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Limsakul A.,Environmental Research and Training Center | Singhruck P.,Chulalongkorn University
Atmospheric Research | Year: 2016

Based on quality-controlled daily station data, long-term trends and variability of total and extreme precipitation indices during 1955-2014 were examined for Thailand. An analysis showed that while precipitation events have been less frequent across most of Thailand, they have become more intense. Moreover, the indices measuring the magnitude of intense precipitation events indicate a trend toward wetter conditions, with heavy precipitation contributing a greater fraction to annual totals. One consequence of this change is the increased frequency and severity of flash floods as recently evidenced in many parts of Thailand. On interannual-to-interdecadal time scales, significant relationships between variability of precipitation indices and the indices for the state of El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) were found. These results provide additional evidence that large-scale climate phenomena in the Pacific Ocean are remote drivers of variability in Thailand's total and extreme precipitation. Thailand tended to have greater amounts of precipitation and more extreme events during La Niña years and the PDO cool phase, and vice versa during El Niño years and the PDO warm phase. Another noteworthy finding is that in 2011 Thailand experienced extensive flooding in a year characterized by exceptionally extreme precipitation events. Our results are consistent with the regional studies for the Asia-Pacific Network. However, this study provides a more detailed picture of coherent trends at a station scale and documents changes that have occurred in the twenty-first century, both of which help to inform decisions concerning effective management strategies. © 2015 Elsevier B.V. Source

Limjirakan S.,Chulalongkorn University | Limsakul A.,Environmental Research and Training Center
Journal of the Meteorological Society of Japan | Year: 2012

Based on updated quality controlled daily records, extreme events were defined using temperature indices proposed by the Commission for Climatology/Climate Variability and Predictability project's Expert Team on Climate Change Detection, Monitoring and Indices, and temporal trends during the 1970-2009 period were examined in Thailand. Results revealed that Thailand has indeed experienced significant country-wide warming over the last four decades, and extreme events associated with both the cold and warm extremes of daily minimum and maximum temperature distributions have changed accordingly. Trends in temperature indices showed much spatial trend coherence and widespread significant warming, generally consistent with the regional evidence recently documented in other Asia-Pacific Network countries. Significant upward trends in temperature extreme indices were found in the annual number of warm nights and days, the annual occurrence of warm spells, tropical nights, summer days, and the highest and lowest values of daily minimum temperatures. In contrast, significant downward trends were observed in the annual number of cold nights and days, the annual occurrence of cold spells, diurnal temperature range and annual extreme temperature range. Changes in these temperature extreme indices were consistent with a significant shift in the temperature distribution toward warmer conditions over the recent decades. To address changes in Thailand's temperature more clearly, however, the plausible underlying mechanisms, including urbanization effects, need to be further studied. © 2012, Meteorological Society of Japan. Source

Limsakul A.,Environmental Research and Training Center | Limjirakan S.,Chulalongkorn University | Suttamanuswong B.,Environmental Research and Training Center
EnvironmentAsia | Year: 2010

The Asian monsoon is an important component of the Earth's climate. Its associated rainfall variability is a crucial factor for Thailand's socio-economic development, water resources and agricultural management. An analysis shows that the Thailand rainfall annual cycle is in phase with the Indian summer monsoon (ISM) and the western North Pacific summer monsoon (WNPSM). On the basis of the Empirical Orthogonal Function (EOF) analysis, the dominant spatial-temporal interannual variability in summer monsoon rainfall (Jun.-Sep.) during 1975-2006 could be explained by the first two EOF modes, accounting for 34% of the total variance. The EOF1 was spatially dominated by strong positive signals in the central and east, whereas the EOF2 exhibited dipole variability. The coefficient time series of EOF1 significantly correlated positively with ISM index, but negatively with WNPSM index. The results suggest that summer monsoon rainfall in Thailand is higher (lower) than normal during the strengthening (weakening) of ISM. In contrast, rainfall in the north-east (central) is surplus (deficit) during the strengthening (weakening) of WNPSM. These findings imply that, on an interannual time scale, ISM and WNPSM exert their influence to a different extent on summer monsoon rainfall in Thailand. A clear picture of linking mechanisms and interactions with another climate mode in the Indo-Pacific sector needs to be understood. This knowledge is essential for effectively adapting to climate-related hazards and rainfall extremes and for better management of water resource and agriculture in Thailand, especially under current/future warming conditions. Source

Nawaz R.,Asian Institute of Technology | Parkpian P.,Asian Institute of Technology | Garivait H.,Environmental Research and Training Center | Anurakpongsatorn P.,Kasetsart University | And 2 more authors.
Communications in Soil Science and Plant Analysis | Year: 2012

The impacts of simulated acid rain on leachability of major plant nutrients, toxic element [aluminum (Al)], and acidity development in highly weathered tropical soils of Thailand were studied. Leaching experiments were conducted on soil columns with acidic solutions of pH 5.0, 4.0, 3.0, 2.0, and with water of pH 7.0 as a control treatment. Leaching losses of base cations from all soils increased with the decrease in pH associated with simulated acid rain (SAR) additions, and were found to be quite high under SAR with pH 2.0. The leaching removal of these cations was lesser at pH 3.0, 4.0, and 5.0 but greater than that in pH 7.0. The leaching of base cation from the soils depended not only on acid rain pH but also on soil properties, especially cation exchange capacity, soil texture, and initial base content. The significant losses of major plant nutrients [such as potassium (K+), calcium (Ca2+), and magnesium (Mg2+)] from the plant root zone over extended periods could cause nutrient imbalance and lower soil productivity. © 2012 Copyright Taylor and Francis Group, LLC. Source

Yamashita N.,Asia Center for Air Pollution Research | Ohta S.,Kyoto University | Sase H.,Asia Center for Air Pollution Research | Kievuttinon B.,1 Phaholyothin Road | And 3 more authors.
Geoderma | Year: 2011

Seasonal changes in multi-scale spatial variation in soil chemical properties, which may be controlled simultaneously by biotic and abiotic factors, have not been studied in tropical dry forests. We evaluated the spatial variation of physico-chemical soil properties, plant litter and terrain attributes at multiple scales in a tropical dry evergreen forest using multivariate geostatistics. Soil samples were collected at different depths using nested interval sampling during 1- and 10-m intervals in both the wet and dry seasons. We measured pH, exchangeable cations (Ex-K+ and Ex-Ca2+), acidity (Ex-H+ and Ex-Al3+), particle size (clay and sand contents), and forest floor mass (Oi and Oa). Pronounced spatial variation in pH was observed in surface soil (0-5cm) but not in deeper soil (5-55cm). Multi-scale spatial structures with short (20m) and long (86m) ranges were observed in the auto- and cross-variograms of soil, litter and slope gradient. Pronounced multi-scale structures were observed simultaneously in pH and Ex-Ca2+ both in the wet and dry seasons. Only a short-range structure was observed in Ex-K+ and Oa, whereas a long-range structure was pronounced in sand contents and slope gradients. Although the variograms had similar shapes between wet and dry seasons for almost all variables, the short-range structure of the cross-variogram between Oa with pH and base cations was more pronouncedly developed in the wet season than in the dry season. Scale-dependent correlation coefficients suggest that a small-scale spatial variation in pH was connected to heterogeneous litter accumulation via base-cation input, whereas long-range spatial variation was simultaneously linked to particle size and slope gradient. This multivariate geostatistical approach applied within a stand detected biotic and abiotic factors controlling spatial variation in soil properties at both short and long distances. © 2011 Elsevier B.V. Source

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