Homogeneity and trends in long-term rainfall data, Kelantan River Basin, Malaysia

ABSTRACT

The Kelantan River Basin, situated in the northeastern Malaysian Peninsula, suffers serious flood/inundation damage, related to the northeast monsoon season (November–January), every few years. In this river basin, rainfall observation systems have been progressively developed since 1948, and long-term time-series data at distributed rainfall stations have been accumulated. This study firstly investigated the homogeneity of the accumulated time-series data for the purpose of constructing a reliable database for various hydrologic analyses. The homogeneity of rainfall time-series data was established using four absolute homogeneity tests: the Pettitt test, standard normal homogeneity test, Buishand range test, and von Neumann ratio test. It was found that among 50 rainfall stations within the river basin, 9 were flagged by the tests. Of these, inhomogeneous time-series data from four stations were omitted from further analysis. Secondly, using the homogenous time-series rainfall data, a trend analysis of annual rainfall variability was conducted by means of the Mann–Kendall (MK) test. To investigate long- and short-term characteristics of rainfall variability, three sampling methods of the MK test were applied: 30-year, sequentially increased, and 10-year moving segmented sampling. The MK test using the 30-year sampling showed a decreasing trend between 1957 and 1987, and an increasing trend between 1981 and 2011. The MK test using the sequentially increased sampling detected neither significant increasing nor decreasing trends through the same 70-year period. The MK test using 10-year moving segmented sampling clearly showed significant rainfall variability, which corresponded to the El Niño and La Niña events of 1972, 1982, 1988, the mid-1990s, and 2000–2004. Extending the plot, by comparing the turning points with the occurrence of El Niño and La Niña events, the results showed that the influence of the El Niño southern oscillation (ENSO) is the most likely to significantly influence rainfall trends in the Kelantan River Basin.

Keywords:

• Rainfall time-series
• homogeneity test
• Mann–Kendall
• El Niño
• La Niña

Acknowledgements

The authors acknowledge the cooperation of the Department of Drainage and Irrigation Malaysia (DID/JPS) for providing the data required for this study.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was conducted as part of a Science and Technology Research Partnership for Sustainable Development (SATREPS) project supported by the Japan International Cooperation Agency (JICA) and the Japan Science and Technology Agency (JST), and as part of a long-term research grant scheme supported by the Ministry of Higher Education Malaysia (MOHE) under the project ‘Research and Development for Reduction Geo-Hazard Damage in Malaysia caused by Landslide and Flood’ [grant number 01201306LRGS].