Chao Phraya Research Articles

A Report on Classical Cytogenetics of Hihgfin Barb Fish, <i>Cyclocheilichthys armatus</i> (Cypriniformes, Cyprinidae)

Conventional staining and Ag-NORs banding techniques were applied on the chromosomes of hihgfin barb fish, Cyclocheilichthys armatus. Specimens were collected from the Chao Phraya River, Thailand. The mitotic chromosome preparations were directly obtained from kidney tissues of eight males and eight females. The results revealed that the diploid chromosome numbers of C. armatus was 2n=50 and the fundamental number (NF) was 94 in both males and females. The karyotype consists of four large metacentric, six large submetacentric, two large acrocentric, eight medium metacentric, 12 medium submetacentric, 12 medium acrocentric and six medium telocentric chromosomes. No sex chromosome was observed. Ag-NORs indicating NORs were clearly exhibited at the region adjacent to telomere of the short arm of some chromosomes. The NORs located on chromosomes of the metacentric chromosome pair 3 and the submetacentric chromosome pair 7. The karyotype formula of C. armatus is 2n=50=Lm4+Lsm6+La2+Mm8+Msm12+Ma12+Mt6. Cytogenetic data of cyprinid fishes can be used as the basic knowledge for enhancing the existing cytotaxonomic information and chromosome evolution of the Cyprinidae especially in the genus Cyclocheilichthys.

Quantification of Seasonal Precipitation over the upper Chao Phraya River Basin in the Past Fifty Years Based on Monsoon and El Niño/Southern Oscillation Related Climate Indices

For better water resources management, we proposed a method to estimate basin-scale seasonal rainfall over selected areas of the Chao Phraya River Basin, Thailand, from existing climate indices that represent variations in the Asian summer monsoon, the El Niño/Southern Oscillation, and sea surface temperatures (SST) in the Pacific Ocean. The basin-scale seasonal rainfall between 1965 and 2015 was calculated for the upper Ping River Basin (PRB) and the upper Nan River Basin (NRB) from a gridded rainfall dataset and rainfall data collected at several gauging stations. The corresponding climate indices, i.e., the Equatorial-Southern Oscillation Index (EQ-SOI), Indian Monsoon Index (IMI), and SST-related indices, were examined to quantify seasonal rainfall. Based on variations in the rainfall anomaly and each climate index, we found that IMI is the primary variable that can explain variations in seasonal rainfall when EQ-SOI is negative. Through a multiple regression analysis, we found that EQ-SOI and two SST-related indices, i.e., Pacific Decadal Oscillation Index (PDO) and SST anomalies in the tropical western Pacific (SSTNW), can quantify the seasonal rainfall for years with positive EQ-SOI. The seasonal rainfall calculated for 1975 to 2015 based on the proposed method was highly correlated with the observed rainfall, with correlation coefficients of 0.8 and 0.86 for PRB and NRB, respectively. These results suggest that the existing indices are useful for quantifying basin-scale seasonal rainfall, provided a proper classification and combination of the climate indices are introduced. The developed method could forecast seasonal rainfall over the target basins if well-forecasted climate indices are provided with sufficient leading time.

Major typhoon phases in the upper Gulf of Thailand over the last 1.5 millennia, determined from coastal deposits on rock islands

Rapid growth of Asian megacities, exemplified by the megacity of Bangkok, Thailand, with a population of over 10 million inhabitants, means that an increasing number of people are living in low-lying coastal areas exposed to hazards such as typhoons. While Bangkok has always been considered not to be at risk from typhoon strikes, recent discoveries of elevated carbonate boulder deposits have started to question this assumption. This work reports on findings from the islands of Ko Khang Khao and Ko Phai, farther north and west than earlier studies, and adds to the existing body of evidence for prehistorical typhoon-driven high energy marine inundation (HEMI) events penetrating northwards into the Bay of Bangkok. Elevated carbonate boulder deposits up to 6 m amsl indicate that these were emplaced by waves generating onshore minimum flow velocities between 3.0 and 5.5 m/s, consistent with typhoon-impacted coastlines elsewhere in the tropical Asia-Pacific region. When viewed in conjunction with other data from the Bay of Bangkok their chronologies indicate age clusters around four major phases of activity in AD 600–700, AD 900–1000, AD 1150–1250 and AD 1400–1650. At 250 years duration, the last phase of activity was the longest, but it has also been followed by the longest period of quiescence that has coincided with rapid urban growth in and around the city of Bangkok. The re-occurrence of typhoon-driven HEMI events on the scale of the prehistorical events reported here would threaten all the low-lying coasts in the Bay of Bangkok, including the Chao Phraya delta, and as such these results indicate an urgent need to re-evaluate coastal hazards for the region.

The Influence of Climate Variability Effects on Groundwater Time Series in the Lower Central Plains of Thailand

This research studies the relationship between the climate index and the groundwater level of the lower Chao Phraya basin, in order to forecast the groundwater level in the studied area by using Autoregressive Integrated Moving Average with Explanatory (ARIMAX). The combination of 6 climate indices—Dipole Mode Index, Indian Summer Monsoon Index, Multivariate ENSO Index, Sea Surface Temperature NINO4, Southern Oscillation Index and the Western North Pacific Monsoon Index—were used, along with the groundwater level data from 14 stations during the period 1980–2011 to develop the forecast model and verify it with the data of 2012.The first step was correlation of the ARIMA model with Autocorrelation Function and Partial Autocorrelation Function. The possible model was then selected using BIC statistics. Diagnostic Checking was done to consider the white noise characteristic of estimated residuals by using the statistics of Box and Ljung (Q-statistic). If the selected models were found to be proper, then the Granger Causality Test of the leading parameters or the climate index would be performed as the next step. The results show that there is a relationship between the groundwater level and the climate index. The model could be used to forecast effectively the average RMSE value at 0.6. The last step was to develop the MODFLOW for a conceptual model and synthesize groundwater levels in the study area, which covers around 43,000 km2 and has 8 layers of groundwater, with Bangkok clay on the top. All other boundary values were set to be steady. The calibration was done using the data of 325 observed wells. The normalized RMS value was 9.705%. The results were verified by the data using ARIMAX over the same time periods. To conclude, the simulated results of the monthly groundwater level in 2012 of the wells have a confidence interval of around 95%, which is near the result from the ARIMAX model. The advantages of the ARIMAX model include high accuracy, no requirement for a large amount of data and inexpensive implementation. It is one of the effective tools for the groundwater prediction.

Performance evaluation of Bacteroidales genetic markers for human and animal microbial source tracking in tropical agricultural watersheds.

Microbial source tracking (MST) DNA-based assays have been used to successfully solve fecal pollution problems in many countries, particularly in developed nations. However, their application in developing countries has been limited but continues to increase. In this study, sixteen endpoint and quantitative PCR (qPCR) assays targeting universal and human-, swine-, and cattle-specific Bacteroidales gene markers were modified for endpoint PCR, evaluated for their performance with sewage and fecal samples from the Tha Chin watershed and subsequently validated with samples from the Chao Phraya watershed, Thailand. Sample sizes of 81 composite samples (from over 1620 individual samples) of farm animals of each type as well as 19 human sewage samples from the Tha Chin watershed were calculated using a stratified random sampling design to achieve a 90% confidence interval and an expected prevalence (i.e., desired assay's sensitivity) of 0.80. The best universal and human-, swine-, and cattle-specific fecal markers were BacUni EP, HF183/BFDrev EP, Pig-2-Bac EP, and Bac3 assays, respectively. The detection limits for these assays ranged from 30 to 3000 plasmid copies per PCR. The positive predictive values were high in universal and swine- and cattle-specific markers (85-100%), while the positive predictive value of the human-specific assay was 52.2%. The negative predictive values in all assays were relatively high (90.8-100%). A suite of PCR assays in Thailand was established for potential MST use in environmental waters, which supports the worldwide applicability of Bacteroidales gene markers. This study also emphasizes the importance of using a proper sample size in assessing the performance of MST markers in a new geographic region.

Land-water-energy nexus of sugarcane production in Thailand

Abstract Agriculture is a key economic sector for developing countries confronting challenges on the overexploitation of land and water resources for food and biofuels crop production. Sugarcane is recognized as a promising crop serving both food and bioenergy needs that are being promoted leading to expansion of the plantation areas. The study assesses the land-water-energy nexus of irrigated and non-irrigated sugarcane production systems in the Chao Phraya and Chi watersheds of Thailand using carbon footprint, ecological footprint, and water scarcity footprint. The results indicate that freshwater resource is essential to sugarcane productivity improvement. Irrigation helps increase the sugarcane yields around 23–54% as compared to the non-irrigated system; the carbon and ecological footprint of sugarcane products are also consequently decreased by around 11–36% and 15–35%, respectively. Nevertheless, the water scarcity potential would be increased. Hence, the efficient irrigation technology like drip irrigation is an important factor to drive sustainable sugarcane production in the future. Land-water-energy nexus management measures for improving sustainability of sugarcane production are also recommended.

Ecological Structure of a Tropical Urban Forest in the Bang Kachao Peninsula, Bangkok

Rapid urbanization has changed the structure and function of natural ecosystems, especially floodplain ecosystems in SE Asia. The ecological structure of vegetation stands and the usefulness of satellite images was investigated to characterize a disturbed tropical urban forest located in the Chao Phraya River lower floodplain, Thailand. Nine sample plots were established on the Bang Kachao Peninsula (BKP) within 4 tropical forest types in an urban area: rehabilitation forest, home-garden agroforestry, mangrove and park. The tree habitats were beach forest, swamp forest, moist evergreen forest, dry evergreen forest, mangrove forest and abandoned orchard or home-garden. Normalized difference vegetation index (NDVI) values obtained from Landsat 7 satellite images were correlated with plant structure from field surveys. NDVI had the highest relationship with stand factors for number of families, number of species, Shannon-Weiner index and total basal area. Linear regression predicted well the correlation between NDVI and stand factors for families and basal area. NDVI trends reflected urban tropical forest typing and biodiversity, being high in rehabilitation and mangrove forests, moderate in home-gardens and low in parks. We suggest that the application of NDVI for assessments can be useful for future planning, monitoring and management of the BKP and hence may contribute for increasing biodiversity and complexity of these urban forests.

Infrastructure in the Making: The Chao Phraya Dam and the Dance of Agency

AbstractThe article explores the process behind the construction of the Chao Phraya Dam, the first World Bank-funded water infrastructure project in Thailand, developed during the 1950s. Employing Andrew Pickering's ‘dance of agency’ concept in examining the process of turning financial and technical assistance into a workable project, I argue that development infrastructure, like the Chao Phraya Dam, provides a space to explore the dialectic operations – accommodation and resistance – of agency and the unstable associations among diverse actors, expertise, institutions, and materials, as well as practices. Recounting the history of the dam in the making, I explore a series of entanglements through different dances of agency, namely initiation, assessment, mobilisation, negotiation, adjustment, confrontation, and settlement. Such a multiplicity of dancesinsideandin the makingof infrastructure reflects the techno-political entanglement encompassing the manifold negotiation and adjustment of conflicting goals, interests, recognition, and cooperation among different agencies. The dam, often portrayed as an engineering achievement of the state, is in fact the result of unanticipated relations and the responses to the temporal emerging forms of practices.

Impact of climate change on the groundwater sustainability in the lower Chao Phraya basin, Thailand

This research investigates the impact of climate change on the hydraulic heads of Thailand's Lower Chao Phraya basin. The research also determines the sustainability of groundwater as the result from climate change. In the study, the climatic scenario (IPSL-CM5A-MR) of the Representative Concentration Pathways (RCP) between 2.6, 4.5 and 8.5 were considered, and the simulations were carried out using the three-dimensional groundwater flow model (i.e. MODFLOW-2000) predicting the groundwater behavior between 2017 and 2036. The findings revealed that the impact of climate change on the hydraulic head fluctuation was positively correlated. Specifically, under the IPSL-CM5A-MR RCP 4.5 that has the highest average precipitation, the average hydraulic head increased. In conclusion, the sustainability of groundwater in the Lower Chao Phraya basin was sufficient during the simulated time. However, the groundwater budget was lower than the average groundwater budget during 2009 – 2014 indicating, the groundwater storage was continuously decreased. Specifically, the 2nd, and 3rd (Phra Pradeang and Nakorn Luang) aquifers may be facing the groundwater shortage in the future.

Professor Nara Vaeusorn: the Asia Pacific Society of Cardiovascular Interventional Radiology (APSCVIR) gold medal award recipient for 2018

It was such a memorable moment to have a 2-hour talk with Professor Nara Vaeusorn at the west bank of the Chao Phraya River in Bangkok, the number 1 destination of tourists worldwide, in the vicinity of Siriraj Hospital, the largest hospital in Southeast Asia, where he started his legacy as the first radiological interventionist of Thailand in 1979. Initially aimed to be a radiotherapist but was later advised to be a diagnostic radiologist, Professor Nara Vaeusorn, born in 1934, found his great interest in angiology in his last year of residency at John Hopkins Medicine, 12 years after Dr. Seldinger’s technique had opened the new era of angiology and, later on, radiological intervention in 1953 [1]. After having been working in angiology with Professor Rojana Suvanasuthi who first described and introduced Seldinger’s technique in Thailand in 1959 [2] (but it was Dr. Sillawat Arthachinta who literally put this technique into practice for the first time in Thailand in 1963 [3]), he introduced the first successfully performed interventional procedure in Thailand which was embolization of an arteriovenous malformation at the left shoulder in a young female. The nationwide respect and recognition that interventional radiology obtained as a highly-effective, minimally-invasive treatment of bleeding in patients from obstetric-gynecologic, surgery and internal medicine departments in Siriraj Hospital are attributable to not only the success of this novel kind of treatment, but also his outstanding personality, his effective team, his impeccable system and trust-building among physicians.

Implications of Water Use and Water Scarcity Footprint for Sustainable Rice Cultivation

Rice cultivation is a vital economic sector of many countries in Asia, including Thailand, with the well-being of people relying significantly on selling rice commodities. Water-intensive rice cultivation is facing the challenge of water scarcity. The study assessed the volumetric freshwater use and water scarcity footprint of the major and second rice cultivation systems in the Chao Phraya, Tha Chin, Mun, and Chi watersheds of Thailand. The results revealed that a wide range of freshwater use, i.e., 0.9–3.0 m3/kg of major rice and 0.9–2.3 m3/kg of second rice, and a high water use of rice was found among the watersheds in the northeastern region, like the Mun and Chi watersheds. However, the water scarcity footprint results showed that the second rice cultivation in watersheds, like in Chao Phraya and Tha Chin in the central region, need to be focused for improving the irrigation water use efficiency. The alternate wetting and drying (AWD) method was found to be a promising approach for substituting the pre-germinated seed broadcasting system to enhance the water use efficiency of second rice cultivation in the central region. Recommendations vis-à-vis the use of the water stress index as a tool for agricultural zoning policy were also discussed.

Attitudes Towards Changes in Landscape from Chao Phraya Riverfront Extension Project: Community and Commercial Areas

This research studies public attitudes towards changes in the landscape from Chao Phraya riverfront extension project in urban areas, especially in residential communities and commercial areas in order to propose the guidelines for mitigation of the public attitudes in regard to the changes in the landscape along the river. The research framework is applied from the Visual Impact Assessment. The research may be described in six parts. They are: 1) Reviewing and surveying the study areas, selecting representative sites, 2) Define variables of the research, 3) Define population sampling, 4) Designing photo – questionnaires as photomontage technique was applied on selected pictures to depict the appearance of 4 mock-up riverfront extension areas on the front of 3 representative sites and collect data 105 sets, 5) Data analysis using the statistical tools, 6) Summarizing results and formulating guidelines for appropriate developments. The findings indicates that the extension areas along the Chao Phraya River in the residential communities and commercial areas affects public attitudes in different ways. The positive attitudes towards the changes have decreased in the areas where present conditions are already in good condition and look attractive. However, the negative attitudes have decreased in the areas where current conditions are deteriorated. Therefore, the extension areas may not be only the element affecting public attitudes toward changes. The study result reveals that significant elements which affect the attitudes towards changes in negative ways for all the representative sites are the oversized width of the extension areas along the river.

Vegetation community and factors that affect the woody species composition of riparian forests growing in an urbanizing landscape along the Chao Phraya River, central Thailand

Improved knowledge of the environmental factors that affect woody composition is urgently required for species conservation in riparian zones of urbanizing landscapes. We investigated the environmental factors influencing tree abundance and regeneration in diverse forest types growing in the riparian area of an urbanizing landscape along the Chao Phraya River. We established 252 0.1-ha circular plots in remnant forest patches along 372km of the river. Cluster analysis was applied to classify the forest types. The relationships between environmental variables and tree abundance were assessed with ordination analysis, and generalized linear models were used to assess seedling/sapling abundance. The cluster analysis revealed five forest types, including floodplain forest with three sub-forest types, swamp forest, and mangrove forest. The ordination indicated that tree abundance in the floodplain forest was positively affected by distance to the ocean and the proportion of forested area. Swamp forest was positively influenced by the proportion of urbanized area and mean rainfall. Mangrove forest was negatively related to distance to the river. Seedling/sapling abundance of the dominant species in the floodplain forests was positively affected by lowland plain topography and negatively affected by the proportion of urbanized area, whereas swamp and mangrove forest species were positively influenced by the proportion of urbanized area and estuarine topography. Mature tree density influenced seedling/sapling abundance of all forest types. Tree abundance and regeneration of the riparian landscape was prevented by the urbanized area, floodplain, estuarine topography, and mature tree densities in remnant forests. These results suggest that remnant forest patches of conserved riparian forests along the urbanized landscape of the Chao Phraya River must be protected and the factors determining their colonization must be considered to enhance restoration practices.

Concrete and corruption

Why do Thai citizens look to concrete to reveal political scandal? What do their readings of corruption in overbuilt, failed and obdurate structures tell us about the relationship between politics and construction in Thailand? How do these readings help us better understand the political power of this material and its enactments? In this paper, I trace the relationship between concrete and claims of corruption through three different projects—a recently proposed bike path along the Chao Phraya River, Suvarnabhumi International Airport and the failed Hopewell Rail project. I argue that the materiality of concrete is itself fundamental to these claims of corruption as it helps materialise the social relationships that produce projects rendering them visible and open to public critique. When a project has too much concrete, fails or remains in place long after it has become obsolete, the material allows urbanites to discuss the powerful relationship between capital, political power and the building. Cracking concrete thus reveals both situated political failures and deep structures of political inequality simultaneously.

Deep Shear Wave Velocity of Southern Bangkok and Vicinity

Bangkok is located on the soft marine clay in the Lower Chao Phraya Basin which can amplify seismic wave and can affect the shaking of buildings during an earthquake. Deep shear wave velocity of the sediment in the basin are useful for study the effect of the soft sediment on the seismic wave and can be used for earthquake engineering design and ground shaking estimation, especially for a deep basin. This study aims to measure deep shear wave velocity and create 2D shear wave velocity profile down to a bedrock in the southern Bangkok by the Microtremor measurements with 2 seismographs using Spatial Autocorrelation (2-SPAC) technique. The data was collected during a day time on linear array geometry with offsets varying between 5-2,000 m. Low frequency of natural tremor (0.2-0.6 Hz) was detected at many sites, however, very deep shear wave data at many sites are ambiguous due to man-made vibration noises in the city. The results show that shear wave velocity of the sediment in the southern Bangkok is between 100-2,000 ms-1 and indicate that the bedrock depth is about 600-800 m, except at Bang Krachao where bedrock depth is unclear.

First report on classical and molecular cytogenetics of archerfish, Toxotes chatareus (Perciformes: Toxotidae)

A detailed account of liner delineation of chromosomes of archerfish, Toxotes chatareus (Perciformes: Toxotidae) employing conventional staining, NOR banding and molecular cytogenetics with fluorescence in situ hybridization (FISH) using 5S, 18S rDNAs and microsatellite d(CA)15, d(GA)15, d(CAA)10, d(CGG)10, and retrotransposonable Rex6 probes, is presented for the first time. The specimens were collected from the Chao Phraya River, Thailand. The mitotic chromosome preparations were directly carried out from kidney tissues of eight male and female fish each. The results revealed that the diploid chromosome number of T. chatareus was 2n = 48, the fundamental numbers (NF) were 50 in both male and female. The karyotype composed of two metacentric and 46 telocentric chromosomes. No irregularly sized chromosomes related to sex were observed. The nucleolar organizer regions (NORs) were detected by Ag-NOR banding and 18S rDNA probe mapping. Both techniques revealed the presence NORs located on the long arm adjacent to the centromere of the single pair of the largest telomeric chromosome pair. The 5S rDNA sequences were located in two large telocentric pairs. One of them is coincident with 18S rDNA sites and another is found at interstitial subcentromeric region of the second telomeric pair. FISH with d(CA)15 and d(GA)15 probes showed that hybridization signals are abundantly distributed in all chromosomes, mostly in telomeric regions while d(CAA)10 and d(CGG)10 repeats are distributed in all chromosomes with high accumulation throughout the chromosomes in some pairs. Chromosomal mapping of the Rex 6 sequences, indicate a weak distribution in all chromosomes, with preferential accumulation at the centromere of the chromosome pair 7.

Wavelet relationship between climate variability and deep groundwater fluctuation in Thailand’s Central Plains

Groundwater is constantly under direct and indirect pressures from the anthropogenic effects, long-term climate change, and climate variability. This research investigates the association, in the time-frequency domain, between the groundwater fluctuations in Thailand’s Lower Chao Phraya Basin and specific climate variability forces: the El Nino/Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), and the Asian Summer Monsoons (ASM). The analysis was carried out using the wavelet method and the findings presented in the form of the complete, global, and local wavelet spectrums. In addition, the Pearson correlation was utilized to establish the linkages between the groundwater and the climate variability forces. The results indicated that the deep groundwater signals of the Lower Chao Phraya Basin were linked to the ENSO, IOD and ASM with the absolute correlation coefficients in excess of 0.5. Moreover, the recent climatic indices exerted greater influence on the groundwater than in the past, given the former’s correlation coefficients of 0.9 on average. By comparison, the deep groundwater was strongly associated with the recent ENSO and ASM but weakly linked to the IOD, with the absolute coefficients of around 0.5. The findings revealed the resilience of the deep groundwater under such high frequency signal conditions as the seasonal and tidal oscillations. Moreover, the results showed that the groundwater could be an alternative source of water supply during periods of droughts in the region.

Geochemical characteristics of modern river sediments in Myanmar and Thailand: Implications for provenance and weathering

The elemental composition of organic matter and the major and trace element compositions of stream sediments from Myanmar (Ayeyarwady and Sittaung rivers) and Thailand (Mekong and Chao Phraya rivers, and their tributaries) were determined to examine their distributions, provenance, and chemical weathering processes. Higher total organic carbon (TOC) and total nitrogen (TN) contents in the finer grained sediments indicate hydrodynamic energy may control their distributions. TOC/TN ratios indicate inputs of both aquatic macrophyte and higher vascular plant material to the river sediments. The major element abundances of the sediments are characterized by predominance of SiO2 in coarser fractions and a marked negative correlation with Al2O3, representing primary grain size primarily control on SiO2 content. Marked depletion of most labile elements (Na2O, CaO, K2O, Ba and Sr) relative to UCC (upper continental crust), indicate destruction of feldspar during chemical weathering in the source area or during transport. However, enrichment of some high field strength elements (Zr, Th, Ce and Y) relative to UCC and higher Zr/Sc ratios indicate moderate concentration of resistant heavy minerals in finer-grained samples. Discriminant diagrams and immobile trace element characteristics indicate that the Mekong, and Chao Phraya river sediments were largely derived from felsic sources with compositions close to typical rhyolite, dacite/granodiorite, UCC, I- and S-type granites. Relative enrichment of ferromagnesian elements (e.g. MgO, Cr, Ni) and high Cr/V and low Y/Ni ratios in Ayeyarwady and Sittaung sediments indicate the presence of a mafic or ultramafic component in their sources. The ICV (Index of Compositional Variability), CIA (Chemical Index of Alteration), PIA (Plagioclase Index of Alteration), αAl, Rb/Sr and K2O/Rb ratios indicate that the Ayeyarwady and Sittaung sediments record low to moderate degrees of chemical weathering in their source, compared to moderate to intense chemical weathering in the Mekong and Chao Phraya river basins. These results are compatible with existing major ion data for river waters collected at the same locations.

Water stress index and its implication for agricultural land-use policy in Thailand

Land-use change and expansion for agriculture significantly affect freshwater resource availability which in turn results in different levels of water scarcity and competition among users in different areas and time. The study uses the water stress index as an indicator for determining the potential impact of water use considering water deprivation potential. Considering the case of Thailand, the temporal aspects of water withdrawal and availability have been analyzed and characterized as the monthly water stress index for the 25 watersheds in the country. Wide variations of monthly water stress index are obtained; extreme water stress is observed in the areas of the Chao Phraya and Tha Chin watersheds (the central region) during the dry season because of the large areas cultivating second rice (rice planted in dry season). The target of the Thai government on agricultural land-use change and zoning toward the conversion of about 0.37 M·ha of the upland paddy fields with low productivity to sugarcane was evaluated showing serious implications on the monthly water stress index of the relevant watersheds and the water scarcity footprint potentials of rice and sugarcane production. The results reveal that proper policy can help reduce the amount of water requirement for agriculture in June, July, August and September by about 60–220 M·m3, which in turn results in the decrease in monthly water stress index values. Nevertheless, appropriate measures of water resource management for agriculture still need to be designed to avoid water competition as well as protect the ecosystem.

Variations of characteristics of consecutive rainfall days over northern Thailand

The Chao Phraya basin, Thailand, is frequently inundated by flooding during the southwest monsoon period. Most floods coincide with consecutive rainfall days. This study investigated consecutive rainfall days during the southwest monsoon period at 11 stations over northern Thailand, the upstream area of this basin. The Markov chain probability model was used to study the consecutiveness of days with at least 0.1, 10.1, and 35.1 mm of rainfall. The consecutive length of rainfall days from the model showed good agreement with the observed value. A chi-square test of independence was applied to assess the significance of the consecutiveness, and it was found that days with at least 10.1 mm of rainfall tend to be consecutive over the entire area. Moreover, days with at least 35.1 mm of rainfall were found to be consecutive over the joint area where the mountainous region meets the plain area. However, the consecutiveness of days with less than 10.1 mm of rainfall was not obvious. The rainfall amount on days with at least 10.1 mm of rainfall was also calculated and it showed lower values over the mountainous region than over the plain. Hence, this study established the characteristics of consecutive rainfall days over the plain, mountainous region, and joint area.