The significance of climate change threats and impacts on agriculture and food security is complex problem involving varied interactions among the environment, crops and water. Climate change impacts for whole of South Asia are daunting. The International Food Policy Research Institute (IFPRI) states in its 2009 report, that South Asia will be the most severely impacted by climate change. By 2050 it could lose 50% of its wheat productivity. But in future scenarios climate change alone will not be the only major environmental threat that we face in country but also the food security, specifically in semiarid to arid regions of Pakistan. Crop Growth Models and Global Circulation Models are helpful tools to assess the climate change impact and can also provide a basis for informed decision support and the development of adaptation strategies for the policy makers, researchers, farmers and other end users. Agriculture will be the most vulnerable sector under changing climate scenarios. The future prosperity and economic stability of Pakistan mainly depends upon the quantum of material resources and their judicious exploitation and utilization. There is a dreadful need for advanced planning and research to ensure food security in Pakistan. This study was proposed to evaluate the impact of changing climate on yield of fine transplanted rice under semi-arid conditions using DSSAT and APSIM as multiple models. Early (2012-2039), Mid (2040-2069) and Late (2070-2099) century climate change scenarios were developed by Pakistan Meteorological Department (PMD) using GCM CCSM4 with RCP 4.5 and RCP 8.5 scenarios over baseline (thirty years observed) 1981-2010 weather data for Faisalabad site. CERES-Rice Model under DSSAT was calibrated and evaluated against two years field data and then keeping genetic coefficients same, model was run using seasonal analysis with 32 farmers surveyed data from various locations. Results showed decreasing yield trend in early, mid and late century scenario over baseline data. Fine rice paddy yield ranged between 3003-5251 kg ha^-1, 2741-4517 kg ha^-1, 2376-4464 kg ha^-1 and 1961-4154 kg ha^-1 for baseline, early, mid and late centuries, respectively. Paddy yield decreased by 14.78% for 2012-2039 (early), 24.54% for 2040-2069 (mid) and 36.47% for 2070-2099 late centuries using RCP 4.5 and corresponding values with RCP 8.5 were 24.92%, 39.36% and 52.46% for early, mid and late century scenarios. Economic team collected sample of 32 farmers from Rice-Wheat cropping system. RCP 8.5 midcentury (2040-2069) scenario was taken for Tradeoff Analysis Multidimensional (TOA-MD). The total percentage of gainers and losers were 17.4 and 82.6% for without adaptation. After this Representative Agricultural Pathways (RAPS) would be developed to make the system viable and more adaptable for the farmers. For making comparison between two models, same data would be used within APSIM, and results would be verified after developing three climate scenarios (early, mid and late). In future more studies would be emphasized to bring minor crops and livestock sector also through developing RAPS to make the system more efficient to ensure food security in this part of the world.

Keywords: - Climate Change, Crop Growth Model, Global Circulation Models, Early, Mid and Late Centaury, Tradeoff Analysis Multidimensional, Representative Agricultural Pathways.