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The plains of the Hexi Corridor are the most productive agricultural lands of Gansu Province in Northwest China. Although rainfall is extremely low (50-200 mm), melt water from the Qilian Mountains is abundant. In the three major inland river basins (the Shiyang, Hei and Shule River Basin) canal irrigation systems distribute the water across the plains. In all three river basins, farmers pump shallow groundwater besides the use of canal water. However, pumping quantities vary largely. In this study we analyze the effect of surface water supply on local groundwater development.
In the downstream sub-basin of the Shiyang River excessive groundwater use led to alarming salinization and desertification rates in the 1990s. Since 2007, local water authorities have implemented strict regulations on farmers' groundwater use, targeting a decrease from 600 million m³ in 2005 to 100 million m³ by 2010. To ease the situation surface water supply to the sub-basin has been increased from 100 million m³ to nearly 300 million m³ over the same time. In the other two river basins, groundwater use only developed since the 1990s and is less excessive. At the same time, groundwater management is less influential. In this paper we explore whether surface water re-allocation at an early stage of groundwater development could avoid groundwater over-use later on. We try to answer this question by analyzing the relation between surface water supply and groundwater use based on primary survey data. Our dataset consists of 157 household questionnaires and 15 village leader and well operator questionnaires.
Our findings show that in some districts groundwater use increased over the last ten years due to reduced surface water supply, while in other districts groundwater use decreased as a result of improved surface water supply. In 2013, 67 households used surface water only, while 90 households also used groundwater. A multivariate analysis shows that surface water supply is the most important factor determining spatial variation in farmers groundwater use. The total water use of groundwater using farmers is twice as much as the water use of farmers who only use surface water. The difference is the result of significantly larger cropping areas and more intensive crop water requirements.
We conclude that in the Hei and Shule River Basin water authorities could re-allocate surface water to achieve a more balanced spatial distribution of groundwater use. But, because groundwater use goes hand in hand with land expansion and increased crop water requirements, additional measures are needed to achieve real water savings. Nevertheless, improved surface water supply could increase farmers' acceptance toward groundwater regulations.
