سؤال قراءة ستيب محلول — فهم التفاصيل (تدريب 5622)

(1) Human impact on precipitation There are a number of ways in which human activity affects precipitation. Cloud seeding has probably been one of the more successful. Rain requires particles, such as dust and ice, on which to form. Seeding introduces silver iodide, solid CO2 (dry ice) or ammonium nitrate to attract water droplets. (2) Human impact on evaporation and transpiration The human impact on evaporation and transpiration is relatively small in relation to the rest of the hydrological cycle but is nevertheless important. (3) Dams – there has been an increase in evaporation due to the construction of large dams. For example, Lake Nasser behind the Aswan Dam loses up to a third of its water due to evaporation. Water loss can be reduced by using chemical sprays on the surface, by building sand-fill dams and by covering the dams with plastic. (4) Urbanization leads to a huge reduction in evapotranspiration due to the lack of vegetation. There may also be a slight increase in evaporation because of higher temperatures and increased surface storage. (5) Human impact on infiltration and soil water Human activity has a great impact on infiltration and soil water. Land use changes are important. Urbanization creates an impermeable surface, with compacted soil. This reduces infiltration and increases overland runoff and flood peaks. Infiltration is up to five times greater under forests compared with grassland.