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旱灾和水灾都是所谓天灾中封人民严重威胁的灾害。乾旱可以分为两方面:一方面是土壤乾旱,一方面是空气乾旱。所谓土壤乾旱,就是由於土壤中缺乏水份,不能保证使植物得到足够的水份,以供给植物在蒸发上的需要及维持植物所有生活过程正常机能上的需要。所谓空气乾旱,就是虽然土壤中有水份,但由於空气过度乾燥,或者由於空气的高温,而不能保证使植物完成正常的生活过程。因此空气乾旱又可分为乾枯现象和热枯现象。因空气过度乾燥为害
Droughts and floods are all so-called disasters that seriously threaten people in natural disasters. Drought can be divided into two aspects: on the one hand, soil drought and on the other hand, air drought. The so-called soil drought is due to the lack of water in the soil, which cannot ensure that the plants get enough water to supply the plants with the need for evaporation and to maintain the normal functions of all life processes of the plants. The so-called “air drought” means that although there is moisture in the soil, the air can not be guaranteed to complete the normal life process because the air is too dry or because of the high temperature of the air. Therefore, the drought of the air can be divided into dryness and heat dryness. Damage due to excessive air drying