Changes of karez showed the trend of first increasing and then declining over the last 60 years.The reasons for the dramatic changes of karez might be attributed to followings:(1)Oasis was expanded gradually in the Turpan basin.The changes of karez were consistent with arable land in 1949-1960,namely both increased,and however,the number and water flow of karez declined with increased arable land since the middle of 1960's.(2)Water supply for karez declined.In the beginning of 1960's,surface water began to exploite and many reservoirs and antiseepage canals were constructed.Eight large and middle reservoirs with a capacity of 0.8 × l0⁸ m³ were constructed in 1993,the total length of antiseepage canals reached 4 774 km,and the seepage ratio was 70%,which caused the decline of water supply for karez.(3)Pumped wells were blindly established around the karez irrigation districts and groundwater was exploited in a plunder manner.There were 127 electric pumped wells at the end of 1966 and the number reached 5309 in 2009.Correspondingly,the annual discharge increased from 1.10 × l0⁸ to 7.04 × l0⁸ m³.Moreover,the layout of pumped wells was unreasonable and lots of them were established in the areas where karez was mainly distributed.The groundwater decline and karez drying-up had seriously negative influences on the Turpan basin,which presented in following aspects:Daily life of residents was influenced and many villages were migrated;The areas irrigated by karezs declined from 2.17 × 10⁴hm² in 1957 to 0.88×10⁴hm² in 2003 and meanwhile,the disaster area caused by drought and windstorm increased;The vegetation area was 12.30 × 10³ hm² in 1975 and it declined to 6.72 × 10³ hm² in 2003,reduced by 45.37%.