Exercises: The hydrosphere

State how Earth's water is distributed (oceans, ice caps/glaciers, groundwater, surface water, and atmosphere) using approximate percentages, and calculate what fraction remains available as usable fresh water.

Observe the diagram of the hydrological cycle. Name the processes labelled with numbers 1 to 5 and explain what energy source drives the cycle.

What is an aquifer and how is it recharged? Explain the difference between an unconfined aquifer and a confined aquifer.

Explain what ocean thermohaline circulation is, which two properties of seawater drive it, and why the climate of north-western Europe is milder than that of other regions at the same latitude.

Describe how temperature and salinity vary with depth in the ocean (thermocline and halocline) and what consequence water stratification has for marine life.

Several aquifers along the Mediterranean coast suffer from salinisation due to overexploitation. Explain the mechanism by which extracting more water than is recharged leads to seawater entering the aquifer, and why the damage is so difficult to reverse.

A popular science article states: "Since global warming increases the planet's average temperature, it is impossible for northwestern Europe to experience colder winters or a harsher climate." a) Reasonably refute this statement by justifying the role of salinity, temperature, and density in the engine of the Atlantic Meridional Overturning Circulation (AMOC), and explain how accelerated melting in Greenland can slow it down. b) Predict what consequences this weakening would have for the climate of western Europe and for the oxygenation and primary productivity of the deep ocean in the North Atlantic.

An aquifer stores $500\ \text{hm}^3$ of water and its annual natural recharge is $20\ \text{hm}^3$, but irrigation extracts $35\ \text{hm}^3$ per year. Calculate its theoretical turnover time and annual deficit, and discuss how long this exploitation is sustainable.

In autumn, the sea surface of the Mediterranean frequently reaches anomalies of up to $26\ ^\circ\text{C}$ while pockets of cold air aloft ($-28\ ^\circ\text{C}$ at $9\,000\ \text{m}$) penetrate. a) Physically justify the instability generated by relating the vertical temperature gradient, the release of latent heat of condensation, and the role of the peninsular coastal topography in convective triggering. b) Explain why ocean warming intensifies the torrential nature of precipitation according to the relationship between temperature and the moisture-holding capacity of air. c) Refute the common idea that "every cut-off low (DANA) isolated over the Peninsula automatically causes catastrophic rainfall along the Mediterranean coast."