Original Article Effects of climate and land use changes on water balance in upstream in the Chao Phraya River basin, Thailand Pancheewan Ponpang-Nga, Jessada Techamahasaranont * Department of Agriculture and Resources, Faculty of Natural Resources and Agro-Industry, Chalermphrakiat Sakon Nakhon Province Campus, Sakon Nakhon 47000, Kasetsart University, Thailand article info Article history: Received 3 October 2014 Accepted 8 December 2015 Available online 8 October 2016 Keywords: Chao Phraya River basin Climate change Land use change Water balance abstract A monthly water balance model was used to investigate the effects of climatic and land use changes on water resources upstream in the Chao Phraya River basin. The objective was to simulate and predict the hydrological processes under different climate change and land use change scenarios. The results showed that the climatic conditions and land development had an impact on changing the rainfall, evapo- transpiration and streamflow. The simulated water balance for future climatic conditions and land use change scenarios showed increases during 2010e2099 in rainfall, temperature, evapotranspiration and streamflow. Under all land use conditions, the estimated evapotranspiration trends increased, especially for the worst case (12% forest area) which showed the highest evapotranspiration values in the A2 and B2 climate change scenarios. When discharge was calculated in the future, there was 27e40% of both A2 and B2 climate change scenarios under all land use conditions (12%, 20% and 40% forest area) when compared between 1970 and 1989 (calibration period) and 2090e2099 (prediction period). Increasing streamflow will be useful for human activities but it raises water resources issues such as the frequency of flood and drought events in the future. Copyright © 2016, Kasetsart University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Introduction The hydrology of a watershed is affected by climate and land use among other factors and there is now essential consensus that all of these factors and interactions are influenced by human activities, including fluvial geomorphology and climate (Tomer and Schilling, 2009). The results of studies in many regions have found that streamflow variability is closely associated with climate and land use changes which are both key drivers of water balance change (Tu, 2009). Interactions between these drivers are complex and currently not well understood (Chazal and Rounsevell, 2009). Climate change could be expected to affect many sectors, including water resources, agriculture and food security, ecosystems and biodiversity, human health and coastal zones. Under climate change, predicted rainfall increases over most of Asia, particularly during the summer monsoon, could increase flood-prone areas in East Asia, South Asia and Southeast Asia (United Nations Framework Convention on Climate Change, 2007). Consequently, land use change may have inadvertent, negative effects on the hydrological regime, such as increasing the occurrence of floods and decreasing dry season flow (Lorup et al., 1998). Very few re- searchers have documented the major role of land use/cover change and variability in the climate system (Rai, 2009). To research the impact of climate change on future water re- sources, a hydrological model can be driven by the output (pre- cipitation and temperature) from a general circulation model, or GCM (Watson et al., 1996). However, many studies have used a regional climate model (RCM) which has a high horizontal resolu- tion (25e50 km) and is more appropriate for resolving the small- scale features of topography and land use that have a major influ- ence on climatological variables (Akhtar et al., 2008). RCM-PRECIS was developed to help generate high-resolution climate change information for as many regions of the world as possible (Jones et al., 2003). The Southeast Asia START Regional Center (http://cc. start.or.th) downscaled climate change data from GCMs which used PRECIS and covered Thailand and neighboring countries. It has output data which consists of A2 and B2 scenarios (described later). For the purpose of water resources assessment and the study of climate and land use impacts, a monthly water balance model has * Corresponding author. E-mail address: csnjdt@ku.ac.th (J. Techamahasaranont). Peer review under responsibility of Kasetsart University. Contents lists available at ScienceDirect Agriculture and Natural Resources journal homepage: http://www.journals.elsevier.com/agriculture-and- natural-resources/ http://dx.doi.org/10.1016/j.anres.2016.10.005 2452-316X/Copyright © 2016, Kasetsart University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Agriculture and Natural Resources 50 (2016) 310e320