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Hydrology > Precipitation > Flashcards

Precipitation Flashcards

1
Q

What is precipitation

A

The water reaching a catchment as rainfall, snow, hail, dew or occult forms

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2
Q

What is average annual rainfall for the world and for Lancaster

A

1000 mm

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3
Q

Where was the highest recorded annual rainfall

A

At cherrapunji, India

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4
Q

How much rainfall did Cherrapunji receive

A

26,461 mm/yr in 1861

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5
Q

What was the highest rainfall in the Uk

A

Sprinkling Tarn (Scarfell Pike, Cumbria)

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6
Q

How much annual rainfall was at scarfell pike

A

6,528 mm/yr in 1954

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7
Q

What is rainfall measurement about

A

The areal integration (average across an area) over a network of point measurements (individual raingauges catches)

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8
Q

How many gauges are the UK Meteorological Office network

A

6,800 raingauges

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9
Q

What are most of the gauges at the UK meteorological office

A

Daily storage gauges though they also have a number of monthly storage gauges and rainfall recorders

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10
Q

What is a monthly storage gauge

A

Volumetric measurements taken after a month of collection

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11
Q

What do rainfall recorders do

A

Rainfall intensities recorded automatically on charts or electronic data loggers

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12
Q

How far above ground does the MET office mark II storage gauge stick

A

30cm

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13
Q

Why is the top of the Met price mark II storage gauge sharp

A

So when raindrops hit it they are chopped. Knife edge

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14
Q

What does the drop above funnel in the Met office mark II storage gauge prevent

A

Out splash - water jumping out

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15
Q

Why is the above funnel of the Met office mark II storage gauge narrow

A

To minimise evaporation that’s coming out of the bottle between daily measurements

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16
Q

Why does the Met office mark II storage gauge use a glass bottle inside

A

To prevent water from being attracted to side of bottle when you upend it so all water comes out

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17
Q

Why is the Met office mark II storage gauge 1ft above ground

A

Reduces insplash

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18
Q

Why is the base of the Met office mark II storage gauge splayed

A

So when it’s in the ground it’s less likely to move and water is less likely to evaporate

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19
Q

Why is there an outercan in the Met office mark II storage gauge

A

To catch overflow

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20
Q

Example of monthly storage gauge

A

Clougha Pike in Lancaster

21
Q

Why are rainfall recorders useful

A

We might want to know rainfall every 5 mins or 15 mins so we need some form of automated rain gauge

22
Q

What are the different rain gauges

A

Siphoning tank rain gauge.

Tipping bucket rain gauge.

23
Q

What does the siphoning tank rain gauge do

A

Tells rainfall every 15 mins.
Gubbins - rainfall in big funnel getting directly into tank which fills with water. Inside is float connected to arm of gubbin. Arm goes up which is connected to pen that records volume.when at top it pivots and gets emptied and counter weight pulls it back up.

24
Q

What is the chart created in a siphoning rain gauge

A

Hyetogram - need someone in lab digesting data. Not great

25
Q

How does a tipping bucket rain gauge work

A

Inside is a double bucket and rain comes in funnel and first of all fills the inside bucket which tips and fills other bucket. Magnet behind bucket is reed switch so it you bring magnet towards it you can record time on data logger.

26
Q

Why do you need a check gauge in tipping bucket

A

Due to greater error and freezing problems - if it’s frozen and locked nothing happens.

27
Q

What is the effect of sheltering in raingauge sitting

A

Where you put the raingauge affects the total. Should always have an angle of 30* from rain gauge to highest nearest objected. Should be twice the height away if not degree measurement.

28
Q

What is the effect of turbulence on rain gauges

A

If rain isn’t coming down vertically turbulence blows rainfall away from rain gauge on windy days so to counteract you build a Huddleston turf wall. 1.5 m away. Or institute of hydrology ground level gauge, need to generate rough surface so water can’t run straight in.

29
Q

How do you produce rough ground

A

Anti splash grid around gauge in pit

30
Q

What are the problems of snowfall measurement

A

Burial - not much bother in UK bc not for a lot of snow.

31
Q

How do you counter act burial

A

Lift rain gauge above ground so it doesn’t get covered by drift. Need to get rid of turbulence on rain gauge.

32
Q

After elevating the rain gauge to deter drift, how do you combat turbulence

A

Nipher shield

Alter shield - flap around in wind to remove turbulence

33
Q

What are he problems of rainfall measurements in tropical rainforests like Damon valley field centre, Borneo

A

Has to be 40-60m high bc of high trees.

Have to build out of Borneo iron that doesn’t rust but shiny at night so insects dive into it.

34
Q

Why do they have to put walls around rain gauges in Borneo

A

So elephants don’t trample it but only covers one rain gauge

35
Q

What are the 2 things needed for areal estimation of rainfall

A

Catchment average and spatial patterns

36
Q

What are the 6 methods of areal estimation of rainfall

A 
Arithmetic mean
Thiessen polygon
Hypsometric curve
Isohyetal
Radar
Mathematic surface
37
Q

How to work out arithmetic mean of distribution

A

All rainfall and divide by number of gauges.

38
Q

What does arithmetic mean require

A

Even spacing of rain gauges across catchment - uniform distribution. Can’t have relief

39
Q

What is good for the arithmetic mean

A

Simple
Uniform distribution
Flat terrain

40
Q

How does thiessen polygons work

A

Weight total rainfall according to local area that each gauge represents.
Draw line between rain gauge pairs, middle point of that line, draw another line at tangent to first line and join all them up to generate hexagons across catchment. Copes with uneven totals

41
Q

What does the thiessen polygon deal with that arithmetic meal doesn’t

A

Uneven spacing

42
Q

What is bad about the thiessen polygon method

A

Flat terrain required

43
Q

How much more rainfall do you get if you go up a meter

A

1mm more due to orogrqphic enhancement of rainfall

44
Q

What is a better version of the thiessen polygon

A

Altitude corrected thiessen polygon. Bisection point is median altitude

45
Q

How does the hypsometric curve work

A

Curve of precipitation on the top right hand graph and area under the curve gives total rainfall weighted according to altitude

46
Q

What is the isohyetal method

A

At a particular time you have a total amount of rainfall so you can draw lines between equal rainfall. Tot up rainfall for each area and divide by total area. Gives catchment average rainfall but also patterns of rainfall in catchment.

47
Q

What can isohyetal method be subjectively adjusted for

A

Underlying topography

48
Q

What is radar

A

Radar reflectively calibrates against point gauges means. Firing signals into atmosphere and receiving a return of things in the atmosphere

49
Q

What is the mathematical surface method

A

If you got a rain gauge and their totals you can fit mathematical surfaces into it. Kriging is a method for fitting a mathematical surface through data.

Hydrology (9 decks)

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