Section 3

Question 1

Probable Maximum Precipitation

Answer 1

• Greatest amount of precipitation that would be physically possible in
  a given location at a specific time of year
• Represents the maximum amount of moisture that could be held in
  the atmosphere

Question 2

Density of fresh snow in terms of water

Answer 2

Density
* Fresh snow has density of approximately
10% of liquid water

Question 3

Snowwater Equivalent (SWE)

Answer 3

Liquid water generated from melted snow

Question 4

Ablation

check if correct definition

Answer 4

combined processes (such as sublimation, fusion or melting, evaporation) which remove snow or ice from the surface of a glacier or from a snow-field; also used to express the quantity lost by these processes (2) reduction of the water equivalent of a snow cover by melting, evaporation, wind and avalanches.

Question 5

precipitation examples & formation

Answer 5

*Precipitation includes rainfall, snowfall,
hail and sleet
* Formed by condensation of water
vapour on condensation nuclei

Question 6

Orographic Precipitation (Mountain-Related) Storm type

Answer 6

How It Forms:
Air is forced to rise over mountains, cools as it ascends, and causes condensation.
The windward side of the mountain experiences heavy rainfall.
The leeward side (downwind) gets very little rain, creating a rain shadow effect.
Example Locations:
British Columbia (Canada) – Heavy rain on the coast, dry interior.
Himalayas – Wet conditions in India, dry regions in Tibet.
Key Features:
✅ Long-duration rainfall.
✅ Heavy rainfall on windward side, dry on leeward side.
✅ Common in mountainous regions.

Note:
Windward Side: facing the wind (where air is forced to rise).Wet, cloudy, and rainy – air cools, condenses, and forms precipitation.
Leeward Side :The side of the mountain sheltered from the wind (air moves downward). Dry and warm – air descends, warms up, and absorbs moisture (creating a rain shadow effect)

Question 7

Convective Precipitation (Thunderstorm-Related)

Answer 7

How It Forms:
Sun heats the surface, causing warm, moist air to rise.
As it rises, it cools rapidly, forming clouds and thunderstorms.
Rapid condensation leads to intense, short-lived rainfall.
Example Locations:
Tropics (e.g., Florida, Amazon Rainforest) – Frequent thunderstorms.
Prairies & Midwest (Canada/US) – Afternoon summer storms.
Key Features:
✅ Short-duration, high-intensity rainfall.
✅ Common in warm climates & summer months.
✅ Can cause flash floods & hail

Question 8

Cyclonic (Frontal) Precipitation (Large-Scale Storms)

Answer 8

How It Forms:
Warm air meets cold air at a front (either a warm front or cold front).
Warm air rises above the cold air, cools, and condenses into clouds & rain.
Cold fronts cause intense rain over a short time.
Warm fronts cause lighter, steady rain over a long time.
Example Locations:
Atlantic Canada (Nova Scotia, Newfoundland) – Frequent low-pressure storms.
UK & Europe – Common in winter.
Key Features:
✅ Large, long-lasting storms.
✅ Occurs at warm & cold fronts.
✅ Can bring rain, snow, or hurricanes (tropical cyclones).

🌟 Quick Comparison Table
Storm Type How It Forms Rainfall Intensity Duration Example Locations
Orographic Air forced over mountains Moderate to heavy Long BC, Himalayas
Convective Heating causes air to rise Very intense Short Florida, Prairies
Cyclonic (Frontal) Warm & cold air masses collide Moderate to heavy Long Atlantic Canada, UK
💡 Key Takeaways
✅ Orographic storms occur in mountains due to rising air.
✅ Convective storms are short but intense, caused by surface heating.
✅ Cyclonic storms form at fronts, producing widespread rainfall.

Question 9

3 primary characteristics of rainfall events

Answer 9

Rainfall events have 3 primary
characteristics:
* Intensity
* Duration
* Frequency

Question 10

Return period definition

Answer 10

: the average period of time in years expected between rainfalls of a specific intensity

Question 11

Time of concentration (Tc)

Answer 11

The Time of Concentration of a
catchment represents the travel time
of a wave to move from the
hydraulically most distant point in the
catchment to the outlet
* If the storm duration is equal to or
greater than Tc the whole watershed
will be contributing flow to the outlet Once the “time of concentration” of the watershed has been reached, we can assume
an equilibrium condition in which the runoff rate is equal to rate of effective rainfall.
* We select a storm duration that is equal to the time of concentration of the
watershed, and obtain a rainfall intensity, i, for a design return period from an IDF
curve.
* This means that we will be modeling the worst case scenario…the highest rainfall
intensity that lasts long enough for the whole watershed to contribute at once