.[1] Since large-scale variations in photosynthetically active radiation (PAR) influence the terrestrial carbon sources and sinks through the plant photosynthesis variations, large-scale evaluation of PAR is required. In the present study a simple PAR estimation model was developed for Southeast Asia, where large-scale forest fires occurred during El Niño years. The model considered the smoke aerosol released by forest fires using satellitebased smoke detection methods. A comparison study with ground-based solar radiation data for Malaysia and Thailand indicated that the current model could estimate monthly PAR with 10% (root-mean-square) accuracy and would successfully trace the seasonal and year-to-year variations in PAR, including the forest fire periods. During the peaksmoke month in Indonesia, September 1997, the reduction of PAR by smoke reached 63-75% in the center of the Kalimantan and Sumatra Islands. From the analyses of the smoke and cloud cover impacts on PAR in 1997-1999, annual PAR variations were found to be mostly regulated by smoke variations on the Malay Peninsula, Sumatra, and Kalimantan Islands and cloud cover variations on the Indo-China Peninsula. Thus annual variations in PAR changed with location. These variations did not simply correlate with year-to-year variations in cloud cover associated with the El Niño and La Niña cycle, but exhibited more complicated spatial variations due to the existence of smoke in Southeast Asia.

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Thailand is a one of the nation in Southeast Asia, covered by numerous mangrove areas approximately 244,000 hectares. Phetchaburi province is the one of the province in Thailand where the mangrove area has been increasing continually since King's Royally Initiated Laem Phak Bia Environmental Research and Development Project has been set up. The mangrove ecosystems functions are vital to the livelihood of the surrounding community. Laem Phak Bia community is one that has been served from mangrove ecosystem services. This study assessed the economic value of Laem Phak Bia mangrove ecosystem services in an area approximately 237.44 hectares using Participatory Economic Valuation (PEV) by the villagers ranking and rating the importance of mangrove ecosystem services with a valuable thing for living that is the rice value. The results showed that this mangrove area was worth a total economic value about 100 million Baht per year or 424 thousand Baht per hectares per year. It could be divided into the value of regulation functions, production functions, habitat functions and information functions, which were about 38, 8, 25, and 29 million Baht per year, respectively.

Abstract:Measurements of CO2 flux (FCO2 ) and H2 O flux (FH2O) were carried out on paddy fields of Thailand and Japan during the 2004, 2005 and 2006 growing seasons using the Bowen ratio technique. The objective was to determine the water resource requirement to achieve a certain amount of CO2 assimilation per land area and analyze the ratio between FCO2 and FH2 O (CWFR = FCO2/FH2O). The relationship between FCO2 and FH2O was investigated using regression analysis in 4 growing stages. Relatively high correlations (r 2 = 0.56 0.96, p < 0.01) between FCO2 and FH2O were found when data were grouped by growing stage. Using daytime average data, there was high correlation (r 2 = 0.61 0.94, p < 0.01) between daytime average CWFR (CWFRd) and daytime average vapor pressure deficit (VPDd) in paddy fields of Japan and Thailand for each growing stage. Pooled data from Thailand and Japan showed high correlations (r 2 = 0.61 0.94, p < 0.01) between CWFRd and VPDd for each growing stage. The developed regression equation was tested using an independent published dataset, and it was found that the estimation error was only 2.7%. The regression equations will be useful for estimating CWFRd by only VPDd and accordingly for assessing the water resource requirement. KEYWORDS carbon dioxide flux; carbon dioxide flux and water vapour flux ratio; paddy rice field; vapour pressure deficit; water vapour flux.