inflow = outflow ± change in storage The principle of mass conservation Q in = Q out ± ΔSnon-steady state or transient conditions if ΔS = 0steady state conditions
Fluxes in Global Hydrologic Cycle
Storage in Global Hydrologic Cycle (in %)
Inventory of the World's water reservoirs RESERVOIR VOLUME (cubic kilometres) PERCENTAGE OF TOTAL Oceans1,370,000,00097.25 Glaciers and Ice Sheets 29,000,0002.05 Ground-water9,565,0000.685 Lakes125,0000.01 Rivers1,7000.0001 Atmosphere13,0000.001 Biosphere6000.00001 TOTAL1,408,705,300100
Inventory of the World's water reservoirs
Global values for the major fluxes between reservoirs. RESERVOIRSPROCESS FLUX (cubic kilometres per year) OCEANS-ATMOSPHEREEvaporation400,000 Precipitation370,000 LAND MASSES - ATMOSPHERE Evaporation60,000 Precipitation90,000 LAND MASSES - OCEANSRunoff30,000
Approximate residence time of water found in various reservoirs.
Approximate residence time of water in the Caspian Sea.
Nubian Sandstone Aquifer - the largest reservoir of “fossil” ground-water
Pan-Evaporation Pan evaporation is a measurement that combines or integrates the effects of several climate elements: temperature, humidity, rain fall, drought dispersion, solar radiation, and wind. Evaporation is greatest on hot, windy, dry, sunny days; and is greatly reduced when clouds block the sun and when air is cool, calm, and humid. Pan evaporation measurements enable farmers and ranchers to understand how much water their crops will need.
Pan-Evaporation An evaporation pan is used to hold water during observations for the determination of the quantity of evaporation at a given location. Such pans are of varying sizes and shapes, the most commonly used being circular or square. The best known of the pans are the "Class A" evaporation pan and the "Sunken Colorado Pan". In Europe, India and South Africa, a Symon's Pan (or sometimes Symon's Tank) is used. Often the evaporation pans are automated with water level sensors and a small weather station is located nearby.
Evapo-Transpiration Transpiration: The release of water from plant leaves Evapotranspiration is the sum of evaporation from the land surface plus transpiration from plants. Precipitation is the source of all water.
Evapo-Transpiration Weighing lysimeters
Methods of measurements dry precipitation
Precipitation over a river basin cm/time What is the total volume of water that fell over the basin during the specified time period?
Precipitation over a river drainage basin cm/time If the rain gauge network would be of uniform density i.e. each gauge would be representative of the same area, then a simple arithmetic average of point-rainfall data for each station would be sufficient to determine the effective uniform depth of precipitation over the drainage basin area.
Precipitation over a river drainage basin Isohyetal method Isohyets – interpolated contour lines
Precipitation over a river drainage basin Isohyetal method Effective uniform depth of precipitation = EUDP
Precipitation over a river drainage basin Construction of Thiessen polygons (1) triangulation
Precipitation over a river drainage basin Construction of Thiessen polygons (2) bisecting the laterals of each triangle
Precipitation over a river drainage basin Construction of Thiessen polygons 3) Connecting the bisector into a network of polygons (3) Connecting the bisector into a network of polygons
Storm hydrograph components Interflow and throughflow
Storm hydrograph components Baseflow
Baseflow recession on stream hydrograph
Multi-year baseflow recession of one stream
V tp – total potential ground-water discharge Q o – baseflow discharge rate at the beginning of recession t 1 – time during which Q o 0.1 Q o
Multi-year baseflow recession of one stream V tp – total potential ground-water discharge Q o – baseflow discharge rate at the beginning of recession t 1 – time during which Q o 0.1 Q o The volume of potential baseflow, V t, remaining at some time, t, after the beginning of baseflow recession may be estimated by:
Multi-year baseflow recession of one stream The difference between the remaining potential ground-water discharge at the end of a given baseflow recession and the total potential ground-water discharge at the beginning of the next recession represents the recharge that takes place between the two recessions.