Influence Of Monsoon Research Articles

Emerging influence of the Australian Monsoon on Indian Ocean interannual variability in a warming climate

The Indian Ocean Dipole (IOD) and Tripole (IOT) represent primary modes of interannual variability in the Indian Ocean, impacting both regional and global climate. Unlike the IOD, which is closely related to the El Niño-Southern Oscillation (ENSO), our findings unveil a substantial influence of the Australian Monsoon on the IOT. An anomalously strong Monsoon induces local sea surface temperature (SST) variations via the wind-evaporation-SST mechanism, triggering atmospheric circulation anomalies in the eastern Indian Ocean. These circulation changes lead to changes in oceanic heat transport, facilitating the formation of the IOT. Our analysis reveals a strengthening connection between the Australian Monsoon and the IOT in recent decades, with a projected further strengthening under global warming. This contrasts with the diminished coupling between ENSO and IOD in recent decades from observations and model projections, illustrating evolving Indian Ocean dynamics under the warming climate.

Recurrent Swarms of Planktonic Shrimp Luciferidae De Haan, 1849 (Order: Decapoda) in the Neritic Waters of Tamil Nadu, Southeast Coast of India

ABSTRACTLuciferidae (Decapoda) are an important component of mesozooplankton in pelagic food webs. This study investigated the spatiotemporal distribution and frequency of Luciferidae swarms along the Tamil Nadu coast, as observed during coastal monitoring cruises conducted between 2019 and 2022. Data were collected on various hydrobiological factors, including surface water temperature, salinity, chlorophyll a, zooplankton biomass, and the abundance of other mesozooplankton (such as copepods, cladocerans, and others) across eight locations in the coastal waters of Tamil Nadu, India. Salinity values were generally low (< 30 PSU) throughout the study period, except in September 2019. Microscopic analysis identified Belzebub hanseni Nobili, 1905, as the only organism responsible for swarm formation, with its occurrence peaking in January 2022. During this period, B. hanseni reached a maximum abundance of 3294 ind. m−3 for adults and 4056 ind. m−3 for larvae, together contributing approximately 27% of the total zooplankton abundance. Swarms of B. hanseni were observed a total of seven times over the course of the study, correlating with periods of low sea surface temperature and high food availability. Pearson's correlation analysis revealed a significant relationship between the abundance of copepods and B. hanseni (r = 0.84; p < 0.001), suggesting that both groups may be influenced by similar environmental factors, such as physical transport, food availability, and favorable conditions. This study indicates that the frequent swarming of B. hanseni in the nearshore waters of the Tamil Nadu coast is largely driven by food availability and optimal environmental conditions, including water temperature and monsoonal influences. The findings also suggest that geographical features, such as mangrove habitats, may contribute to the occurrence of B. hanseni swarms in this region.

Investigation of the meteorological conditions, dynamical, and microphysical characteristics of convective precipitation over the rainfall center of South China in the Pre-summer Rainy Season

This study investigates the meteorological conditions, dynamics, and microphysical characteristics of convective precipitation in Longmen, South China, during the Pre-summer Rainy Season (PRS) from 2016 to 2020, focusing on the influence of the South China Sea summer monsoon (SCSSM) onset. Utilizing the ERA5 reanalysis dataset and observations from the C-band Vertical Pointing Radar (VPRC) and Two-Dimensional Video Disdrometer (2DVD), we analyzed 4560 Convective Precipitation Features (CPFs) and classified them into shallow convection (SC), middle convection (MC), and deep convection (DC) based on the maximum height of 35 dBZ echo-top. Key findings reveal that the onset of the SCSSM significantly enhances convective rainfall. Specifically, it increases the proportion of convective rainfall by 11 % and intensifies rainfall duration and intensity by approximately 2.2 times. Enhanced moisture convergence and stronger convective instability drive these changes. The microphysical processes are distinct across different CPF types. SCs display warm-rain processes, MCs indicate mixed-phase processes, and DCs are associated with ice-phase processes. Each type contributes uniquely to precipitation characteristics, vertical reflectivity profiles, and raindrop size distributions. These insights emphasize the SCSSM's critical role in regional precipitation patterns and provide valuable insights into the underlying processes affecting convective systems in South China, ultimately contributing to improving the capabilities of prediction in atmospheric research.

Some characteristics of sediments in Cenozoic basins in Northern Vietnam: implication for Oligocene paleoclimate

Oligocene sediments in northern Vietnam have been extensively studied in terms of geology, stratigraphy, paleogeography, formation environments, tectonics, etc. However, relatively little attention has been paid to the paleoclimate. The Oligocene climate interpreted herein is based on features recorded in sediments taken from the Dong Ho (Hoanh Bo basin), Na Duong (Na Duong basin), and Co Phuc (Red River Trough) formations. These sediments were analyzed using thin-section microscopy, X-ray diffraction, and palynology with the Coexistence Approach. The sediments primarily consist of conglomerate, gritstone, sandstone, siltstone, claystone, and coal shale, deposited in continental environments and dated to the Oligocene based on palynomorph assemblages. The Oligocene paleoclimate is generally warm subtropical, with intermittent hot-humid or cold-dry periods and a slight influence of monsoons. An alternation of hot-humid and cold-dry climates was recorded in the Hoanh Bo basin. In the Red River Trough, the Oligocene climate exhibited a Mean Annual Temperature (MAT) of 9.3-22.2°C and a Mean Annual Precipitation (MAP) of 1122 to 1857 mm, based on the majority of palynological samples, indicating more continental, drier and colder conditions than present. In the Na Duong basin, a warm subtropical climate with a MAT of 9.3-21.7°C and MAP of 1122-1724 mm in the majority of samples was occasionally replaced by hot and humid subtropical periods; the variations in temperature and precipitation followed a similar pattern, suggesting an alternation between dry-cold and humid-hot phases.

Heavy metal bioaccumulation based on seasonal monsoon impact in benthic macroinvertebrates of Korean streams.

This study investigates the influence of seasonal monsoon flooding on heavy metal contamination and bioaccumulation in benthic macroinvertebrate communities within a stream ecosystem. We analyzed sediment and benthic macroinvertebrate samples for eight heavy metals [zinc (Zn), chromium (Cr), nickel (Ni), lead (Pb), copper (Cu), arsenic (As), cadmium (Cd), and mercury (Hg)]) before (BF) and after (AF) a major flooding event. We found significant spatial and temporal variations in heavy metal concentrations were observed, with higher levels after the flood. Chironomidae showed high bioaccumulation factors (BAFs) for several metals, highlighting their role as bioindicators. Notably, elevated Cu accumulation was observed in multiple species, including Radix auricularia (R. auricularia), Cipangopaludina chinensis malleata (C. c. malleata), and Palaemon spp. Non-metric multidimensional scaling (NMDS) analysis revealed shifting correlations between environmental variables and bioaccumulation patterns before and after flooding. Pre-flood, total nitrogen (TN) showed a strong positive correlation with Hg bioaccumulation, while post-flood, large sand content emerged as a more influential factor for Zn, Cr, Ni, and Pb bioaccumulation. Our findings emphasize the complex interplay between seasonal flooding, environmental factors, and heavy metal dynamics, with potential implications for ecological risk assessment and water quality management.

Tsuga leaves from the Neogene Baoshan Basin in southwest China and their palaeoecological implications

Tsuga (Endl.) Carrière (Pinaceae) has a rich fossil record represented by pollen, leaves, wood and seed cones. Although fossil leaves of the genus have been widely documented, most of them have not been examined microscopically, which may limit their taxonomic resolution. In this study, three-dimensionally preserved leaves and leaf fragments of Tsuga from the Neogene (latest Miocene to Pliocene) Baoshan Basin in western Yunnan, southwest China, were examined both morphologically and micromorphologically. The fossil leaves are characterized by flattened and bifacial shape, round to obtuse apex and petiolate base, adaxially sunken and abaxially elevated midvein, adaxial surface without stomata and with elongated, smooth-margined epidermal cells, and abaxial surface with two stomatal bands along the midvein, each stomatal band consisting of 6–8 longitudinal stomatal lines. Based on comparisons with extant species of the genus, we found that the fossil leaves show the closest affinity to Tsuga dumosa (D. Don) Eichler, an extant species growing in the modern western Yunnan. As modern species of Tsuga prefer humid conditions, our fossil find suggests a humid climate in the Baoshan Basin at the time of fossil deposition, probably due to the influence of the Indian summer monsoon from the southwest. This is consistent with previous results of quantitative palaeoclimate reconstructions using spore/pollen fossil assemblages. Our study provides new fossil evidence for the origin of modern conifer diversity in southwest China. It highlights the importance of microscopic studies in the taxonomic resolution of fossil leaves of Pinaceae.

Improved WRF simulation of surface temperature and urban heat island intensity over Metro Manila, Philippines

Accurate representation of the land use/land cover (LULC) in the Weather Research and Forecasting (WRF) model has been shown to be crucial for improved simulation of surface variables and urban heat island (UHI) phenomenon. In this study, a ground truthed LULC dataset over Metro Manila (MM) was integrated in the WRF model to assess and quantify the relative contributions of using an updated land use/land cover (ULULC), activating the single-layer urban canopy model (WSLUCM) and anthropogenic heat (WAH), and consideration of urban surface heterogeneity (LIR) representation on simulated Surface Temperature (ST) relative to the default model settings (CTRL) of the WRF model. Additionally, the study examines the daytime and nighttime UHI features over MM, using a reference simulation where urban grids were replaced with cropland (CRP). Numerical simulations were carried out for April 2018, a typical dry month without monsoonal influence over MM to get a clear UHI characterization. Data from nine weather stations distributed across MM was used for performance evaluation. Results show negligible daytime biases in ST for CTRL, ULULC, and WAH, and underestimated ST for WSLUCM. At night, CTRL and ULULC (WSLUCM and WAH) tend to overestimate (underestimate) ST. Of the four factors analyzed, updating LULC, using SLUCM, including AH, and accounting for urban surface heterogeneity can change daytime ST by 0.3 °C, -0.6 °C, 0.3 °C, and 0 °C, respectively, and nighttime ST by 0.5 °C, -1.2 °C, 0.3 °C, and 0.4 °C, respectively. Widespread daytime warming and a distinct nocturnal UHI following urbanization were confirmed for MM when the LULC accounted for urban heterogeneity. While data limitations for MM limit the specification of the SLUCM, its UHI features are best represented in WRF when an updated land cover dataset is used.

Evolution of evapotranspiration in the context of land cover/climate change in the Han River catchment of China

AbstractEvapotranspiration (ET) stands as a pivotal element in the terrestrial‐atmospheric energy interchange, modulated by a complex array of factors including land use dynamics and climate change. The elucidation of regional and temporal patterns, alongside the mechanisms underpinning ET and its components, amidst environmental shifts, has emerged as a focal point in contemporary hydrological discourse. The Han River catchment, under the influence of the subtropical monsoon, presents an exemplary case study for hydrological inquiry due to its distinct catchment characteristics. This research probes the evolution and influencing mechanisms of ET within the catchment from 2000 to 2018, employing the improved Shuttleworth–Wallace model (i.e., SWH model), multivariate statistical techniques and additional methodologies. Findings reveal that (1) the annual mean ET, evaporation (E) and vegetation transpiration (T) within the Han River catchment from 2000 to 2018 were quantified at 1156.77, 784.21 and 372.56 mm, respectively. The overall spatial pattern showed a gradual decrease from the Chaoshan Plain area identified as having higher values compared to other regions, which may be attributed to the weakened vegetation cooling effect and the indirect effect of the heat island effect brought about by construction land expansion. (2) The significant decrease of E may be attributed to the optimization of vegetation growth conditions in the catchment, resulting in more solar radiation intercepted by the vegetation canopy. (3) Climatic alterations exerted a notable influence on ET, E and T than land use changes. Temperature, Normalized Difference Vegetation Index (NDVI), net radiation and wind speed were identified as the most consequential factors affecting ET. This study lays a scientific groundwork for subsequent exploration into the spatio‐temporal dynamics and mechanisms influencing evapotranspiration and its elements in the Han River catchment, contributing to a broader understanding of hydrological cycling.

Comparative Analysis of Gravity Wave Characteristics in China and the United States Using High Vertical Resolution Radiosonde Observations

AbstractThe characteristics of gravity waves in China are investigated through an extensive analysis of high vertical resolution radiosonde observations collected over eight years across 120 stations, and are subsequently compared to those in the United States. These characteristics encompass energy density, intrinsic frequencies, horizontal and vertical wavelengths, as well as vertical and horizonal propagation directions. China and the United States, situated in mid‐latitude regions with prominent western topographical features, the Qinghai‐Tibet Plateau and Rocky Mountains respectively, demonstrate striking similarities in the generation and distribution of gravity waves. Both landmasses exhibit the strongest gravity waves during winter and the weakest during summer. And within the troposphere, the maximum energy of gravity waves is generated over and immediately downstream of the topographies. In addition, the energy level is amplified in the lower stratosphere. However, unique regional contrasts in summer are result from the differences of summer monsoon influence and the distinct western topographies. The maximum gravity wave energy in summer troposphere is observed over the north side of the Qinghai‐Tibet Plateau in China, contrasting with its location downstream of the Rockies in the United States.

The Monsoon's Influence on Central Asia's Subsequent Periods of Drought and Flooding

AbstractCentral Asia and its southern neighbors are being ravaged by more frequent and intense droughts and floods. While research on droughts is abundant, their interaction with floods and monsoons, especially when originating in the south, has been understudied. This study employed temperature, precipitation, standardized precipitation evapotranspiration index (SPEI), and agricultural drought indices such as water deficit index (WDI), cumulative water deficit (CWD), and Palmer drought severity index (PDSI) to investigate the role of monsoons in increasing drought and flooding in the southern part of central Asia, including Afghanistan and Pakistan, over a 31‐year period. Findings revealed increasing severity and intensity of droughts over time, along with their duration and peaks, contrasting with irregular fluctuations in flood intensity. Rising regional temperatures coincide with declining precipitation. During summer monsoon (SM), average precipitation ranged from 0.03 mm/day (2004) to 0.05 mm/day (2010), with variations across the region. The temperature varied between −14.35°C (2009) and 37.05°C (1991), with a sharp increase up to 0.114°C in Turkmenistan and Uzbekistan, as well as in northern Pakistan, Afghanistan, and western Tajikistan. A temperature drop during SM was revealed on the Mountains range of Himalaya, Hindu Kush, Karakoram, Parmir, Kunlun Shan and Tian Shan, and in Pakistan, down to −0.054°C. WDI showed a strong positive connection (0.71 and 0.64) with temperature (Tmax and Tmin) and a weak negative correlation (−0.5) with precipitation during normal time. However, during the monsoon season, it demonstrated a negative correlation with both within a no significant (−0.08) range for maximum temperature.

East Asian monsoon and westerly jet driven changes in climate and surface conditions in the NE drylands of China since the Late Pleistocene

The East Asian summer monsoon (EASM) is a major component of the global climate yet, the causes for the past spatiotemporal variability of EASM rainfall, its interactions and impacts remain unresolved. Here we use the Sr–Nd isotopes and rare earth elements composition of dust in a peat record from northeast (NE) China to investigate the relationship between aeolian dust, the East Asian monsoon and Westerly Jet (WJ) over East Asia since the Late Pleistocene (14 cal ka BP). The NE drylands of China dominate the dust fraction (Hunshandake, Horqin; 44–88%) with a contribution from the deserts of NW China (Badain Jaran, Tengger, Taklamakan; 10–44%), suggesting an influence of the WJ. Dust deposition varied during the Holocene, displaying a minimum between 8.0 and 6.0 cal ka BP and two peaks at 5.8–3.8 and 1.7–0.3 cal ka BP. Changes in dust flux are opposite to the East Asian winter monsoon intensity profile, suggesting a limited influence of the winter monsoon. The EASM appears to have played a more significant role in the dust cycle, with increasing dust fluxes corresponding with lower EASM precipitation. Variations in dust flux from NE drylands display shifts reflecting changes in EASM precipitations and dune activity along the EASM margin, where the dust originates from. To account for the influence of the WJ, we propose that the meridional position and intensity of the WJ also affected dust emission in the drylands’ region. A more northward position of the WJ allows the EASM front further north, generating more precipitations over the NE drylands, reducing the extent of arid areas, and resulting in less dust emission from dune activity, while the opposite occurs with a strong, more southerly WJ. Anthropogenic activities are likely to have had an increasing impact on the dust cycle over the late Holocene. Nevertheless, the presence of inconsistencies in records, coupled with a simultaneous decline in climatic conditions (mainly precipitations) during the same timeframe, hinders the precise assessment of the influence of human activities on dust emissions in the region.

Characteristics of the Urban Heat Island in Dhaka, Bangladesh, and Its Interaction with Heat Waves

This study examines the characteristics of the urban heat island (UHI) in Dhaka, the densely populated capital city of Bangladesh under the influence of the South Asian monsoon, and its interaction with heat waves. For this, meteorological data at Dhaka (urban) and Madaripur (rural) stations and reanalysis data for the period of 1995–2019 are used for analysis. Here, the UHI intensity is defined as the urban-rural difference in 2-m temperature, and a heat wave is defined as the phenomenon which persists for two or more consecutive days with the daily maximum 2-m temperature exceeding its 90th percentile. The UHI intensity in Dhaka is in an increasing trend over the past 25 years (0.21 °C per decade). The average UHI intensity in Dhaka is 0.48 °C. The UHI is strongest in winter (0.95 °C) and weakest in the monsoon season (0.23 °C). In all seasons, the UHI is strongest at 2100 LST. The average daily maximum UHI intensity in Dhaka is 2.15 °C. Through the multiple linear regression analysis, the relative importance of previous-day daily maximum UHI intensity (PER), wind speed, relative humidity (RH), and cloud fraction which affect the daily maximum UHI intensity is examined. In the pre-monsoon season, RH is the most important variable followed by PER. In the monsoon season, RH is the predominantly important variable. In the post-monsoon season and winter, PER is the most important variable followed by RH. The occurrence frequency of heat waves in Dhaka shows a statistically significant increasing trend in the monsoon season (5.8 days per decade). It is found that heat waves in Bangladesh are associated with mid-to-upper tropospheric anticyclonic-flow and high-pressure anomalies in the pre-monsoon season and low-to-mid tropospheric anticyclonic-flow and high-pressure anomalies in the monsoon season. Under heat waves, the UHI intensity is synergistically intensified in both daytime and nighttime (nighttime only) in the pre-monsoon (monsoon) season. The decreases in relative humidity and cloud fraction are favorable for the synergistic UHI-heat wave interaction.

Integrating paleolimnological hydrogen and oxygen isotope records during the Holocene on the Tibetan Plateau

Stable isotopes are effective proxy indicators for past climate and environment changes. Paleolimnological hydrogen and oxygen isotopes have been used to reconstruct changes in precipitation isotopes and continental climates. However, the stable hydrogen and oxygen isotope records from lakes are rarely compared and integrated directly to study past changes in climate and environment due to their different fractionation pathways. Combined studies on hydrogen and oxygen isotopes would provide much more information than single isotope records. Here, we reanalyzed published lacustrine hydrogen and oxygen isotope records across the Tibetan Plateau, to investigate how both isotope records reveal the influences of the Indian summer monsoon and the westerlies on the Plateau throughout the Holocene. Principal component analysis (PCA) shows that the first principal component (PC1) of 16 lacustrine hydrogen isotope records resembles that of 28 oxygen isotope records. The PC1s of the hydrogen and oxygen isotope records were generally low at 12–6 ka BP, followed by gradual increase since 6 ka BP, suggesting the influence of the Indian summer monsoon. Reconstruction of Holocene precipitation isotopes showed that the slopes of segmented precipitation isotope lines generally followed changes in monsoon intensity. The PC2s for hydrogen and oxygen isotope records remained relatively low at ∼8–4 ka BP, coinciding with moisture variation in westerlies dominated regions. The millennial-scale variations in both hydrogen and oxygen isotope records, revealed by the PC3-PC6, likely responded to the ice drift events in the North Atlantic Ocean, as well as differences in the isotope fractionation pathways at specific sites. The reanalysis of stable hydrogen and oxygen records across the Tibetan Plateau suggests that the water vapor source is the most important factor affecting the isotope variation, though the isotopic fractionation processes may differ significantly. Our results revealed nonlinear variations of monsoon and westerlies on the Tibetan Plateau during the Holocene. This review shows that integration of the stable hydrogen and oxygen isotope records would provide comprehensive understanding of the atmospheric circulation on the Tibetan Plateau.

Improving Water Productivity Using Subsurface Drip Irrigation in the Southwest Monsoon Area in Yunnan Province of China

Due to the influence of the Asian southwest monsoon, seasonal drought is serious and water resources are scarce in the Yunnan province of Southwest China. More effective water-saving irrigation methods should be developed to solve the problem of water scarcity in the dry season. In this study, a subsurface drip irrigation method was used to improve the water productivity of tomato cultivation. Deficit irrigation was conducted. We controlled the lower limit of soil moisture at three different levels (55~65%, 65~75%, and 75~85% of the field capacity). The results indicated that the subsurface drip irrigation treatment significantly increased tomato height in the later stage of tomato growth. Due to the buried pipes, the root/shoot ratio was 8~18% higher for subsurface drip irrigation than for surface drip irrigation methods. Though the yields using subsurface drip irrigation methods were slightly lower than those obtained using surface drip irrigation methods, the tomato quality and water productivity improved significantly. The subsurface drip irrigation methods improved the water productivity by 8.5~21.8% at different soil moisture levels and improved the chlorophyll content by 9.1~17.3%. The VC, soluble sugar, soluble solids, and the ratio of sugar to acid increased by 6.5~15.2%, 7.3~21.6%, 4.1~6.6%, and 3.2~20.8%. This study also indicated that by optimizing the irrigation methods and patterns, water productivity and fruit quality could be improved by more than 50%. This research will be helpful for guiding irrigation during the drought season in the southwest monsoon area in Asia.

Speleothem records from western Thailand indicate an early rapid shift of the Indian summer monsoon during the Younger Dryas termination

Mainland Southeast Asia experiences complex and variable hydroclimatic conditions, mainly due to its location at the intersection of Asian monsoon subsystems. Predicting future changes requires an in-depth understanding of paleoclimatic conditions that is currently hindered by a paucity of records in some regions. In this paper, we present the first speleothem stable isotope records from western Thailand detailing the Bølling-Allerød interstadial, Younger Dryas termination, and early- to mid-Holocene period. We find evidence of higher precipitation during the Bølling-Allerød (14,321–12,824 years before present (1950: BP)) compared to a Younger Dryas termination that starts 11,702–11,674 BP, has a rapid shift centered on 11,660–11,641 BP, and ends 11,603–11,589 BP. In addition, our records show Holocene monsoon intensity peaking at 8250 BP or before, a multi-millennia delay from the Northern Hemisphere summer insolation peak, followed by a trend to drier conditions until at least 750 BP. Assessment of the timing of the Younger Dryas termination in paleoclimate records across Southeast Asia reveals an earlier shift of the Indian Summer Monsoon to global climate shifts when compared to East Asian Summer Monsoon records. The causes of this are currently unknown. Some potentially important aspects include: an Indian Summer Monsoon influence on East Asian Summer Monsoon strength via the Indian Ocean Dipole climate pattern, the role of the Tibetan Plateau in monsoon dynamics, and exposure of the Sundaland shoreline. More high-resolution paleoclimate records, especially on the pathway of Indian Summer Monsoon to East Asian Summer Monsoon, are required for further discussion on the mechanisms controlling the differences between climate regimes.

Sensitivity of the Land–Atmosphere Coupling to Soil Moisture Anomalies during the Warm Season in China and its Surrounding Areas

Significant temporal and spatial variability in soil moisture (SM) is observed during the warm season in China and its surrounding regions. Because of the existence of two different evapotranspiration regimes, i.e., soil moisture-limited and energy-limited, averaging the land–atmosphere (L–A) coupling strength for all soil wetness scenarios may result in the loss of coupling signals. This study examines the daytime-only L–A interactions under different soil moisture conditions, by using two-legged metrics in the warm season from May to September 1981–2020, partitioning the interactions between SM and latent heat flux (SM–LH, the land leg) from the interactions between latent heat flux and the lifting condensation level (LH–LCL, the atmospheric leg). The statistical results reveal large regional differences in warm-season daytime L–A feedback in China and its surrounding areas. As the soil becomes wetter, the positive SM–LH coupling strength increases in arid regions (e.g., northwest China, Hetao, and the Great Indian Desert) and the positive feedback shifts to the negative one in semi-arid/semi-humid regions (northeast and northern China). The negative LH–LCL coupling is most pronounced in wet soil months in arid regions, while the opposite is true for the Tibetan Plateau. In terms of intraseasonal variation, the large variability of SM in north China, the Tibetan Plateau, and India due to the influence of the summer monsoon leads to the sign change in the land segment coupling index, comparing pre- and post-monsoon periods. To further examine the impact of SM anomalies on L–A coupling and to explore evapotranspiration regimes in the North China Plain, four sets of sensitivity experiments with different soil moisture levels over a period of 10 years were conducted. Under relatively dry soil conditions, evapotranspiration is dominated by the soil moisture-limited regime with positive L–A coupling, regardless of external moisture inflow. The critical soil moisture value separating a soil moisture-limited and an energy-limited regime lies between 0.24 m3/m3 and 0.29 m3/m3. Stronger positive feedback under negative soil moisture anomalies may increase the risk of drought in the North China Plain.

Attribution of Moisture Sources for Summer Precipitation in the Upstream Catchment of the Three Gorges Dam

Abstract Currently, there is a lack of investigating moisture sources for precipitation over the upstream catchment of the Three Gorges Dam (UCTGD), the world’s largest dam. Using the dynamical recycling model (DRM), trajectory frequency method (TFM), and the Climate Forecast System Reanalysis (CFSR), this study quantifies moisture sources and transport paths for UCTGD summer precipitation from 1980 to 2009 based on two categories of sources: region-specific and source-direction. Overall, the land and oceanic sources contribute roughly 63% and 37%, respectively, of the moisture to UCTGD summer precipitation. UCTGD and the Indian Ocean are the most important land and oceanic sources, respectively, in which the southern Indian Ocean with over 10% of moisture contribution was overlooked previously. Under the influence of the Asian monsoon and prevailing westerlies, the land contribution decreases to 57.3% in June, then gradually increases to 68.8%. It is found that for drought years with enhanced southwest monsoon, there is a weakening of the moisture contribution from the C-shaped belt along the Arabian Sea, South Asia, and UCTGD, and vice versa. TFM results show three main moisture transport paths and highlight the importance of moisture from the southwest. Comparison analysis indicates that, generally, sink regions are more affected by land evaporation with their locations more interior to the center of the mainland. Furthermore, correlations between moisture contributions and indices of general circulation and sea surface temperature are investigated, suggesting that these indices affect precipitation by influencing moisture contributions of the subregions. All of these are useful for comprehending the causes of summer UCTGD precipitation. Significance Statement Quantitative research on the moisture sources of summer precipitation has been implemented for the upstream catchment of the Three Gorges Dam (UCTGD), which is of particular hydrological significance but has not been investigated previously. The dynamical recycling model (DRM)–trajectory frequency method (TFM) approach is used to quantify and interpret the results of the moisture sources both in different specific subregions and directions, which produce more meaningful results than a single method for the areal division of moisture sources. Furthermore, antecedent indices that significantly influence the following moisture contributions of the subregions and then summer UCTGD precipitation are studied in terms of large-scale general circulation indices, which would help our understanding of precipitation forecast for UCTGD.

Holocene process-based hydroclimate evolution coupled with human behaviours in Dian Lake basin, Southwest China

Lakes are considered excellent archives for the reconstruction of sedimentary processes and related hydroclimatic variations. Dian Lake in south-western China was selected to demonstrate the impacts of Indian summer monsoon-induced water and sediment availabilities on land surface changes and human behaviours. A new sediment core from Dian Lake in the vicinity of Hebosuo village was analyzed by grain size composition, geochemical content, and minerals to detect land-lake processes that responded to hydroclimatic variations and human impacts through the Holocene. Our data suggest that Dian Lake levels during the last 9.8 cal. ka BP were controlled by the variations of the Indian summer monsoon moisture supply according to the displacements of the Intertropical Convergence Zone. A low lake level stage of ∼ 4 m lower than present was determined between 3.1 and 1.73 cal. ka BP, allowing the residents of the Dian culture to occupy the low terrains for settlement and farmland cultivation. With lake level rise at around 1.73 cal. ka BP (220 CE) the high input of clay-fine silt-sized sediments rich in rubidium and barium indicates intensified soil erosion in the Dian Lake basin. Former paddy farmlands and mountain slopes were drained by artificial and natural channels towards the lake in response to strengthened rainfalls covering low terrains by coarse and red alluvial sediments that fostered the residents to abandon the lowlands in the southern basin until 1368 CE. However, the surface erosion process during this period promoted the elevation of the south-eastern delta so that it could be re-occupied since Ming Dynasty. The Indian summer monsoon influence comparable to the modern pattern was responsible for lake level rise to the present level since then but also triggered high seasonality in flood and drought events to foster manual regulation of flood discharge during the last centuries.

Understanding the role of climate change in disaster mortality: Empirical evidence from Nepal

Climate-related disaster impacts, such as loss of human life as its most severe consequence, have been rising globally. Some studies attribute this increase to population growth, while others point to climate change as the primary cause. However, empirical evidence linking climate change to disaster impacts remains limited, particularly in the Global South. This study addresses the impact attribution question in Nepal, a low-income and highly disaster-prone country. We applied a robust regression-based method that accounts for the role of hazard, exposure and vulnerability in flood and landslide mortality, using subnational scale empirical data from 1992 to 2021.Historically, flood and landslide mortality has been highest in central and eastern Nepal due to the stronger influence of the Indian monsoon. However, disaster impacts have surged in recent years in western Nepal, driven largely by an increase in extreme precipitation events. For example, a one standardized unit increase in maximum one-day precipitation increases flood mortality by 33%, and heavy rain days increases landslide mortality by 45%. In contrast, a one standardized unit increase in per capita income reduces landslide and flood mortality by 30% and 45%, respectively. While reductions in vulnerability have helped lower disaster mortality, population exposure has not played a significant role. Therefore, the rise in flood and landslide mortality, particularly in western Nepal, is primarily attributable to the increase in precipitation extremes linked to climate change. With climate change expected to further intensify such extremes, disaster mortality is likely to increase unless significant efforts are made to reduce vulnerability.

Summer monsoon promotes the energy transfer efficiency of the zooplankton community in northern South China sea

The summer monsoon shows a fundamental influence on the pelagic ecosystem of the South China Sea. Zooplankton are a major link for energy transfer between primary producers and upper trophic levels. Therefore, evaluating the energy transfer efficiency (ETE) of zooplankton is crucial to understand the function of pelagic ecosystem under the influence of monsoon. In this study, field surveys were conducted during May (intermonsoon) and August 2021 (summer monsoon) focusing on the variation of zooplankton size and trophic structures across the shelf and slope. The result showed that the summer monsoon reinforced the gradient of abundance, biovolume, and biomass from slope to shelf, and greatly intensified the role of environmental factors in driving spatial variation in most taxa. Both the results of size and trophic structures indicated that the ETE of zooplankton decreased from slope to shelf. The size structure also indicated that the ETE of zooplankton significantly increased under the influence of summer monsoon. These results were consistent with previous studies by different methods, suggesting that these approaches of size and trophic structures had important potential value in assessing changes in the function of marine pelagic ecosystem, especially when compared with sufficient historical data or reanalyzing historical samples.