Thailand plays a central economic and policy-making role in Southeast Asia. Although climate change adaptation is being mainstreamed in Thailand, a well-organized overview of the impacts of climate change and potential adaptation measures has been unavailable to date. Here we present a comprehensive review of climate-change impact studies that focused on the Thai water sector, based on a literature review of six sub-sectors: riverine hydrology, sediment erosion, coastal erosion, forest hydrology, agricultural hydrology, and urban hydrology. Our review examined the long-term availability of observational data, historical changes, projected changes in key variables, and the availability of economic assessments and their implications for adaptation actions. Although some basic hydrometeorological variables have been well monitored, specific historical changes due to climate change have seldom been detected. Furthermore, although numerous future projections have been proposed, the likely changes due to climate change remain unclear due to a general lack of systematic multi-model and multi-scenario assessments and limited spatiotemporal coverage of the study area. Several gaps in the research were identified, and ten research recommendations are presented. While the information contained herein contributes to state-of-the-art knowledge on the impact of climate change on the water sector in Thailand, it will also benefit other countries on the Indochina Peninsula with a similar climate.

In northeast Thailand, 17% of the total agricultural land is classified as salt-affected. In the future, climate change may exacerbate salt-affected soil problems. Therefore, in this study, we conducted a field survey to evaluate seasonal changes in soil electrical conductivity (ECe) in salt-affected paddy areas of Ban Phai District, Khon Kaen Province, northeast Thailand. Fifteen soil samples were collected every 2 weeks from October 2016 to December 2018, and the ECe, soil water content, and soil textures were analyzed. Then, the HYDRUS-1D model was applied to estimate seasonal changes in the salinity level, and the simulated results corresponded well with observed data. Using HYDRUS-1D and the global circulation model (MIROC5) outputs under the Representative Concentration Pathways 8.5 scenario, future ECe was predicted. Under a temperature increase of 2.8°C from 2016 to 2100, annual potential evapotranspiration increased from 1,430 mm (2016-2025) to 1,584 mm (2081-2100). The average ECe in cultivation season increased from 2.63 dS/m (2016-2025) to 3.31 dS/m (2081-2100). As a countermeasure to mitigate soil salt accumulation, a 5 cm reduction in groundwater level offsets the negative impact of climate change, and a 10 cm reduction significantly improves the soil ECe relative to the current soil salinity level.

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Field experiment was carried out at Agronomy Experimental Farm, Faculty of Agriculture, Khon Kaen University in 2015-2016 to investigate the response of cassava to supplementary irrigation during the dry season month. The experiment was laid out in split plot design with four replications. The main plots comprised two cassava varieties (Huaybong 80 and Rayong 11). The sub l included four levels of drip irrigation [I-20, EV-40 mm (crop received 20 mm of water when daily cumulative pan evapolation value reached 40 mm during the dry season months)]; [I-20, EV-60 mm] ; [I-10, EV-40 mm] ; [I-10, EV-60 mm] and [I-10] (cassava under rainfed condition without additional irrigation)]. Results indicated that irrigation at (I-20, EV-40 mm) produced maximum the fresh (52 t ha-1) and dry (22 t ha-1) storage root yield. Huaybong 80 variety a gave significantly higher the storage root yield than that of Rayong 11 variety. The highest starch content also was obtained in the (I-20, EV-40 mm) treatment. There was no significant difference in the starch content between the two cassava varieties. Water were applied in treatment [I-20, EV-40 mm], [I-20, EV-60 mm], [I-10, EV-40 mm] and [I-10, EV-60 mm] was an average 299 mm, 194 mm, 150 mm and 97 mm, respectively during the growing season. Water use efficiency was the highest (35.3 kg ha-1 mm-1) in the [I-20, EV-60 mm] treatment.

In northeast Thailand, the irrigated agricultural land was only 7.6% (in 2012) of total and others were classified as rain-fed so that climate change makes agricultural production unstable and also makes negative impact to the societies and economics in rural area. To mitigate these issues, it is desirable to develop enhanced adaptation measures. In this study, we focused on weather induced economic damages and effectiveness of index-based insurance system in Northeast Thailand. Firstly, we evaluated how affect the seasonal rainfall amount and patterns on rice yield and production through regression analysis by using the meteorological and agricultural statistic data. 8 province had positive correlation R>0.3 with Jul-Sep accumulated rainfall. And then, probability analysis was applied to monthly rainfall which was employed for insurance index value. As a result, setting amount and periods of insurance index was suitable. Secondly, household survey was conducted to investigate farmers' conditions of water use, cultivation, income balance.In recent year, agricultural damage on farmers' income was not so large (less than 3%), because 65% of farmers' income relied on non-agricultural sector. That might be the one reason of constraints of insurance sales.

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Northeast Thailand is the largest rice cultivation region in Thailand, but the rice yield there is quite low. Soil salinity is one of the major yield restricted factors, is derived from underground rock salt, and is predicted to expand in the future. This study focused on evaluating rice productivity related to salinity conditions in Khon Kaen Province, Northeast Thailand. The field investigations were conducted from 2017 to 2019 in farmer fields in severe, moderate, and slight soil salinity classes determined by the Land Development Department of Thailand. The soil salinity on the basis of the electric conductivity of saturated soil extract (ECe) varied year to year, which seemed to be associated with precipitation. The difference in soil salinity between classes was obvious only in the drought year 2018, and reflected in the rice yield, although severe drought devastated rice yield in some fields. Plenty of rainfall may have alleviated soil salinity and rice yield reduction in other years, causing differences in rice yield that were not significant among soil salinity classes. However, salinity level evaluation by the USDA based on ECe showed that rice yield was damaged depending on the level. This study indicates that ECe-based evaluation is recommended for soil salinity in relation to rice productivity. The spatial and temporal evaluation for rice production may benefit farmers. The results in this study also showed rice production largely varied even in similar salinity levels, implying that salinity damage can be alleviated by farmer management.