السلام عليكم
قرأت بمجله علميه ان العلماء الاوستراليين يعزون تشكل صحراء بقلب استراليا لدور الانسان في تخريب الغابات (عن طريق قطع الاشجار) مما ادى بمرور الزمن لارتفاع حراره التربه بتلك المنطقه وبالتالي ارتفاع الظغط
وعندما ننظر لتوزع الامطار هذا الموسم نجد ان دول جنوب اوروپا التي تحتل فيها الغابات مساحات واسعه تشهد موسما مطيرا للغايه (تجاوز ال 1000 ملمتر بعديد المناطق من شمال ووسط ايطاليا وغرب اليونان) بينما بالضفه المقابله لهم (اي بالوطن العربي) وعلى بعد مسافات لا تتجاوز 300/500 كيلومتر نعاني من نقص الامطار(اغلب الوطن العربي لم تتجاوز به كميه الهطول 300 ملمتر بعد)
فهل ان ضعف مساحه الغابات بالوطن العربي سيتسبب على المدى الطويل بتصحر منطقتنا (مثلما صار بوسط اوستراليا) ونحن نشهد الان بدايه هذا التغير؟
http://www.ciesin.columbia.edu/docs/...9/002-159.html
n order to determine the effects of deforestation, Meher-Homji (1980a, 1980b) selected two groups of meteorological stations with long records of rainfall and rainy days in the Western Ghats. One group of stations had undergone considerable loss of forests in their vicinity (in recent years); the other group was free of such devastation. A statistical comparison produced at least some evidence of declining tendency of rainfall and rainy days becoming more apparent after large-scale deforestation.
For the Nilgiri district, Padmavalli (1976) noted a change in the pattern of the normal rainfall years with the reduction in the wooded land. The area under forest diminished from about 65% in 1944 to 50% in 1961 and 43% still later on. Corresponding to these changes, the normal rainfall years waned from 47% in the earlier period to 36% in the later. Udhagamandalam (Ootaeamund), the hill station of this district, also presents a waning trend of rainfall in association with declining forest cover. Average rainfall and number of rainy days of successive 20-year periods, as well as 20-year moving averages, show a net decline for recent years, the record lowest rainfall being 800 mm in 1982 (Meher-Homji, 1984). The average 20-year rainfall has declined from 1415 mm in 1902-1921 to 1200 mm for the 20-year period 1965-1984. The corresponding decline in rainy days is from 106 to 89, a decline of 16%. Legris and Blaseo (1969) observed diminishing rainfall for Udhagamandalam from the turn of the century. The frequency of dry years with less than 1300 mm of rainfall increased from eight years between 1902 and 1922 to 12 years between 1954 and 1964, with six consecutive years receiving less than this mean value. von Lengerke (1977) stated that the sub-normal rainfall of the years 1967-1970 at Udhagamandalam led farmers and planters to suggest a change of climate, but he himself found no clear indication of a large-scale shift in rainfall. At the same he noted a decrease from 1965 onwards.
The number of rainy days reported for this station for the five-year period 1886-1890, excluding the months June, July and August, when the rains are of monsoonic origin and not local, was 417 (Meher-Homji, 1984). The figures for the successive five-year periods presented in table I bring out the diminishing tendency of rainy days, though the decline is not gradual. The percentage decline in rainy days from the period 1886-1890 to the period 1978-1982 is of the order of 35% although one should make allowance for instrumental and observational difficulties. figure 1 depicts the vegetation of Nilgiri district. It shows (a) the area remaining under forest at present and (b) the area that was under forest till recently (according to the Survey of India topographic map) but that has been subsequently converted into degraded vegetation and grassland or transformed into plantations of tea, coffee and forest species, food-crop cultivation or lakes (Bellan, 1985; Gaussen et al., 1961).
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رد: مناقشة الأحوال الجوية الحاليه والمتوقعه من 1 فبراير وحتى 15 فبراير لعام 2014
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