ES1002 Week 4: Water and the Environment

What role does water vapour in the atmosphere play in Earth's climate?

It traps energy as radiation, creating a strong greenhouse effect.

How do clouds impact Earth's climate?

Clouds cool the Earth by reflecting sunlight.

How does ice affect Earth's temperature?

Ice reflects sunlight, which helps cool the Earth.

Why do oceans influence the pace of climate change?

Due to their huge heat capacity, they absorb and release heat slowly.

Where is most of Earth’s water stored?

In the oceans (96.5%), where it remains for thousands of years.

How long does water typically stay in the atmosphere?

Just a few days (0.001% of Earth's water).

What factors affect precipitation?

Soil moisture, vegetation, salinity, and latitude.

Why are the tropics wet and the subtropics dry?

Ascending air at the equator causes rain; descending air in the subtropics leads to dryness.

What causes precipitation to occur?

When rising air cools, water vapour condenses to form clouds and rain.

What are three main mechanisms that push air upwards to cause precipitation?

1. Frontal systems, 2. Convection, 3. Orographic lifting.

What is the rain shadow effect?

When moist air rises over a mountain, it rains on the windward side and dries on the leeward side.

Why must evaporation balance precipitation globally?

Otherwise, water vapour would rain out within 10 days.

Which surface has the most evaporation?

Oceans, due to their large area and water availability.

What factors increase evaporation?

Dry air (vapour pressure deficit), warm surface temperature, wind speed, and soil moisture.

How is specific humidity (q) defined?

Mass of water vapour / total mass of air.

What is the mixing ratio (r)?

Mass of water vapour / mass of dry air.

Why is the mixing ratio always slightly larger than specific humidity?

Because its denominator excludes the water vapour mass.

What is vapour pressure (pv)?

The portion of atmospheric pressure from water vapour.

How is relative humidity defined?

The percentage of water vapour relative to the maximum possible (saturation).

What is saturation vapour pressure?

The maximum pressure water vapour can exert; increases with temperature.

How can air be brought to saturation?

Add water vapour, cool the air, or mix warm moist air with cold air.

What is the relationship between temperature and relative humidity?

They are inversely proportional.

What is physical hydrology?

The study of water’s movement and properties on and beneath Earth’s surface.

What is the water table?

The level where groundwater rises to in a well.

What is groundwater?

Water stored in the saturated zone beneath the water table.

What is a drainage basin or catchment?

The area that drains into a specific river or stream.

What is hydraulic head?

A measure of groundwater's potential energy, measured by water level in wells.

What is the difference between confined and unconfined aquifers?

Confined aquifers have impermeable boundaries and pressure; unconfined ones are closer to the surface and affected by drought.

What does Darcy’s Law describe?

The rate of groundwater flow through sediment.

What is the equation for Darcy’s Law?

Q = K × A × (h/L)

🌦️ Climate Modeling and Change

Why are climate models uncertain?

Due to limited computational capacity and structural uncertainty in simulating processes.

How does climate change affect water vapour and precipitation?

Warmer air holds more vapour, increasing humidity and precipitation, but precipitation increases slower.

What is a tropical cyclone?

A rotating system of clouds and wind over tropical oceans with low-level circulation.

When do tropical cyclones typically form?

Late summer and early autumn.

What are the stages of cyclone development by wind speed?

Tropical depression (<17 m/s), Tropical storm (18–32 m/s), Hurricane (≥33 m/s).

What causes tropical cyclones to form?

Thermodynamic disequilibrium between ocean surface and the atmosphere.

What are the impacts of tropical cyclones?

Wind damage, storm surge, waves, and heavy rain.

What determines wind damage severity in hurricanes?

The storm’s category (1–5), based on sustained wind speed.

How does climate change affect tropical cyclones?

Increases their intensity and rainfall due to warmer sea surface temperature