Trends in Rainfall Pattern and Spatial Variation – Case Study: Langat River Basin

Climate change is a global issue that has impact on every living being in the world. Since Malaysia is located in the tropical area where there is no distinct four seasons, analysing rainfall has therefore become one of the common assessment tools for climate change. In this study, rainfall trends and spatial variations of Langat River Basin will be determined for the period of 1971-2012. Only rainfall time series with duration more than 25 years will be considered for this study. Checking of missing rainfall data will then be carried out for all the selected rainfall time series, and only rainfall time series with less than 10% of missing data will be used for this study. Data refilling will be done using the Inverse Distance Weighted Interpolation Method for the selected rainfall time series prior to process of data analysis. In order to check on the homogeneity of the rainfall time series, four homogeneity tests, namely Standard Normal Homogeneity Test, Buishand range Test, Pettitt Test and Von Neumann Test, will be performed. Finally, the non-parametric rank-based MannKendall Test and Spearman’s Rho Test will be applied to analyse and detect the trends of the rainfall time series. Trend detection will be carried out on monthly, seasonal (monsoon) and annual basis. Holt-Winters Method will also be applied to track the underlying mean and trend in the rainfall time series that could have changed over the time. After performing the rainfall pattern analyses, spatial variations of rainfall time series will be analysed, traced and presented in GIS maps. The river basin will be partitioned based on the locations of rainfall stations using Thiessen’s Polygons Method, and the spatial variations of each polygon will be presented in the GIS maps. Similarly, analysis of spatial variations will be carried out on annual, seasonal and monthly rainfall basis.