Research Article Investigation into the Effects of Climatic Change on Temperature, Rainfall, and Runoff of the Doroudzan Catchment, Iran, Using the Ensemble Approach of CMIP3 Climate Models Abolghasem Sayadi , 1 Nasser Taleb Beydokhti , 2 Mohsen Najarchi, 3 and Mohammad Mahdi Najafizadeh 4 1 Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran 2 Faculty of Civil and Environmental Engineering, Shiraz University, Shiraz, Iran 3 Department of Civil Engineering, Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran 4 Department of Mechanical Engineering, Arak Branch, Islamic Azad University, Arak, Iran Correspondence should be addressed to Nasser Taleb Beydokhti; nassertaleb@gmail.com Received 17 August 2018; Revised 16 December 2018; Accepted 6 February 2019; Published 11 March 2019 Academic Editor: Panagiotis Nastos Copyright © 2019 Abolghasem Sayadi et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. is study investigated the effects of climatic changes on temperature, rainfall, and runoff in the Doroudzan catchment in the northeast of Fars province, Iran. Temperature and rainfall changes in three periods including 2011–2030, 2046–2065, and 2080–2099 were downscaled and studied using 15 Coupled Model Intercomparison Project, Phase 3 (CMIP3) climatic models, under three scenarios of greenhouse gas emissions A2, B1, and A1B, from the database of the LARS-WG model. e difference in the amount of changes in temperature and rainfall in these three periods and the observational amounts under the 15 models indicated the uncertainty of the changes values. To reduce this uncertainty and limit the results to the management and planning of water resources, ensemble approach was considered. For the preparation of the ensemble approach, the parameters from the files of the 15-model scenarios were averaged so that a climatic ensemble model could be obtained for each period. en, the runoffs of the next three periods, under the second approach and three emission scenarios, were produced using the feedforwad neural network. e results indicated an increase in the average monthly maximum temperature and the minimum temperature in all three periods under the three scenarios. e results also showed a decrease in the rainfall in the early months of the year as well as an increase in the rainfall in the spring in most scenarios. Generally, the average annual rainfall in all these three periods under the climatic ensemble model, and three emission scenarios showed a reduction in the average annual rainfall in the three periods. e maximum amount of reduction was in 2080–2099 (101mm) under the scenario B1. Besides, a reduction occurred in the average runoff of the catchment under three ensemble models and the emission scenario in all three periods, as compared to the average of the long-term observational values in most years. 1. Introduction Climatic changes and management of the existing water resources have recently been a serious challenge worldwide. Climatic changes caused by the increase of greenhouse gasses in the earth’s atmosphere result in the rise of temperature and reduction of rainfall along with drought and devastating floods in many parts of the world including Iran. Increased temperature leads to the enhanced surface water evaporation and water consumption; this, concomi- tant with the reduction of rainfall and surface water re- sources, can cause many problems for human societies. e Hindawi Advances in Meteorology Volume 2019, Article ID 6357912, 16 pages https://doi.org/10.1155/2019/6357912