The Role of large scale Vegetation and Land Use in Water Cycle and climate in Monsoon Asia

By: Jannat Iftikhar 16

Nimrah Zahid 17

Summayya Tahir 18

Salma Shehzadi 19

Tayyaba Latif 201

Monsoon

• Monsoon is traditionally defined as

“a seasonal reversing wind accompanied by corresponding changes in precipitation”.

• But now it is used to describe seasonal changes inatmospheric circulation and precipitation associated with theasymmetric heating of land and sea.

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Major Monsoon Systems

• The major monsoon systems of the world consist of

a) The West African and Asia-Australian monsoons.

b) The North and South American monsoons.

c) Asian monsoon

Indian monsoon (South-Asian)

East-Asian monsoon

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Asian Monsoon as a Huge Water Cycling system• Well known land-atmosphere-ocean system.

• Two water channels

a) From Tibetan Plateau to Indian Ocean

b) From Tropical Pacific Ocean towards east and southeastAsian countries

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Asian Monsoon

• This monsoon transports huge amount of water vapours over south, southeast and east Asia.

• This plays an essential role in maintaining cumulus convection and precipitation over “monsoon Asia”.

• Which reinforces the monsoon circulation system through latent heat release.

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Asian Countries

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Impacts of Monsoon

• Monsoon circulation results in cool, dry winters and warm,wet summer over the continents.

• This humid monsoon climate maintains dense vegetation zonecalled “the green belt”. (from tropical southeast Asia to sub-polar Siberia)

• Changes in this convectively active region can result in severedraught, or flood over the large densely populated regions.

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Precipitation

• Most important factor for life on land

vegetation and water resources

• Origins: Tropical monsoon Asia, water vapour transport with C should be moisture source

• Evapotranspiration

• Data from analysis of atmospheric water balance by ECMWF revealed time space characteristics of P C E relationship.

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• Humid tropics: Both C and E contribute, C is main source

• The Indian sub- continent and indo china peninsula, C is larger than E

• In mid to high latitudes: E is source, P is far smaller than in tropics

• Contribution of E to P suggests the essential role of vegetation in surface water balance by transpiration

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• Tropics: C plays role in P, E from vegetative surface is equally important, compare to mid/ high latitudes.

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Is monsoon rainfall decreasing?Impact of deforestation on water cycle

In Thailand rainfall in late monsoon show a remarkable trend from 1950.

•Decrease in rainfall

•Change the surface water balance

•Change the vegetation

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• According to recent model decreasing trend of September rainfall may be due to recent deforestation in Thailand which likely to induce

• Reduction of surface roughness

• Evaporation efficiency

• Increase of albedo

• Which result

evaporation

sensible heating

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Sensible heat and surface heat

• Sensible heat is a thermal energy whose transfer to or from a substance results in a change of temperature.

• When the Sun warms the Earth, warm air rises into the atmosphere. As it rises, it expands and cools. Water vapor condenses out of the cool air to form a cloud, this is called surface heat.

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• Change in surface heating, affects the atmosphericstability, cumulus convection and rainfall.

• However the effect of deforestation decreasing rainfall isnoticeably only in September when southern monsooncurrent has become week.

• In July and August when monsoon current is still strong ittend to change the distribution of rainfall rather thendecrease the overall rainfall amount over the deforestedarea.

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Do Water-Fed Rice Paddy Fields Increase Rainfall in Monsoon Asia?

• Rice paddy fields occupy a huge area in Southeast and East Asia.

• Thailand

• Southern China

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Thailand

• Deforestation and widespread mixed shrub/paddy fields reduce rainfall

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Surface roughness

Bowen ratio

Evaporative efficiency

Southern China

• Water-fed paddy fields increase evaporation compared todrier farmland and fields.

• In June and July, the China plain is strongly affected by theMeiyu (or Baiu in Japanese) frontal activity, which is a majorpart of the Asian monsoon system in East Asia.

• The southwest monsoon current from South and SoutheastAsia is a main moisture source for rainfall in the Meiyu frontalzone.

• Based upon cloud-resolving meso-scale model:

Water-fed paddy fields latent heat flux dominates

Farmland sensible heat flux dominates

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Fig. Land use affects rainfall: simulations by Shinoda and Uyeda (2001) show that where rice paddy fields exist (upper graph), the atmospheric boundary layer becomes wetter than that for the farmland (lower graph), and deep convection easily develops to produce strong rainfall

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Taiga-permafrost system in Siberia• It is well known that one climatic zone corresponds well with

one dominant vegetation type.

• However, we should also note that vegetation over a broadregion effects the atmosphere and also the climate of acountry.

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• This implies that we should consider vegetation and climate as an interactive system rather than one way relation from one to other.

• Eastern Siberia is a broad permafrost zone and taiga forest is distributed on it.

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• Long-term energy and water flux measurement in typical Taiga forest of Lena river basin has revealed some interesting features in the seasonal change of this eco-climate system.

• The east Siberia has the Lena river that starts from south and ends in north in Arctic sea.

• It is the 11th longest river in the world and the 3rd largest river in Asia.

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• In spring snow melt occurs from April to May but sensible heat flux was dominant and latent heat flux was very small or negligible.

• The latent heat flux suddenly increased in June when foliation of trees started.

• Now question arises that why did evapotranspiration started so suddenly?

• The best answer to it is that the melting process of the permafrost and root depth are likely to be closely related to this problem.

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• When depth of melted layer reached 20cm where a large portion

of larch roots are present the foliation and transpiration from theleaves may have started.

• On the other hand we noted that most water vapor forprecipitation in summer is occupied by evapotranspiration fromsurface of this area implying that most water is recyclingbetween vegetation and atmosphere in summer.

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Taiga-permafrost symbiotic system• The hydro-meteorological studies in Siberia have strongly

suggested a symbiotic system of climate and vegetation through the hydrological cycle, where Taiga maintains itself by recycling water between atmosphere and vegetated surface of permafrost layer.

• While the permafrost is also maintained by the Taiga through suppressing sensible heating in summer.

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• This rapid Global warming in Siberia which may be inducing melting of permafrost may affect this “ Taiga-permafrost symbiotic system”

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