Wang, Jingyu

Despite the recent recognition of ¹⁷O-excess as a promising new tracer for hydrological processes, our knowledge of the control mechanisms underlying ¹⁷O-excess in tropical regions remains limited. To understand how microphysical processes during tropical convection affect precipitation isotope ratios, particularly ¹⁷O-excess, in Singapore, we collected precipitation samples at minute intervals from six rain events associated with cold surges during the Northeast Monsoon seasons and analyzed their triple oxygen isotopes. Our results show that precipitation δ¹⁸O decreases in the convective zones and then gradually increases in the stratiform zones, while d-excess exhibits an inverse trend. This correlation between δ¹⁸O and d-excess indicates that rain evaporation plays a crucial role in regulating precipitation isotopes. Moreover, the rain events with a higher upstream rainout amount have lower δ¹⁸O and higher ¹⁷O-excess values, suggesting that precipitation δ¹⁸O and ¹⁷O-excess likely reflect the integrated upstream convective activity. Microphysical processes associated with upstream convection, such as rain evaporation and vapor recycling, are potential mechanisms that increase ¹⁷O-excess values along moisture transport pathways for a rain event, and hence, undermine the effectiveness of ¹⁷O-excess as a tracer of moisture source humidity. Contrary to the negative correlation observed in monthly precipitation, there is generally a positive correlation between d-excess and ¹⁷O-excess at the event scale. However, this correlation weakens as convective rain intensifies, suggesting that stronger convection can attenuate the positive correlation between d-excess and ¹⁷O-excess. Therefore, it is crucial to consider how tropical convection alters ¹⁷O-excess when utilizing this tracer to interpret atmospheric dynamics and hydrological processes.

The heavy global demand for sand in various sectors of the economy subjects the Vietnamese Mekong Delta to correspondingly high amounts of sand mining—a process that started in the early 1990s contributing significantly to the Vietnamese economy. The impacts of intensive sand mining and mining-related industries damage the integrity of the river and local communities. Much of the literature focuses on the former, exposing people to the deleterious implications of sand mining on the physical environment. This study aims to fill the gap on the less explored latter through the lenses of place and landscape per human geography tradition, using qualitative methods of thirty-five interviews with locals, video recordings, and sound measurements to highlight the impacts of sand mining and mining-related industries. This study revealed that sand mining and its associated activities are responsible for people’s perceptions of notable air, land, and noise pollution, as well as substantial harm to the urban environment. Over 80 percent of interviewed locals acknowledged the disruptions to their daily lives and a substantial loss of their sense of place. These findings shed light on narratives frequently overlooked by policymakers, emphasizing the urgency of addressing these issues for a sustainable future.

The Kuroshio intrusion (KI) is a northwestward-flowing branch of the Kuroshio Current, which enters the South China Sea (SCS) and regulates its temperature, salinity, and water mass exchanges. However, limited direct observations hinder our understanding of KI's mechanisms and responses to climate change. Here, we present a 60-year bi-monthly resolved coral oxygen isotope (δ¹⁸Oc) record from Dongsha Atoll, the northern SCS. The dry-season (December–March) δ¹⁸Oc record reveals interannual to decadal variabilities of the KI. The impact of the East Asian winter monsoon (EAWM) on Dongsha δ¹⁸Oc was more pronounced during the 1970s and 1980s and after the early 2000s, while the influence of the El Niño-Southern Oscillation (ENSO) on Dongsha δ¹⁸Oc was higher between the 1980s and 1990s. The Pacific Decadal Oscillation (PDO) may have a relatively minor effect on KI strength or may indirectly modulate KI strength through its influence on ENSO activities. Our Dongsha δ¹⁸Oc record highlight the importance of the EAWM, ENSO, and PDO in predicting future KI changes.

Reliable Subseasonal-to-Seasonal (S2S) forecasts of precipitation are critical for disaster prevention and mitigation. In this study, an innovative hybrid method CSG-UNET combining the UNET with the censored and shifted gamma distribution based ensemble model output statistic (CSG-EMOS), is proposed to calibrate the ensemble precipitation forecasts from ECMWF over the China mainland during boreal summer. Additional atmospheric variable forecasts and the data augmentation are also included to deal with the potential issues of low signal-to-noise ratio and relatively small sample sizes in traditional S2S precipitation forecast correction. The hybrid CSG-UNET exhibits a notable advantage over both individual UNET and CSG-EMOS in improving ensemble precipitation forecasts, simultaneously improving the forecast skills for lead times of 1–2 weeks and further extending the effective forecast timeliness to ∼4 weeks. Specifically, the climatology-based Brier Skill Scores are improved by ∼0.4 for the extreme precipitation forecasts almost throughout the whole timescale compared with the ECMWF. Feature importance analyze towards CSG-EMOS model indicates that the atmospheric factors make great contributions to the prediction skill with the increasing lead times. The CSG-UNET method is promising in subseasonal precipitation forecasts and could be applied to the routine forecast of other atmospheric and ocean phenomena in the future.

Sand is a vital ingredient for modern structures and to meet demand, a substantial volume of sand is extracted illegally from riverbeds globally. The Vietnamese Mekong Delta is one of the largest delta in Asia and it has a long history of riverbed sand mining. We quantified the illegal sand mining rate in this major sand mining hotspot, as the difference between the actual volume of sand mined and the allowable rate of sand extraction set by the provincial government. The volume of illegally mined sand decreased from 16.7 Mm³/yr in 2013 to 15.5 Mm³/yr in 2018-2020. An increase in the allowable rate of sand extraction from 11.5 Mm³/yr to 15.1 Mm³/yr reduced the volume of illegally mined sand. We recommend that scientific research should be conducted to assess the allowable rates of sand extraction and the volume of sand reserve.

Climate change-driven sea level rise has intensified salinity intrusion (SI) in deltas worldwide, posing significant threats to the exploitation of freshwater resources. In the Vietnamese Mekong Delta (VMD), the third largest delta globally, SI is a recurring challenge along the coastline, degrading freshwater resources for agricultural and domestic use and affecting socio-economic development. In this paper, we investigate the spatiotemporal extent of salinity intrusion in the Ben Tre Province, the hotspot of salinity disaster within the VMD. Long-term salinity monitoring data (25 years from 1996 to 2020) has been analyzed, and a 1D (Mike 11) coupled with 3D hydrodynamic model (Mike 3) was developed. Three scenarios were used to investigate the freshwater resources exploitation: (i) the year of investigation (2021), (ii) 2021 to 2030 climate change impacts, considering different annual exceedance probability of the upstream Mekong discharge (i.e., average flow, relatively low, low and very low), and (iii) extreme salinity intrusion (i.e., the 2016 condition). Our results indicated that salinity patterns are well-stratified at the beginning and end of the dry season but well-mixed during the middle period. Furthermore, over the last 25 years, SI has progressively increased and started earlier in the dry season. The modeling scenarios for SI have also revealed a growing complexity in the exploitation of freshwater resources, highlighting challenges related to timing, depth, and geographical location. The exceedance probability scenarios disclosed higher and deeper salinity intrusion along the channel in VMD, ranging from 50 % to 95 %. This poses significant limitations on the feasibility of freshwater exploitation throughout the Ben Tre Province. Under the current trajectory of climate change, the 2030 scenario anticipates salinity intrusion reaching further inland from the 2021 scenario. This is likely to exacerbate the existing challenges in freshwater resource exploitation, even with comprehensive water infrastructure. We, therefore, propose several management strategies to adapt to salinity intrusion: storing freshwater in main rivers, maintaining consistent operation of water infrastructure systems, and encouraging water-saving distribution and exploitation methods. Moreover, we also recommend supporting the development of new drought-tolerant crop patterns.