Improvement of the ESA CCI land cover maps for water balance analysis in tropical regions: A case study in the Muda River Basin, Malaysia

Study region: The Muda River Basin (MRB), Malaysia. Study Focus: This study proposed a framework to improve the European Space Agency Climate Change Initiative Land Cover (ESA CCI LC) products through the integration with the Annual Oil Palm Dataset (AOPD). The improved land use land cover (LULC) maps were then used to produce five LULC scenarios as input maps into the Soil and Water Assessment Tool (SWAT) model for analyzing the impact of LULC changes on water balance in the MRB. New hydrological insights for the region: The improved LULC maps have good performance in representing rubber and oil palm, with an overall accuracy up to 81 %. In addition, SWAT simulated monthly streamflow well for the MRB, with the highest R2 and NSE values of 0.84 and 0.86, respectively. During the 2001–2016 period, the MRB experienced an expansion of oil palm from 7.10%–17.36 %, a reduction of rubber from 34.93 % to 26.38 % and a slight decrease in forest from 54.23%–52.80 %. The urban expansion scenario showed significant increment in surface runoff, while the reforestation scenario helped to reduce surface runoff, while increase lateral flow and groundwater. Oil palm expansion led to a higher reduction in lateral flow and groundwater than rubber trees due to the higher soil water absorption rate. The proposed framework can be duplicated and applied in other tropical basins, particularly in Indonesia and Malaysia

Projected changes of future climate extremes in Malaysia

Mitigating and adapting to the impacts of climate change at regional level require downscaled projection of future climate states. This paper examined the possible changes of future climate extremes over Malaysia based on the IPCC SRES A1B emission scenario. The projected changes at 17 stations were produced by bias correcting the UKMO PRECIS downscaling simulation output. The simulation expected higher probability of rainfall extreme occurrences over the west coast of Peninsular Malaysia during the autumn transitional monsoon period. In addition, possible early monsoon rainfall was projected for certain stations located over East Malaysia. The simulation also projected larger increase of warm temperature extremes but smaller decrease of cold extremes, suggesting asymmetric expansion of the temperature distribution. The impact of the elevated green house gases (GHG) is higher in the night time temperature extremes as compared to the day time temperature extremes. The larger increment of warm night frequencies as compared to the warm day suggests smaller diurnal temperature ranges under the influence of higher greenhouse gases. Stations located in East Malaysia were projected to experience the largest increase of warm night occurrence

Forecasting El Niño - Southern Oscillation (ENSO) events : a neural network approach

Neural network models were used to seasonally forecast the tropical Pacific sea surface temperature anomalies (SSTA) in the Nino 3.4 region (6°S - 6°N, 120°W - 170°W). The inputs to the neural networks (i.e. the predictors) were the first seven wind stress empirical orthogonal function (EOF) modes of the tropical Pacific (20°S - 20°N, 120°E - 70°W) for four seasons and the Nino 3.4 SSTA persistence for the final season. The period 1952-1981 was used for training the neural network models, and the period 1982-1992 for forecast validation. At 6-month lead time, neural networks attained forecast skills comparable to the other El Nino - Southern Oscillation (ENSO) models. The results suggested that neural network models were viable for ENSO forecasting even at longer lead times of 9 to 12 months. It appeared that at these longer leads, the underlying relationship between the wind stress and Nino 3.4 SSTA became increasingly nonlinear. Two types of neural network models were further compared for forecasting the SSTA over several standard equatorial Pacific regions (Nino 3, 3.4, 3.5, 4, P2, P4 and P5). The first type used the sea level pressure (SLP) as predictor, 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 the earlier models. The wind stress models had better forecast skill at short lead times, while the SLP models generally had better skill at lead times of 6 months or longer. The western-central regions of the equatorial Pacific Ocean were best forecasted, with the Nino 4 region (6°S - 6°N, 160°E - 150°W) having the highest skiU, foUowed by Nino 3.4 and 3.5 (10°S - 6°N, 120°W - 180°), then Nino 3 (6°S - 6°N, 90° W - 150°W). The eastern boundary regions P4 (0 - 10°N, 80°W - 100°W) and P5 (10°S - 0, 80°W - 100° W) had much lower skill, while the western boundary region P2 (10°S - 10°N, 140°E - 180°) had no forecast skill. In an attempt to understand the inner working of the models, smaller networks were constructed with the extended empirical orthogonal functions (EEOF) of the SLP field as inputs. These smaller networks delivered forecasting skills similar to those of earlier models. By network pruning and spectral analyses, four important inputs were identified: modes 1, 2 and 6 of the SLP EEOFs and the SSTA persistence. Mode 1 characterized the low frequency oscillation (LFO, with 4 - 5 years period), and was interpreted as the typical ENSO signal, while mode 2, with a period of 2 - 5 years, appeared to characterize the quasi-biennial oscillation (QBO) plus the LFO. Mode 6 was dominated by decadal and interdecadal variations. Thus, forecasting ENSO seems to require information from the QBO, and the decadal-interdecadal oscillations. The nonlinearity of the networks tended to increase with lead time, and to become stronger for the eastern regions of the equatorial Pacific Ocean.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

Current circulation pattern in waters around Pulau Tinggi, Johor

The current circulation pattern in waters around Pulau Tinggi, Johor was deduced based on the results of the Acoustic Doppler Current Profiler (ADCP) measurements during a period of 16 – 19 August 2004. It appears that the currents, regardless of tidal cycle, were predominantly southerly or southeasterly with average speeds of between 30 – 50 cm s-1. There appears to be current speed horizontal gradient toward the island as the current became weaker as it gets closer to the island. In the upper 10-15 m the currents were slowed by the prevailing winds which were predominantly southeasterly during the period. In the lower layer, about 10 m from seabed, the current speed reduced drastically due to bottom friction. The circulation pattern proves to be a typical pattern of a flow around an island where an evident of an eddy was captured in the observation data in a station located south of the island. Estimated shallow water Reynolds number indicates that the flow may produce a pair vortex of opposite direction and a central return flow at the southern end of the island

Projection of storm surge climate extreme over sunda shelf based on IPCC SRES A2 scenario

The historical and future storm surge climate over the South China Sea Sunda Shelf was derived using a barotropic two dimensional model. The atmospheric forcings were obtained from the UKMO regional climate modeling system, PRECIS (Providing Regional Climates for Impacts Studies), forced at the boundary by the ECHAM4 simulation output under the SRES A2 emission experiment. In general, the model simulates historical sea surface elevation characteristics satisfactory although there is a substantial underestimation for the sea level elevation at local scales. The climate change analysis suggests that the storm surge extreme over the Sunda Shelf is expected to increase along the coastal area of the Gulf of Thailand and east coast of Peninsular Malaysia in the future (2071 – 2100). The projected increment is averagely ~9% over the Sunda Shelf region by the end of the 21st century corresponding to about 5% stronger wind speed as compare to the baseline period of 1961-1990

Climate change and variability over Malaysia: gaps in science and research information

This paper provides an overview of the current available scientific knowledge pertaining to climate change and climate variability over Malaysia. Malaysia is situated in the western part of the Maritime Continent of the Southeast Asian region. Hence, regional climate change and climate variability over this region are of central importance to the understanding of climate change in Malaysia. The latest regional climate downscaling study indicates that, depending on the emission scenario, the mean surface temperature over Malaysia would increase by 3-5oC by the end of the 21st century. The mean precipitation is projected to decrease (increase) during Northern Hemisphere winter (summer). However, future variabilities associated with regional phenomena such as the monsoon, El Nino-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Madden-Julian Oscillation (MJO) are largely unknown. Current knowledge on the intensity and frequency of future extreme events (drought and flood) is limited. This is also the case for regional sea level rise and long-term changes in regional seas, especially in the southern region of the South China Sea. We conclude that knowledge gap in the science of climate change over Malaysia and the surrounding region remains wide

SouthEast Asia HydrO-meteorological droughT (SEA-HOT) framework: A case study in the Kelantan River Basin, Malaysia

A holistic framework was introduced to project the potential hydro-meteorological droughts of the Kelantan River basin, Malaysia. The framework integrates the multi-model high-resolution climate projections of the Coordinated Regional Climate Downscaling Experiment – Southeast Asia (CORDEX-SEA) and the widely applied Soil and Water Assessment Tool (SWAT) model. The quantile mapping approach was used to reduce the biases in the CORDEX-SEA projections before applying into SWAT. The SWAT-simulated standardized streamflow index (SSI) was validated with observed data to check the capability of SWAT in drought estimation. The result indicated that SWAT was able to reproduce the historical 1982, 1987 and 1997–1998 droughts and simulate SSI from one to twelve-month scales well, with the NSE and R2 values of 0.74–0.79 and 0.76–0.80, respectively. Overall, the annual precipitation, maximum and minimum temperatures are projected to change from −8.19 to 13.11% (−13.35 to 10.10%), 0.45 to 2.41 °C (0.43 to 3.99 °C) and 0.73 to 2.98 °C (0.70 to 4.69 °C), respectively, by the end of the 21st century under the RCP4.5 (RCP8.5) scenario. This would cause the future annual streamflow to vary from −10.37 to 31.09% and − 19.87 to 13.24% under RCP4.5 and RCP8.5, respectively, with the reductions are mainly found in the north-western region of the basin. Monthly precipitation and streamflow would be likely to decrease in January and February and increase in September. Robust evidence shows that the meteorological drought duration is likely to become longer in the 2081–2100 period under RCP4.5. Meanwhile, there is not enough evidence to claim that hydrological drought will become more significant in the near future

On the roles of the northeast cold surge, the Borneo vortex, the Madden-Julian Oscillation, and the Indian Ocean Dipole during the extreme 2006/2007 flood in southern Peninsular Malaysia

The mid-December 2006 to late January 2007 flood in southern Peninsular Malaysia was the worst flood in a century and was caused by three extreme precipitation episodes. These extreme precipitation events were mainly associated with strong northeasterly winds over the South China Sea. In all cases, the northeasterlies penetrated anomalously far south and followed almost a straight trajectory. The elevated terrain over Sumatra and southern Peninsular Malaysia caused low-level convergence. The strong easterly winds near Java associated with the Rossby wave-type response to Madden-Julian Oscillation (MJO) inhibited the counter-clockwise turning of the northeasterlies and the formation of the Borneo vortex, which, in turn, enhanced the low-level convergence over the region. The abrupt termination of the Indian Ocean Dipole (IOD) in December 2006 played a secondary role as warmer equatorial Indian Ocean helped in the MJO formation