Precipitation MCQ Quiz - Objective Question with Answer for Precipitation - Download Free PDF

Explanation:

A Symons rain gauge is a non-recording type of rain gauge. It collects rain in a cylindrical container, and the collected water is then measured using a measuring glass or cylinder with a graduated scale to determine the depth of rainfall manually, usually in millimeters.

Additional Information A digital display –

• Digital displays are used in modern automated rain gauges, not in the traditional Symons rain gauge.
• Symons rain gauge is a manual instrument and does not involve electronics or digital readouts.

A rotating drum –

• This is typically found in self-recording rain gauges (like the tipping bucket type with chart recorders), not in the Symons type.
• The Symons rain gauge does not use any mechanical recording device.

A pressure sensor –

• Pressure sensors are used in advanced weather instruments but are not part of the Symons rain gauge design.

Isohyets: It is a line joining points of equal rainfall for a given interval. Isohyets are contours of equal precipitation analogous to contour lines on a topographic map.

In the isohyetal method, precipitation values are plotted at their respective stations on a suitable base map, and isohyets are drawn to create an isohyet map.

Different forms of Precipitation are as follows:

i) Rain: It is the most common form of precipitation. In this the water droplet size are larger than 0.5 mm and smaller than 6 mm.

On the basis of intensity, rainfall is classified as:

ii) Snowfall: 

• Snowfall is another important form of precipitation. Snow is made up of ice crystals which usually combine to form flakes.
• When these flakes reach the earth’s surface then snowfall occurs. The average density of snow is 0.1 g/cm3.

iii) Drizzle: 

• A fine sprinkle of numerous water droplets which have size less than 0.5 mm and intensity of these water droplets is less than 1 mm/hr, then we call them drizzle.

iv) Glaze: 

• When the water droplet (rain or drizzle) come in contact with ground which have a temperature near about 0° C or less than it, these water drops freeze and form ice coating on ground surface which is called glaze or freezing rain.

v) Sleet: 

• It is frozen raindrops which have transparent grains. These are formed when rainfall is at subfreezing temperature.
• Sleet denotes both rain and snow and the size of sleet is less than 5 mm.

vi) Hail: 

• It is a large size of snow which have size greater than 8 mm. They are in the form of irrigator pellets or lumps of ice.

Explanation:

ϕ Index: 

• It gives the total runoff depth of a catchment is defined as the constant infiltration capacity that would yield the actual total runoff for a given rainfall amount and is represented as

Φ = (P-R/t) 

Φ-Index = (Precipitation-Total Runoff Depth/Duration of Excess Rainfall)

Calculation:

Rainfall excess = i = P - Φ × t

i = 1.6 - 0.20 × 5 = 0.6 cm = 6 mm

Explanation:

Factors Influencing Precipitation

The type and amount of precipitation that falls in a given area are influenced by several factors such as vegetation type, orographic lift, Earth's axial tilt, and proximity to bodies of water. Here's a detailed analysis of each option:

1. "Vegetation type" (Influences Precipitation)

   • Vegetation can influence precipitation through processes like transpiration and affecting local humidity levels.

   • Dense vegetation can lead to increased local rainfall due to higher moisture content in the air.

2. "Orographic lift" (Influences Precipitation)

   • Orographic lift occurs when air is forced to rise over a mountain range, causing cooling and condensation, leading to rainfall.

   • This process is responsible for significant precipitation on the windward side of mountains.

3. "Earth's axial tilt" (Does NOT directly influence Precipitation)

   • Earth's axial tilt primarily affects the seasons and the distribution of solar energy, not the immediate type and amount of precipitation in a specific area.

   • While it does influence broader climate patterns, its impact on local precipitation is indirect.

   • Therefore, it is the correct answer for the factor that does NOT directly influence precipitation.

4. "Proximity to bodies of water" (Influences Precipitation)

   • Bodies of water provide a significant source of moisture for the atmosphere, leading to increased evaporation and subsequent precipitation.

   • Regions close to large water bodies often experience higher humidity and more rainfall.

Concept

While selecting the site for rain gauge stations the following points should be considered:

• The site should be on level ground and on open space. It should never be on sloping ground.
• The site should be such that the distance between the gauge station and the objects (like a tree, building, etc) should be at least twice the height of the objects.
• In the hilly area, where level ground is not available, the site should be so selected that the station may be well shielded from high wind.
• The site should be easily accessible to the observer.
• The site should be well protected from cattle by wire fencing.

Concept:

Precipitation- It is the fall of water in various forms on the earth from the clouds.

The usual forms of precipitation are as follows:

Note:

Concept

The optimum number of rain gauges is given by

\(N = {\left( {\frac{{{C_v}}}{\epsilon}} \right)^2} \)

Where,

Cv is the coefficient of variation

ϵ is error percentage

The coefficient of variation is given by

\({C_v} = \frac{{{\sigma _{n - 1}}}}{{\bar P}}\)

Where,

\(\bar P\) is average rainfall

σ is the standard deviation

Calculation:

Given,

Number of Rain gauge = 5, error = 6 %, C_v = 20

The optimum number of rain gauge → n = (20/6)² = 11.11 we take it as 12 

∴ The number of Optimum Gauges = 12.

As asked about the additional number of Stations i.e. 12 - 5 = 7.

∴ Number of Additional Stations = 7

Explanation:

Isohyetal method:

• This method is used to estimate the mean precipitation across an area by drawing lines of equal precipitation and uses topographical and other data to yield reliable estimates.
• Isohyets are contours of equal ppt analogous to contour lines on a topographical map.
• In the isohyetal method, ppt values are plotted at their respective station on a suitable base map, and isohyets are drawn to create an isohyetal map.
• Isohyetal lines are based on interpolation between rain gauge stations. While constructing isohyets, it is assumed that rainfall between 2 stations varies linearly, unless abrupt changes in topography indicate otherwise.
• So, a gently sloped basin is most suitable for linearly changing rainfall and hence for the isohyetal method

For Undulating countries, rainfall will not vary linearly, and for the plain country, rainfall is assumed to be constant over the area, hence the isohyetal method doesn't yield accurate results for these 2 cases but can be used if required

Snow precipitation is generally not taken into consideration for drawing isohyets

Concept: 

N = \({\left( {\frac{{{{\rm{C}}_{\rm{v}}}}}{{\rm{\varepsilon }}}} \right)^2}\)

where

N = optimum number of rain gauges

Cv = Coefficient of variation

\({{\rm{C}}_v} = \frac{{\rm{\sigma }}}{{{\rm{\bar X}}}} \times 100\)

σ = standard deviation = \(\sqrt {\frac{{\sum {{\left( {{{\rm{X}}_{\rm{i}}} - {\rm{\bar X}}} \right)}^2}}}{{{\rm{n}} - 1}}} \)

X̅ = Mean Precipitation

n = number of rain gauge stations

Calculation:

Given,

Coefficient of variation (Cv) = 29.54%

The allowable degree of error in the estimate of mean rainfall (ϵ) = 10 

N = \({\left( {\frac{{{{\rm{C}}_{\rm{v}}}}}{{\rm{\varepsilon }}}} \right)^2}\)

\(\epsilon{} = \frac{{{C_v}}}{{\sqrt n }}\)

\(10 = \frac{{29.54}}{{\sqrt n }}\)

\(\sqrt n = \frac{{29.54}}{{10}} =2.95\)

n = 8.72

n ≈ 9

Concept:

Thiessen polygon method:

In this method, the rainfall recorded at each station is given a weightage on the basis of area closest to the station. The average precipitation over the catchment area is given as,

\({P_{avg}} = \frac{{{P_1}{A_1} + {P_2}{A_2} + {P_3}{A_3} + \ldots {P_n}{A_n}}}{{{A_1} + {A_2} + {A_3} + \ldots {A_n}}} = \frac{{{P_1}{A_1} + {P_2}{A_2} + {P_3}{A_3} + \ldots {P_n}{A_n}}}{A}\)

Where, \(\mathop \sum \limits_{i = 1}^n \frac{{{A_i}}}{A}\) is called the weightage factor

Calculation:

Given,

P_avg = 5 cm

P_B = 5 cm, P_C = 4 cm, P_D = 5 cm

P_A =?

Weightage factor for station A, B, C and D is given, 0.15, 0.25, 0.30 and 0.30.

∵ We know, The average rainfall

\({P_{avg}} = \frac{{{P_A}{A_A} + {P_B}{A_B} + {P_C}{A_C} + {P_D}{A_D}}}{{{A_A} + {A_B} + {A_C} + {A_D}}} = \frac{{{P_A}{A_A} + {P_B}{A_B} + {P_C}{A_C} + {P_D}{A_D}}}{A}\)

5 = P_A × 0.15 + 5 × 0.25 + 4 × 0.30 + 5 × 0.30

5 = P_A × 0.15 + 3.95

P_A = 7 cm

Concept:

\(\emptyset - {\rm{index}} = \frac{{{\rm{P}} - {\rm{R}}}}{{\rm{t}}}\)

Where,

R (Runoff) (m): It is defined as the part of water cycle that flows over land as surface water instead of being absorbed into the ground water or evaporated. Runoff is that part of precipitation that appears in uncontrolled surface streams, rivers drains or sewers.

P (Precipitation) (m): It is any liquid or frozen water that forms in the atmosphere and falls back to the earth. Precipitation is any product of the condensation of atmospheric water vapour that falls under gravity from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail.

Infiltration Capacity: It is the rate at which water infiltrates into ground is called infiltration capacity. For consistency, in hydrological calculations, a constant value of infiltration rate for the entire storm duration is adopted.

The average infiltration rate is called the infiltration index and two types of infiltration indices commonly used:

1. 𝛗 – Index: It is defined as the rate of infiltration above which volume equals the runoff volume.
2. w – index: It is the average infiltration rate during the time when the rainfall intensity exceeds the infiltration rate.

Calculation:

Given, Rainfall (P) = 16cm and t = 6 hours

Runoff \({\rm{R}} = {\rm{\;}}\frac{{1.2{\rm{\;}} \times {{10}^8}}}{{1200 \times {{10}^6}}} = 0.1{\rm{m}} = 10{\rm{cm}}\)

\(\emptyset - {\rm{index}} = \frac{{{\rm{P}} - {\rm{R}}}}{{\rm{t}}} = \frac{{16 - 10}}{6} = \frac{6}{6} = 1{\rm{cm}}/{\rm{hr\;}}\)

Concept:

Optimum number of rain gauges is given by

\(N = {\left( {\frac{{{C_v}}}{ϵ}} \right)^2}\)

Where,

Cv is coefficient of variation

ϵ is error percentage

Coefficient of variation is given by

\({C_v} = \frac{{{\sigma _{n - 1}}}}{{\bar P}}\)

Where,

\(\bar P\) is average rainfall

σ is standard deviation

Calculation

Optimum number of rain gauge is

\(N = {\left( {\frac{{{C_v}}}{ϵ}} \right)^2}\)

When error reduced to half, ϵ' = 0.5ϵ 

\(n = {\left( {\frac{{{C_v}}}{0.5ϵ}} \right)^2} =4{\left( {\frac{{{C_v}}}{ϵ}} \right)^2} \)

Additional rain gauges = n - N = \(4{\left( {\frac{{{C_v}}}{ \in }} \right)^2} - 1{\left( {\frac{{{C_v}}}{ \in }} \right)^2} = 3{\left( {\frac{{{C_v}}}{ \in }} \right)^2}\)= 3N

So, Additional rain gauges are required in a catchment = Thrice the present number

Concept-

Isohyets are the imaginary lines joining the points of equal rainfall.

An isohyet is a contour line drawn on maps that connect places or points that received the same amount of rainfall or precipitation at a given period of time.

It is used to represent areas that received a similar amounts of rain or equal density of rain during a particular storm.

These lines help to estimate the various rainfall parameters like the minimum and maximum, an average rainfall of a particular region.

A map formed by these isohyetal lines is called the isohyetal map.

Important Points

Explanation:

Instruments used in the measurement