Geography · Year 12 · The Water and Carbon Cycles · Summer Term

Global Water Stores and Flows

Examine the distribution of water in different stores (oceans, ice, groundwater) and the processes of the global hydrological cycle.

• National Curriculum Attainment Targets
• A-Level: Geography - Water and Carbon Cycles
• A-Level: Geography - Hydrology and Drainage Basins

About This Topic

Hydrological systems focus on the drainage basin as a fundamental unit of study. Students analyze the water balance, exploring how precipitation is partitioned into evaporation, transpiration, surface runoff, and groundwater flow. A key part of the curriculum is the study of storm hydrographs and how they are influenced by both physical factors (like geology and relief) and human activities (like urbanization and deforestation).

At A-Level, students must understand the drainage basin as an open system with inputs, stores, transfers, and outputs. They also examine how climate change is intensifying the hydrological cycle, leading to more frequent and severe floods and droughts. This topic comes alive when students can physically model the impact of different land uses on runoff and infiltration through hands-on experiments and simulations.

Key Questions

1. Analyze the relative importance of different global water stores.
2. Explain the key processes of the global hydrological cycle (evaporation, condensation, precipitation).
3. Predict how climate change might alter the balance of global water stores.

Learning Objectives

• Analyze the relative volume of water stored in oceans, ice caps, glaciers, groundwater, and surface freshwater bodies.
• Explain the key processes of the global hydrological cycle, including evaporation, transpiration, condensation, precipitation, and surface runoff.
• Compare the characteristics and significance of different water stores, such as oceans, ice, and groundwater.
• Predict how changes in global temperatures might alter the rates of evaporation and ice melt, impacting water availability.
• Synthesize information to illustrate the interconnectedness of global water stores and the processes that move water between them.

Before You Start

Earth's Spheres: Atmosphere, Hydrosphere, Lithosphere, Biosphere

Why: Students need a foundational understanding of these interconnected spheres to grasp how water moves between them.

States of Matter and Phase Changes

Why: Understanding evaporation, condensation, and freezing is crucial for comprehending the movement and storage of water in different forms.

Key Vocabulary

Hydrological Cycle	The continuous movement of water on, above, and below the surface of the Earth, driven by solar energy and gravity.
Aquifer	An underground layer of permeable rock, sediment, or soil that holds and transmits groundwater.
Cryosphere	The parts of the Earth's surface where water is in solid form, including ice sheets, glaciers, sea ice, and snow cover.
Permafrost	Ground that remains frozen for two or more consecutive years, found in high-latitude and high-altitude regions.
Surface Runoff	The flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources can no longer sufficiently rapidly infiltrate in the soil.

Watch Out for These Misconceptions

Common Misconception

Groundwater is a giant underground lake.

What to Teach Instead

Groundwater is actually water held in the tiny pores and cracks of rocks (aquifers). Using a sponge to demonstrate how water is stored in solid material can help students visualize this correctly.

Common Misconception

Deforestation only affects the area where the trees were cut down.

What to Teach Instead

It affects the entire drainage basin by increasing runoff and sediment load downstream. A 'flow chart' activity can help students trace the knock-on effects of land-use change through the whole system.

Active Learning Ideas

Inquiry Circle: The Hydrograph Challenge

Groups are given a set of 'catchment characteristics' (e.g., steep slopes, clay soil, urbanized). They must draw the predicted storm hydrograph and explain their reasoning to the class, focusing on lag time and peak discharge.

45 min·Small Groups

Think-Pair-Share: Hard vs. Soft Flood Management

Students compare a traditional dam with a 'natural flood management' project like rewilding beavers. They discuss with a partner which is more sustainable in the face of climate change and share their ideas.

25 min·Pairs

Simulation Game: The Infiltration Race

Using different materials (sand, clay, concrete), students simulate how quickly water moves through different surfaces. They record the data and use it to explain why urban areas are more prone to flash flooding.

40 min·Small Groups

Real-World Connections

• Climate scientists use global hydrological models to predict the impact of rising temperatures on glacier melt in the Himalayas, which affects water supplies for millions in South Asia.
• Water resource managers in arid regions like Australia assess groundwater reserves in aquifers to ensure sustainable agricultural and urban water use during prolonged droughts.
• Engineers designing flood defenses for coastal cities such as Venice must understand how sea-level rise, linked to melting ice stores, will increase the frequency and severity of inundation.

Assessment Ideas

Discussion Prompt

Pose the question: 'If you had to prioritize which global water store to protect from climate change impacts, which would it be and why?' Facilitate a class debate, encouraging students to justify their choices using data on water volume, accessibility, and vulnerability.

Quick Check

Provide students with a blank world map. Ask them to label the approximate locations of the largest freshwater ice stores and major groundwater reserves. Then, ask them to draw arrows indicating the primary processes that move water away from these stores.

Exit Ticket

On a slip of paper, students should write down one key process of the hydrological cycle and one significant factor that influences its rate. For example, 'Evaporation: influenced by solar radiation and surface area.'

Frequently Asked Questions

What is a 'storm hydrograph'?

It is a graph that shows how a river's discharge changes over time in response to a specific rainfall event. It helps geographers predict and manage flood risk.

How does urbanization affect the hydrological cycle?

It replaces permeable soil with impermeable surfaces like concrete, which increases surface runoff and decreases infiltration, leading to higher peak discharges and shorter lag times.

What is 'natural flood management'?

It is an approach that uses natural processes to reduce flood risk, such as planting trees to increase interception or restoring meanders to slow down river flow.

How can active learning help students understand hydrology?

Active learning, such as the infiltration race or hydrograph modeling, allows students to see the 'cause and effect' of the water cycle in real-time. It moves the lesson from a static diagram to a dynamic system, helping students grasp how small changes in one part of the basin can have huge impacts elsewhere.