Crop Type Change Monitoring by Remote Sensing in an Irrigated District under Water Resources Restrictions

In this paper, the Qingtongxia irrigated area of Ningxia Hui Autonomous Region of China will be used as the study area. The local agriculture depends absolutely on irrigation because of rare rainfall and very dry climate conditions. It is located in the upstream of the Yellow River. In the last few decades, the irrigation area has enlarged a lot under the encouraged land reclamation policy. Serious land salinization problem has been resulted due to the local custom of wasting irrigation. A lot of water was diverted for agriculture. The situation has changed since 2000, however, because the permitted water volume to be diverted from the Yellow River for this district was reduced to about 60% of the former actual water diversion due to the implementation of the water resources reallocation program along the whole Yellow River basin. Under such situation, this irrigated area was forced to adjust their crop planting patterns for water saving purposes. In this study, the evolution process will be monitored using remote sensing technology. Result shows that three aspects of the water resources related problems can be reflected clearly. It is found that new cultivated land has increased a lot in nearly twenty years time. Land salinization problem is also serious due to long time high groundwater level and strong evaporation. Results also show that the irrigated area has adjusted a lot to reduce its irrigation water diversion. It is clearly shown that area of the high water consumption crop such as paddy has reduced, while that of low water consumption crop such as wheat and corn increased more since 1999. It is hoped that the result can help the irrigation manager to make more reasonable irrigation plan in the future. The result will also be of positive meanings to the whole Yellow River basin that will face with long-term water-saving requirement.