ABSTRACT:The purpose of this study is to determine the hydrological impacts of land use/land cover (LULC) change in the Yom watershed in central-northern Thailand over a 15-year period using an integration of remote sensing, Geographic Information System, statistical methods, and hydrological modelling. The LULC changes showed an expansion of urban areas by 132% (from 210 km 2 in 1990 to 488 km 2 in 2006). The Yom River's daily discharge long-term trend significantly increased at most of the measurement stations (p value <0.05), and the rate of increase in discharge at areas downstream of the rapid urbanisation was significantly greater than that at areas upstream. There were no significant long-term trends in precipitation characteristics in the basin, except for one station. The rate of change in discharge after changes in LULC showed a systematic increase over a range from 0.0039 to 0.0180 m 3 s −1 day −1 over a 15-year period, with the increase in urbanised area spanning a range from 81 to 149% in two flood-prone provinces. A rainfall-runoff model simulated a small increase (∼10%) in peak flows. The coupling of surface observations, remote sensing, and rainfall-runoff modeling demonstrated the impacts of changes in LULC on peak river discharge, hence flooding behaviour, of a major river in central-northern Thailand.

The catastrophic implication of harmful algal bloom (HAB) events in the Arabian Gulf is a strong indication that the study of the spatiotemporal distribution of chlorophyll-a and its relationship with other variables is critical. This study analyzes the relationship between chlorophyll-a (Chl-a) and sea surface temperature (SST) and their trends in the Arabian Gulf and the Gulf of Oman along the United Arab Emirates coast. Additionally, the relationship between bathymetry and Chl-a and SST was examined. The MODIS Aqua product with a resolution of 1 × 1 km2 was employed for both chlorophyll-a and SST covering a timeframe from 2003 to 2019. The highest concentration of chlorophyll-a was seen in the Strait of Hormuz with an average of 2.8 mg m−3, which is 1.1 mg m−3 higher than the average for the entire study area. Three-quarters of the study area showed a significant correlation between the Chl-a and SST. The shallow (deep) areas showed a strong positive (negative) correlation between the Chl-a and SST. The results indicate the presence of trends for both variables across most of the study area. SST significantly increased in more than two-thirds of the study area in the summer with no significant trends detected in the winter.

Rubber plantations have rapidly replaced natural forests (NFs) in Mainland Southeast Asia, yet the relevant impacts on the terrestrial carbon cycle remain uncertain especially with an increase in drought frequency. Our study compared eddy‐covariance measurements of carbon and water fluxes from two rubber monoculture plantations (at a northern marginal site and a southern traditional plantation site) with a second‐growth NF between 2015 and 2018, and their responses to a prolonged drought during 2015/2016. The NF had higher light use efficiency, water use efficiency and gross primary productivity (GPP, 2.94 ± 0.41 kg C m−2 yr−1) than the northern rubber (NR) monoculture (2.45 ± 0.17 kg C m−2 yr−1), while lower ecosystem carbon use efficiency (eCUE) caused a lower net ecosystem productivity (NEP, 0.75 ± 0.25 kg C m−2 yr−1) compared to the plantation (1.19 ± 0.22 kg C m−2 yr−1). Drought decreased the NF eCUE by 23% with significant carbon uptake restrictions across multiple seasons, while the rubber GPP reduction was only substantial in the warm‐dry season with an overall 17% decline in eCUE. The NR site's GPP was mainly controlled by soil water content throughout the year. Higher light availability offset the negative effect of drier conditions on the rubber GPP, resulting in larger carbon uptake compared to the southern plantation (GPP, 2.12 ± 0.12 kg C m−2 yr−1; NEP, 1.07 ± 0.14 kg C m−2 yr−1). In contrast, the NF GPP was mainly restricted by vapor pressure deficit, especially during the drought.

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