The Hydrological Role of Vegetation

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Last Updated on July 29, 2018 by Naeem Javid Muhammad Hassani

THE HYDROLOGICAL ROLE OF VEGETATION IN A WATERSHED: OR 

EFFECT OF VEGETATION ON STREAM FLOW/ WATER YIELD/ EROSION:

Vegetation affects in the following ways:

  1. Interception
  2. Root effects
  3. Shoot effects
  4. Temperature regulation
  5. Physical effects
  6. Chemical effects
  7. Transpiration
  8. Minimize erosion
  9. Nitrogen fixation
  10. Soil fertility



Interception:- (interception loss )

The amount of water which is intercepted is called Interception.” Interception can be technically defined as the capture of precipitation by the plant canopy and its subsequent return to the atmosphere through evaporation or sublimation.

Net interception = gross interception – Effective precipitation

(Where; effective precipitation = stem flow + branch flow, etc)

Interception - Forestrypedia

Interception occurs in two strata of vegetation, the canopy and in the litter. The interception is important because,

  • Precipitation (Ppt) retarded by the canopy is subjected to evaporation and finally last for stream flow.
  • Ppt without vegetation cover falls freely and covers the soil uniformly.
  • A delay in the time when the rain reaches the ground usually raindrops falling from drip points has the larger size and having more K.E than free-falling rain.
  • Litter on the ground forms also part of the vegetation. It causes interception and losing it again by evaporation. Therefore vegetation increases the interception and decreases the defective ppt.

Precipitation that is not intercepted can be influenced by the following processes: (as shown in above figure)

  • Stemflow – is the process that directs precipitation down plant branches and stems. The redirection of water by this process causes the ground area around the plant’s stem to receive additional moisture. The amount of stemflow is determined by leaf shape and stem and branch architecture. In general, deciduous trees have more stemflow than coniferous
  • Canopy drip – some plants have an architecture that directs rainfall or snowfall along the edge of the plant canopy. This is especially true of coniferous On the ground, canopy drip creates areas with a higher moisture content that are located in a narrow band at the edge of the plant canopy.
  • Throughfall – describes the process of precipitation passing through the plant canopy. This process is controlled by factors like plant leaf and stem density, type of the precipitation, the intensity of the precipitation, and duration of the precipitation event. The amount of precipitation passing through varies greatly with vegetation type.

Root effects:

  • The superficial/ shallow root system can penetrate up to surface soil to sub-surface soil whereas deep root system can penetrate up to parent material
  • Root system increases porosity which increases the storage of water that results in less runoff/ streamflow and thus regulating water yield and decreasing erosion.
  • Photosynthesis processes need water thus the absorption of water is needed. Water is taken up by plants by the process of Osmosis. Similarly, transpiration loss also results in the taking up of water by plants through roots. Thus soil becomes deficient in moisture/ water. The infiltration and percolation capacity of the soil increases. All these effects become the resultant of less runoff/ erosion, and increased water yield.

Shoot effects:

  • Of all the effects caused by the shoots, the most important one is ‘Interception’ which has been discussed in detail (above).
  • Leaves/litter cover the surface of the soil. When precipitation falls on the ground these decrease its Kinetic Energy, similarly, the momentum is also reduced. Water gets more time to infiltrate and percolate thus less runoff and erosion and increased water yield.
  • Transpiration is the loss of water from Cuticle of the leaf. It is one of the important factors determining the amount of water in the soil. As explained in the Photosynthesis process.
  • Litter when decomposes converts into humus and organic matter. These increase the porosity of the soil thus more chance of infiltration and percolation and regulated water yield.
  • Leaves also reduce the velocity of runoff, thus yet again water gets more time to infiltrate and percolate. These increase the absorption in the soil
  • The shade of vegetation regulates the melting of snow and increases the time to melt and to be absorbed in the soil.

Other hydrologic roles of vegetation:

  1. Temperature regulation
  2. Physical effects
  3. Chemical effects
  4. Transpiration
  5. Minimize erosion
  6. Nitrogen fixation
  7. Soil fertility

For correction and improvements please use the comments section below.




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Naeem Javid Muhammad Hassani

NJMH is working as Deputy Conservator of Forests in Balochistan Forest & Wildlife Department (BFWD). He is the CEO of Tech Urdu (techurdu.net) Forestrypedia (forestrypedia.com), Majestic Pakistan (majesticpakistan.pk), All Pak Notifications (allpaknotifications.com), Essayspedia, etc & their YouTube Channels). He is an Environmentalist, Blogger, YouTuber, Developer & Vlogger.

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