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In this study, five simulations were conducted using the weather research and forecasting (WRF) model with different cumulus parameterizations schemes (CPSs) for the period from 2013 until 2018. A one-year simulation of 2013 with three different horizontal resolutions of 25, 5, and 1.6 km was also performed. The CPSs used were Kain–Fritsch (KF), Grell–Devenyi (GR), Betts–Miller–Janjic (BM), and a non-parameterized scheme (NC). In assessments of model resolutions, both the 25 and 5 km resolutions depicted a strong negative bias in the northeastern part of Peninsular Malaysia during December–January–February (DJF), with marginal differences between the two simulations. Among all 5 km experiments, the best performing scheme was the BM scheme for almost all seasons. Furthermore, the 5 km simulation did not exhibit significant differences relative to the 25 km of the diurnal cycle. The 1.6 km simulation showed significant added value as it was the only simulation that was able to simulate the high precipitation intensity in the morning and a precipitation peak during the evening. The 1.6 km resolution was also the only resolution capable of picking up the precipitation signals in the R4 region (South Peninsular Malaysia) compared to the other two resolutions. While both CPSs and resolutions are important for accurate predictions, the role of CPSs became less significant in a higher resolution simulation. [ABSTRACT FROM AUTHOR]

This paper assesses the reliability of regional climate downscaling products from the Coordinated Regional Downscaling Experiment-Southeast Asia (CORDEX-SEA) in reproducing the present-day wind at the East Coast of Peninsular Malaysia (ECPM). A total of five CORDEX-SEA products, namely CNRM-CM5(RegCM4), CSIRO-Mk3-6-0(RegCM4), EC-EARTH(RegCM4), HadGEM2-ES(RegCM4) and MPI-ESM-MR(RegCM4), with a resolution of 25 km, were compared to reference data from the European Centre Medium-Range Weather Forecasts (ECMWF) fifth generation atmospheric reanalysis ERA5 spanning 1980–2005. This study focused on the period of the southwest monsoon, specifically the months of June, July and August (JJA), as wind during this season is known to play an important role in generating upwelling at the ECPM. The results obtained show that only three of the CORDEX-SEA products, CSIRO-Mk3-6-0(RegCM4), HadGEM2-ES(RegCM4) and MPI-ESM-MR(RegCM4), were able to reproduce the wind in terms of wind speed, wind stress curl and wind pattern as effectively as ERA5. An ensemble was made from these three CORDEX-SEA products, and it was found that the ensemble was able to reproduce a value of the Upwelling Index (UI) that was similar to the reference data, albeit with some bias. Hence, only the three stated CORDEX-SEA products and their ensemble are suitable to be used for future climate change studies within the region. [ABSTRACT FROM AUTHOR]

Understanding the changes in temperature extremes is important for managing and coping with the risks associated with regional climate change. However, the climatological characteristics of temperature extremes and their variabilities is still not adequately studies in Malaysia. This study evaluates the spatial and temporal variations of temperature extremes over Malaysia for the period 1985–2018. This study includes four phases: (a) collection, quality control and homogeneity analysis of temperature data; (b) general (TXmean, TNmean, TMmean and DTR), warm (TXx, TNx, TX90p and TN90p) and cool (TXn, TNn, TX10p and TN10p) temperature extreme indices calculations; (c) trend analysis of temperature extremes using the Mann‐Kendall and Sens's slope test; and (d) analyses of correlations between temperature extremes and El Niño‐Southern Oscillation (ENSO). The results indicate a warming of surface temperature across Malaysia, particularly in Peninsular Malaysia. In general, TXmean, TNmean and TMmean increased significantly at 5% significance level by 0.12°C/decade, 0.27°C/decade and 0.17°C/decade, respectively. A significant decreasing trend in DTR by 0.12°C/decade is seen, which is related to the higher increasing rate of TNmean. All of the warm extreme indices, TXx, TNx, TX90p and TN90p presents significant increasing trends by 0.19°C/decade, 0.28°C/decade, 2.86%/decade and 3.08%/decade, respectively. For the cool extreme indices, TX10p and TN10p decreased significantly by 0.95%/decade and 3.18%/decade, respectively, though the trend in TXn by 0.11°C/decade is not statistically significant. The only cool index presenting a significant increasing trend is TNn by 0.44°C/decade, indicating a reduction of cool nights. Besides that, major cities in the northern and western parts of Peninsular Malaysia generally exhibit a higher warming trend compared to rural and highland area. These are possibly related to the intensified urban heat island effect under the rapid urbanization. This study also found that the ENSO affected warm extreme indices much stronger than cool extreme indices in Malaysia. [ABSTRACT FROM AUTHOR]

This study aims to provide a basis for understanding the mechanisms of diurnal rainfall variability over Peninsular Malaysia by utilising the Non-Hydrostatic Regional Climate Model (NHRCM). The present day climate simulations at 5 km resolution over a period of 20 years, from 1st December 1989 to 31st January 2010 were conducted using the six-hourly Japanese re-analysis 55 years (JRA-55) data and monthly Centennial in situ Observation Based Estimates (COBE) of sea surface temperature as lateral and lower boundary conditions. Despite some biases, the NHRCM performed reasonably well in simulating diurnal rainfall cycles over Peninsular Malaysia. During inter-monsoon periods, the availability of atmospheric moisture played a major role in modulating afternoon rainfall maxima over the foothills of the Titiwangsa mountain range (FT sub-region). During the southwest monsoon, a lack of atmospheric moisture inhibits the occurrence of convective rainfall over the FT sub-region. The NHRCM was also able to simulate the suppression of the diurnal rainfall cycle over the east coast of Peninsular Malaysia (EC sub-region) and afternoon rainfall maximum over the Peninsular Malaysia inland-valley (IN sub-region) area during the northeast monsoon. Over the EC sub-region, daytime radiational warming of the top of clouds enhanced atmospheric stability, thus reducing afternoon rainfall. On the other hand, night-time radiational cooling from cloud tops decreases atmospheric stability and increases nocturnal rainfall. In the early morning, the rainfall maximum was confined to the EC sub-region due to the retardation of the north-easterly monsoonal wind by the land breeze and orographic blocking. However, in the afternoon, superimposition of the sea breeze on the north-easterly monsoonal wind strengthened the north-easterly wind, thus causing the zone of convection to expand further inland. [ABSTRACT FROM AUTHOR]

This study compares five readily available gridded precipitation satellite products namely: Climate Hazards Group Infrared Precipitation with Station Data (CHIRPS) at 0.05° and 0.25° resolution, Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis (TMPA 3B42v7) and Princeton Global Forcings (PGFv3), both at 0.25°, and Global Satellite Mapping of Precipitation Reanalysis (GSMaP_RNL) at 0.1°, and evaluates their quality and reliability against 41 rain gauge stations in Malaysia. The evaluation was based on three numerical statistical scores (r, Root Mean Squared Error (RMSE) and Bias) and three categorical scores (Probability of Detection (POD), False Alarm Ratio (FAR) and Critical Success Index (CSI)) at temporal resolutions of daily, monthly and seasonal. The results showed that TMPA 3B42v7, PGFv3, CHIRPS25 and CHIRPS05 slightly overestimated the rain gauge data, while the GSMaP_RNL underestimated the value with the largest bias for monthly data. The CHIRPS25 showed the best POD score, while TMPA 3B42v7 scored highest for FAR and CSI. Overall, TMPA 3B42v7 was found to be the best-performing dataset, while PGFv3 registered the worst performance for both for numerical (monthly) and categorical (daily) scores. All products captured the intensity of heavy rainfall (20–50 mm/day) rather well, but tended to underestimate the intensity for categories of no or little rain (rain <1 mm/day) and extremely heavy rain (rain >50 mm/day). In addition, overestimation occurred for low moderate (2–5 mm/day) to low heavy rain and (10–20 mm/day). In the case study of the extreme flooding event of 2006/2007 in the southern area of Peninsular Malaysia, TMPA 3B42v7 and GSMaP_RNL performed well in capturing most heavy rainfall events but tended to overestimate light rainfalls, consistent with their performance for the occurrence intensity of rainfall at different intensity level. [ABSTRACT FROM AUTHOR]

The quantile mapping (QM) bias correction algorithm was applied to bias-correcting the daily rainfall over the Malaysia based on the APHRODITE gridded observed dataset. The quality of the bias correction in reducing the biases of regional climate models in frequency (FREQ), mean intensity (SDII) and 90th percentile (Q90) of the daily rainfall was assessed. The result shows that QM performs well in correcting the rainfall statistics. The QM bias correction method was then applied to seven Regional Climate Models (RCMs) projection output from the CORDEX Southeast Asia (CORDEX-SEA) dataset, to obtain high resolution rainfall change scenarios over the Malaysia, based on the IPCC's representative concentration pathways (RCP) 4.5 and 8.5 scenarios. The ensemble mean of seven RCMs suggests that the future projection expected a decrease in the rainfall frequencies over the Malaysia toward the 21st century for both RCP scenarios. Meanwhile, the rainfall intensity and extremes over the Peninsular Malaysia (East Malaysia) is likely to decrease (increase) especially during the winter (summer and autumn) months by the end of the century. A remarkable decrement of rainfall frequency and extremes was found in western Peninsular Malaysia, with changes of around −4 to −8% with respect to the historical period driven by the RCP4.5 and RCP8.5 scenario respectively. • Bias correction technique was used to adjust the systematic biases in the CORDEX-SEA simulations output over Malaysia. • The future changes of daily rainfall characteristics were examined. • The projections expected decrement in rain days frequency under warmer climate. • The changes of future rainfall intensity and extremes show considerable spatial-temporal variations. [ABSTRACT FROM AUTHOR]