Assessment of climate extremes and the performance of precipitation products in Peninsular Malaysia / Ng Cia Yik

Ng , Cia Yik (2024) Assessment of climate extremes and the performance of precipitation products in Peninsular Malaysia / Ng Cia Yik. PhD thesis, Universiti Malaya.

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Abstract

The occurrence of extreme climate events is expected to become more intense and frequent in a warming climate. Therefore, understanding historical changes in climate extremes is crucial for developing comprehensive and long-term climate resilience solutions. Although numerous studies have been conducted, trend patterns in Peninsular Malaysia are still poorly understood due to inconsistent findings from these studies without attributing them to climate-driving factors. Recent studies have identified substantial uncertainties inherent in precipitation products, which serve as data sources for climate studies. However, these studies focused solely on satellite or ground-based products, without considering reanalyses or new products that benefit from advancements in numerical climate models and data merging techniques. To address these knowledge gaps, this study aims to assess the past changes in climate extremes and the accuracy of precipitation products in estimating rainfall in Peninsular Malaysia. To achieve these aims, the following objectives have been designed: (i) to assess the spatiotemporal trends of precipitation extremes and their driving factors in Peninsular Malaysia during 1989–2018, (ii) to examine the trends and possible causes of severe droughts, as well as the suitability of Evaporative Demand Drought Index for drought monitoring in Peninsular Malaysia during 1989–2018 and (iii) to evaluate the performance of high-resolution precipitation products in estimating rainfall at daily, monthly and seasonal timescales, as well as their ability to capture the annual cycle and interannual extremes during 2014–2019. Hourly rainfall records were obtained from the Malaysia Department of Irrigation and Drainage to compute climate extreme indices and evaluate precipitation products. The modified Mann-Kendall and Sen's slope tests were performed to detect the significance and magnitude of trends, while the skills of seven precipitation products were quantified using both numerical and categorical metrics. The trend analysis reveals increasing intensity and frequency of wet extremes over Peninsular Malaysia, especially during the northeast monsoon season. However, spatial analysis demonstrates clear variations in patterns between wet and dry regions, primarily attributed to the influence of the tropical monsoon system. Climate extremes in Peninsular Malaysia are strongly modulated by the effects of the El Niño–Southern Oscillation, particularly in the northern, eastern and southwest regions. Drier (wetter) conditions are observed during the El Niño (La Niña) phase due to regional atmosphere-ocean coupled interactions. The evaluation of precipitation products shows considerably poor performance in daily comparison, with median modified Kling–Gupta efficiency scores ranging from 0.12 to 0.45. However, a notable improvement is observed at the monthly timescale as median modified Kling–Gupta efficiency scores increase by approximately 0.18 to 0.43. The skills of these precipitation products vary seasonally, with the highest scores observed during the northeast monsoon season. All precipitation products perform reasonably well in simulating the annual cycle but poorly in capturing the interannual extremes. Among all precipitation products, the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement (IMERG) and the Climate Prediction Center Morphing Technique (CMORPH) are the best performers overall. These findings have great regional implications for water resources management and align with Sustainable Development Goal 13: Climate Action.

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