J Arid Land (2017) 9(4): 530–546 doi: 10.1007/s40333-017-0020-8 Science Press Springer-Verlag ∗ Corresponding author: SUN Jingsheng (E-mail: jshsun623@163.com) The first and second authors contribute equally to this work. Received 2016-12-23; revised 2017-04-23; accepted 2017-05-05 © Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Science Press and Springer-Verlag Berlin Heidelberg 2017 http://jal.xjegi.com; www.springer.com/40333 A proposed surface resistance model for the Penman-Monteith formula to estimate evapotranspiration in a solar greenhouse GONG Xuewen 1,2 , LIU Hao 1 , SUN Jingsheng 1* , GAO Yang 1 , ZHANG Xiaoxian 3 , Shiva K JHA 2,4 , ZHANG Hao 1,2 , MA Xiaojian 1,2 , WANG Wanning 1,2 1 Key Laboratory of Crop Water Use and Regulation, Ministry of Agriculture, Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang 453003, China; 2 Graduate School of Chinese Academy of Agricultural Sciences, Beijing 100081, China; 3 Department of Sustainable Soils and Grassland Systems, Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, United Kingdom; 4 National Maize Research Program, Nepal Agricultural Research Council, Chitwan 44209, Nepal Abstract: Greenhousing is a technique to bridge season gap in vegetable production and has been widely used worldwide. Calculation of water requirement of crops grown in greenhouse and determination of their irrigation schedules in arid and semi-arid regions are essential for greenhouse maintenance and have thus attracted increased attention over the past decades. The most common method used in the literature to estimate crop evapotranspiration (ET) is the Penman-Monteith (PM) formula. When applied to greenhouse, however, it often uses canopy resistance instead of surface resistance. It is understood that the surface resistance in greenhouse is the result of a combined effect of canopy restriction and soil-surface restriction to water vapor flow, and the relative dominance of one restriction over another depends on crop canopy. In this paper, we developed a surface resistance model in a way similar to two parallel resistances in an electrical circuit to account for both restrictions. Also, considering that wind speed in greenhouse is normally rather small, we compared three methods available in the literature to calculate the aerodynamic resistance, which are the r a1 method proposed by Perrier (1975a, b), the r a2 method proposed by Thom and Oliver (1977), and the r a3 method proposed by Zhang and Lemeu (1992). We validated the model against ET of tomatoes in a greenhouse measured from sap flow system combined with micro-lysimeter in 2015 and with weighing lysimeter in 2016. The results showed that the proposed surface resistance model improved the accuracy of the PM model, especially when the leaf area index was low and the greenhouse was being irrigated. We also found that the aerodynamic resistance calculated from the r a1 and r a3 methods is applicable to the greenhouse although the latter is slightly more accurate than the former. The proposed surface resistance model, together with the r a3 method for aerodynamic resistance, offers an improved approach to estimate ET in greenhouse using the PM formula. Keywords: canopy resistance; surface resistance; aerodynamic resistance; sap flow system; micro-lysimeter; weighing lysimeter Citation: GONG Xuewen, LIU Hao, SUN Jingsheng, GAO Yang, ZHANG Xiaoxian, Shiva K JHA, ZHANG Hao, MA Xiaojian, WANG Wanning. 2017. A proposed surface resistance model for the Penman-Monteith formula to estimate evapotranspiration in a solar greenhouse. Journal of Arid Land, 9(4): 530–546. doi: 10.1007/s40333-017-0020-8