PHASES OF THE WATER CYCLE ATMOSPHERE OCEANS BIOSPHERE TERRESTRIAL LITHOSPHERE
The water cycle http://earthobservatory.nasa.gov/Library/Water/water.html % of all water Oceans 97.47 Freshwater 2.53 % of freshwater Ice & snow 69 Groundwater 30 Rivers & lakes 0.03 Atmospheric Water 0.04
IMPORTANCE OF OCEANS • Oceans as stores or sinks: Water, CO2 , heat, dissolved salts, sediments. • Ocean currents as transfer systems. • Importance of evaporation: source of atmospheric moisture, latent heat and energy transfer.
Importance of Ice Caps, glaciers and snow cover • Store of water in frozen form (consequences for sea-level if ice melts) • Isostatic effects of ice cover and ice melt • Albedo of ice caps affects global heat budget • Extent of glaciation depends on air temperature and on amount of precipitation as snow fall – wet periods favour glaciation.
The evaporation process • Conversion of liquid water to water vapour • Depends on: • ENERGY and WATER TEMPERATURE (related to solar radiation) • Capacity of air to take up moisture (related to air temperature, air humidity, wind speed)
PRECIPITATION Cloud formation output of energy as latent heat Condensation Cooling Adiabatic processes Convection Convergence/frontal systems Orographic uplift warming Uplift of air Input of energy as latent heat Evaporation
Distribution of Cloud Coversource Pidwirny (on line) January ’84-’91 Red = high cover Green/yellow = intermediate cover Blue = zero cover July ’83-’90
Water on the land evapotranspiration evaporation precipitation soil water vegetation runoff rivers lakes surface water water resources natural ecosystems agriculture groundwater domestic water supply industry etc. human livelihoods geomorphological processes
Vegetation and hydrology Interception & evaporation of water: direct loss of water to he atmosphere Biomass of above ground vegetation Infiltration: absorption of precipitation by the soil Vegetation cover Surface root mass Soil organic content Transpiration: use of soil moisture by plants Leaf area, size and structure Root mass and rooting depth
Significance of hydrological effects of vegetation • Evaporation of intercepted water and transpiration (evapotranspiration) = loss of water to the atmosphere; reduction in water available to rivers and groundwater • Infiltration controls surface runoff process; low infiltration leads to overland flow and possible erosion; low soil moisture levels inhibit vegetation growth.
Vegetation and hydrology 2 EXERCISE: For two selected biomes describe the way in which the vegetation cover effects hydrological processes. • WATER AVAILABILITY • Is this biome found on a wet or dry area? • Is precipitation seasonal? • Is rainfall characteristically intense? • INTERCEPTION • Does the above ground biomass act as an effective interceptor of water? • INFILTRATION • Is there a good ground cover that will protect the soil from the impact of raindrops? Does it vary seasonally? • Is there a good root matt close to the soil surface? • Is the underlying soil rich in organic matter? • TRANSPIRATION • Is there a high leaf biomass? • Is the vegetation evergreen or deciduous? • Are the leaves adapted to prevent excessive water loss? • How deep are the roots?