L. 1: Hydrologic Cycle Flashcards
Triple point of water
The point (temp. and pressure) at which vapor, solid and liquid all exist in equilibrium. (At 4.6 torr, <1 atm and 0.0098 deg C)
Latent Heat
As water changes its physical phase (e.g., from liquid to vapor or liquid to solid), heat is either absorbed or released. The heat associated with a phase change of a substance is called the latent heat.
Amount of water in earth’s hydrosphere
97% saline water, 3% fresh water.
Only 0.3% of fresh water stored in lakes, reservoirs and river systems with easy access, 75% in ice and permanent snow (cryosphere) and 24.5% groundwater.
Saturation humidity and relative humidity
The amount of moisture the air can hold at a given temp., and increases with the temp. of air.
R.H. Is the ratio of the measured humidity (g-water/meter-3 air) to the saturation humidity. Evaporation ceases when 100% relative humidity is reached.
Residence time
Average amount of time that a particle (water) spends in a particular reservoir.
Size of the pool (km3)/ flux out of pool (km3/yr) = residence time
Of water in oceans 2500 years Lakes 100 years shallow groundwater 200 years Deep groundwater 10,000 years Glaciers 40 years Seasonal snow cover 0.4 year Soil moisture 0.2 year Atmosphere 9 days Rivers 16 days
Condensation (precipitation)
As an air mass cools, its saturation humidity decreases, and relative humidity of the air mass increases leading to condensation if R.H. Exceeds 100%.
Flux
The amount that flows through a unit area per unit of time.
Steady state
The condition where, integrated over time, inputs equal outputs, resulting in no net change in the volume of a pool/reservoir.
Reservoir/pool
Any physical subdivision of the natural world that is at least semi-independent from other system and in which some sort of processes occur and in which matter or energy could be said to have some residence time.
Water Budget
P (precipitation, rain + snow) = E (evaporation) + T (transpiration) + RO (runoff) + I (infiltration)
Evapotranspiration minus Precipitation (E - P) is indicator of moisture balance and availability
E - P is generally positive (dry) in the subtropics (~30 N/S) and negative (wet) in the tropics (equator) and high latitudes
Globally, E = P
Evapotranspiration
Flux of water from surface to the atmosphere, = evaporation and transpiration (removal of water through stomata by plants during photosynthesis) and sublimation. Controlled by energy available, water holding capacity of the air (warm and dry more), wind speed
Hydrograph
Rate of flow (discharge) over time at a single point on a river or stream
Watershed
Area of land where surface water from rain and snow converges on a single point at a lower elevation
