| Based on the biological characters of different vegetations,the ecological water demand of crops in every 10 days from March to October was estimated,and the variations of the planting area of crops,the irrigation area and the water demand of croplands and natural oasis in recent 20 years were analyzed,by using the meteorological data of Zhangye and Ejinaqi observatories.The results showed that the area of cash crops was increased while that of grain crops was dropped by 26.6%,as a result of industry structure adjustment in the oasis region.There were differences of the apex of water demand among wheat,corn and forests,i.e.,their apex time was the middle ten days of June,the middle ten days of August and the last ten days of August,and the apex quantity of was 6.14mm,8.6 mm and 8.0 mm respectively.The apex time and amount of regional average ecological water demand in the artificial oasis was the middle ten days of June and 6.37 mm/d,and that in the natural oasis was the last ten days of August and 6.06 mm/d.As for the whole Heihe valley,the apex time of water demand was the middle and last ten days of June,and the apex amount was 6.03 mm/d.The time discrepancy of water demand between the artificial oasis in the middle reaches and the natural oasis in the lower reaches of Heihe valley provides the basis for reasonable distribution of water resource. |