Abstract: In this study, the semivariant function analysis, model selection and spatial interpolation analysis on groundwater depth in the years of 1986, 1991, 1996, 2001, 2006 and 2010 were carried out based on the monitoring data of groundwater depth in Linze County in middle reaches of the Heihe River Basin during the period of 1984-2010, GS⁺, ArcGIS and geostatistics. The results showed that the groundwater depth in all the irrigated areas in Linze County was holistically in a drawdown under the effects of topographic conditions and land use change. Monthly fluctuation of groundwater depth was very low in the Gobi deserts and riparian wetlands, its curve was bimodal in oasis cropland ecosystem, oasis marginal zone and oasisdesert ecotone, and the two peaks occurred in May and December. The theoretical model of groundwater depth is an exponential model. Spatial change of groundwater depth was mainly caused by the structural factors, such as climate change, terrain and geology conditions. There was no significant regional difference of groundwater depth change. Groundwater depth was deep in the south and north areas but shallow in the central area. Area of the regions where groundwater depth was shallower than 4 m  was reduced by 337.01 km² and accounted for 12.58% of the total area in the county; however, the proportion of area of the regions where groundwater depth was deeper than 6 m was expanded by 66.7%.

Key words: groundwater depth, geostatistics, landscape zone, spatiotemporal variation, Linze County, Heihe River Basin