Estimation of Missing Rainfall Data Using GEP: Case Study of Raja River, Alor Setar, Kedah

Water resources and urban flood management require hydrologic and hydraulic modeling. However, incomplete precipitation data is often the issue during hydrological modeling exercise. In this study, gene expression programming (GEP) was utilised to correlate monthly precipitation data from a principal station with its neighbouring station located in Alor Setar, Kedah, Malaysia. GEP is an extension to genetic programming (GP), and can provide simple and efficient solution. The study illustrates the applications of GEP to determine the most suitable rainfall station to replace the principal rainfall station (station 6103047). This is to ensure that a reliable rainfall station can be made if the principal station malfunctioned. These were done by comparing principal station data with each individual neighbouring station. Result of the analysis reveals that the station 38 is the most compatible to the principal station where the value of R2 is 0.886. 1. Introduction The importance of precipitation is identifying precipitation characteristics, occurrence and temporal and spatial variability, statistical modeling and forecasting of precipitation, and resolving the problems such as floods, droughts, and landslides as stated by Silva et al. [1]. But, in some cases, a large number of stations could be down at the same time, thus creating many inaccurate readings or missing data [2, 3]. In Malaysia, the number of rain gauge stations with complete records for a long duration is very scarce. Rainfall records often contain missing data values due to malfunctioning of equipment and severe environmental conditions. Thus, the estimation of rainfall is needed if missing data happened at the principal rainfall station. This study was to investigate the possibilities of correlating monthly rainfall of principal rainfall station to its six neighbouring stations. This was done to ensure that a reliable rainfall station can be done before proceeding with water resources management and flood management modelling. 1.1. Description of the Study Area The study area was carried out in Alor Setar city, the capital of Kedah state in Malaysia. It is located within the Raja River catchment. It is prone to flood due to its flat and low elevation. In 1992, Department of Irrigation and Drainage (DID) carried out the Flood Mitigation Project to solve the flooding problems of Alor Setar city where the whole Raja River system was converted to concrete lined channel. It was separated from Kedah River by gated structure and pumping station [4]. A study is being conducted to investigate how