Two questions motivated this study: 1) Will meteorological droughts become more frequent and severe during the twenty-first century? 2) Given the projected global temperature rise, to what extent does the inclusion of temperature (in addition to precipitation) in drought indicators play a role in future meteorological droughts? To answer, we analyzed the changes in drought frequency, severity, and historically undocumented extreme droughts over 1981–2100, using the standardized precipitation index (SPI; including precipitation only) and standardized precipitation-evapotranspiration index (SPEI; indirectly including temperature), and under two representative concentration pathways (RCP4.5 and RCP8.5). As input data, we employed 103 high-resolution (0.44°) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), based on a combination of 16 global circulation models (GCMs) and 20 regional circulation models (RCMs). This is the first study on global drought projections including RCMs based on such a large ensemble of RCMs. Based on precipitation only, ~15% of the global land is likely to experience more frequent and severe droughts during 2071–2100 versus 1981–2010 for both scenarios. This increase is larger (~47% under RCP4.5, ~49% under RCP8.5) when precipitation and temperature are used. Both SPI and SPEI project more frequent and severe droughts, especially under RCP8.5, over southern South America, the Mediterranean region, southern Africa, southeastern China, Japan, and southern Australia. A decrease in drought is projected for high latitudes in Northern Hemisphere and Southeast Asia. If temperature is included, drought characteristics are projected to increase over North America, Amazonia, central Europe and Asia, the Horn of Africa, India, and central Australia; if only precipitation is considered, they are found to decrease over those areas.

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Northeasterly cold surges strongly influence the rainfall patterns over the Malay Peninsula during the northeast monsoon season. This study looks at the changes in the cold surges and Madden–Julian oscillation (MJO) characteristics through the northeast monsoon season and their interaction. Nearly 75% of the cold surge events tend to cross the equator around the Java Sea area (100°–110°E) in February–March with drier conditions prevailing over the Malay Peninsula and increased rainfall over Java. Both the cold surges and the MJO undergo seasonal variations with well-defined regional features. Wavelet analysis shows that MJO amplitude and high-frequency rainfall variations over Southeast Asia peak in November–December. MJO amplitude is suppressed during February and March. This is linked to the high-frequency surges of meridional winds that are prominent during the early part of the season, but February–March is dominated by low-frequency (~20–90 days) cross-equatorial monsoon flow. These prolonged periods of strong meridional flow at the equator interact with the MJO both dynamically and thermodynamically and act as a barrier for convection from propagating from the Indian Ocean to the Maritime Continent (MC). These interactions may have implications for weather and seasonal forecasting over the region. An evaluation of the properties of cold surges and their interaction with the seasonal cycle in the Met Office Unified Model is performed. The atmosphere–ocean coupled model performs better in representing the pattern of influence of the cold surges despite the biases in intensity and spatial distribution of rainfall extremes. These diagnostics are presented with the aim of developing a set of model evaluation metrics for global and regional models.

Abstract. We constructed two types of neural network models for forecasting the sea surface temperature anomaly (SSTA) over several standard equatorial Pacific regions (Nifio 3, 3.4, 3.5, 4, P2, P4, and P5). The first type used the sea level pressure (SLP) as predictors, while the second one used the wind stress. By ensemble averaging over 20 forecasts with random initial weights, the resulting forecasts were much less noisy than those in our earlier models. The models performed best in the western-central equatorial regions and less well in the eastern boundary regions. At longer leads of 9 -12 months, the cross-validated skills (1952 -1993) for the models using the tropical Pacific SLP as predictors were statistically higher than those using the wind stress. Overall, the models using the tropical SLP showed usable cross-validated skills up to 12-month lead. The true out-of-sample forecast performances during the 1982-1993 period for the Nifio 3.5 SSTA at lead times of 9, 12, and 15 months attained correlation skills of 0.78, 0.80, and 0.75, respectively.

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.

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The characteristics of diurnal variation of precipitation in terms of amount (PA), frequency (PF), and intensity (PI) over Sumatra have been investigated using rain‐gauge data from 186 stations. Mean PA and PF show spatial variations significantly affected by the terrain elevation and stations' distance to the west coastline of Sumatra. A slightly larger PA and PF appear over the middle and western sections of the Barisan mountains, in which the mean PI is smaller in these regions. Most stations with large rainfall amount also have large rainfall frequencies, indicated by a strong correlation between PA and PF. The timing of the diurnal peak of PA, PF, and PI also has prominent regional characteristics. The cluster analysis reveals different grouping of stations with distinctive diurnal peaks. The prevailing afternoon and early‐evening peaks, that is, 1500–2000 LST, appear mostly over mountain ranges where amplitude of PA and PF tended to increase with elevation. Moreover, the amplitude of diurnal cycles tended to decrease as distance from the Sumatra's west coastline increases. On the western side of Barisan's mountain range, high amplitude of diurnal cycle prevails compared to the eastern side. We also found a strong relationship between rain event duration with diurnal cycle pattern. Generally, rain event with a long duration tended to have a peak occurring at a later time compared with those events of shorter duration. The diurnal variation of precipitation corresponds to the temporal evolution of the low‐level convergences and wind vectors, and cloud migration modulated by land‐sea breeze system.