Agricultural Water Management 128 (2013) 55–64 Contents lists available at SciVerse ScienceDirect Agricultural Water Management j ourna l h omepage: www.elsevier.com/locate/agwat Estimation of regional irrigation water requirement and water supply risk in the arid region of Northwestern China 1989–2010 Yanjun Shen a,∗ , Shuo Li a,b , Yaning Chen c , Yongqing Qi a , Shuowei Zhang d a Key Laboratory for Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China b College of Resources and Environmental Sciences, Hebei Normal University, Shijiazhuang 050016, China c State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China d Department of Geography, The State University of New York-Buffalo, Buffalo, USA a r t i c l e i n f o Article history: Received 9 November 2012 Accepted 21 June 2013 Keywords: Irrigation water requirement Crop water requirement Water resources Penman–Monteith equation Water supply risk Arid region in Northwestern China (ARNWC) a b s t r a c t Water use in agricultural sector shares more than 90% of the total water withdrawal in the arid region of Northwestern China (hereafter, ARNWC). Irrigation water demand is therefore essential to the water resources allocation to economy and natural ecosystems in the highly water deficit region. In this study, we analyzed the spatial and temporal variations of irrigation water demand as well as crop water require- ment by combining the modified Penman–Monteith equation recommended by FAO and GIS technology. Crop and irrigation water requirements for 5 main crops, including wheat, corn, cotton, oilseed and sugar beet, from 1989 to 2010 were calculated and the spatio-temporal variations were analyzed. The results suggested that the demand of irrigation water in the ARNWC showed increasing trend during the past two decades, which mainly caused by fast increase in cotton cultivation areas, because irrigation water requirement for cotton was much larger than the other crops. The changes in cotton growing area sig- nificantly affected the spatial pattern of water demand. A total of 44.2 billion m 3 water was withdrawn for irrigation in year 2010. Larger amount of water was consumed for crops in Northern Xinjiang and Tarim River Basin than Qilian-Hexi region. Irrigation water requirement reaches its maximum in July and August. It is revealed that the critical period for water supply is during April and May through comparing the monthly irrigation water requirement with water availability, i.e. river discharge. Even though the annual water resources are much larger than the requirement, but for some basins, there is severe phys- ical water shortage during the critical water use period in April and May. The water resource supply is expected to be facing more difficulties in future. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Water is one of the essential resources in arid and semi-arid regions especially for agriculture. The arid region in Northwestern China (ARNWC) is one of the mostly water stressed regions in the world (Shen and Chen, 2010). This region is also an important food- and cotton-producing region in China, but the imbalance between water supply and demand is also very prominent in the region. Agricultural irrigation consumed most water resources in this region, and accounted for 91.8% of the total water consumption (Geng et al., 2006). The shortage of water resources has become a major limiting factor for the socio-economic development in the ARNWC. Even in places with relatively abundant water resources, it is not sufficient to meet the water demand of crop growth all the year round. With increasing acreage of crop growing, unreasonable ∗ Corresponding author. Tel.: +86 311 85825464; fax: +86 311 85815093. E-mail address: yjshen@sjziam.ac.cn (Y. Shen). crop planting structure, high irrigation quota, and low water use efficiency, the shortage of water resources is becoming increas- ingly serious. Therefore, quantifying agricultural irrigation water demand in the region, and analyzing the spatial and temporal characteristics of the irrigation water demand, are of importance to help improve the water management toward sustainable use. Currently, there are several methods to calculate crop irrigation water requirement, including ground observation (based on crop planting structure and irrigation model), the crop model method, the remote sensing method, and the Penman–Monteith method recommended by the UN Food and Agriculture Organization (FAO). Ground observation can help calculating accurate water consump- tion estimation at farmland scale, but can hardly estimate the water requirement in a region. Remote sensing method always com- bines with ground meteorological observations and crop survey to estimate crop water demand (Ma et al., 2005; Mohamed et al., 2004). However, due to the error originated from the spatial and temporal resolutions of remote sensing data, there are still many technical issues need further, e.g. the interpolation method from 0378-3774/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.agwat.2013.06.014