Proceedings of the 19 th IAHR-APD Congress 2014, Hanoi, Vietnam ISBN 978604821338-1 1 ASSESSMENT OF RICE PRODUCTIVITY UNDER CLIMATE CHANGE FOR CA MAU PROVINCE, VIETNAM Proloy Deb *1 , Duong Anh Tran 2 and Nguyen Mai Dang 3,4 1 Water Engineering and Management, School of Engineering and Technology, Asian Institute of Technology, P.O. Box 4 KlongLuang, Pathumthani 12120, Thailand 2 Lehrstuhl für Wasserbau und Wasserwirtschaft Technische Universität München 21, D-80333 München, Germany 3 Center for International Education, Hanoi, Vietnam 4 Institute for Hydrology, Environment and Climate Change, Hanoi, Vietnam *Corresponding author. Tel.: +662524 5793. E-mail address: debproloy@gmail.com (P.Deb) ABSTRACT The present study analyzes the spatial and temporal impacts of climate change on paddy yield for autumn- winter (AW) and summer-autumn (SA) cropping pattern. Climate variables for the future time windows were derived from general circulation model (HadCM3) which were further downscaled using SDSM 4.2 at three different stations for three future time periods (2025s, 2055s and 2085s). AquaCrop 4.0 was used to project the future paddy yield for the considered stations. Our results illustrate that climate change will elevate the maximum and minimum temperatures for all the stations ranging from 1.60 to 2.65°C and 2.08 to 2.97°C respectively for 2085s. An increase in average annual rainfall is also observed ranging from 8.8 to 35.3% for the three stations for the corresponding time window. Simulation for rice productivity shows a decline of paddy yield by -13.75 and -9.76% by 2085s relative to baseline climate for SA cropping season in case of A2 and B2 scenarios respectively. However, an increasing trend in paddy yield was observed in AW season with a boost of 12.5 and 8.12% for corresponding scenarios for period. Keywords:Climate change; rice yield;SDSM v 4.2;AquaCrop v 4.0;Ca Mau;Vietnam 1. INTRODUCTION Increase in agricultural production is a leading challenge in present context due to the dependence of economy on agriculture for developing nations like Vietnam. In spite of the major agricultural developmental plans of the Vietnamese government over the past 20 years, a significant fluctuation in the productivity of rice has been detected (IRRI 2013) in addition, more than 30 million children have been identified mal-nourished in the country (NIN 2010). In terms of GDP, agriculture accounts 22% share of Vietnam’s economy (World Bank 2012). Being the second largest exporter of rice in the world, production is intensified and is expected to be more in forthcoming years (APN 2007). Additionally, rice is also the staple food of the people of Vietnam. Although a major proportion of agriculture is rainfed, in addition to the available rain water, rice productivity is also dependent on accessible water of acceptable quality for irrigation (Trinh et al. 2013). The overwhelming dependence of Vietnam’s economy on rainfedagriculture makes it sensitive to climatic variables. Vietnam is identified to be in the top five developing nations which are impressionably susceptible to the impacts of climate change. In addition to high intensity droughts in recent years Vietnam has also experienced sea level rise by approximately 20 cm in past 50 years (Sadoff& Muller 2009; IPCC 2007a). It is also anticipated that the nation will experience a sea level rise of 1 m by the end of this century affecting 10% of GDP in terms of economic loss; approximately 31% of land area in Mekong delta including 9800 km 2 agricultural area (MONRE 2009). Due to the intensified agricultural policy in Vietnam, the extensive use of groundwater resources in Mekong delta for farming operations during dry season has enforced the saline water intrusion at an overwhelming rate (IUCN 2011). Additionally it has also been estimated that, considering today as the baseline, there is an expected reduction in total volume of freshwater by 4, 9 and 14% for the year 2025, 2070 and 2100 respectively (DWRM 2008). This will enforce the farmers to use the invaded saline groundwater for rice cultivation in the dry season. Climate change is expected to have a wide-ranging effect on the environment and socio-economic sectors particularly in the water and agriculture (IPCC 2007b; Mestre-Sanchís&Feijoo-Bello 2009). It affects the spatial and temporal pattern of precipitation and temperature which actively changes the plant phenological process and consecutively affects productivity (Tao et al. 2003). Specifically change in temperature can affectively alter