Biochar has been recommended as a soil amendment to improve soil fertility and mitigate methane (CH₄) emissions from rice cultivation. Its effects, however, vary depending on soil type, biochar characteristics, and application rate. This study was aimed to evaluate the potential of mangrove biochar on CH₄ mitigation, soil properties, and the productivity of rice cultivated in a clay loam soil in Thailand. Biochar was used at a rate equivalent to 10 t ha⁻¹ season⁻¹, both with (biochar + fertilizer: BF) and without (biochar alone: BI) fertilizer, for two cultivation seasons. BI reduced CH₄ flux at most stages of rice growth. Relative to control soil (no biochar, no fertilizer: CT), BI significantly decreased cumulative CH₄ emissions by 21.1% in the first season and 24.9% in the second season. CH₄ emissions from BF soil were also less than those from the use of fertilizer alone (FE). Rice grain yield in BI was 7.85% and 14.4% greater than in CT, and in BF by 1.47% and 3.72% greater than FE, in the first and second seasons, respectively. The decrease in CH₄ emissions and increase in rice grain yield decreased CH₄ emission intensity under biochar treatments. Soil pH, organic carbon, cation exchange capacity, and available nutrients in the soil increased with biochar addition. The soil organic carbon stock was significantly increased by 32.6% in BI and 27.5% in BF after the first season, and by 43.5% in BI and 39.6% in BF after the second season. © 2021 Informa UK Limited, trading as Taylor & Francis Group.

This study explores spatio-temporal patterns of surface water-groundwater interactions in the Yom and Nan River basins, a vulnerable and essential agricultural region in northern Thailand, under various future climate conditions. The SWAT-MODFLOW model performs the coupled simulation of surface/subsurface hydrological processes in the watershed, with projected climate conditions from the three Global Climate Models (MIROC5, CNRM-CM5, and MPI-ESM-MR) under the minimum and maximum Green House Gas emission scenarios, represented as the RCPs 2.6 and 8.5. The results demonstrate that, in the near future (2026–2045) under the two scenarios, a raised air temperature at 0.5–1.0 °C with a 2–16% increment of annual rainfall cause a 7–20% decrease in groundwater recharge from surface water percolation, followed by a 11–21% depletion of groundwater flow to river, while aquifer recharge from the river change negligibly. In the intermediate future (2051–2070) and far future (2076–2095), changes in surface water-groundwater interactions under RCP 2.6 are rather similar to the near future because of insignificant differentiation in climate conditions. Whereas, under RCP 8.5, annual rainfall increases by 26% and produces 4–14% increments of groundwater recharging and groundwater discharge to streamflow, while river seepage increases by 1–18%. These provide key insights into northern Thailand watershed systems to deal with future impacts of climate change on water supply.

The purpose of this study is to improve a simultaneous simulation of surface water and groundwater regimes with groundwater extraction to assess the implications for water management and propose primary solution approaches. The SWAT-MODFLOW model is performed for the Yom and Nan river basins during 2007–2016. The results demonstrate that the model provides an accurate depiction of the streamflow and groundwater heads when groundwater pumping is included. The recharges of surface water and groundwater are 2 times higher than the annual average value in the wet year (2011), whereas they are 3 times below the annual average in the dry year (2015). The downstream of Yom River basin is vulnerable to flooding, while high-terrain areas in Nan River basin are vulnerable to drought events. Capturing surplus water volumes during the wet season by recharging into the aquifer, coupled with improving the river capacity and forest areas, should be a sustainable solution for these issues.