The upper and middle reaches of Heihe River Basin (HRB), which is the second largest inland river basin in the arid area of the northern China, was chosen as study area. Based on monthly normalized difference vegetation index (NDVI) derived from MODIS sensor, monthly temperature and precipitation data observed by meteorological stations, DEM and basic geographical information, the authors analyzed the spatio-temporal change of NDVI and its relationship with climate from 2000 to 2015 using empirical approach. It was found that NDVI in the upper and middle reaches of Heihe River basin increased generally; the increasing rate of NDVI in summer was higher than that in autumn and spring; the area with rapid increasing rate of NDVI was mainly located in the oasis along the Heihe river; the significant decrease of NDVI occurred in the urban areas of Zhangye, Jiuquan and other cities. It is concluded that the correlation of NDVI with precipitation in summer was higher than that with temperature, whereas NDVI in spring and autumn exhibited higher correlation with temperature. NDVI in the grassland, gobi and desert far away from the main river had significant correlation with precipitation in summer, but NDVI in oasis adjacent to the main river did not show the significant correlation with precipitation. The memory effects was also recognized when NDVI responding to precipitation. The general time lag of NDVI variation in summer responding to precipitation was about a month, but it could extend to 2 months. The results are proposed to provide references for regional vegetation restoration and ecosystem management.

Based on many data sources, such as basic geographic information, land use and cover information and statistic data of irrigation areas, the authors picked agricultural irrigation areas in the middle reaches of Heihe river as a study area and analyzed the spatial-temporal distributions of ecological water requirement with Penman-Monteith equation and NDVI data. Considering the real water diversion and consumption per unit grain yield, the efficiency of water allocation was also analyzed. The results show that the annual potential evapotranspiration is between 800 and 1200 mm and the peak occurs between June and August. Average annual potential evapotranspiration is between 614 and 999 mm while maximum of demand appears from April to August. Ecological water requirement reduces from southeast to northwest gradually which is relatively larger along the Heihe river. Ground water plays major role in water diversion while underground water is minor. The yield of water diversion is the largest in 2008 and irrigation areas which have more water diversions flock around the Heihe river. Overall, water resource allocation overthere is fair good. Water supply-demand rate around Heihe river is generally greater than 1 while it is opposite in Shandan and Minle. Nearly 80% of the irrigation areas can be considered as efficient or relative efficient regions. There are four irrigation districts are inefficient and only one is short of water diversion. Therefore, adjustment of water diversion in some certain regions with promotion of water saving technology can enhance the efficiency of water allocation roundly. The results provide feasible reference to improve the efficiency of water allocation in arid area.

This research takes oasis in the middle reaches of Heihe Basin in northwestern inland as study area, based on land use data, basic geographic information database, DEM, soil database, climatic data and DEMSP/OLS night light database, applies multiple time-series Logistic stepwise regression model to analyze driving factors for landscape types changes during 1986–1995, 1995–2000, 2000–2010, and reveals to what extent that water resource spatial distribution constrains to cropland and construction land. Conclusions are obtained as follows. 1) No general driving factors affect cropland increasing during each time period, while elevation and human activities present general driving factors for cropland decreasing. General driving factors for construction land increasing are elevation, distance and human activities, which have different driving directions based on different time periods. 2) Pumped wells and waterways share similar influential pattern on cropland and construction land changes with influential scope from 1 km to 1.5 km. Waterways constrain more than pumped wells. 3) The elevation influential scope on cropland and construction land is beneath 3500 m, with main constraint from topographic relief effect. The research results reveal the key instructional meanings for optimizing water and land resources spatial distribution, and improving utilization of water resource in oasis area.

Based on the land use data (1986, 1995, 2000 and 2010) and InVEST model, this paper analyzes the land-use change of the middle reaches of Heihe River in the recent 25 years and simulates the water yield of the study area under different land use patterns. Multiple linear regression model is used to explore the influence on the water yield caused by different land use types. The results show that 1) the main types of land use in the middle reaches of Heihe river are bare ground, grass land and farmland. The structure of land use has been changed a lot since 2000. A large number of farmland has transformed into construction land meanwhile water area starts a substantial reduction. 2) 7.3 is considered as the suitable Z value for the study area. From the perspective of subwatershed, the water depth is diminishing from southeast to northwest. 3) The increase of woodland may restrain the water yield. On the contrary, grassland, construction land and bare ground may promote the water yield. Farmland will cause positive or negative hydrological effects due to the different patterns of utility. These results can provide reference for the balance of oasis’ land and water resources.