Monsoon Climate Zone Research Articles

Isolation and characterization of mung bean (Vigna radiata L.) rhizobia in Myanmar

AbstractWe collected soil samples from six major mung bean cropping regions in Myanmar: Sagaing, Mandalay, Nay Pyi Taw, and Magway in the tropical savanna climate zone and Bago and Yangon in the tropical monsoon climate zone. All fields grew mung bean for at least 5 years and had no history of rhizobial inoculation. Mung bean ‘Yezin-11’, a popular cultivar in Myanmar, was inoculated with soil suspensions. From the nodules formed on the roots, we isolated 55 rhizobial strains. Identification of the isolates revealed the dominant species of indigenous rhizobia in each region. We identified 53 Bradyrhizobium strains and 2 Ensifer strains. Bradyrhizobium yuanmingense was dominant in the tropical savanna zone and Bradyrhizobium sp. (B. liaoningense or B. diversitatis) and B. centrosematis were dominant in the tropical monsoon zone. Principal component analysis indicates that the dominance of B. yuanmingense in the tropical savanna zone might be due to high concentration of NO3-N and P2O5 in the soil. It also indicates that the dominance of B. centrosematis in the tropical monsoon zone might be caused by drastically low pH and high concentration of NH4 in the soil. Bradyrhizobium centrosematis YGN-M9, B. yuanmingense SGG-M3, and Bradyrhizobium sp. BGO-M5 significantly increased nodulation (nodule number and nodule dry weight), acetylene reduction activity, and shoot dry weight, respectively, relative to Ensifer terangae MDY-M6. Co-inoculation with these three strains increased nodulation significantly compared with single inoculation of BGO-M5. The characterization of mung bean rhizobia and selection of microbial inoculant candidates will be useful for the development of microbial inoculants in Myanmar.

Differences in Nitrogen Sources and Contributions in Shallow Groundwater in Plateau Lake Area with Different Climate Types

Clarifying the concentration, major sources, and contribution differences of nitrogen in shallow groundwater in plateau lake areas with different climate types can provide a novel direction for the control of nitrate （NO3-） pollution in regional groundwater. Taking the shallow groundwater around Erhai Lake in the subtropical monsoon climate zone and Chenghai Lake in the dry-hot valley area of the Jinsha River as the research objects, using hydrochemical indexes and multi-isotope techniques （δ15N-NO3-, δ18O-NO3-, δ18O-H2O, and δ2H-H2O） combined with the stable isotope （SIAR） model； the differences in nitrogen concentration in shallow groundwater around Erhai Lake and Chenghai Lake were analyzed, the sources of NO3- were identified, and the contribution rates of each pollution source were calculated. The results showed that water quality of more than 33% and 5% of shallow groundwater sampling points around Erhai Lake and Chenghai Lake was worse than the groundwater Class Ⅲ quality requirements （GB/T 14848） of 20 mg·L-1 for nitrate nitrogen （NO3--N）, respectively. The δ18O-H2O and δ2H-H2O in shallow groundwater around Erhai Lake and Chenghai Lake were parallel to the global and Chinese atmospheric precipitation lines, and a large intercept was present, indicating that atmospheric precipitation was not the major recharge source of groundwater in the two regions. The contribution rate of different NO3- sources in shallow groundwater around Erhai Lake was the highest for soil organic nitrogen （53.77%）, followed by nitrogen fertilizer （21.75%） and manure and sewage （21.55%）, and atmospheric deposition nitrogen （2.93%） was the lowest. Denitrification occurred in the transformation process of nitrogen in groundwater. The contribution rate of different NO3- sources in shallow groundwater around Chenghai Lake was manure and sewage （44.88%） > soil organic nitrogen （37.03%） > nitrogen fertilizer （16.17%） > atmospheric deposition nitrogen （1.92%）, and nitrification occurred in the transformation process of nitrogen in groundwater. The climate type significantly affected the shallow groundwater level, altering the migration and transformation process of nitrogen, thereby affecting the nitrogen concentration in groundwater and the contribution of NO3- as the chief source. However, the major source of NO3- was not affected by the climate type； however was more affected by land use, agricultural activities, and manure treatment methods.

Distinctive water bodies surrounding lakes: An effective indicator for drought monitoring and assessment

The response mechanisms of surface water to drought and the potential and performance of water body changes in drought monitoring and assessment remain insufficiently elucidated. We take the Poyang Lake Basin, which suffers from drastic water body changes and frequent droughts, as a representative. Through integrating multisource data to extract long-term precise water bodies, we construct standardized water body area/number anomaly indices (SAAI/SNAI). Subsequently, we quantify the correlation and time lag response between SAAI, SNAI and drought. Our findings reveal that overall, water body area and number in the Poyang Lake Basin all exhibit a significant correlation with typical drought indices. Among them, the large water body area has a higher correlation coefficient with drought, making it a more effective indicator for drought monitoring. Water body changes of Poyang Lake surrounding area offer a more precise reflection of drought conditions than other sub-basins and exhibit greater sensitivity to drought. Meanwhile, water body area changes in Poyang Lake surrounding area lag behind meteorological drought by approximately half a month. And the basin’s water body area can typically respond with changes to some prolonged and severe hydrological droughts about 1 to 2 months in advance. We propose an integrated mechanism for drought monitoring and assessment informed by these conclusions and use actual drought events for qualitative validation. The results indicate that it is possible to assess water body drought conditions for the next approximately half month based on current meteorological drought conditions. Also, combining water body area changes with meteorological drought severity can aid in evaluating hydrological drought conditions for the following about 1–2 months. We extend our investigation to explore the universality of these phenomenon across eight shallow lakes globally characterized by significant water fluctuations. The results reveal that the water body changes in most of these lakes exhibit good potential for drought monitoring and assessment, and present a strong consistency with deep soil moisture, allowing for the accurate reflection of deep soil drought conditions. The lag response patterns between water bodies and drought in Dongting Lake, Hongze Lake, and Tonlé Sap Lake—also situated in the monsoon climate zone—are more similar to those observed in Poyang Lake. These distinctive lake water bodies can serve as an innovative indicator for drought monitoring and assessment, providing potential support for endeavors in drought prevention and mitigation.

Parasite diversity among domestic goats of tropical monsoon climatic zone in India.

Among different climatic zones in India, the tropical monsoon region comprises a diverse ecosystem characterized by the endemic nature of several parasites including certain emerging and re-emerging vector-borne pathogens of humans, whereas a systematic investigation of the occurrence of different parasites among domestic goats in this area is not yet explored. The goal of the present study is to explore the parasite diversity focusing on molecular identification of vector-borne hemoparasites and its health impacts on domestic goats reared in the tropical monsoon climate zone of Kerala, India. Among 227 goats presented to the Teaching Veterinary Clinical Complex (TVCC) in the monsoon months of 2023, thirty animals were recruited for the study. The animals were screened for the presence of different hemoparasites (Anaplasma spp., Theileria spp., and Babesia spp.), ectoparasites (ticks, lice, and fleas), and gastrointestinal (GI) parasites (hookworms, threadworms, tapeworms, whipworms, and coccidia). The isolated hemoparasites were further characterized by sequencing and phylogenetic analysis. The correlation studies to elucidate the association between the occurrence of different parasites and clinical manifestations (hyperthermia, pallor of mucous membrane, circulatory failure, respiratory signs, neurological instability, and GI signs), blood picture (anemia, leukopenia, thrombocytopenia), demographics (sex and age), and treatment history (hemoparasitic therapy, ectoparasiticidal application, and prophylactic deworming) were conducted. The co-infection status of these parasites was also evaluated. A substantial portion of the goats in the study group was found to be affected by vector-borne hemoparasitic diseases and their arthropod vectors or GI parasites or both. This can be attributed to the constantly warm and humid climate of the region, which is favorable for the survival and growth of different life cycle stages of these parasites and vectors. A strategic parasitic disease surveillance-cum-control program is the need of the hour for ensuring climate resilience and profitable goat farming in the region.

Trade-Off and Synergy Mechanism of Agricultural Water Resource Spatial Allocation in Monsoon Climate Areas Based on Machine Learning: A Case Study of Reservoir Layout Optimization in Shandong Province, China

Influenced by increasing global extreme weather and the uneven spatiotemporal distribution of water resources in monsoon climate areas, the balance of agricultural water resources supply and demand currently faces significant challenges. Conducting research on the spatial allocation trade-offs and synergistic mechanisms of agricultural water resources in monsoon climate areas is extremely important. This study takes the spatial layout of reservoir site selection in water conservancy projects as an example, focusing on Shandong Province as the research area. During the site selection process, the concept of water resource demand is introduced, and the suitability of reservoir siting is integrated. It clarifies ten influencing factors for suitability degree and five influencing factors for demand. A bi-objective optimization model that includes suitability degree and demand degree is established. Utilizing machine learning methods such as the GA_BP neural network model and the GA-bi-objective optimization model to balance and coordinate the supply and demand relationship of agricultural water resources in the monsoon region. The study found that: (1) in the prediction of suitability degree, the influencing factors are most strongly correlated with the regulatory storage capacity (regulatory storage capacity > total storage capacity > regulating storage coefficient); (2) compared with single-objective optimization of suitability degree, the difference between water supply and demand can be reduced by 74.3% after bi-objective optimization; (3) according to the spatial layout optimization analysis, the utilization of water resources in the central and western parts of Shandong Province is not sufficient, and the construction of agricultural reservoirs should be carried out in a targeted manner. This study provides new ideas for promoting the efficient use of water resources in monsoon climate zones and the coordinated development of humans and nature, reflecting the importance of supply and demand balance in the spatial allocation of agricultural water resources, reducing the risk of agricultural production being affected by droughts and floods.

Remote Sensing-Based Analysis of Precipitation Events: Spatiotemporal Characterization across China

Precipitation occurs in individual events, but the event characteristics of precipitation are often neglected. This work seeks to identify the precipitation events on both spatial and temporal scales, explore the event characteristics of precipitation, and reveal the relationships between the different characteristics of precipitation events. To do this, we combined the Forward-in-Time (FiT) algorithm with the gridded hourly precipitation product to detect precipitation events in time and space over China. The identified precipitation events were analyzed to determine their characteristics. The results indicate that precipitation events can be detected and identified in time and space scales based on the FiT algorithm and the gridded hourly precipitation product. The precipitation total, duration, and intensity of these events decrease gradually from the southern (eastern) coastal regions to northern (western) inland areas of China. The event precipitation totals are strongly correlated with event duration and event maximum intensity; the totals are more strongly correlated with event maximum intensity and event intensity in the regions with lower precipitation than the regions with higher precipitation. More than 90% of precipitation events are shorter than 6 h, and events with long duration normally occur in temperate monsoon (TM) and subtropical/tropical monsoon (ST) climate zones. Heavy precipitation events with a duration longer than 7 h generally occur more than seven times per year in TM and ST climate zones. Our results suggest that precipitation analyses should sufficiently consider the characteristics of events across different regions.

Integrated effect of aspect ratio and tree spacing on pedestrian thermal comfort of street canyon.

Increasing heat stress in urban environments due to climate change has a significant adverse impact on human work and daily life. Street canyons as the main component of the underlying surface of the city and the main place of residents' activities, a comprehensive understanding of street morphology and tree planting practices can help to improve thermal comfort. Based on survey data and field experiments, this study designed 30 scenarios and employed ENVI-met model (version 5.0.3) to quantify the effect of street aspect ratio (H/W: H is building height and W is street width) and tree spacing (TS) on pedestrian thermal comfort in two differently oriented streets (north-south and east-west) in Taiyuan, China. Results showed that H/W ratio and TS significantly influenced the street thermal comfort mainly owing to shading. H/W ratio played a pivotal role in reducing mean radiant temperature (Tmrt) and physiological equivalent temperature (PET), and was negatively correlated with Tmrt and PET. Compared to no-tree scenarios, street trees significantly improved thermal comfort (mean reductions of Tmrt and PET were 12.74℃ and 5.66℃, respectively), and PET and Tmrt were significantly negatively correlated with TS. The improvement effect of street trees on Tmrt and PET in east-west oriented street was better than north-south oriented street. H/W = 1.0 and TS = 6m appeared as the proposed combination to mitigate the summer thermal comfort in the temperate monsoon climate zone. These quantitative results provide new insights into renewal and design strategies for future urban planning.

Soil biological fertility evolution in a chronosequence under long‐term rice cultivation after land reclamation in China

AbstractLand use significantly affects soil biological fertility through impacts on carbon (C) and nitrogen (N) cycling. The present study investigated the effects of long‐term rice cultivation after tidal flat reclamation on soil C and N metabolism, microbial biomass and biological fertility. Eighteen composite topsoil (0–20 cm) samples were identified in a chronosequence of coastal reclamation areas (0–700 years old) in subtropical monsoon climate zone, namely tidal flat (T0), salt marsh soil (S10) and paddy soil (P50, P100, P300 and P700). Using ANOVA analysis, mono‐exponential regression model, and multiple linear regressions, soil organic matter (SOM), total nitrogen (TN), cumulative C mineralization content (Ct) and N mineralization content (Nt), basal soil respiration (BSR) and microbial biomass C and N (MBC and MBN) in the P50‐P700 samples were significantly higher than those in the T0 and S10 samples, whereas C metabolic quotients (qCO2) in the P50‐P700 were significantly lower than those in the T0 and S10 samples. The time to steady state for SOM and TN are 357 years and 80 years, respectively; 133 and 221 years for Ct and Nt, respectively; and 318 and 183 years for MBC and MBN, respectively. Also, a soil biological fertility index (SBFI) was calculated on the basis of SOM, BSR, Ct, MBC, qCO2 and qCM. P100‐P300 samples had the highest SBFI score (28.7) and ranked in the class V (very high) of biological fertility, achieving steady‐state conditions after 146 years. SBFI was significantly positively correlated with SOM, TN, MBC, MBN, BSR, Ct and Nt, whereas it was significantly negatively correlated with pH, qCO2 and C mineralization quotient (qCM). MBC and qCM were two independent variables with considerable positive effects on SBFI. Long‐term rice cultivation could facilitate C and N accumulation and enhance biological fertility in soils via microbial activity, especially within 300 years. Our findings demonstrate that rice cultivation has the potential to enhance soil C and N accumulation. Carbon‐related SBFI is suitable for assessing soils under long‐term rice cultivation, mainly because the rice paddy field is an intensive and conservative system.

Association between heatwaves and risk and economic burden of injury related hospitalizations in China

BackgroundPublic health is greatly affected by heatwaves, especially as a result of climate change. It is unclear whether heatwaves affect injury hospitalization, especially as developing countries facing the impact of climate change. ObjectivesTo assess the impact of heatwaves on injury-related hospitalization and the economic burden. MethodsThe daily hospitalizations and meteorological data from 2014 to 2019 were collected from 23 study sites in 11 meteorological geographic zones in China. We conducted a two-stage time series analysis based on a time-stratified case-crossover design, combined with DLNM to assess the association between heatwaves and daily injury hospitalization, and to further assess the regional and national economic losses resulting from hospitalization by calculating excess hospitalization costs (direct economic losses) and labor losses (indirect economic losses). To determine the vulnerable groups and areas, we also carried out stratified analyses by age, sex, and region. ResultsWe found that 6.542% (95%CI: 3.939%, 9.008 %) of injury hospitalization were attributable to heatwaves during warm season (May to September) from 2014 to 2019. Approximately 361,447 injury hospitalizations were attributed to heatwaves each year in China, leading to an excess economic loss of 5.173 (95%CI: 3.104, 7.196) billion CNY, of which 3.114 (95%CI: 1.454, 4.720) billion CNY for males and 4.785 (95%CI: 3.203, 6.321) billion CNY for people aged 15–64 years. The attributable fraction (AF) of injury hospitalizations due to heatwaves was the highest in the plateau mountain climate zone, followed by the subtropical monsoon climate zone and the temperate monsoon climate zone. ConclusionsHeatwaves significantly increase the disease and economic burden of injury hospitalizations, and vary across populations and regions. Our findings implicate the necessity for targeted measures, including raising public awareness, improving healthcare infrastructure, and developing climate resilience policies, to reduce the threat of heatwaves to vulnerable populations and the associated disease and economic burden.

Influence of Foehn Winds of Truong Son Mountains on the High Temperatures Observed in North-Central Vietnam during 31 May–5 June 2017

Abstract North-central Vietnam often experiences high temperatures. Foehn winds originating from the Truong Son Mountains (also known as Laos winds) are believed to contribute to abnormally high temperatures; however, no quantitative research has focused on foehn warming in Vietnam. In this study, we conducted numerical simulations using the Weather Research and Forecasting (WRF) Model to investigate the contribution of foehn warming to abnormally high temperatures in north-central Vietnam in early June 2017. Generally, May–June is the monsoon period in Vietnam. Consequently, foehn warming during this season is thought to be mainly caused by latent heating and precipitation mechanism. However, the primary factor in the cases covered in this study was foehn warming with an isentropic drawdown mechanism. Diabatic heating with turbulent diffusion and sensible heat flux from mountain slopes also plays significant roles. The warming effect of the foehn winds on the temperatures during the events was approximately 2°–3°C. It was concluded that the high temperature events from 31 May to 5 June 2017 were caused by synoptic-scale warm advection and foehn warming. Sensitivity experiments were conducted on the WRF Model, utilizing three atmospheric boundary layer turbulence schemes (YSU, ACM2, and MYNN), consistently yielding results for simulated temperature and relative humidity. The wind speed bias for the MYNN scheme was found to be lower than that of the other schemes. However, this study did not delve into the underlying reasons for these differences. The optimal performance of each scheme remains an open question. Significance Statement It was hypothesized that north-central Vietnam often experiences high temperatures owing to foehn winds (also known as Laos winds) descending from the Truong Son Mountains. This study conducted numerical experiments to validate this hypothesis and investigate the associated mechanisms of foehn winds in this region. Surprisingly, despite the monsoon season, the isentropic drawdown mechanism without precipitation effects provides the primary explanation for the high temperatures caused by foehn winds in north-central Vietnam, and not the latent heating and precipitation mechanism with precipitation effects that researchers expected. The results of this study contribute to better prediction of high temperatures in this region and improve our understanding of foehn winds in tropical monsoon climate zones.

Impact of aerosol concentration changes on carbon sequestration potential of rice in a temperate monsoon climate zone during the COVID-19: a case study on the Sanjiang Plain, China.

The emission reduction of atmospheric pollutants during the COVID-19 caused the change in aerosol concentration. However, there is a lack of research on the impact of changes in aerosol concentration on carbon sequestration potential. To reveal the impact mechanism of aerosols on rice carbon sequestration, the spatial differentiation characteristics of aerosol optical depth (AOD), gross primary productivity (GPP), net primary productivity (NPP), leaf area index (LAI), fraction of absorbed photosynthetically active radiation (FPAR), and meteorological factors were compared in the Sanjiang Plain. Pearson correlation analysis and geographic detector were used to analyze the main driving factors affecting the spatial heterogeneity of GPP and NPP. The study showed that the spatial distribution pattern of AOD in the rice-growing area during the epidemic was gradually decreasing from northeast to southwest with an overall decrease of 29.76%. Under the synergistic effect of multiple driving factors, both GPP and NPP increased by more than 5.0%, and the carbon sequestration capacity was improved. LAI and FPAR were the main driving factors for the spatial differentiation of rice GPP and NPP during the epidemic, followed by potential evapotranspiration and AOD. All interaction detection results showed a double-factor enhancement, which indicated that the effects of atmospheric environmental changes on rice primary productivity were the synergistic effect result of multiple factors, and AOD was the key factor that indirectly affected rice primary productivity. The synergistic effects between aerosol-radiation-meteorological factor-rice primary productivity in a typical temperate monsoon climate zone suitable for rice growth were studied, and the effects of changes in aerosol concentration on carbon sequestration potential were analyzed. The study can provide important references for the assessment of carbon sequestration potential in this climate zone.

Effect of agricultural management practices on rice yield and greenhouse gas emissions in the rice–wheat rotation system in China

Agricultural management practices (AMPs) have the potential to significantly enhance crop yield, albeit with the possible side effect of escalating greenhouse gas emissions. Few studies have undertaken a comprehensive quantification of the impact of AMPs on crop production and soil GHG, particularly in identifying the optimal AMPs for rice cultivation within rice-wheat rotation system. Here, we combined data analysis and keyword search methods on 1433 individual experimental observations from 172 studies on diverse soil types in the subtropical monsoon climate zone of China to assess the impact of AMPs on rice yield, CH4 and N2O emissions, total greenhouse gas emissions (TGHGE). We focused on four key AMPs: mineral N fertilizer management (including ordinary N fertilizer and slow−/controlled-release fertilizer (SCRF)), organic material management (incorporating organic fertilizer, biochar amendment, and straw return), water-saving irrigation, and no-tillage. Our result showed the rice yield ranged from 2525 to 31,196 kg ha−1, and mineral N fertilizer and organic material management boosted rice yield by 2.84–16.19 % and 2.47–8.52 %, respectively. In terms of N2O emissions, biochar amendment resulted in a decrease of 13.05 %, while ordinary N fertilizer, organic fertilizer, and water-saving irrigation led to increases of 63.16 %, 136.66 %, and 37.41 %, respectively. The implementation of SCRF, water-saving irrigation, and no-tillage significantly curtailed CH4 (6.83 %–35.91 %) and TGHGE (6.22 %–20.59 %). Conversely, organic fertilizer and straw return significantly escalated CH4 emissions by 102.20 % and 33.64 % and TGHGE by 85.03 % and 32.40 %. Rice yield and GHG emissions are mainly influenced by variables such as soil bulk density, pH, soil organic carbon, soil texture, mean annual temperature, and total nitrogen. Our study demonstrates that the application of SCRF, water-saving irrigation, and no-tillage can effectively reduce GHG without compromising yield. These practices are particularly effective under climatic and soil conditions of rice-wheat rotation systems in China, thereby contributing to the sustainable rice farming.

Quantification and mapping of the cooling effect of urban parks on the temperate monsoon climate zone

As a major type of Nature-based solutions(Nbs)to combat urban climate challenges in densely developed urban areas, urban parks (a combination of blue and green infrastructure) could mitigate regional microclimate by providing a significant cooling effect. In this study, the cooling effects of 50 urban parks in the temperate monsoon climate zone of China were comprehensively evaluated from the maximum perspective and accumulative perspective using four cooling indices, namely, park cooling area (PCA), park cooling efficiency (PCE), park cooling intensity (PCI) and park cooling gradient (PCG). Results have shown that 90 % of urban parks generate significant cooling effects, with land surface temperature (LST) averaging 3.35 °C lower than ambient LST. The park's characteristics significantly influenced the cooling effect (especially PCE, PCI, and PCG). Park size was the main factor contributing to the increase of PCA and the decrease of PCE. Additionally, the threshold value of efficiency for a 130-ha land area was calculated based on PCA. It was difficult to balance the simultaneous growth of cooling range efficiency and accumulative LST reduction efficiency. In the case of limited space, targeting parks with high PCE or PCI and PCG was recommended by designing the complexity of park shapes or increasing the proportion of water bodies. These findings help in the planning and construction of urban parks to rationalize resources to meet the different cooling needs of residents.

Impacts of Thermal Differences in Surfacing Urban Heat Islands on Vegetation Phenology

Urbanization has significantly changed thermal environments and vegetation phenology. However, the effects of spatially different land surface temperatures (LST) on vegetation phenology, rather than differences between urban areas and rural areas, remain unclear. In this study, four cities with similar vegetation types located in temperate monsoon climate zones were selected to map vegetation phenological metrics and discuss their responses to spatially heterogeneous LST within urban areas. First, Sentinel 2-A and 2-B data were used to estimate phenological metrics by combining Savitzky–Golay filtering, and Landsat 8 TIRS data was used to obtain LST. Second, buffer zones (from the urban center to the urban edge at 1 km intervals) were used to extract the averaged phenological metrics and LST. The response of the phenological metrics to LST from the urban center to the urban edge was then analyzed. Results show that spatial differences in LST and vegetation phenology exist inside urban regions as well as between urban and peri-urban areas. In addition, the response of phenology to LST within urban areas is also obvious. SOS is negatively related to spring LST from the urban center to the urban edge, whereas EOS is positively related to autumn LST.

Urban vegetation cooling capacity was enhanced under rapid urbanization in China

The cooling capacity of urban vegetation, which forms “urban cooling islands” (UCI), can play an important role in mitigating urban heat islands (UHI). However, the spatiotemporal changes in UCI intensity at the national scale have not been fully explored under rapid urbanization in China. In this study, based on 23,081 Landsat images from the Google Earth Engine, spatiotemporal UCI was obtained for 320 cities in China from 2000 to 2018 and correlated with meteorological and urbanization parameters to uncover the factors driving UCI changes. The direct and indirect effects of the driving factors on UCI were investigated using structural equation modeling. Our results showed that China experienced 12.38%, 181.23%, 83.6%, and 22.63% increases in population density, gross domestic product (GDP), the impervious surface, and leaf area index (LAI), respectively, between 2000 and 2018. Furthermore, we found more rapid urbanization in the temperate continental climate (TCC) zone than in the temperate monsoon climate (TMC) and subtropical monsoon climate (SMC) zones in China. The national averaged UCI was 2.47 °C, with the largest UCI recorded in small cities and TCC zones. From 2000 to 2018, over 70% of cities showed an increasing trend in UCI intensity, mainly concentrated in TMC and megacities. At the national scale, the increase in UCI was likely explained by a combination result of the intensified wind speed, decrease in urban areas, and enhanced LAI. We also identified that the driving mechanisms of UCI were very different in different climatic zones. In TCC, precipitation had a major impact on UCI intensity at a threshold of 78.92 mm. In TMC and SMC, in addition to temperature, urbanization factors significantly influenced UCI. The main factors in TMC were LAI, with a specific threshold of 1.15. These results deepen the understanding of UCI formation and provide new insights into the regional adaptation of urban vegetation to mitigate urban heat waves.

Total and cause-specific mortality attributable to cold spells in China: A multicity and multicounty study

Climate change has resulted in an increase in the frequency and intensity of extreme cold weather events, but few multicity or multicounty researches have explored the association between cold spells and mortality risk and burden. We collected daily data on climate, sociodemographic factors and mortality in 18 cities/counties across 11 geographical regions for the period of November to March 2014–2018. A distributed lag nonlinear model was used to examine the association between cold spells and mortality after adjustment for confounding factors. Twelve definitions of cold spells were used. Multi-meta regression analysis was applied to pool the impacts over different regions. Cold spells were significantly associated with all-cause mortality at lag 0–21 (CRR:1.38, 95%CI:1.21,1.57). In addition to respiratory diseases and circulatory system diseases, digestive, endocrine and nervous system diseases and injury were also affected by cold spells. The magnitude of the impacts of cold spells on mortality varied among the diseases investigated, with the highest risk estimate found for influenza and pneumonia (CRR: 2.00, 95%CI: 1.45, 2.76) and the lowest estimate found for injury (CRR: 1.26, 95%CI: 1.09,1.46). The fraction of all-cause mortality attributable to cold spells was 2.31% (95%CI: 0.90%, 3.46%). Among the regional differences, the attributable burden of all-cause mortality was higher in rural areas and subtropical monsoon climate zone, with attributable fractions of 2.85% (95%CI: 1.23%, 4.11%) and 3.36% (95%CI: 0.55%, 5.35%), respectively. Cold spells increased mortality from a range of diseases. Women, older adults and residents of rural areas and subtropical monsoon climate zone were more vulnerable to cold spells impacts. The findings may help to formulate preventive strategies and early warning response plans to reduce mortality burden of extreme cold events.

High-Resolution National-Scale Mapping of Paddy Rice Based on Sentinel-1/2 Data

Rice has always been one of the major food sources for human beings, and the monitoring and planning of cultivation areas to maintain food security and achieve sustainable development is critical for this crop. Traditional manual ground survey methods have been recognized as being laborious, while remote-sensing technology can perform the accurate mapping of paddy rice due to its unique data acquisition capabilities. The recently emerged Google Earth Engine (GEE) cloud-computing platform was found to be capable of storing and computing the resources required for the rapid processing of massive quantities of remote-sensing data, thereby revolutionizing traditional analysis patterns and offering unique advantages for large-scale crop mapping. Since the phenology of paddy rice depends on local climatic conditions, and considering the vast expanse of China with its outstanding geospatial heterogeneity, a zoning strategy was proposed in this study to separate the monsoon climate zone of China into two regions based on the Qinling Mountain–Huaihe River Line (Q-H Line), while discrepant basic data and algorithms have been adopted to separately map mid-season rice nationwide. For the northern regions, optical indices have been calculated based on Sentinel-2 images, growth spectral profiles have been constructed to identify phenological periods, and rice was mapped using One-Class Support Vector Machine (OCSVM); for the southern regions, microwave sequences have been constructed based on Sentinel-1 images, and rice was mapped using Random Forest (RF). By applying this methodological system, mid-season rice at 10 m spatial resolution was mapped on the GEE for the entire Chinese monsoon region in 2021. According to the accuracy evaluation coefficients and publicly released local statistical yearbook data, the relative error of the mapped areas in each province was limited to 10%, and the overall accuracy exceeded 85%. The results could indicate that mid-season rice can be mapped more accurately and efficiently on a China-wide scale with relatively few samples based on the proposed zoning strategy and mapping methods. By adjusting the parameters, the time interval for mapping could also be further extended. The powerful cloud-computing competence of the GEE platform was used to map rice on a large spatial scale, and the results can help governments to ascertain the distribution of mid-season rice across the country in a short-term period, which would be well suited to meeting the increasingly efficient and fine-grained decision-making and management requirements.

Improved Constraints on the Recent Terrestrial Carbon Sink Over China by Assimilating OCO‐2 XCO2 Retrievals

AbstractThe magnitude and distribution of China's terrestrial carbon sink remain uncertain due to insufficient observational constraints; satellite column‐average dry‐air mole fraction carbon dioxide (XCO2) retrievals may fill some of this gap. Here, we estimate China's carbon sink using atmospheric inversions of the Orbiting Carbon Observatory 2 (OCO‐2) XCO2 retrievals within different platforms, including the Global Carbon Assimilation System (GCAS) v2, the Copernicus Atmosphere Monitoring Service, and the OCO‐2 Model Inter‐comparison Project (MIP). We find that they consistently place the largest net biome production (NBP) in the south on an annual basis compared to the northeast and other main agricultural areas during peak growing season, coinciding well with the distribution of forests and crops, respectively. Moreover, the mean seasonal cycle amplitude of NBP in OCO‐2 inversions is obviously larger than that of biosphere model simulations and slightly greater than surface CO2 inversions. More importantly, the mean seasonal cycle of the OCO‐2 inversions is well constrained in the temperate, tropical, and subtropical monsoon climate zones, with better inter‐model consistency at a sub‐regional scale compared to in situ inversions and biosphere model simulations. In addition, the OCO‐2 inversions estimate the mean annual NBP in China for 2015–2019 to be between 0.34 (GCASv2) and 0.47 ± 0.16 PgC/yr (median ± std; OCO‐2 v10 MIP), and indicate the impacts of climate extremes (e.g., the 2019 drought) on the interannual variations of NBP. Our results suggest that assimilating OCO‐2 XCO2 retrievals is crucial for improving our understanding of China's terrestrial carbon sink regime.

Promotion effect of ultraviolet light on graphene oxide aggregation in the presence of different climatic zone's humic and fulvic acid

Aggregation of graphene oxide (GO) is significantly affected by dissolved organic matter (DOM) in natural waters, while DOM's climate zone and light irradiation is seldom considered. This study investigated the effect of humic/fulvic acid (HA/FA) from various climate zones of China on aggregation of small (200 nm) and large (500 nm) GO under 120-h UV irradiation. GO aggregation was promoted by HA/FA because UV irradiation decreased hydrophilicity of GO and steric forces among particles. GO generated electron and hole pair under UV irradiation, which reduce GO with more hydrophilic oxygen-containing functional group (C-O) to rGO with high hydrophobicity and oxidize DOM into organic matter with smaller molecular weight. Most severe GO aggregation was observed with Makou HA from Subtropical Monsoon climate zone and Maqin FA from Plateau and Mountain climate zone, which was primarily because HA/FA's high molecular weight and aromaticity dispersed GO initially that facilitated UV penetration. GO aggregation ratio was positively correlated with graphitic fraction content (R2 = 0.82-0.99) and negatively correlated with C-O group content (R2 = 0.61-0.98) in the presence of DOM under UV irradiation. This work highlights different dispersity of GO during photochemical reactions in various climate zones, providing new insight into the environmental implications of nanomaterial release.

Downstream carbon transport and surface CO2 evasion in the Hanjiang River Network and their implications for regional carbon budget

Fluvial carbon fluxes have been increasingly recognized as important components of the global carbon budget. However, it is challenging to accurately quantify carbon fluxes in river networks; therefore, the role of carbon fluxes in the regional carbon budget remains poorly understood. The Hanjiang River Network (HRN) is located in a subtropical monsoon climate zone, and its material transport has a notable impact on the Changjiang River. In this study, it was hypothesized that the total fluvial carbon fluxes from the river network in the subtropical monsoon climate zone are dominated by vertical CO2 evasion and account for a large fraction of terrestrial net primary productivity (NPP) (e.g., 10 %) and fossil CO2 emissions (e.g., 30 %), which is roughly equivalent to the global average. Therefore, the downstream export of three carbon fractions and CO2 evasion were estimated in the HRN over the last two decades and the findings were compared with NPP and fossil CO2 emissions in the basin. The results suggest that approximately 2.14–6.02 Tg C year−1 (1 Tg = 1012 g) of carbon is exported in the HRN. Vertical CO2 evasion represents the largest destination at 1.22–5.34 Tg C year−1 or 68 % of the total fluvial carbon flux component, corresponding to 1.5 %–11 % of the fossil CO2 emissions. Downstream export of dissolved inorganic carbon is the second largest destination with a magnitude of 0.56–1.92 Tg C year−1. Downstream organic carbon export plays a relatively small role with a magnitude of 0.04–0.28 Tg C year−1. The findings also indicate that the offset of total fluvial carbon fluxes from terrestrial NPP is unexpectedly small (2.0 %–5.4 %). Data availability and the simplification of carbon processes introduced uncertainty; therefore, future research should incorporate a fuller representation of fluvial carbon processes and fractions to improve regional-scale carbon accounting.