The Amazon basin has experienced an extreme drought that started in the austral summer of 2022-23 and extends into 2024. This drought started earlier than other previous droughts. Although some rain fell during the au...The Amazon basin has experienced an extreme drought that started in the austral summer of 2022-23 and extends into 2024. This drought started earlier than other previous droughts. Although some rain fell during the austral summer, totals remained below average. Higher temperatures during austral winter and spring 2023, which affected most of Central South America, then aggravated drought conditions. This coincided with an intense El Niño and abnormally warm tropical North Atlantic Ocean temperatures since mid-2023. Decreased rainfall across the Amazon basin, negative anomalies in evapotranspiration (derived from latent heat) and soil moisture indicators, as well as increased temperatures during the dry-to-wet transition season, September-October-November (SON) 2023, combined to delay the onset of the wet season in the hydrological year 2023-24 by nearly two months and caused it to be uncharacteristically weak. SON 2023 registered a precipitation deficit of the order of 50 to 100 mm/month, and temperatures +3˚C higher than usual in Amazonia, leading to reduced evapotranspiration and soil moisture indicators. These processes, in turn, determined an exceptionally late onset and a lengthening of the dry season, affecting the 2023-2024 hydrological year. These changes were aggravated by a heat wave from June to December 2023. Drought-heat compound events and their consequences are the most critical natural threats to society. River levels reached record lows, or dried up completely, affecting Amazonian ecosystems. Increased risk of wildfires is another concern exacerbated by these conditions.展开更多
Surface 03 production has a highly nonlinear relationship with its precursors. The spatial and temporal heterogeneity of O3-NOx-VOC-sensitivity regimes complicates the control- decision making. In this paper, the indi...Surface 03 production has a highly nonlinear relationship with its precursors. The spatial and temporal heterogeneity of O3-NOx-VOC-sensitivity regimes complicates the control- decision making. In this paper, the indicator method was used to establish the relationship between 03 sensitivity and assessment indicators. Six popular ratios indicating ozone-precursor sensitivity, HCHO/NOy, H2O2/ HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz, were evaluated based on the distribution of NOx- and VOC-sensitive regimes. WRF-Chem was used to study a serious ozone episode in fall over the Pearl River Delta （PRD）. It was found that the south-west of the PRD is characterized by a VOCsensitive regime, while its north-east is NO y-sensitive, with a sharp transition area between the two regimes. All indicators produced good representations of the elevated ozone hours in the episode on 6 November 2009, with H202/HNO3 being the best indicator. The threshold sensitivity levels for HCHO/NOy, H2O2/HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz were estimated to be 0.41, 0.55, 10.2, 14.0, 19.1, and 0.38, respectively. Threshold intervals for the indicators H2O2/HNO3, O3/ NOy, O3/NOz, O3/HNO3, and H202/NOz were able to identify more than 95% of VOC- and NOx-sensitive grids. The ozone episode on 16 November 16 2008 was used to independently verify the results, and it was found that only H2O2/HNO3 and H2O2/NOz were able to differentiate the ozone sensitivity regime well. Hence, these two ratios are suggested as the most appropriate indicators for identifying fall ozone sensitivity in the PRD. Since the species used for indicators have seasonal variation, the utility of those indicators for other seasons should be investigated in the future work.展开更多
Evaluating environmental flow(EF)is pivotal for conserving and restoring riverine ecosystems.Yet,prevalent EF evaluations presume that a river reach's hydraulic conditions are exclusively governed by inflow discha...Evaluating environmental flow(EF)is pivotal for conserving and restoring riverine ecosystems.Yet,prevalent EF evaluations presume that a river reach's hydraulic conditions are exclusively governed by inflow discharge,presupposing a state of equilibrium in the river channel.This presumption narrows the scope of EF evaluations in expansive alluvial rivers like the Middle Yangtze River(MYR),characterized by marked channel alterations.Here we show the profound channel erosion process and its impact on EF requirements for riparian habitats within the MYR.Our research unveils that:(i)pronounced erosion has led to a mean reduction of 1.0-2.7 m in the riverbed across four sub-reaches of the MYR;(ii)notwithstanding a 37-107%increase in minimal discharges post the Three Gorges Project,the lowest river stages at some hydrometric stations diminished owing to bed erosion,signifying a notable transformation in MYR's hydraulic dynamics;(iii)a discernible rightward shift in the correlation curve between the weighted useable area and discharge from 2002 to 2020 in a specific sub-reach of the MYR,instigated by alterations in hydraulic conditions,necessitated an increase of 1500e2600 m^(3)s^(-1)in the required EF for the sub-reach;(iv)it is deduced that macroinvertebrate biomass rapidly decreases as the flow entrains the riverbed substrate,with the maximum survivable velocity for macroinvertebrates being contingent on their entrainment threshold.These findings highlight the importance of incorporating channel morphological changes in devising conservation strategies for the MYR ecosystem.展开更多
Groundwater inundation occurs when rivers with high water levels are hydraulically connected to the adjacent riversides.Huge barrages constructed in South Korea have caused the river water levels and groundwater level...Groundwater inundation occurs when rivers with high water levels are hydraulically connected to the adjacent riversides.Huge barrages constructed in South Korea have caused the river water levels and groundwater levels in the riversides to increase.We used a discriminant model with seven input variables,namely the sediment thickness,difference between the land elevation and river water level,difference between the groundwater and river water levels,soil drainage type,topsoil texture,subsoil texture,and hydrological soil feature classification,to develop a map of the groundwater inundation vulnerability along the basins of the Nakdong River.We estimated the groundwater levels in unmonitored areas with a linear regression model developed from the relationship between the distance from the river and the depth to the groundwater in 91 monitoring wells.We produced a grid map for the vulnerability with an optimum grid size of 100 m.We validated the groundwater inundation vulnerability map by comparing highly susceptible areas with swampy fields observed in a field survey.This result indicates that the vulnerability map will be helpful to forecast and prepare inundation in the riversides during the rainy season when the river water levels are inevitably high.展开更多
文摘The Amazon basin has experienced an extreme drought that started in the austral summer of 2022-23 and extends into 2024. This drought started earlier than other previous droughts. Although some rain fell during the austral summer, totals remained below average. Higher temperatures during austral winter and spring 2023, which affected most of Central South America, then aggravated drought conditions. This coincided with an intense El Niño and abnormally warm tropical North Atlantic Ocean temperatures since mid-2023. Decreased rainfall across the Amazon basin, negative anomalies in evapotranspiration (derived from latent heat) and soil moisture indicators, as well as increased temperatures during the dry-to-wet transition season, September-October-November (SON) 2023, combined to delay the onset of the wet season in the hydrological year 2023-24 by nearly two months and caused it to be uncharacteristically weak. SON 2023 registered a precipitation deficit of the order of 50 to 100 mm/month, and temperatures +3˚C higher than usual in Amazonia, leading to reduced evapotranspiration and soil moisture indicators. These processes, in turn, determined an exceptionally late onset and a lengthening of the dry season, affecting the 2023-2024 hydrological year. These changes were aggravated by a heat wave from June to December 2023. Drought-heat compound events and their consequences are the most critical natural threats to society. River levels reached record lows, or dried up completely, affecting Amazonian ecosystems. Increased risk of wildfires is another concern exacerbated by these conditions.
基金Acknowledgements Financial supports from the Special Fund for Meteorological-scientific Research in the Public Interest of China （No. GYHY201406031）, National Science Foundation for Distinguished Young Scholars （No. 41425020）, National Key Technology Research and Development Program of the Ministry of Science and Technology of China （Grant No. 2014BAC21B02）, Foshan Environmental Protection Bureau Project （GDJAFS 2015046G） are gratefully acknowledged by the authors. We acknowledge Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund （the second phase） and National Supercomputing Center in Guangzhou （NSCC-GZ）. At the same time, we are grateful for Guangzhou Meteorological Service for the Meteorological data, and Guangzhou Environmental Monitoring for air quality observational data.
文摘Surface 03 production has a highly nonlinear relationship with its precursors. The spatial and temporal heterogeneity of O3-NOx-VOC-sensitivity regimes complicates the control- decision making. In this paper, the indicator method was used to establish the relationship between 03 sensitivity and assessment indicators. Six popular ratios indicating ozone-precursor sensitivity, HCHO/NOy, H2O2/ HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz, were evaluated based on the distribution of NOx- and VOC-sensitive regimes. WRF-Chem was used to study a serious ozone episode in fall over the Pearl River Delta （PRD）. It was found that the south-west of the PRD is characterized by a VOCsensitive regime, while its north-east is NO y-sensitive, with a sharp transition area between the two regimes. All indicators produced good representations of the elevated ozone hours in the episode on 6 November 2009, with H202/HNO3 being the best indicator. The threshold sensitivity levels for HCHO/NOy, H2O2/HNO3, O3/NOy, O3/NOz, O3/HNO3, and H2O2/NOz were estimated to be 0.41, 0.55, 10.2, 14.0, 19.1, and 0.38, respectively. Threshold intervals for the indicators H2O2/HNO3, O3/ NOy, O3/NOz, O3/HNO3, and H202/NOz were able to identify more than 95% of VOC- and NOx-sensitive grids. The ozone episode on 16 November 16 2008 was used to independently verify the results, and it was found that only H2O2/HNO3 and H2O2/NOz were able to differentiate the ozone sensitivity regime well. Hence, these two ratios are suggested as the most appropriate indicators for identifying fall ozone sensitivity in the PRD. Since the species used for indicators have seasonal variation, the utility of those indicators for other seasons should be investigated in the future work.
基金supported by the National Natural Science Foundation of China(Grant Nos.U2040215,51725902,U2240206,52379079)was partly supported by the Natural Science Foundation of Hubei Province(2021CFA029)+1 种基金the Special Project on Knowledge Innovation of Wuhan Science and Technology Bureau(2022020801020132)the Fundamental Research Funds for the Central Universities(2042023kf0160).
文摘Evaluating environmental flow(EF)is pivotal for conserving and restoring riverine ecosystems.Yet,prevalent EF evaluations presume that a river reach's hydraulic conditions are exclusively governed by inflow discharge,presupposing a state of equilibrium in the river channel.This presumption narrows the scope of EF evaluations in expansive alluvial rivers like the Middle Yangtze River(MYR),characterized by marked channel alterations.Here we show the profound channel erosion process and its impact on EF requirements for riparian habitats within the MYR.Our research unveils that:(i)pronounced erosion has led to a mean reduction of 1.0-2.7 m in the riverbed across four sub-reaches of the MYR;(ii)notwithstanding a 37-107%increase in minimal discharges post the Three Gorges Project,the lowest river stages at some hydrometric stations diminished owing to bed erosion,signifying a notable transformation in MYR's hydraulic dynamics;(iii)a discernible rightward shift in the correlation curve between the weighted useable area and discharge from 2002 to 2020 in a specific sub-reach of the MYR,instigated by alterations in hydraulic conditions,necessitated an increase of 1500e2600 m^(3)s^(-1)in the required EF for the sub-reach;(iv)it is deduced that macroinvertebrate biomass rapidly decreases as the flow entrains the riverbed substrate,with the maximum survivable velocity for macroinvertebrates being contingent on their entrainment threshold.These findings highlight the importance of incorporating channel morphological changes in devising conservation strategies for the MYR ecosystem.
基金supported by the Daejeon University Research Grants(2016)scheme.
文摘Groundwater inundation occurs when rivers with high water levels are hydraulically connected to the adjacent riversides.Huge barrages constructed in South Korea have caused the river water levels and groundwater levels in the riversides to increase.We used a discriminant model with seven input variables,namely the sediment thickness,difference between the land elevation and river water level,difference between the groundwater and river water levels,soil drainage type,topsoil texture,subsoil texture,and hydrological soil feature classification,to develop a map of the groundwater inundation vulnerability along the basins of the Nakdong River.We estimated the groundwater levels in unmonitored areas with a linear regression model developed from the relationship between the distance from the river and the depth to the groundwater in 91 monitoring wells.We produced a grid map for the vulnerability with an optimum grid size of 100 m.We validated the groundwater inundation vulnerability map by comparing highly susceptible areas with swampy fields observed in a field survey.This result indicates that the vulnerability map will be helpful to forecast and prepare inundation in the riversides during the rainy season when the river water levels are inevitably high.
