E-proceedings of the 38 th IAHR World Congress September 1-6, 2019, Panama City, Panama 1476 CLIMATE CHANGE IMPACT ON IRRIGATION WATER REQUIREMENT IN BARITO KUALA SOUTH KALIMANTAN INDONESIA MAYA AMALIA ACHYADI (1) , KOICHIRO OHGUSHI (2) , TOSHIHIRO MORITA (3) , SU WAI THIN (4) & WATARU KAWAHARA (5) (1) Saga University, Saga, Japan & Lambung Mangkurat University, Banjarbaru, Indonesia, e-mail : 17654904@edu.cc.saga-u.ac.jp (2) Saga University, Saga, Japan, e-mail : ohgushik@cc.saga-u.ac.jp (3,4,5) Saga University, Saga, Japan ABSTRACT Indonesia is the most populous country with more than 265 million people in 2018. Food security is persistent challenges, and the country's levels are seriously high. Now the world must face climate change conditions. The important impacts of climate change on agricultural production and productivity in Indonesia are compounded by increasing urbanization that has a significant impact on agricultural land and increased pressure on scarce water resources. Rice production will continue to decrease in Java Island, in future so that Indonesia has to expand to other islands such as Kalimantan. Barito Kuala district is located in South Kalimantan and the coast of Barito River. Evapotranspiration is an important component of a hydrological cycle and the largest source of water loss, as well as for agricultural water requirements. The crop water requirements for water irrigation practices and efficient use of water. This study's objective is to predict Barito Kuala's water requirements for rice under the climate change scenario. First is to analyze the rainfall pattern and temperature using statistical methods, linear regression with daily observed data for 30 years. Second, the reference evapotranspiration (ETo) was computed using the Penman-Monteith method. Third, climate change scenario using the CMIP5 with the daily historical simulations over the period 1981–2009, and future projection series of the periods 2050s and 2090s. The result of this study shows impact of climate change on water requirement due to evapotranspiration value for deciding related to irrigation water resources management in Barito Kuala, South Kalimantan. Keywords: Barito Kuala, Climate Change, Lowland, Tidal Irrigation, Water Requirement 1 INTRODUCTION The Indonesian population expected to reach 321 million in 2050 (United Nation, 2015) and 321.2 million in 2090 (Guilmoto, 2016). This condition predicted that Indonesia will need 36.59 million ton/year in 2050 and 36.62 million ton/year in 2090. Food security for the population of Indonesia is the main focus of Indonesia government. Especially rice as a major staple food. On the other hand, food security limited to climate change and water resources, affecting not only harvest yields but also agriculture sector continues to emit great amounts of greenhouse effect gases (GHGs) (FAO, 2018). Over the past decades, climate change impacts on crop production have attracted great attention (Gahatraj, 2018). Climate change will result in changes in precipitation patterns, temperature decreases or increases and changes in the hydrological cycle. Which will have an impact on agricultural yield productivity especially for rice production? (WorldBank, 2008). Rainfall and temperature, which are the most risk-increasing parameters, positively related to rice yield variability (Kim, 2009). Water resources system models can be useful tools to study the effects of climate change and to identify adaptation strategies in the water sector (Andreu, Martin-Carrasco, & Idlesias, 2011). Three different types of long term climatic patterns have been identified for "Central" (Java, NTB, NTI, southern Kalimantan and Sulawesi), “Western" (North Sumatra, western Kalimantan) and "Eastern" (northern Sulawesi, Maluku, Halmahera) Indonesia (Aldrian, 2003). The combination of high population density and high levels of biodiversity together with a staggering 80,000 km of coastline and 17,508 islands, make Indonesia one of the most vulnerable countries to the impacts of climate change (Case, Ardiansyah, & Spector, 2007). Most of the studies have focused solely on the local and regional aspects of irrigation water demand. On the other hand, global analyses today have largely focused on water availability – for both agriculture and other sectors – using hydrological models to estimate changes in precipitation, evapotranspiration, and river runoff, which are of importance to water resources (Fischer & Tubiello, 2007). This present study quantifies change on irrigation water requirement in Barito Kuala, South Kalimantan Indonesia. The objective of these studies will be highly useful for the policy makers and farmers to adapt the impact of climate change. doi:10.3850/38WC092019-0878