This study investigates the southwest monsoon circulation and temperature along the east coast of Peninsular Malaysia by using the Regional Ocean Modeling System at 9 km resolution. The simulated circulation shows strong northward flowing western boundary currents along the east coast of Peninsular Malaysia with maximum speed of approximately of 0.6-0.7 ms-1. The western boundary current, that extends to a depth of about 35 m, continues flowing northward up to approximately 7oN where it changes direction eastward. The circulation along the east coast of Peninsular Malaysia is also characterized by two anti-cyclonic eddies. Furthermore, an elongated of cooler sea surface temperature that stretches along the coast was also simulated. The existence of this cool SST pattern is associated with coastal upwelling process due to localized lifting of isotherms near the coast as a response to the southerly-southwesterly wind stress along the coast during the southwest monsoon.
The statistical characteristics of wind direction that was recorded at maximum wind speed in Peninsular Malaysia for two monsoons from 1999 to 2008 for seven stations were analyzed in this study. Modeled by von Mises distribution, the change in parameters values namely mean direction and concentration parameter was measured. Statistical summary, graphical representations, Watson-William Test and linear-circular correlation are used in the analysis. It is found that there is a significant change in the mean direction of wind over the period of ten years for most stations in Peninsular Malaysia. However, there is a weak relationship between wind direction and wind speed. This study suggested the presence of prominent direction of wind that blows in Peninsular Malaysia by monsoon. This finding may provide useful information on giving a better understanding of the behavior of the wind in Peninsular Malaysia and the potential use of wind as an alternative source of energy.
Analysis of observed Indian Summer Monsoon precipitation reveals more increase in extreme precipitation (in terms of its magnitude) over south India compared to north and central India during 1971-2017 (base period: 1930-1970). In the future, analysis of precipitation from the Coordinated Regional Downscaling Experiment indicates a southward shift of precipitation extremes over South Asia. For instance, the Arabian Sea, south India, Myanmar, Thailand, and Malaysia are expected to have the maximum increase (~18.5 mm/day for RCP8.5 scenario) in mean extreme precipitation (average precipitation for the days with more than 99th percentile of daily precipitation). However, north and central India and Tibetan Plateau show relatively less increase (~2.7 mm/day for RCP8.5 scenario). Analysis of air temperature at 850 mb and precipitable water (RCP4.5 and RCP8.5) indicates an intensification of Indian Ocean Dipole in future, which will enhance the monsoon throughout India. Moisture flux and convergence analysis (at 850 mb) show a future change of the direction of south-west monsoon winds towards the east over the Indian Ocean. These changes will intensify the observed contrast in extreme precipitation between south and north India, and cause more extreme precipitation events in the countries like Myanmar, Thailand, Malaysia, etc.
This study investigated the spatial pattern and trends of the daily rainfall data in Peninsular Malaysia based on seasonal rainfall indices. Five rainfall indices which describe the main characteristics of rainfall, the total amount of rainfall, frequency of wet days, rainfall intensity, extreme frequency, and extreme intensity, were employed in this study. The statistics of rainfall indices were calculated in terms of their means for four regions in Peninsular Malaysia for the period 1975 to 2004. The findings indicate that the southwest monsoon had the greatest impact on the western part of the Peninsula, particularly in characterizing the rainfall pattern of the northwest region. During this season, the northwest region could be considered as the wettest region since all rainfall indices tested are higher than in other regions of the Peninsula. Otherwise, the northwest region is denoted as the driest part of the Peninsula during the northeast monsoon period. The northwest region is less influenced by the northeast monsoon because of the existence of the Titiwangsa Range, which blocks the region from receiving heavy rainfall. On the other hand, it is found that the lowlands areas such as the eastern part of the Peninsula are strongly characterized by the northeast monsoonal flow. Based on the results of the Mann-Kendall test, as the trend of the total amount of rainfall and the frequency of wet days during the southwest monsoon decrease at most of the stations, the rainfall intensity increases. In contrast, increasing trends in both the total amount of rainfall and the frequency of wet days were observed at several stations during the northeast monsoon, which give rise to the increasing trend of rainfall intensity. The results for both seasons indicate that there are significantly decreasing trends in the frequency of wet days during the extreme events for most of the stations on the peninsula. However, a smaller number of significant trends was found for extreme intensity.
This study attempts to trace changes in the wet spells over Peninsular Malaysia based on the daily rainfall data from 32 selected rainfall stations which include four sub-regions; northwest, west, south and east, for the period of 1975 to 2004. Six wet spells indices comprising of the main characteristics (maximum, mean, standard deviation), the persistency of two consecutive wet days and the frequency of the short and long duration of wet spells will be used to identify whether or not these indices increase or decrease over Peninsular Malaysia during the monsoon seasons. The study indicates that the eastern areas of the peninsula could be considered as the wettest areas since almost all the indices of wet spells over these areas are higher than over the other regions during the northeast monsoon (NE). The Mann-Kendall (MK) trend test revealed that almost all of the stations located in the eastern areas of the peninsula exhibited a positive trend in the mean, variability and persistency of wet spells indices during the NE monsoon, while a negative trend was observed during the southwest monsoon (SW) in these areas. Moreover, these indices showed a positive trend, and at the same time a decreasing trend was observed in the frequency of the long wet spells in most stations located over the west coast of Peninsular Malaysia during the SW monsoon for the period of 1975 to 2004.
Typhoons have devastating impacts across many Asian countries. Vietnam is presently one of the most disaster-prone nations. Typhoons regularly disrupt human lives and livelihoods in various ways and cause significant damage. Making efficient policy decisions to minimize the vulnerability of affected communities is crucial. This requires a deep understanding of the factors that make a society vulnerable to extreme events and natural disasters. An appropriate approach is integrating the three dimensions of hazard, exposure and sensitivity, and community adaptive capacity. However, the vulnerability and adaptive capacity response to typhoons within Vietnam is poorly investigated. Here, we develop a conceptual framework that incorporates 21 indicators to identify vulnerability and adaptive capacity (VAC) using geospatial techniques at regional scales, applied over Vietnam. We find large spatial differences in VAC and are able to identify the top-priority regions that need to enhance their adaptation to typhoons. The Southern Coastal area, South East and Red River Delta demonstrate high and very high vulnerability because of their physical features and the intensity of typhoons that frequently cross these parts of Vietnam. The lower Mekong Delta and Northern Coastal areas are vulnerable to typhoon-driven flood threats, in particular where compounded by sea-level rise. Our framework successfully identified the spatial distribution and different levels of VAC within acceptable limits of uncertainty. It can therefore serve as a template to tackle national issues in disaster risk reduction in Vietnam and assist in the development of suitable mitigation strategies to achieve sustainable outcomes.
Stormwater runoff is recognized as a cause of water quality degradation because it may carry nitrogen (N) and other pollutants to aquatic ecosystems. Stormwater ponds are a stormwater control measure often used to manage stormwater runoff by holding a permanent pool of water, which reduces the peak flow, magnitude of runoff volume, and concentrations of nutrients and pollutants. We instrumented the outlet of a stormwater pond in an urban residential neighbourhood in Florida, United States to (1) investigate the concentration and composition of N forms during the summer rainy season (May to September 2016), and (2) determine the bioavailability of organic N in the stormwater pond with a bioassay experiment. A total of 144 outflow water samples over 13 storm events were collected at the outlet of the stormwater pond that collects runoff from the residential catchment. Samples were analysed for various inorganic N [ammonium (NH4-N), nitrate (NO3-N)], and organic N forms [dissolved organic nitrogen (DON), and particulate organic nitrogen (PON)]. Flow-weighted mean concentration of total N (TN) in pond outflow for all collected storm events was 1.3±1.42 mg L-1, with DON as the dominant form (78%), followed by PON and NO3-N (each at 8%), and NH4-N (6%). In the bioassay experiment, organic N (DON+PON) was significantly decreased by 25-28% after 5 days of incubation, suggesting that a portion of the DON carried from the pond outflow to receiving water bodies may be bioavailable. These results suggest that efforts to mitigate stormwater N outflows from urban ponds should incorporate both inorganic and organic N in management plans.
This study was carried out during the period 1989-2011. The following areas were included: Vietnam, Laos, Cambodia, Indonesia, and Malaysia. Climax tropical forest and anthropogenically transformed ecosystems, including those damaged by the chemical warfare program of the United States in Vietnam, were investigated. Some regularities in the structure dynamics and functioning of forests ecosystems under a tropical monsoon climate have been revealed. The principles of classification of tropical forests have been elaborated. The major results of investigation of the tropical monsoon forests in Vietnam are given.