Lecture 3

Introduction to Global Hydrological Cycle

• Basic Processes

• Global Water Reservoirs

• Global Water Transport

• Terms to Remember

Evaporation

Evaportion is a process of transforming liquid water at the surface to gaseous water in the atmosphere.

Condensation

Condensation is a process of gaseous water molecules condensing on nuclei to become liquid or solid water

Precipitation

• Liquid precipitation: rainfall, drizzle, dew, mist

• Solid precipitation: snow, hail

Ground Water

Subsurface water in soils and rocks that are fully saturated

Transpiration

Transpiration is the process of water loss through the stomates of plant leaves during photosynthesis.

EvapotranspirationEvapotranspiration = Evaporation + Transpiration

Runoff

Streamflow resulting from gravity on water in channels of varying size from the smallest trickles to the largest rivers.

Global Water Cycle

Ward and Robinson (2000)

Significance: represents the largest movement of matter at the Earth’s surface; associates with the global climate system; affects human activities (population distribution, industry, transportation, etc.)

Global Water Distribution and Characteristics

Reservoirs1. Ocean

Largest store Little limitation to evap.

Heat redistributionLow turnover rate

2. Terrestrial Waters(1) Deep Groundwater

Low turnover Amount uncertain

Poor quality

(2) Shallow Groundwater 14 times higher turnover

14% of freshwaterImportant source for humans

(3) Soil Water Often unsaturated

Important to Agri./ecosystemsAffects ET, T. and heat flux

(4) Lakes/Inland Waters Useful if fresh

High turnoverAccumulate pollutants

3. Atmospheric WatersSmallest storedirectly related to climateaffects vegetationhigh turnover

(5) Rivers Smallest store over land High turnover Most important to humans Balances the land-ocean system

(6) Terrestrial Ice Consists of snow cover and glaciers 85% of fresh water Small runoff Sensitive to climate change Very low turnover

Exchange between reservoirs

Global water vapor distributionSeptember 6, 2005, 00:15 UTC

http://www.ghcc.msfc.nasa.gov/GOES/globalwv.html

Nine Year Global Monthly Mean Soil Moisture Variation (1992-2000)

http://www.ipf.tuwien.ac.at/radar/ers-scat/animation_frame.htmVienna University of Technology

Terms to Remember (2)2 Fluxes: Average or instantaneous rate of water flow (gaseous, liquid, solid) per unit surface per unit time, i.e. g/(m2 s), or g/(m2 d), or mm/d, mm/h. All hydrological processes involve the flow of water, i.e. water fluxes. Hydrological cycles results from fluxes between reservoirs. 3Recycling time: Time that a hypothetical water molecule to return to the same point in a cycle. Usually involves more than one processes 4Turnover rate (residence time): Time required to empty (completely) and recharge a storage EEnergy: Hydrological cycles require energy and are driven by the solar energy, either directly or indirectly at the global scale.

Terms to Remember (2)

Terms related to the processes for transforming energy into water fluxes

• Latent heat of vaporization: energy required for transforming water in liquid forms to gaseous forms

• Latent heat of melting: energy required for transforming water in solid forms to liquid forms

• Latent heat of sublimation: energy required for transforming water in solid forms directly to gaseous forms

 Heat related terms:• Specific heat of water (Cw): heat energy per unit volume of water,

i.e., J/m3

• Specific heat capacity of water: the amount of energy required to increase water temperature by one temperature unit, i.e., J/(m3 K)