Lecture 2 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 A process of liquid or solid water falling to the surface due to gravity 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. Evapotranspiration Evapotranspiration = 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

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/(m 2 s), or g/(m 2 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 the 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 (C w ): heat energy per unit volume of water, i.e., J/m 3 Specific hear capacity of water: the amount of energy required to increase water temperature by one temperature unit, i.e., J/(m 3 K)