precipitation - cold air holds less water vapour than warm air
intensity of precipitation
type of precipitation (rain or snow)
seasonal variation
duration of precipitation
diurnal (day + night)
- less evaporation at night
- not a big issue in the uk
- tropics, day: ground gets heated, convection currents forming + big storm clouds develop. afternoon: rainfall
- pattern in arctic, precipitation too cold to occur and night
saturated overland flow: winter and spring higher levels of precipitation, soil moisture store lower in the summer
amount of precipitation falling in a given time
the length of time that a precipitation event lasts
rain: most rain upon reaching the ground flows quickly into streams + rivers.
snow: in high latitudes + mountainous catchments, precipitation falls as snow
remains on ground for several months
creating a significant time lag between snowfall and run off
high-intensity precipitation moves rapidly overland into streams and rivers. flashfloods
this in turn effects the type of overland flow
saturated overland flow: ground is saturated/waterlogged, no more can be absorbed, normally water table rises up to the surface.
infiltration excess overland flow: rate of precipitation is greater than the rate it can infiltrate the soil. summer, ground is dry/baked over a long period of time, hard crust on surface, few pour spaces, takes longer for rain to wet it, flows over the surface
infiltration excess overland flow: occur any time of year, but summer in the uk, heavy thunderstorms in summer (stronger convection currents and temperature)
can't flow until solid, overland flow insignificant, only until snow melts
either overland or infiltration excess, depending in intensity of rain (infiltration excess) or long duration (saturated overland flow)
prolonged events, linked to depression + frontal systems may deposit exceptional amounts of precipitation and cause river flooding
saturated overland flow, more likely to occur