Surface Hydrology 1: Precipitation

Question 1

What is the significance of a hyetograph?

Answer 1

A hyetograph is a plot of rainfall (precipitation) over time, useful for analyzing rainfall intensity and patterns

Question 2

What are the main processes that lead to vertical movement of air?

Answer 2

Convection: Local heating of surface air.
Orographic ascent: Air forced over a mountain.
Shear ascent: Wind shear causing turbulence.
Frontal ascent: Collision of air masses leading to uplift.

Question 3

What is relative humidity, and how is it calculated?

Answer 3

Relative humidity r = e_d / e_a × 100, where e_d is the actual vapor pressure and e_a is the saturation vapor pressure.

Question 4

What is the maximum amount of water vapour an air parcel can hold dependent on?

Answer 4

Temperature

Question 5

When does an air parcel become saturated?

Answer 5

Dew point

Question 6

What are the key types of manual rain gauges?

Answer 6

Common types include the Met Office Mk 2, Snowdon, Octopent, and Bradford gauges.

Question 7

When does condensation happen?

Answer 7

When air masses are cooled down until they reach their dew point

Question 8

What is absolute humidity?

Answer 8

The mass of water vapour per unit volume of air

Question 9

What is a tipping bucket rain gauge, and how does it work?

Answer 9

A tipping bucket rain gauge measures rainfall by collecting water in a small bucket, which tips when a set amount of water is collected, recording each tip.

Question 10

How do manual gauges vary?

Answer 10

• Orifice diameter
• Height above ground
• Shape

Question 11

What is the role of weather radar in measuring precipitation?

Answer 11

Weather radar measures backscattered microwave radiation from water droplets, providing spatial precipitation data. Uses a narrow beam

Question 12

What factors influence the accuracy of rain gauge measurements?

Answer 12

Errors can arise from airflow deflection around the gauge (upward or downward), leading to inaccurate readings

Question 13

How do satellites measure precipitation?

Answer 13

Satellites use active and passive microwave sensors and infrared data to measure cloud properties and precipitation, as seen in systems like the Global Precipitation Measurement Mission.

Question 14

Why is spatial interpolation necessary for precipitation data?

Answer 14

Precipitation is measured at points, so interpolation is needed to estimate the total flux over a catchment area, which is critical for water balance calculations.

Question 15

What are isohyets, and what is their purpose?

Answer 15

Isohyets are lines of equal precipitation, drawn by hand or software, used to estimate spatial precipitation patterns in a catchment. Accurate but subjective

Question 16

What is the intensity-duration-frequency (IDF) curve?

Answer 16

An IDF curve relates the intensity, duration, and frequency of rainfall events, which is important for storm analysis and flood risk assessment.

Question 17

What makes it difficult to detect trends in rainfall?

Answer 17

The inherent stochastic nature of precipitation

Question 18

What is kriging, and how is it used in hydrology?

Answer 18

Kriging is a statistical method for interpolating point observations, commonly used in Geographic Information Systems (GIS) for spatial analysis of precipitation data.

Question 19

What is the importance of rainfall frequency analysis?

Answer 19

Rainfall frequency analysis examines both the magnitude and duration of rainfall events, which helps predict the likelihood of extreme weather events like floods

Question 20

What is the assumption that can be made for IDF curves?

Answer 20

Precipitation can represented as a statistical phenomenon with stationary characteristics -> may be invalidated by climate change