The hydrosphere
The same litre of water may have been vapour in an Atlantic cloud, rain falling on a Cantabrian forest, groundwater in an aquifer for decades and, finally, the tap water of a city. The hydrosphere is not a collection of isolated reservoirs: it is a system in continuous circulation that connects oceans, atmosphere, continents and living things.
The distribution of water and the hydrological cycle
From space the Earth looks like a blue sphere because water covers more than $70\ \%$ of its surface, yet a castaway in the middle of the ocean would die of thirst within a few days: of all that immense mass of water, only a tiny fraction contains no dissolved salt. How exactly is the planet's water distributed, and which mechanisms keep it constantly on the move?
State how Earth's water is distributed (oceans, ice caps/glaciers, groundwater, surface water, and atmosphere) using approximate percentages, and calculate what fraction…
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.
Observe the diagram of the hydrological cycle. Name the processes labelled with numbers 1 to 5 and explain what energy source drives the cycle.
Explain what evapotranspiration is and what role it plays in the water cycle, discussing why a forested basin returns more water to the atmosphere than a deforested one.
Explain what evapotranspiration is and what role it plays in the water cycle, discussing why a forested basin returns more water to the atmosphere than a deforested one.
Groundwater and aquifers
After several months of summer without a single drop of rain, many springs and farm wells are still pouring out clean, cool water at a practically constant flow. Where is that invisible volume of fresh water stored, and what determines whether we can extract it without exhausting it?
What is an aquifer and how is it recharged? Explain the difference between an unconfined aquifer and a confined aquifer.
What is an aquifer and how is it recharged? Explain the difference between an unconfined aquifer and a confined aquifer.
Distinguish between surface water, groundwater and soil (edaphic) water, and indicate one typical human use of each and what management problem each type poses.
Distinguish between surface water, groundwater and soil (edaphic) water, and indicate one typical human use of each and what management problem each type poses.
Several aquifers along the Mediterranean coast suffer from salinisation due to overexploitation. Explain the mechanism by which extracting more water than is recharged…
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.
The ocean: salinity, stratification and currents
Explain what the salinity of seawater is, its average value ($35\ \text{g}$ of salts per litre) and name a process that increases it locally (intense evaporation,…
Explain what the salinity of seawater is, its average value ($35\ \text{g}$ of salts per litre) and name a process that increases it locally (intense evaporation, freezing) and another that decreases it (the mouth of a river, rainfall, melting ice).
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…
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.
The great surface currents form gyres in each ocean. Explain the role of the prevailing winds and of the Coriolis effect in their formation, and discuss why the currents…
The great surface currents form gyres in each ocean. Explain the role of the prevailing winds and of the Coriolis effect in their formation, and discuss why the currents of the western margin (the Gulf Stream, Kuroshio) are warm and narrow and those of the eastern margin (the Canaries, California) cold and wide.
Tides and large-scale ocean phenomena
On the Atlantic or Cantabrian coasts, the water's edge on a beach advances and retreats hundreds of metres twice a day, exposing rocky seabeds that hours later lie under four metres of water. What astronomical force rhythmically moves thousands of millions of tonnes of seawater from one end of the coast to the other?
What are tides and which celestial bodies cause them? Distinguish between spring tides and neap tides and explain why the tidal range is much greater in the Cantabrian…
What are tides and which celestial bodies cause them? Distinguish between spring tides and neap tides and explain why the tidal range is much greater in the Cantabrian Sea than in the Mediterranean.
Explain what happens during El Niño in the equatorial Pacific (weakening of the trade winds, warming of the waters off Peru) and one of its far-reaching consequences…
Explain what happens during El Niño in the equatorial Pacific (weakening of the trade winds, warming of the waters off Peru) and one of its far-reaching consequences (collapse of the anchovy fishery, changes in the rainfall of half the world).
A popular science article states: "Since global warming increases the planet's average temperature, it is impossible for northwestern Europe to experience colder winters…
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.
Water as a resource: management and risks
The water footprint measures the total water used to produce a good. Calculate the difference between a ten-minute shower ($50\ \text{L}$) and consuming a kilo of rice…
The water footprint measures the total water used to produce a good. Calculate the difference between a ten-minute shower ($50\ \text{L}$) and consuming a kilo of rice (about $2\,500\ \text{L}$ of production water), and explain what the "virtual water" that travels with the food trade is.
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…
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.
You are part of the technical committee responsible for evaluating a request for a transfer of $30\ \text{hm}^3$ from the headwaters of the Tagus to the Segura in a…
You are part of the technical committee responsible for evaluating a request for a transfer of $30\ \text{hm}^3$ from the headwaters of the Tagus to the Segura in a scenario where the donor reservoirs are at $27\,\%$ of their capacity. a) Technically justify whether you would authorize the transfer by prioritizing the principle of river basin unity and the guarantee of the ecological flow over the socioeconomic demands of the receiving irrigated land. b) Evaluate the alternatives available in the demanding basin (seawater desalination, tertiary wastewater reuse), analyzing their limitations in terms of energy cost, emissions, and brine discharge. c) Design an operating rule with objective indicators and quantitative thresholds that prevents discretionary decisions during drought periods.