Middle And Lower Reaches Of The Yangtze River Research Articles

Mapping winter fallow arable lands in Southern China by using a multi-temporal overlapped area minimization threshold method

ABSTRACT In China, a nation facing farmland scarcity, accurate mapping of winter fallow arable lands is crucial for enhancing crop rotation and land use efficiency. The Dynamic Threshold (DT) method commonly used in phenology and winter fallow land studies often employs empirically set subjective thresholds. This approach tends to uniformly apply a single threshold across diverse vegetation types and geographical regions, neglecting the variations in physiological traits and spatial heterogeneity. This study developed a multitemporal overlapping area minimization threshold method (MOAMT). This approach constructed Normalized difference vegetation index (NDVI) probability density functions for both winter fallow and non-winter fallow arable land across a time series to attain a statistically significant threshold. We use MOAMT and DT methods for winter fallow arable land extraction in southern China, respectively. And then, comparison of identification accuracy between MOAMT and DT has been implemented by using confusion matrix method. Compared to the DT method, MOAMT exhibits better performance. The mapping of winter fallow arable lands highlighted their predominant distribution in the middle and lower reaches of the Yangtze River (MLR-YR) Basin, covering approximately 20.8 million hectares, with potential for development. This study will provide information support for the optimization of planting layouts in China, offering new opportunities for further increasing grain production. While in the sense of research approach, this study indicates the superiority of threshold obtained through statistical probability calibration over empirical universal thresholds for classification accuracy. We advocate for prioritizing threshold calibration in future applications of threshold classification methods.

Different mechanisms of air temperature anomalies in the Yangtze River between early and late summer

The middle and lower reaches of the Yangtze River (MLRYR) exhibit notable interannual variability in seasonal-mean air temperature amid ongoing global warming. This study elucidates the specific mechanisms governing anomalous air temperatures during early (June) and late summer (July to August) in the MLRYR. Early summer temperatures arise from anomalous sinking driven by negative anomalies in moist enthalpy advection in the lower troposphere, as a response to warm sea surface temperature anomalies (SSTA) in the tropical western Pacific. This induces a low-level cyclone anomaly over Southeast Asia, reducing specific humidity and determining anomalous vertical motion over the MLRYR. In contrast, late summer temperatures are induced by mid-upper tropospheric descending anomalies over the MLRYR. The combined influence of SSTA in the western Pacific and North Atlantic sustains warmer air by reinforcing a barotropic anticyclone over North China through a mid-latitude wave train. Subsequent anomalous negative potential vorticity advection in the upper troposphere strengthens sinking motion over the MLRYR. The seasonal evolution of the East Asian summer monsoon and SSTA is pivotal in the distinct mechanisms governing warmer air temperatures over the MLRYR. While numerical experiments capture general features, the regulation of SSTA is subject to uncertainty due to the atmospheric intrinsic patterns. This research distinguishes predictability sources of air temperature anomalies over the MLRYR between early and late summer, emphasizing the combined influence of SSTA beyond the ENSO domain on East Asian climate.

Effects of Extreme Weather Events on Nitrous Oxide Emissions from Rice-Wheat Rotation Croplands.

Cropland ecosystems are significant emission sources of N2O, but a limited number of studies have focused on the impact of extreme weather events on N2O fluxes from cropland. This present study integrated field observations and model simulations to explore the responses of N2O fluxes to extreme weather events in typical rice and wheat rotation croplands in the middle and lower reaches of the Yangtze River (MLRYR) in China. The findings revealed that the studied rice-wheat rotation cropland exhibited a net source of N2O over the three-year monitoring period, with annual cumulative N2O emissions ranging from 190.4 to 261.8 mg N m-2. N2O emissions during the rice and wheat growing seasons accounted for 29% and 71% of the total yearly emissions, respectively. Extreme heat events led to a 23% to 32% increase in observed N2O emissions from cropland. Observed N2O emissions from irrigated rice fields during extreme precipitation events were 45% lower than those during extreme drought events. In contrast, extreme precipitation events raised observed N2O emissions from rain-fed wheat fields by 36% compared to the multi-year average, while extreme drought events reduced N2O emissions from wheat fields by 20%. Regional simulations indicated that annual cumulative N2O emissions from croplands in the MLRYR are projected to increase from 207.8 mg N m-2 under current climate to 303.4 mg N m-2 in the future. Given the episodic nature and uncertainties associated with N2O emissions from cropland, further validation is necessary for utilizing the model to explore the effects of extreme weather events on N2O in cropland ecosystems.

Characteristic Identification of Heat Exposure Based on Disaster Events for Single-Season Rice along the Middle and Lower Reaches of the Yangtze River, China

As global warming continues, heat stress events are expected to increase and negatively affect rice production. Spatiotemporal changes in single-season rice exposure to heat stress were explored along the middle and lower reaches of the Yangtze River (MLRYR) in China during 1971–2020 based on created heat thresholds in different phenological stages, derived from comparison of historical heat records for single-season rice and agro-meteorological data. The feature importance (IF) provided by the Random Forest model was used to modulate the relationship between threshold accumulated temperature and yield reduction rate caused by heat stress. In addition, critical temperature thresholds at different phenological stages were determined by combining Overall Accuracy and the Receiver Operating Characteristic (ROC) curve. According to historical disaster records, the heat stress occurred before the reproductive phase (i.e., the tillering–jointing stage) and ended in the filling stage. Critical temperature thresholds of Tmax at tillering–jointing, booting, flowering and filling were quantified as 36, 35, 35 and 38 °C, with higher IF values of 13.14, 10.93, 17.15 and 13.15, respectively. The respective values of Overall Accuracy and the areas under the ROC curve were greater than 0.85 and 0.930, implying that each threshold performed excellently in identifying heat occurrence. Based on the determined critical thresholds, accumulated harmful temperature (Tcum), number of heat days (HD), first heat date (FHD) and last heat date (LHD) were presented to characterize heat exposure. It was clear that Tcum and HD exhibited a north-to-south increasing trend from 1971 to 2020, with the obvious increasing occurrence in most parts of the study region through the period of 2010 to 2020. FHD occurred earlier in most stations except the northeast parts, while LHD ended later in southern MLRYR. Exploring heat critical thresholds at different phenological stages highlighted in this study can help decision-makers monitor and evaluate heat exposure to single-season rice in MLRYR and further develop mitigation strategies to ensure rice production security.

Analysis of genetic diversity and population structure of Puccinia striiformis f. sp. tritici infers inoculum relationships from Yunnan to the middle and lower reaches of the Yangtze River

AbstractWheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an important cereal fungal disease worldwide, including in the major wheat‐producing areas in China. In 2019, there was a widespread epidemic of the disease in the middle and lower reaches of the Yangtze River (MLRYR) area, including Zhejiang, Jiangsu, Anhui and Guangxi. However, in north‐western China, the postulated inoculum source of MLRYR, disease occurred mildly. Therefore, the origin of the Pst inoculum source for the MLRYR epidemic is still an open question. To address it, we collected 210 Pst uredinium samples from the Yangtze River basin and analysed their genetic structure with 13 pairs of simple‐sequence repeat (SSR) markers that we coupled with an upper airflow trajectory analysis. Our results suggest that the autumn inoculum sources of wheat stripe rust in MLRYR in 2019 probably came from south‐western over‐summering areas of Pst through long‐distance migration. We also found that Jingzhou and adjacent areas in Hubei Province function as an important bridge or stopover for inoculum sources.

Contributions of Multiple Water Vapor Sources to the Precipitation in Middle and Lower Reaches of Yangtze River Based on Precipitation Recycle Ratio

Global warming weakened the summer monsoon and increased the evaporation, leading to more contribution of local evaporation moisture to the local precipitation for the monsoon areas. However, the descriptions of the contribution of the local moisture to the total precipitation and its characteristics have not been known very well. In this paper, taking the middle and lower Reaches of the Yangtze River (MLRYR) as a case and using the precipitation recycling process model, we analyzed the characteristics of the contribution of the local moisture to the total precipitation and the possible reasons. The results show that: the seasonal difference in precipitation recycling rates is obvious, the precipitation recycling rates in spring and summer are small (18.30% and 19.30%), the maximum in autumn is 30.50%, and the precipitation recycling rates in all seasons except summer show a significant upward trend (about 1.70%/10a). Additionally, the water vapor input into MLRYR from four boundaries significantly reduced except for the eastern boundary, and the water vapor contribution from the South and East borders is in summer, and the water vapor contribution from the North and West borders is in autumn, winter and spring. We suggest that the model of the precipitation recycling rate is important to evaluate the contribution of different water vapor sources, and help to further improve the ability of river water prediction in flood season.

Monitoring 2019 Drought and Assessing Its Effects on Vegetation Using Solar-Induced Chlorophyll Fluorescence and Vegetation Indexes in the Middle and Lower Reaches of Yangtze River, China

Monitoring drought precisely and evaluating drought effects quantitatively can establish a scientific foundation for understanding drought. Although solar-induced chlorophyll fluorescence (SIF) can detect the drought stress in advance, the performance of SIF in monitoring drought and assessing drought-induced gross primary productivity (GPP) losses from lush to senescence remains to be further studied. Taking the 2019 drought in the middle and lower reaches of the Yangtze River (MLRYR) as an example, this study aims to monitor and assess this drought by employing a new global, OCO-2-based SIF (GOSIF) and vegetation indexes (VIs). Results showed that the GPP, GOSIF, and VIs all exhibited significant increasing trends during 2000–2020. GOSIF was most consistent with GPP in spatial distribution and was most correlated with GPP in both annual (linear correlation, R2 = 0.87) and monthly (polynomial correlation, R2 = 0.976) time scales by comparing with VIs. During July–December 2019, the precipitation (PPT), soil moisture, and standardized precipitation evapotranspiration index (SPEI) were generally below the averages during 2011–2020 and reached their lowest point in November, while those of air temperature (Tem), land surface temperature (LST), and photosynthetically active radiation (PAR) were the contrary. For drought monitoring, the spatial distributions of standardized anomalies of GOSIF and VIs were consistent during August–October 2019. In November and December, however, considering vegetation has entered the senescence stage, SIF had an obvious early response in vegetation physiological state monitoring compared with VIs, while VIs can better indicate meteorological drought conditions than SIF. For drought assessment, the spatial distribution characteristics of GOSIF and its standardized anomaly were both most consistent with that of GPP, especially the standardized anomaly in November and December. All the above phenomena verified the good spatial consistency between SIF and GPP and the superior ability of SIF in capturing and quantifying drought-induced GPP losses. Results of this study will improve the understanding of the prevention and reduction in agrometeorological disasters and can provide an accurate and timely method for drought monitoring.

Diagnosing anomalous characteristics of atmospheric water cycle structure during seasonal-scale drought events: A case study in middle and lower reaches of Yangtze River

Anomalous characteristics of the atmospheric water cycle structure are highly significant to the mechanisms of seasonal-scale meteorological droughts. They also play an important role in the identification of indicative predictors of droughts. To better understand the causes of seasonal meteorological droughts in the middle and lower reaches of the Yangtze River (MLRYR), characteristics of the atmospheric water cycle structure at different drought stages were determined using standardized anomalies. The results showed that the total column water vapor (TCWV) was anomalously low during drought occurrence periods. In contrast, there were no anomalous signals at the drought persistence and recovery stages in the MLRYR. Moreover, there was no significant temporal correlation between the TCWV anomaly and seasonal-scale drought index (the 3-month standardized precipitation index (SPI3)). During drought events, water vapor that mainly originated from the Bay of Bengal was transported southwest of the MLRYR. Meanwhile, the anomalous signal of water vapor transport was negative at the drought appearance stage. At the drought persistence stage, the negative anomalous signal was the most significant. Water vapor flux divergence in the MLRYR showed significant positive anomalous signals during drought events, and the signal intensity shifted from an increasing to a decreasing trend at different drought stages. In addition, a significant positive correlation existed between the anomaly of water vapor flux divergence and regional SPI3. Overall, water vapor flux divergence is more predictive of droughts in the MLRYR.

Decadal change of extreme consecutive dry days in spring over the middle and lower reaches of the Yangtze River around the early 2000s: The synergistic effect of mega-El Niño/Southern Oscillation, Atlantic Multidecadal Oscillation, and Arctic sea ice

Base on daily station precipitation data from 1960 to 2019, the variability of extreme consecutive dry days (extreme-CDDs) over the middle and lower reaches of the Yangtze River (MLRYR) during spring sowing time (March–April) is investigated. It is found that the extreme-CDDs over MLRYR experienced a significant decadal increase around the early 2000s. Associated with this decadal change, the Mongolian high and western North Pacific anticyclone (WNPA) are significantly intensified and weakened, respectively. The intensified Mongolian high and weakened WNPA lead to anomalous northerlies and water vapor divergence over MLRYR, providing favorable atmospheric conditions for more extreme-CDDs over the region. Further mechanism analyses suggest that the transition of mega-El Niño/Southern Oscillation (mega-ENSO) from negative-phase to positive-phase contributes to the decadal weakening of WNPA. And the phase transition of Atlantic Multidecadal Oscillation (AMO) and decadal decrease of sea ice over the Barents Sea lead to intensified Mongolian high through exciting atmospheric wave train. Multiple linear regression shows that there could be a synergistic role of mega-ENSO, AMO, and sea ice over the Barents Sea in the decadal change in extreme-CDDs over MLRYR around the early 2000s. Analysis on the simulation of 14 models in the Atmospheric Model Intercomparison Project (AMIP) experiment from phase 6 of the Coupled Model Intercomparison Project (CMIP6) shows that the models can reproduce the observed decadal intensification of the Mongolian high and weakening of WNPA around the early 2000s, which indicates the contribution of mega-ENSO, AMO, and sea ice over the Barents Sea to the decadal changes in Mongolian high, WNPA and extreme-CDDs over MLRYR.

The climatic effects of irrigation over the middle and lower reaches of the Yangtze River, China

Characterizing climatic effects of agricultural irrigation is of great importance and challenging to understand the full influence of water management on the Earth's environment and hydroclimatic cycle. The investigation of the local and remote climatic responses to irrigation in the middle and lower reaches of the Yangtze River (MLRYR), a typical humid region, was previously unidentified. A novel combined subgrid-scale irrigation scheme for wheat (dynamic irrigation) and rice (fixed irrigation) was developed and incorporated into the Weather Research and Forecasting (WRF) modeling framework. The comprehensive climatic effects on energy balance, temperature, precipitation and the planetary boundary layer, were assessed by numerical experiments with irrigation off/on for ten crop growth seasons from 2007 to 2016. Both the simulated irrigation amounts of wheat and rice were generally in agreement with actual values. Surface energy and water budgets have been substantially altered by irrigation, and the magnitudes were dependent on the irrigation amounts. Irrigation increased latent heat flux and reduced sensible heat flux, especially during summer. The warm bias in the simulation without consideration of irrigation was reduced by the cooling effects of irrigation. The mean surface air temperature decreased significantly by 0.12–0.24 °C and 0.4–0.8 °C for spring and summer, respectively. Meanwhile, irrigation presented stronger cooling effects on daytime temperature than nighttime temperature, resulting in the reductions of diurnal temperature range in irrigated area. Moreover, the irrigation-induced increase of geopotential height and anomalous anticyclones led to the decreases in precipitation over the MLRYR. The changes of precipitation in remote areas were generally related to the irrigation induced large-scale circulation change. Furthermore, although the climatic effects of irrigation in grid scale were not relatively high due to the relatively low irrigation fraction, they exhibited apparently stronger in the subgrid scale, which can be used to investigate the impacts of climatic effects of irrigation on crop growth.

Mapping Threats of Spring Frost Damage to Tea Plants Using Satellite-Based Minimum Temperature Estimation in China

Spring frost damage (SFD), defined as the disaster during the period of newly formed tea buds in spring caused by lower temperature and frost damage, is a particular challenge for tea plants (Camellia sinensis), whose capacity to adapt to extreme weather and climate impacts is limited. In this paper, the region of the Middle and Lower Reaches of the Yangtze River (MLRYR) in China was selected as the major tea plantation study area, and the study period was focused on the concentrated occurrence of SFD, i.e., from March to April. By employing the standard lapse rate of air temperature with elevation, a minimum temperature (Tmin) estimation model that had been previously established was used based on reconstructed MYD11A1 nighttime LST values for 3 × 3 pixel windows and digital elevation model data. Combined with satellite-based Tmin estimates and ground-based Tmin observations, the spatiotemporal characteristics of SFD for tea plants were systematically analyzed from 2003 to 2020 in the MLRYR. The SFD risks at three scales (temporal, spatial, and terrain) were then evaluated for tea plants over the MLRYR. The results show that both SFD days at the annual scale and SFD areas at the daily scale exhibited a decreasing trend at a rate of 2.7 days/decade and 2.45 × 104 ha/day, respectively (significant rates at the 0.05 and 0.01 levels, respectively). The period with the highest SFD risk appeared mainly in the first twenty days of March. However, more attention should be given to the mid-to-late April time period due to the occurrence of late SFD from time to time. Spatially, areas with relatively higher SFD days and SFD risks were predominantly concentrated in the higher altitude areas of northwestern parts of MLRYR for both multi-year averages and individual years. Fortunately, in regions with a higher risk of SFD, the distribution of tea plants was relatively scattered and the area was small. These findings will provide helpful guidance for all kinds of people, including government agencies, agricultural insurance agencies, and tea farmers, in order that reasonable and effective strategies to reduce losses caused by spring frost damage to tea plants may be recommended and implemented.

Assessing the Impacts of Extreme Precipitation Change on Vegetation Activity

Extreme climate events frequently have more severe effects on terrestrial vegetation activity than long-term changes in climate averages. However, changes in extreme climate events as well as their potential risk on vegetation activity are still poorly understood. By using the Middle and Lower Reaches of the Yangtze River (MLR-YR) in China as an example, this paper aims to understand the vegetation response to changes in extreme precipitation events from 1982 to 2012 using the maximum normalized difference vegetation index (NDVI) as an indicator. By applying extreme value theory (EVT), the potential risks of extreme precipitation events on vegetation activity were analyzed by conducting return period analysis. Results indicated that vegetation activity could be affected by extreme precipitation events, especially the combined effects of the frequency and intensity of precipitation extremes. For instance, vegetation activity could be enhanced in the regions with weakened intensity but increased occurrence of extreme precipitation events. In addition, we found potential risk of extreme precipitation events on vegetation activity from the results of precipitation extreme trend and return period analysis. These phenomena can be associated with the local occurrence of extreme precipitation events, different land cover types, and soil moisture cumulative effect on vegetation growth. This study stresses the importance of considering both current changes in and the potential risk of extreme precipitation events to understand their effects on vegetation activity.

Application of Normalized Difference Vegetation Index (NDVI) for the Detection of Extreme Precipitation Change

Remote sensing has frequently been employed to monitor extreme climatic events, especially droughts, by identifying the anomalies of vegetation activity from the regional to global scale. However, limited research has addressed the performance of remote sensing on detecting extreme precipitation events. By using the Middle and Lower Reaches of the Yangtze River (MLR-YR) in China as an example, this paper examines the application of the satellite-derived normalized difference vegetation index (NDVI) for detecting the change of extreme precipitation events from 1982 to 2012. The performances of three NDVI-based indices, including minimum, mean, and maximum NDVIs, were examined to capture the sensibility of vegetation activity to changes in extreme precipitation events. The results show not only common enhanced trends, but also obvious spatial discrepancies between the intensity and frequency of extreme precipitation events in the MLR-YR. As to its application on terrestrial vegetation, changes in extreme precipitation intensity coincided with that of the vegetation activity, which was represented as the maximum and the minimum NDVIs, especially the maximum NDVI. In addition, similar patterns were found between the standard deviation of the maximum NDVI and the trend of extreme precipitation intensity. Furthermore, the correlation coefficients were relatively greater between the maximum NDVI and extreme precipitation intensity than that of the minimum NDVI. Our results support the hypothesis that maximum NDVI is more suited to capture the response of vegetation activity to extreme precipitation events in the MLR-YR region, in comparison to the other two NDVI indices.

Spring Frost Damage to Tea Plants Can Be Identified with Daily Minimum Air Temperatures Estimated by MODIS Land Surface Temperature Products

Tea (Camellia sinensis) is one of the most dominant economic plants in China and plays an important role in agricultural economic benefits. Spring tea is the most popular drink due to Chinese drinking habits. Although the global temperature is generally warming, spring frost damage (SFD) to tea plants still occurs from time to time, and severely restricts the production and quality of spring tea. Therefore, monitoring and evaluating the impact of SFD to tea plants in a timely and precise manner is a significant and urgent task for scientists and tea producers in China. The region designated as the Middle and Lower Reaches of the Yangtze River (MLRYR) in China is a major tea plantation area producing small tea leaves and low shrubs. This region was selected to study SFD to tea plants using meteorological observations and remotely sensed products. Comparative analysis between minimum air temperature (Tmin) and two MODIS nighttime land surface temperature (LST) products at six pixel-window scales was used to determine the best suitable product and spatial scale. Results showed that the LST nighttime product derived from MYD11A1 data at the 3 × 3 pixel window resolution was the best proxy for daily minimum air temperature. A Tmin estimation model was established using this dataset and digital elevation model (DEM) data, employing the standard lapse rate of air temperature with elevation. Model validation with 145,210 ground-based Tmin observations showed that the accuracy of estimated Tmin was acceptable with a relatively high coefficient of determination (R2 = 0.841), low root mean square error (RMSE = 2.15 °C) and mean absolute error (MAE = 1.66 °C), and reasonable normalized RMSE (NRMSE = 25.4%) and Nash–Sutcliffe model efficiency (EF = 0.12), with significantly improved consistency of LST and Tmin estimation. Based on the Tmin estimation model, three major cooling episodes recorded in the "Yearbook of Meteorological Disasters in China" in spring 2006 were accurately identified, and several highlighted regions in the first two cooling episodes were also precisely captured. This study confirmed that estimating Tmin based on MYD11A1 nighttime products and DEM is a useful method for monitoring and evaluating SFD to tea plants in the MLRYR. Furthermore, this method precisely identified the spatial characteristics and distribution of SFD and will therefore be helpful for taking effective preventative measures to mitigate the economic losses resulting from frost damage.

Rossby wave packets in the upper troposphere and their associations with climatological summertime daily precipitation in MLRYR of China

AbstractUsing the NCEP/NCAR reanalysis and station observations in China during 1979–2018, features of propagation of baroclinic wave packets in the upper troposphere and their relationships with precipitation over the middle and lower reaches of the Yangtze River (MLRYR) in daily climatology are investigated after having components with periods longer than 9 days filtered out. It is demonstrated that in the filtered daily climatology, the baroclinic wave packets still exist. The wave packet migrates eastward on the northern sides of the westerly jet stream axis whereas it does not move explicitly in the southern side of the axis in the upper troposphere. The filtered daily precipitation over MLRYR is mainly affected by the wave packets in the region south of the westerly jet axis. These results are very meaningful for better understanding behaviors of Rossby waves in daily climatology and the causes of daily precipitation variations in MLRYR.

Modeling Green Roof Potential to Mitigate Urban Flooding in a Chinese City

The Middle and Lower Reaches of the Yangtze River (MLRYR) region, which has humid subtropical climate conditions and unique plum rain season, is characterized by a simultaneous high-frequency urban flooding and reduction in groundwater levels. Retrofitting the existing buildings into green roofs is a promising approach to combat urban flooding, especially for a densely developed city. Here, the application potential of the Green Roof System (GRS) and the Improved Green Roof System (IGRS) designed to divert overflowing water from green roofs to recharge groundwater were analyzed in a densely developed city, Nanchang, China. For the first time, the influence of GRS on the hydraulic condition of Combined Sewage System/Storm Water System (CSS/SWS) is analyzed, which is a direct reflection of the effect of GRS on alleviating urban flooding. The simulation results show that GRS can retain about 41–75% of precipitation in a 2-hour timescale and the flooding volumes in the GRS/IGRS region are 82% and 28% less than those of the Traditional Roof System (TRS) in 10- and 100-yr precipitation events, respectively. In the continuous simulations, GRS also enhances Evapotranspiration (ET), which accounts for 39% of annual precipitation, so that reduces the cumulative surface runoff. Considering the IGRS can provide more hydrological benefits than the GRS under the same climate conditions, we may conclude that the widespread implementation of both the GRS and the IGRS in Nanchang and other densely developed cities in the MLRYR region could significantly reduce surface and peak runoff rates.

Frequency of Persistent Blocking and Ridge Events Related to Precipitation over Eastern China during August and Its Preceding Atmospheric Signals

Abstract Based on a recently developed approach that can recognize both persistent blocking and ridge events effectively, the contributions of the frequency of these persistent events (FOPE) over different regions in Eurasia to precipitation over eastern China were investigated. The results reveal that, the FOPE over the longitudinal range of 110°–130°E, near the Stanovoy Mountains and the Okhotsk Sea, is significantly correlated with precipitation over the middle and lower reaches of the Yangtze River (MLRYR) during summer, particularly in August. The preceding full July (or 1–20 July) mean Balkhash Lake–Caucasus geopotential height index, which measures the combined effect of the Balkhash Lake and Caucasus geopotential height anomalies, is closely related to the August geopotential height anomaly around the Stanovoy Mountains and the Okhotsk Sea, and can therefore reflect the August 110°–130°E FOPE. The predictability based on this preceding atmospheric signal seems to be attributable to slow-varying atmospheric processes on a subseasonal (20-day mean) time scale. On this time scale, the Balkhash Lake and Caucasus geopotential height anomalies occur prior to, and seem to modulate, the geopotential height anomaly around the Stanovoy Mountains and the associated 110°–130°E FOPE through an eastward extension and through exciting a positive–negative–positive pattern in 500-hPa geopotential heights, respectively. As a result of the slow-varying atmospheric processes, this preceding atmospheric signal performs well in predicting the August 110°–130°E FOPE, which also facilitates the prediction of the MLRYR precipitation.

Human activities determine quantity and composition of dissolved organic matter in lakes along the Yangtze River

Dissolved organic matter (DOM) plays important roles in the aquatic biogeochemical cycle and the global carbon cycle. However, it is highly spatially and temporally varied due to complex sources from the catchment (allochthonous) and from within the system (autochthonous). Satellite remote sensing provides the ability to monitor DOM and identify the spatio-temporal variations in lakes on a global or regional scale. In this study, field work was conducted in 55 lakes in August 2012 along the middle and lower reaches of the Yangtze River (MLR-YR), where most lakes were characterized by eutrophication due to intense human activities. The results showed that both colored DOM (CDOM) and total DOM differed significantly by and were linearly related to the human-induced trophic state index (TSI), with R2 = 0.41 and 0.61, respectively. Autochthonous substances by phytoplankton contributed to 38.5% of CDOM and 35.2% of DOM, and allochthonous terrestrial substance indexed by land cover change and aquaculture contributed to almost half, with 49.7% of CDOM and 49.8% of DOM. In total, human activities explained as much as 81.7% and 87.5% of the variations in CDOM and DOM, respectively. Finally, a flowchart for estimating DOM from satellite-derived TSI was proposed. This study has great significance for synchronously monitoring and managing aquatic environment quality in regional eutrophic lakes around the world.

Human-induced eutrophication dominates the bio-optical compositions of suspended particles in shallow lakes: Implications for remote sensing

Suspended particulate matter (SPM) is generally divided into inorganic (SPIM) and organic (SPOM) parts; they come from different sources, and have different impacts on the optical properties and/or water quality of lake. However, in a specific remote sensing process, they are not retrieved separately. Using in-situ data of 59 lakes along the middle and lower reaches of the Yangtze River (MLR-YR) in dry season (April) and wet season (August) in 2012, we first studied the absorption properties and sources of different SPM. On this basis, we proposed a workflow for simultaneously estimating SPIM and SPOM from satellite data. Our results are as follows: Bio-optical compositions of SPM in these eutrophic shallow lakes tempo-spatially varied greatly and were dominated by human-induced eutrophication. Phytoplankton contributed 18.42 ± 18.92% of SPIM and 26.22 ± 19.24% of SPOM in April 2012, but 30.4 ± 23.41% of SPIM and 47.03 ± 18.1% of SPOM in August 2012. The trophic state index explained 42.84% of SPOM variation in April 2012, and 54.64% in August 2012. Moreover, there were strong linear relationships between SPIM concentration and non-algal particle absorption coefficient (Pearson's r = 0.73; p < 0.01) and between SPOM concentration and phytoplankton absorption coefficient (r = 0.76; p < 0.01). Based on these results, SPIM and SPOM concentrations in the lakes along the MLR-YR could be retrieved from OLCI/Sentinel-3A satellite data, respectively. This study has a great significance for real-time monitoring and managing aquatic environment in various eutrophic and/or shallow lakes as a group.

Potential yields, yield gaps, and optimal agronomic management practices for rice production systems in different regions of China

Understanding crop potential yields, yield gaps, and optimal agronomic management practices helps in identifying the limiting factors, scope, and ways to achieve sustainable intensified agricultural production. Here, using detailed field trial data collected from 1981 to 2009 at 11 agro-meteorological experimental stations and the crop model CERES–Rice, we investigated changes in potential yields, water- and nitrogen-stressed yields, and yield gaps of rice in the major rice cultivation regions of China during the collection period. We further identified the optimal nitrogen application rate, transplanting date, and cultivar traits for the sustainable intensification of rice production systems in different regions. Owing to climate change, the potential rice yields declined or changed little in the Middle and Lower Reaches of the Yangtze River (MLRYR), while they increased or changed little in the Northeastern China Plain (NECP) during 1981–2009. Rice yield gaps shrank in the major rice production regions because the actual yields increased and approached the potential yields. The average yield gap was 16.0% in the 2000s, with water and nitrogen stresses being the limiting factors in the NECP and water stress being the major limiting factor in the MLRYR. The nitrogen application rate was suggested to be increased by 47.5% and 21.7% for single rice (i.e., rice cultivated in a single season per year) in the NECP and MLRYR, respectively, and increased by 5.2% for early rice (i.e., rice cultivated in the early season in a rice–rice rotation system per year). However, it was suggested to be reduced by 13.1% for late rice (i.e., rice cultivated in the late season in a rice–rice rotation system per year). Early transplanting could increase the yield, while late transplanting could decrease the yield. The impacts were greater for single rice in the NECP and late rice in the MLRYR than for single rice and early rice in the MLRYR. Cultivars with longer growth durations, and greater spikelet numbers and grain weights, could significantly increase the rice yield by 14.8%–45.6%. The optimal cultivars, combined with advancing transplanting by 10 d, could increase rice yields by 29.2%–68.9%. Our findings provide new approaches, important insights, and effective options for the sustainable intensification of rice production systems in different regions of China.