

• The hydrological cycle is called a closed system because the amount of water on the Earth does not fluctuate. While water changes forms as it flows through the hydrological cycle, there is no significant input or output of water from the planet. Rain, snow and ice that rains down onto the planet eventually melt and evaporate, thereby replacing the water that precipitated from the atmosphere.

• The vast majority of water on planet Earth has been here for billions of years. While small amounts of water are formed or broken down in various chemical processes, the processes tend to balance.

• While water never leaves the planet in any significant quantities, sometimes water stops flowing through the hydrological cycle for a period of time. For example, the water that makes up the polar ice caps has been frozen for millions of years, and very little of it has flowed in an ocean or formed a cloud in the atmosphere since the time that it froze.

Homework-

Read through pages 2-5 to make sure you understand what we have covered so far, in particular read and make additional notes on the ‘accessible water for human life support’

Copy out the table- page 3 of your textbook to show the stores, volume, percentage of total water, percentage of fresh water and the residence time.

Define the following (pg. 4):

- Residence time

- Precipitation

- Evaporation

- Transpiration

- Groundwater flow

- Fossil water (explain why it is not renewable).