precipitation Flashcards
rain
liquid water droplets between 0.5-0.7 mm diameter
drizzle
rain subset with droplets of less than 0.5 mm
sleet
freezing raindrops, combination of snow and rain
snow
complex ice crystals agglomerated
hail
balls of ice between 5-125mm diameter
conditions for precipitation formation
for formation:
- air must cool to dew point
-condensation nuclei must be present
- droplets must grow
For sustaining:
-continuous import of water
dew point
temperature at which air mass is saturated by water vapor (reach 100% relative humidity)
airmass
mass of air with relative homogenous temperature and density
convective lifting
air warmer than surrounding is less dense -> will rise
frontal lifting
cold front meeting hot front will cause hot air to rise as fronts migrates
orographic lifting
air forced to rise because of physical presence of mountains
condensation nuclei
small particles/ aerosols upon which water vapor attaches to initiate condensation
condensation
process driving change from water vapor to liquid water
tipping bucket rain gauge functioning
count small increment of rain collected
How:
-rain falls via funnel into container divided in 2 equal part
- when specified amount of rain has drained into a part -> bucket tilt
problem of tipping bucket gauge
undercatch of precipitation because:
-wind turbulence
-evaporation loss
-wetting loss
-rain splash effect
typical climate station will record:
wind speed & direction
rainfall
relative humidity & temperature
radiation
Snow variables
amount & distribution of snow
liquid water content
unfroze water existing in snowpack
relative density
ratio of snowpack to water density
SWE
height of water that would be on ground if snowpack melted in place
Snowmelt dynamic (3 phases)
1.Warming phase = cold snowpack require energy to rain temperature to 0 Celsius
2.Ripening = warm snowpack gains additional energy inputs and retain initial meltwater (until water holding capacity is exceeded)
3.Output = continued input of energy to melt remaining snow and ice AND water leaving by base of snowpack
snow course
when multiple measurement of snow depth&SWE are made on path between 2 fixed points
Measuring snowfall as SWE
weighing bucket gauge -> heated tipping bucket
snow pillow -> weight of snow forcing fluid in panel into pressure transducer
measuring snow on the ground
with ruler
with snow surveys
with ultrasonic depth sensor -> continuous record of depth
rainfall hyetograph
plot of rainfall depth/intensity as function of time
cumulative rainfall hyetograph
plot of summation of rainfall increments as function of time
rainfall intensity
plot of depth of rainfall per unit time
how to compare rainfall event using:
duration
average rainfall intensity
max rainfall intensity
magnitude (total rainfall amount)
Method for Estimating rainfall over larger area
Arithmetic
Thiessen polygon
Isohyetal
Inverse distance weighting
Problems of arithmetic method
gages must be inside watershed
need uniformly distribution
need not too large outliers
Problem of isohyetal method
value of delineation varies depend on density of gauge
Issues converting snow into SWE
-time lag from precipitation to melting
-snowmelt enter watershed where it melts -> not where it falls
Interception
fraction of gross precipitation that wets & adheres to above ground object, doesn’t reach the ground and returns to atmo with evaporation
Gross precipitation
measured above canopy or in a clearing
Throughfall
precip reaching surface directly or via canopy drip
stemflow
water reaching surface by running along trunks and stems
total interception loss
sum of all canopy interception and losses
Why is interception critical
-significant water source for evapo
-strongly influence runoff
-canopy drips increase local erosion
Issues measuring interception
Spatially variable (diff vegetation, wind, etc.)
Temporally variable (begin VS end of storm)
Interception by vegetation hierarchy
conifer
broadleaves & tropical forest
Soybean, corn, wheat (grasses)
Factors affecting interception
vegetation type
duration
precipitation intensity
wind
precipitation type (snow VS rain)
precipitation frequency
depression storage
precip retained in ground surface depressioin
detention storage
short-term storage depleted via flow away
retention storage
long-term storage depleted via evaporation
wetlands
transitional system between terrestrial and aquatic system where water table is at/near surface
criteria for wetlands to meet:
-hydrophytic vegetation
-hydric soils
-hydrologic conditions (saturated substrate some time during growing period)
