ISSN No. (Print): 0975-1130 ISSN No. (Online): 2249-3239 Optimum Water Allocation between Irrigated and Rainfed Lands in different Climatic Conditions Hadi Ramezani Etedali*, Khaled Ahmadaali**, Abdolmajid Liaghat**, Masoud Parsinejad**, Ali Reaz Tavakkoli*** and Behnam Ababaei**** *Department of Water Engineering, Imam Khomeini International University, Qazvin, IRAN **University College of Agriculture and Natural Resources, University of Tehran. Karaj, IRAN ***Agricultural Engineering Research section, Agricultural Research Center of Semnan Province, Shahrood, IRAN ****Young Researchers and Elites Club, Science and Research Branch, Islamic Azad University, Tehran, IRAN (Corresponding author: Khaled Ahmadaali) (Received 29 April, 2015, Accepted 27 May, 2015) (Published by Research Trend, Website: www.researchtrend.net khahmadauli@alumni.ut.ac.ir) ABSTRACT: In this study, water allocation managements between irrigation and rainfed lands were surveyed in different climate conditions. The optimization model results in the Qazvin Plain indicated net benefit increased under new management in case of water conveyance from 2000, 4000, 6000, 8000 and 10000 meters in a climatically normal year to be 11.1, 13.5, 19.2, 16.6 and 15.8 percent, respectively, while in a wet year 9.0, 10.9, 17.0, 15.9 and 13.4 and in a dry year 8.05, 12.5, 16.1, 19.1 and 19.9, respectively. Barley was the best choice for deficit irrigation in three climate conditions. Depths of deficit irrigation were 20, 25 and 30 mm in the first decade of November and 50, 50 and 60 mm in the second decade of May in normal, wet and dry conditions. Also lentil was the first choice for supplementary irrigation. The best treatments for supplementary irrigation in lentil rainfed fields were 75 mm in the third decade of May in normal years, 75 mm in the second decade of May in wet years and 100 in the second decade of May in dry years. Keywords: Deficit Irrigation, Irrigated lands, Qazvin plain, rainfed lands, Supplementary Irrigation, Water Allocation Management. INTRODUCTION Many studies have been devoted to improve water and cropping pattern management in irrigated farming. Raju and Kumar (1999) and Singh et al. (2001) used linear programming (LP) to determine optimum cropping pattern for maximizing the goal function of total net income with a given volume of water. Mainuddin et al. (1997) developed a linear optimization model to determine optimum cropping pattern and used LINGO to solve it. Reca et al. (2001) developed a nonlinear programming model for optimum water allocation and changed the economic goal function into a linear problem using a discontinuous function. Carvallo et al. (1998) used MINOS to develop a nonlinear programming model and solved a similar problem. Among the previous studies, many had focus on cropping pattern and optimum allocation of water and/or soil resources (Paudyal & Gupta 1990; Sethi et al., 2002) and some paid attention to simultaneous optimization of groundwater management (Sethi et al., 2006), surface water resources and integrated management of surface and groundwater resources besides total net income (Hallaji &Yazicigil 1996). Nonetheless, optimum allocation of water between irrigated and rainfed lands had received little attention. Most studies have dealt with optimum water allocation and choosing the best cropping patter in irrigated lands. So, there are opportunities to extend this kind of studies and pay more attention to the management of water allocation to rainfed lands for supplementary irrigation. In Iran, 7.8 and 6 million hectares of cultivated lands are irrigated and rainfed, respectively, indicating a 43 percent share for rainfed agriculture. Moreover, about 10% of raw agricultural products are being produced by rainfed agriculture (Tavakkoli 2010). It is obvious that the contribution of the country's rainfed products is much less than the global averages. The analysis of rainfed yields revealed that between 25 to 50% of potential yield is achievable under rainfed conditions, while this ratio is about 20% in Iran (Rockström et al., 2010). Taking into consideration erratic spatial pattern of precipitation, especially in dry and semi-dry regions of the world, the management of water supply in these areas should receive the highest priority. Biological Forum – An International Journal 7(1): 1556-1567(2015)