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Mandy McLean

Title:Graduate Student, Department of Environmental Earth System Science
Primary Affiliation:Department of Environmental Earth System Science
Office Location:Geocorner 208
Research Group:Hydrogeology & Water Resources Program
Phone:650-842-0657
E-mail:mdmclean@stanford.edu

Research

Thesis abstract:

This thesis presents a remote sensing-based approach to the quantification of agricultural water consumption in the Zhangye Basin. Water consumed for agriculture is difficult to quantify, especially in regions such as Northwestern China, where groundwater is used extensively and is not monitored or well regulated. One of the best proxies for estimating agricultural water consumption is actual evapotranspiration (ET). Using ET as a proxy for plant water use, this thesis calculates crop specific water consumption for seed corn and wheat in the year 2007 throughout the basin using two different methods, the FAO Single Crop Coefficient method and the Surface Energy Balance Algorithms for Land (SEBAL) method. The motivation for this thesis comes from a booming demand for seed corn, which has given rise to increased production of this variety in the Zhangye Basin, primarily for export to Eastern China. This thesis shows that seed corn can be up to 50% more water intensive than wheat, the main crop it has been replacing in recent years, over a growing season that is approximately 43 days longer. It is therefore important for this agricultural community to be aware of how much additional water will be consumed by this transition. This is particularly important in the Zhangye Basin where groundwater resources are essential for the livelihoods of millions of people and they are extremely limited, yet they are being severely over drafted. Groundwater flow models (Huang, 2012; Wang et al., 2011) conclude that in recent years (2008 to 2010) over 0.1 billion cubic meters of groundwater has been over drafted annually from the Zhangye Basin in the middle reaches. In other words, approximately 110% of the annual groundwater recharge to the Zhangye Basin is being extracted each year. Results from this thesis are compared with available field data, pan evaporation and LAS sensible heat fluxes. Results compare well with the pan evaporation data during the growing season and NDVI values are used to adjust pan evaporation data during the non-growing season to make it more applicable to local surface and weather conditions. The sensible heat flux tends to be underestimated with SEBAL.

 

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