<S3-2> Possibility of evapotranspiration estimates by the hourly hydrologic data based short-time period water-budget method in a rainforest watershed at Lambir Hills National Park

This proceeding is a compilation of findings and progress activities of research collaboration between the Forest Department Sarawak (FDS) and the Japan Research Consortium for Tropical Forests in Sarawak (JRCTS). To highlight the research findings, An International Symposium entitled "Frontier in Tropical Forest Research: Progress in Joint Projects between the Forest Department Sarawak and the Japan Research Consortium for Tropical Forests in Sarawak" was ii held in Kuching, Sarawak on 21-22 September 2015.The hydrological cycle in tropical rainforests is very active. Hydrological data such as rainfall, runoff, and evapotranspiration (ET) are important for not only forecasting of global-scale environmental changes and predicting disaster but also managing local agriculture, industry, human health and environment; however, it is difficult to obtain long-term hydrological data in such areas. We intermittently observed runoff at the Lambir Hills National Park, Sarawak, Malaysia. The climate is humid tropical with a weak seasonal change in rainfall and little seasonal variation in temperature. To estimate ET values in this study site, we applied the short-time period water-budget method. This method is usually used for temperate zone watersheds, with daily rainfall and runoff data collected over the course of a year. Because of the rainfall characteristics such as short duration and high intensity with no substantial seasonal climate change in the study region, we applied hourly data to this method instead of daily data. By using daily data, we were able to estimate ET for approximately 50 % of the observation period. ET could be estimated before and after large rainfall events; however, it was difficult to estimate during the frequent intensive rainfall periods and the dry period. By using hourly rainfall and runoff data, we were able to estimate ET during most of the total observation period. Annual ET was approximately 1700 mm in this watershed. We believe that the hourly short-time period water-budget method was appropriate because of the characteristics of the rainfall