Now showing 1 - 8 of 8
  • Publication
    Metadata only
    Deadly disasters in southeastern South America: Flash floods and landslides of February 2022 in Petrópolis, Rio de Janeiro
    (European Geosciences Union, 2023)
    Alcantara, Enner
    ;
    Marengo, Jose A.
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    Mantovani, Jose Roberto
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    Londe, Luciana
    ;
    Lau, Rachel Yu San
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    ;
    Lin, Nina Yunung
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    ;
    Mendes, Tatiana Sussel Goncalves
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    Cunha, Ana Paula
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    Pampuch, Luana
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    Seluchi, Marcelo
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    Simoes, Silvio
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    Cuartas, Luz Adriana
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    Goncalves, Demerval
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    Massi, Klecia
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    Alvala, Regina
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    Moraes, Osvaldo
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    Filho, Carlos Souza
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    Mendes, Rodolfo
    ;
    Nobre, Carlos
    On 15 February 2022, the city of Petrópolis in the highlands of the state of Rio de Janeiro, Brazil, received an unusually high volume of rain within 3 h (258 mm), generated by a strongly invigorated mesoscale convective system. It resulted in flash floods and subsequent landslides that caused the deadliest landslide disaster recorded in Petrópolis, with 231 fatalities. In this paper, we analyzed the root causes and the key triggering factors of this landslide disaster by assessing the spatial relationship of landslide occurrence with various environmental factors. Rainfall data were retrieved from 1977 to 2022 (a combination of ground weather stations and the Climate Hazards Group InfraRed Precipitation – CHIRPS). Remotely sensed data were used to map the landslide scars, soil moisture, terrain attributes, line-of-sight displacement (land surface deformation), and urban sprawling (1985–2020). The results showed that the average monthly rainfall for February 2022 was 200 mm, the heaviest recorded in Petrópolis since 1932. Heavy rainfall was also recorded mostly in regions where the landslide occurred, according to analyses of the rainfall spatial distribution. As for terrain, 23 % of slopes between 45–60∘ had landslide occurrences and east-facing slopes appeared to be the most conducive for landslides as they recorded landslide occurrences of about 9 % to 11 %. Regarding the soil moisture, higher variability was found in the lower altitude (842 m) where the residential area is concentrated. Based on our land deformation assessment, the area is geologically stable, and the landslide occurred only in the thin layer at the surface. Out of the 1700 buildings found in the region of interest, 1021 are on the slope between 20 to 45∘ and about 60 houses were directly affected by the landslides. As such, we conclude that the heavy rainfall was not the only cause responsible for the catastrophic event of 15 February 2022; a combination of unplanned urban growth on slopes between 45–60∘, removal of vegetation, and the absence of inspection were also expressive driving forces of this disaster.
    WOS© Citations 6Scopus© Citations 19  30
  • Publication
    Embargo
    The changing rainfall patterns drive the growing flood occurrence in Phnom Penh, Cambodia
    (Elsevier, 2024)
    Huang, Wanxin
    ;
    ; ;
    Sophal, Try

    Study region
    Urban flooding is an intensifying issue in the rapidly developing lowland cities of Southeast Asia. Cambodia’s Phnom Penh City, located at the confluence of the Mekong and Tonle Sap Rivers in the lower Mekong Basin, recently saw increasingly prevalent flash floods, resulting in casualties and damages.

    Study focus
    While flood planning and impact assessments have been done in the Mekong basin, flood causes in the face of climate change remain insufficiently understood. In this paper, the drivers of the increasingly prevalent floods in Phnom Penh are investigated through analysis of remote sensing and instrumental data.

    New hydrological insights for the region
    With precipitation records from the Climate Hazards Group InfraRed Precipitation and gauge station dataset, a general precipitation increase of 7 mm/year and a notable shift to a wetter regime were observed. Strong periodicities of 1/3-year, 1/2-year, 1-year and ∼5-year cycles were also identified, which generally showed a considerable increase in intensity from 1981 to 2021. Over the past 40 years, precipitation patterns have intensified. Yet, the average water levels of the rivers surrounding Phnom Penh have declined by 1–2 m from 1981 to 2021, indicating the pressure from climate change is a major hydrological driver contributing to Phnom Penh's flash floods. Meanwhile, Phnom Penh's vulnerability to flash flooding is also likely aggravated by drastic land use changes, which have increased the city's impervious surfaces and reduced its wetlands by 30 % since the 1980s.

      6  28
  • Publication
    Metadata only
    Extent of saltwater intrusion and freshwater exploitability in the coastal Vietnamese Mekong Delta assessed by gauging records and numerical simulations
    (Elsevier, 2024)
    Tran, Dung Duc
    ;
    Pham, Thi Bich Thuc
    ;
    ;
    Phan, Thi Thanh Hang
    ;
    Duong, Ba Man
    ;

    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.

    Scopus© Citations 6  19
  • Publication
    Metadata only
    Landscape and social disruption from sand mining and mining-related activities: A case from the Vietnamese Mekong delta
    (Springer, 2024)
    Li, Samuel Li Chen
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    ;
    Tran, Dung Duc
    ;
    Yuen, Kai Wan
    ;

    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.

      11
  • Publication
    Embargo
    Severe decline in extent and seasonality of the Mekong Plume after 2000
    (Elsevier, 2024)
    Feng, Yikang
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    ; ;
    Feng, Lian
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    Tran, Dung Duc
    The Mekong plume, which sustains the geomorphology and rich biodiversity along the coastal zone of the Vietnamese Mekong Delta (VMD), has been under intensifying threats from dams, riverbed mining and sea level rise. However, our understanding of how much the intensifying stressors have altered the long-term spatiotemporal dynamics of the plume remains limited. In this paper, we investigate the spatiotemporal dynamics of the Mekong plume over 1988–2022 based on remote sensing, in-situ hydrological data, and continuous wavelet transform. Specifically, we analyze (1) the variability of the long-term average seasonal plume extent, (2) the interannual trends of the seasonal suspended sediment discharge and alongshore drift, and (3) changes in the long-term exposure of coastal mangroves to suspended sediment. Field suspended sediment concentration (SSC) data from five major gauging stations representing the upstream, midstream, and downstream sections of the VMD between 2010–2021 were used to calibrate 101 Landsat surface reflectance observations to estimate SSC. The top-performing algorithm with band combination (NIR SWIR2) * (G / R) was selected for SSC retrieval (R2 = 0.72, SE = 40.6 mg L−1). Our results reveal a 63 % decline in plume extent in the dry season (Dec–May) and an 83 % decline in the wet season (Jun–Nov) between 1988–1999 and 2000–2022. The seasonal variation in suspended sediment discharge (SSD) remained relatively constant until 2014 but significantly weakened thereafter. Despite the decline in the plume, the surface SSC at the alongshore drift began to rise in 2008, marking a reversal in the trend after two decades of descent. The upswing in the surface SSC is associated with rising SSD in the dry season, which we attribute mainly to the release of water from dams upstream of the VMD. However, if the post-2014 decline of wet season SSD persists in the long term, it would deplete sediment deposition around the estuary and starve the alongshore drift. Along the coastline of the Mekong Delta, the annual exposure to suspended sediments declined by 37–54 % between 1988–1999 and 2000–2022, corresponding to a maximum annual mangrove loss of 15 % by coastal erosion. The decrease in plume and coastal exposure is primarily attributed to reduced terrestrial sediment flux, largely influenced by the construction and operation of transnational dams. To restore the Mekong plume, it is imperative to advocate for cross-border governance of dam operations.
      14  2
  • Publication
    Metadata only
    The characterization, mechanism, predictability, and impacts of the unprecedented 2023 Southeast Asia heatwave
    (Springer, 2024)
    Lyu, Yang
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    Zhi, Xiefei
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    Wang, Xianfeng
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    Zhang, Hugh
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    Wen, Yonggang
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    Lee, Joshua
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    Wan, Xia
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    Zhu, Shoupeng
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    Tran, Dung Duc
    In April and May 2023, Southeast Asia (SEA) encountered an exceptional heatwave. The Continental SEA was hardest hit, where all the countries broke their highest temperature records with measurements exceeding 42 °C, and Thailand set the region’s new record of 49 °C. This study provides a comprehensive analysis of this event by investigating its spatiotemporal evolution, physical mechanisms, forecast performance, return period, and extensive impacts. The enhanced high-pressure influenced by tropical waves, moisture deficiency and strong land-atmosphere coupling are considered as the key drivers to this extreme heatwave event. The ECMWF exhibited limited forecast skills for the reduced soil moisture and failed to capture the land-atmosphere coupling, leading to a severe underestimation of the heatwave’s intensity. Although the return period of this heatwave event is 129 years based on the rarity of temperature records, the combination of near-surface drying and soil moisture deficiency that triggered strong positive land-atmosphere feedback and rapid warming was extremely uncommon, with an occurrence probability of just 0.08%. These analyses underscore the exceptional nature of this unparalleled heatwave event and its underlying physical mechanisms, revealing its broad impacts, including significant health repercussions, a marked increase in wildfires, and diminished agricultural yields.
      9
  • Publication
    Metadata only
    Extent of illegal sand mining in the Mekong Delta
    (Nature Research, 2024)
    Yuen, Kai Wan
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    Tran, Dung Duc
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    Loc, Ho Huu
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    Feng, Lian
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    Gruel, Charles-Robin
    ;
    Switzer, Adam D.

    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.

    Scopus© Citations 11  8
  • Publication
    Open Access
    Soil moisture observations from shortwave infrared channels reveal tornado tracks: A case in 10-11 December 2021 tornado outbreak
    (Wiley, 2023) ;
    Lin, Yun
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    McFarquhar, Greg M.
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    Gu, Yu
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    Su, Qiong
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    Fu, Rong
    ;
    Lee, Kee Wei
    ;
    Zhang, Tianhao
    Satellite-based post-tornado assessments have been widely used for the detection of tornado tracks, which heavily relies on the identification of vegetation changes through observations at visible and near-infrared channels. During the deadly 10–11 December 2021 tornado outbreak, a series of violent tornadoes first touched down over northeastern Arkansas, an area dominated by cropland with rare vegetation coverage in winter. Through the examination of Moderate Resolution Imaging Spectroradiometer multi-spectral observations, this study reveals significant scars on shortwave infrared channels over this region, but none are captured by visible and near-infrared channels. The dominant soil type is aquert (one of vertisols), whose high clay content well preserves the severe changes in soil structure during the tornado passage, when the topmost soil layer was removed and underlying soil with higher moisture content was exposed to the air. This study suggests a quick post-tornado assessment method over less vegetated area by using shortwave infrared channels.
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