Hydrology – Precipitation i.e. Rainfall

Precipitation

Precipitation is any type of moisture reaching ground from atmosphere. When the water vapour reaches saturation, it gets densed which is also be called condensation. It forms tiny water droplets in cloud. Rain, fog, snow, ice, etc are all forms of precipitation. Forms of precipitation can be tabulated..

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Precipitation can broadly be classified in two forms Water droplet and Ice crystal, which depending upon sizes can be further classified in rain, drizzle, snow, slit, hail.

 

Rainfall season

There are mainly three seasons Summer, Winter and Monsoon.
There are three rainfall seasons too. They are Monsoon season, Post Monsoon season and Winter rains

  • Monsoon Season – Duration of the season is last week of may to first week of October. It covers whole India except Tamilnadu and Jammu & Kashmir. South-West winds cause these rains.
  • Post-Monsoon Season – Duration of this season is first week of November to first week of December. Only Tamilnadu and Jammu & Kashmir receives rain in this season. North-East winds cause these rains.
  • Winter Rains – From December last week to February last week this rain falls over areas of J&K and surrounding extreme north. This includes snowfall and rainfalls.

 


Kerala and Assam receives first rain of the Monsoon Season, whereas Delhi receives very last rain after whole India had experienced the Monsoon.


Measurement of Rainfall (Precipitation)

The statistics of precipitation are used as base for many hydrological studies. It plays a role of basic input in hydrological analysis. Thus Measurement of rainfall i.e. precipitation data is important.

Considering the rain fallen on a plane ground and measuring the vertical height of the water will give the precipitation. It is considered that the precipitation retained where it fell.

As the parameter of measurement of depth is measurement of precipitation, unit of precipitation is millimeter or centimeter.

The ground is not even or plane anywhere. To measure rainfall Rain-gauges are made. Raingauges can also be called as Ombro-meters or Pluviometers. They can either be recording type or non recording type.

 

Types of Rain-Gauges :

  1. Non-Recording type – These are very cheap and simple working. These type of rain gauges are only able to measure rainfall.
  2. Recording type – These are costlier than other. These gauges record each and every detail of rainfall.

 

* Non Recording type rain gauges –

  • Symon’s Gauge
  • Indian Standard (IMD) Rain Gauge

 

* Recording type rain gauges –

  • Weighing Bucket Rain-gauge
  • Tipping Bucket Rain-gauge
  • Float Type rain-gauge or Syphon’s Rain-gauge
  • Radar Measurement

 


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