| Abstract | This research is an output of analysis of water accounting of the Upper Chao Phraya basin(UCPB) by using water accounting plus (WA+) framework for the year 2009. UCPB is located in the northern part of Thailand. It covers an area of 104,086km2over 17 provinces including Chiangmai, Lamphun, Tak, Kamphaeng phet, Nakhonsawan, Lampang, Phrae, Sukhothai, Phitsanulok, Phichit, Phayao, Uttaradit, Nan, and Phetchabun in 4 sub-basins which includes Ping, Wong, Yom, and Nan basin. There are 7 reservoirs including Mae kuang Udom Thara, Mae Ngat Somboon Chon, Kio Lom, Sirikit, Bhumibol, Kio Kho Ma, and Khwaenoi Bamrungdaen with full capacity of 24,715 MCM. Large, medium and small scale irrigation system existed which cover total area of 3,725 km2.The WA+ framework of UCPB has been presented in 3 sheets including resource base sheet, productivity sheet, and withdrawal sheet. Secondary data was taken from various departments which were used to estimate the water balance for 2009. The results for year 2009 showed that total annual inflow is 119,457 MCM from precipitation. From the surface water storage, a volume of 3,155 MCM has been decreased. Evapotranspiration of rainfall or “landscape ET” was 92,687 MCM, which is 90% of total depletion. “Incremental ET” due to utilized flow was 9,977 MCM, which is 10% of total depletion. The UCPB had utilizable outflow of about 4,767 MCM. Outflow supplied to MWA, Lower Chao Phraya Basin (LCPB) and environmental are 15,181 MCM. The crop yield of UCPB was considered as low. In addition, the crop water productivity was not water efficient. Considering the result of water accounting analysis, the UCPB is still open to new development. Therefore, water use efficiency should be considered into basin policy and the irrigation system. Surface water and groundwater should be developed together. Finally, it can be recommended that the results can be used for water accounting analysis that will contribute to the integrated water resources management. |