Hydrology Theory

weather

short-term changes in the atmosphere, including changes in temperature, precipitation, wind, humidity etc

climate

persistent or long-term trends in weather conditions

circulation patterns are caused by:

uneven heating of the earth driven by surface solar input and the rotation of the earth

Hadley cell

low latitude air movement toward the equator that with heating, rises vertically, with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates

Ferrel cell

A mid-latitude atmospheric circulation cell for weather named by — in the 19th century. In this cell the air flows poleward and eastward near the surface and equatorward and westward at higher levels

Polar cell

Air rises, diverges, and travels toward the poles. Once over the poles, the air sinks, forming the polar highs. At the surface air diverges outward from the polar highs. Surface winds in the polar cell are easterly (polar easterlies)

jet stream

bands of high-speed winds that circle the earth in both hemispheres

air mass

a large mass of air that usually takes on the characteristics of the region they are formed. • They can form over land ( continental air mass) or form over water (Maritime air mass)

where do air masses ussually form?

Arctic, Polar, and Tropics

cold front

Cold air moving over warm - fast, produce dramatic changes in weather like hail

warm front

Warm Air moving over cold - slow, often brings stormy weather as the warm air mass at the surface rises above the cool air mass, making clouds and storms

stationary front

air masses locked in place

occluded front

cold air over warm front

vapour pressure

the partial pressure exerted by water vapour ONLY

Saturated Vapour Pressure

The partial pressure excerted by water vapour only, and when the air is completely saturated

snow sublimation

when snowpack is lost to the atmosphere, turning directly into water vapor without melting first, bypassing the liquid water phase entirely

potential evapotransiration (PET)

the amount of evaporation that would occur if a sufficient water source were available

humidity

the amount of water vapour in the air/atmosphere which can be expressed in different ways

relative humidity

expressed as a %, ratio of the air’s actual water vapour compared to the amount of water vapour at saturation for that temperature

specific humidity

expressed as g/kg - the mass of water vapour in a unit mass of moist air

major factors that explain a watershed’s response to a rainfall event

1. drainage area,

2. channel length/slope,

3. vegation/soil type/land use/land cover,

4. the shape, slope, and characteristics of the floodplain

5. main channel and tributary characteristics (channel morphology)

factors that influence lake of evaporation

• occurs when the surface of the lake heat up from solar irradiation

• the latent heat of evaporation is the energy required to evaporate the water from liqiod to vapour on the surface of the lake

1. windspeed

2. relative humidity of the air above the lake

3. mass transfer and energy - affect lake of evaporation

plant available water

the max amount of water stored in a soil profile that can be used by plants

permanent wilting point

soil particles hold the water so strongly that it becomes difficult for plants roots to extract it - atp, transpiration and consquenty other processes vital to plant survival will come to a near stop

7% in sandy soils

24% in clay soils

500 - 3000 kPA soil matric potential

field capacity (FC)

the threshold where water in larger pores has been drained away by the force of gravity - ideal for plant growth and irrigation goal

20% sandy soils

40% clay soils

SMP 10 - 33 kPa

saturation

all the pores are filled with water, reduces oxygen availbale to plants

30% sandy soil, 60% clay soils

hygroscopic water

tightly held water that forms a thin layer around soil particles or other materials and is held by strong molecular forces

infiltration

the movement of water from the surface of the soil into the soil

redistribution

the subsequent movement of infiltrated water in the unsaturated zone - may involve exfiltration

recharge/deep percolation

the movement of percolating water from unsaturated to subjacent saturated zone

capillary rise

movement from saturated upward into unsaturated zone due to surface tension