DEFORESTATION AROUND THE WORLD - India Environment Portal

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16 Deforestation Around the World Fig. 4. The annual and the seasonal (June, July and August) evaporation anomalies (i.e deforest –forest) for South Asia (a,d), Sri Lanka (b,e) and Southeast Asia (c,f) for 1988. Evaporation is in millimeters (mm) with a contour interval of 200 mm for annual plot and 50 mm for the seasonal plot.
The Climatic Effects of Deforestation in South and Southeast Asia 4. Discussion Deforestation leads to warmer and drier climatic conditions. As a result of deforestation less moisture is available at the land surface, leading to a reduction in evapotranspiration. This in turn leads to an increase in temperature and a decrease in precipitation over land. These changes then work together to alter the moisture convergence in the region. These changes are seen not only during the monsoon season but through the entire year. The monsoon is primarily driven by the pressure gradient created by the differential heating of the ocean and land. Land regions especially the Tibetan plateau warms up more than the Indian Ocean during the summer due to the small heat capacity of land. This creates a thermal low pressure over land and the resulting pressure gradient between ocean and land initiates the monsoon flow. Subsequently, the monsoon is sustained by the release of latent heat into the atmosphere. Therefore warmer temperatures should intensify the monsoon, increasing precipitation over land. But this is not seen in the results. The reasons for this are regionally specific. Over Sri Lanka it is likely that the warming of the land itself is reducing the amount of precipitation. The initial step in the formation of precipitation is the rising of parcels of warm moist air. The air being warm and moist by itself is not sufficient to cause rising motion. For air to rise the density of a parcel of air has to be lower than that of the surrounding air, that is the parcel temperature must be warmer than that of the surrounding (cooler) air. When deforestation warms the air over land, it reduces this difference, creating a more stable atmosphere which inhibits the rising of air and hence also weakens the atmospheric moisture convergence. Therefore even if the atmosphere otherwise holds plenty of moisture this process reduces the amount of precipitation that can form. Therefore the weakened moisture convergence together with the reduced evaporation causes the reduction in precipitation. The conditions are different in the Indian subcontinent where the summer monsoon is at its’ strongest. The warming of the land region now results in a stronger moisture convergence indicating the possibility that the monsoon might become stronger over the region. It is possible that the warming over the Indian subcontinent (which has a smaller magnitude than the warming in Sri Lanka) is insufficient to stabilize the atmosphere. But as discussed in the results section the reduced evapotranspiration at any rate plays the dominant role in reducing the annual and the seasonal precipitation. The changes in the climatic conditions due to deforestation can have a strong impact on society. Warmer and drier conditions can have far reaching consequences in many different ways. The elevated temperatures alone can cause life loss especially if the number of heat waves increases. India would be more susceptible to this as parts of the country experience high summer temperatures prior to the onset of the monsoon, a time during which people are vulnerable to the excess heat. The warm temperatures can also kill livestock and destroy stored goods. The reduction in precipitation in combination with the warmer temperature can have a negative impact on agriculture in the region. These climatic changes can result in reduced crop yields, a shift in the life cycle of the crop and change the length of the growing season and the timing of the harvest. Also the regions that are the best suited for growing crops may migrate. As the warm and dry conditions act as positive feedbacks, deforestation can lead to persistent droughts. This may then result in desertification making some regions no longer viable as agricultural land and marginally habitable regions unsuitable for living. In 17
Page 1 and 2: DEFORESTATION AROUND THE WORLD Edit
Page 5 and 6: Contents Preface IX Part 1 Deforest
Page 9 and 10: Preface Forests are giant reservoir
Page 11: Preface XI thankful to Maja Bozicev
Page 15: Part 1 Deforestation Impacts
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92 5. Conclusions Deforestation Aro
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Geospatial Analysis of Deforestatio
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Unsupervised Classification of Aeri
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10 Deforestation and Waodani Lands
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Deforestation and Waodani Lands in
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11 Sustainable Forest Management Te
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Sustainable Forest Management Techn
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12 Bunjil Forest Watch a Community-
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Bunjil Forest Watch a Community-Bas
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13 Remnant Vegetation Analysis of G
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Remnant Vegetation Analysis of Guan
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Part 3 Preventing Deforestation
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324 3. Results and discussion Defor
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338 Characteristics of livestock pr
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344 Land use systems Aboveground tr
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354 Southgate (1990) Larson (1991)
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356 Barrett (1991) Jones and O’Ne
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366 7. Acknowledgment Deforestation
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