Determination of Forest Water Yield in Malaysian Tropical Watershed Using Calibrated Satellite-based Rainfall Data Mohd. Rizaludin Mahmud¹, Mazlan Hashim² ¹Department of Surveying Science and Geomatics Faculty of Architecture, Planning, and Surveying Universiti Teknologi MARA Perlis 02600, Arau,Perlis, MALAYSIA ²Institute of Geospatial Technology Faculty of Geoinformation Science and Engineering Universiti Teknologi Malaysia 81310,Skudai, Johor, MALAYSIA ABSTRACT This study investigates the potential of the calibrated satellite- based rainfall estimates data product from Tropical Rainfall Measuring Mission (TRMM) satellites, known as TRMM 3B43 Version 6 or TRMM Multi-Satellites Precipitation Analysis (TMPA) water run-off modeling at tropical forested watershed scale in Peninsular Malaysia. The calibrated satellite-based rainfall is used as the main input in the Thornthwaite water balance equation to estimate the water run-off (yield) at monthly basis from 1998 to 2007. Four forested watershed which located in each main region in the Peninsular Malaysia are used as sample to evaluate the model performance. Preliminary assessment of the calibrated satellite-based rainfall at the selected forested watershed indicates good agreement with the ground rainfall measurement with average bias of ±43.35mm per month. The monthly estimated water run-off for all forested watershed in all region also shows good agreement and comparable with the simulated run-off using the rain gauged data. The average bias for the satellite-based derived water run-off for all forested watershed in all Peninsular Malaysia region is 22.7mm per month except for east region where higher values are recorded which reach 55.5mm per month. 1. INTRODUCTION Water is a limited and valuable resource that is essential for sustaining life. In most developing countries such as Malaysia, the search for an effective water management approach remain a national interest in order to support huge populations growth, rapid economic development, large irrigation areas, and increasing domestic water consumption. It is identified that the watersheds are the main water resources with rainfalls as their main water inputs. Therefore, accurate rainfall measurement is crucial for run-off estimations from watershed. However, water run-off assessment from rainfall- run-off based models is commonly inadequate due to the existing weakness of conventional rainfall measurements [1]. Even though that the ground rain gauged provides high accuracy measurements, it is only reliable for the surrounding areas. In developing region, where the rain gauge is sparse, especially in remote areas, the uncertainties of rainfall measurements are increased. High cost maintenance and deployment are the main constraints of establishing the effective rain gauge distributions, especially for large areas. Therefore, the usage of satellite-based technology as an alternative data source is considered to be a practical solution [2]. Advancement of satellite-based technology enables us to estimate the rainfall before it reaches the ground surface, through radar reflectivity [3,4]. The nature of the orbiting satellite at high altitude in space provides consistent and regular rainfall measurements over large coverage areas. Recent studies show that the satellite- based precipitation data is able to provide good measurement with reliable accuracy for many regions in the world [5,6]. The latest version of the satellite-based precipitation data from Tropical Rainfall Measuring Mission (TRMM) is capable to provide daily rainfall estimation with three-hour interval measurement at high spatial resolution of 0.25 degrees. In addition, the data can be further localized to reach higher spatial resolution [7]. Peninsular Malaysia, the main region of Malaysia, which is located nearly at the centre of the Southeast Asia, is in need of more comprehensive water monitoring supports tools in order to cope with the increasing water demand as well as water induced disaster. Although the distributions of rain gauge stations are quite abundant throughout the entire regions, the rain gauged measurements, however, is inconsistent and poorly conducted during heavy rainfall. Furthermore, the high rainfall dynamics over different monsoon season bring difficulties for the existing discrete-based conventional 2010 International Conference on Science and Social Research (CSSR 2010), December 5 - 7, 2010, Kuala Lumpur, Malaysia 978-1-4244-8985-5/10/$26.00 ©2010 IEEE 804