Yangtze-Huaihe River Basin Research Articles

Relationship Between Summer Compound Hot and dry Extremes in China and the Snow Cover Pattern in the Preceding Winter

With global warming, the probability of summer compound hot and dry extreme (CHDE) days, which are higher risk compared with single-factor extreme events, increases in some regions. However, there have been few studies on the winter precursor signals of such events. In this study, we found that summer CHDEs have generally increased in the last 20 years, with the increases in the middle and lower reaches of the Yangtze River region and Southwest China being more than double those in other regions of China. The dominant mode of summer CHDEs in China is characterized by more hot–dry days in the Yangtze–Huaihe River Basin (YHRB). Importantly, we found that there is an obvious cross-seasonal relationship between the first mode of winter snow cover in the Northern Hemisphere (NH) and summer CHDEs in China. When the mode of winter snow cover in the NH is in a positive phase with a negative-phase Arctic Oscillation (AO), i.e., more snow cover in Europe, Northeast China, and the northern United States, and less snow cover in central Asia and the midlatitudes in winter, more CHDEs in China in the following summer. Compared with the signals from the AO, these signals from winter snow can be better stored and transmitted into summer through the snow, soil and ocean, inducing a northward shift of the upper-level westerly jet and strengthening of South Asia high. Through the strong dynamic forcing of negative vorticity advection with the change of westerly jet, the subsidence movement in the western Pacific subtropical high (WPSH) region is strengthened, resulting in the stable maintenance of the WPSH in the YHRB. Under the synergy of a remote mid- and high-latitude wave train in summer, which also relates closely to winter snow cover, more CHDEs ultimately occur in the YHRB of China.

The optimal bias correction for daily extreme precipitation indices over the Yangtze-Huaihe River Basin, insight from BCC-CSM1.1-m

Due to the considerable biases of model simulation, bias correction is a widely used method to reduce the model biases. It is necessary to evaluate the performance of multiple bias corrections before selecting the optimal one. In this study, four statistical bias correction methods, i.e., the linear scaling (LS), quantile mapping (QM), distribution mapping (DM), and cumulative distribution function transform (CDFt), are introduced to correct the simulated of daily precipitation in Yangtze-Huaihe River Basin (YRB) in China from BCC-CSM1.1-m model. Furthermore, we evaluate their performance in reproducing the probability distribution of observed summer daily precipitation as well as the precipitation extremes. Results show that BCC-CSM1.1-m exhibits systematic biases in simulating the daily precipitation, especially for the tail of the distribution. The bias corrected simulation can significantly reduce the systematic biases. Among them, QM has the most significant improvement in simulating the probability distributions of daily precipitation with Brier scores (BS) dropping to 0 and while the significance scores (Sscore) rise to 1 quickly. For the domain averages and spatial consistency of extreme precipitation, QM, CDFt, and LS have well simulation capabilities in the total precipitation and moderate rainy days. Meanwhile, only QM can reduce the biases of the rainfall days, precipitation intensity, and 95% quantile precipitation simultaneously. For example, the relative errors for 95% quantile precipitation are reduced from −57.8% in raw simulation to −2.76% in bias corrected simulation, and the spatial correlation coefficients are increased from −0.12 to 0.64. It is noted that the continuous dry days, are failed to be well corrected. The DM, based on the Gamma distribution, is less effective in characterizing the probability distribution of model-simulated precipitation, especially for the heavy precipitation. We believe that the QM and CDFt are the optimal methods used for applying the bias corrections in the extreme precipitation in the YRB.

Influences of the boreal winter Arctic Oscillation on the peak-summer compound heat waves over the Yangtze–Huaihe River basin: the North Atlantic capacitor effect

Influences of the boreal winter Arctic Oscillation on the peak-summer compound heat waves over the Yangtze–Huaihe River basin: the North Atlantic capacitor effect

Subseasonal Variation of 2020 Meiyu Rainfall With Extremely Long Duration Over the Yangtze–Huaihe River Basin in China

An observed fact is proposed that the 2020 record-breaking Meiyu over the Yangtze–Huaihe River Basin (YHRB) is characteristic of significant subseasonal variation. The anomalously enhanced rainfall experiences a southward retreat from the northern YHRB in June to the southern YHRB in July. The meridional shift of abnormal rainbelt is closely related to the different anomalous Meiyu front circulations. The first stage features a warm Meiyu front with an extremely strong northward transport of warm-and-wet air, whereas a cold front forms with a convergence between the strong northeasterlies and southwesterlies in July. Another significant subseasonal variation of the 2020 Meiyu is that the Meiyu rainfall evolves in a periodic quasi-biweekly oscillation (QBWO). On the scale of the QBWO, the cold air activities over East Asia contribute significantly to Meiyu; each intense southward invasion of cold air corresponds well to the enhancement of Meiyu rainfall. However, the location of the western Pacific subtropical high, the subtropical East Asia summer monsoon (SEASM), and the intensity of the East Asia subtropical westerly jet exhibit opposite QBWO characteristics in June and July. For an increasing (decreasing) of Meiyu rainfall, the western Pacific subtropical high marches northward (retreats southward), the subtropical East Asia summer monsoon weakens (strengthens), and the East Asia subtropical westerly jet accelerates (decelerates) in June. The opposite holds true in July. Further analyses reveal that the filtered cyclone over Northeast China benefiting the southward intrusion of cold air is associated with the eastward propagation of a wave train over the mid-high latitudes in June, whereas it arises from both the westward propagation of a wave train over the mid-high latitudes and the northward propagation of cyclonic circulation from the tropics in July.

Eutrophication causes microbial community homogenization via modulating generalist species

Eutrophication substantially influences the community structure of aquatic organisms and has become a major threat to biodiversity. However, whether eutrophication is linked to homogenization of microbial communities and the possible underlying mechanisms are poorly understood. Here, we studied bacterial and fungal communities from water and sediments of 40 shallow lakes in the Yangtze-Huaihe River basin, a representative area characterized by intensifying eutrophication in China, and further examined the beta diversity patterns and underlying mechanisms under eutrophication conditions. Our results indicate that eutrophication generally caused biotic homogenization of bacterial and fungal communities in both habitats showing decreased community variations for the sites with a higher trophic state index (TSI). In the two habitats, community dissimilarities were positively correlated with TSI changes for both taxonomic groups, while the local contribution to beta diversity (LCBD) remarkably declined with increasing TSI for the fungal community. These phenomena were consistent with the pivotal importance of the TSI in statistically accounting for beta diversity of bacterial and fungal communities in both habitats. In addition, we found that physicochemical factors such as water temperature and pH were also important for bacterial and fungal communities in water, while heavy metal elements were important for the communities in sediments. Interestingly, generalist species, rather than specialist species, were revealed to more dominantly affect the variations in beta diversity along the trophic gradient, which were quantified by Bray-Curtis dissimilarity and LCBD. Collectively, our findings reveal the importance of generalist species in contributing to the change of beta diversity of microbial communities along trophic gradients, which have profound implications for a comprehensive understanding of the effects of eutrophication on microbial community.

Assessment of plum rain\u2019s impact on power system emissions in Yangtze-Huaihe River basin of China

As a typical climate that occurs in the Yangtze-Huaihe River basin of China with a size of 500,000 km2, plum rain can reduce the photovoltaic (PV) potential by lowering the surface irradiance (SI) in the affected region. Based on hourly meteorological data from 1980 to 2020, we find that plum rain can lower the SI in the affected region with a weekly peak drop of more than 20% at the most affected locations. This SI drop, coupled with a large number of deployed PV systems, can cause incremental CO2 emissions (ICEs) of local power systems by increasing the additional thermal power. Using a cost optimization model, we demonstrate that the ICEs in 2020 already reached 1.22 megatons and could range from 2.21 to 4.73 megatons, 3.47 to 7.19 megatons, and 2.97 to 7.43 megatons in 2030, 2040, and 2050, respectively, considering a change trend interval of a ±25% fluctuation in power generation and demand in the different years. To offset these ICEs, we compare four pathways integrated with promising technologies. This analysis reveals that the advanced deployment of complementary technologies can improve the PV utilization level to address climate impacts.

Joint effects of three oceans on the 2020 super mei‐yu

An unexpected super mei-yu struck in 2020 in the Yangtze–Huaihe River basin, southern Korea, and southern Japan (hereafter referred to as the mei-yu regions), causing many casualties and huge economic losses. The super mei-yu was characterized by a remarkably early onset (around 1 June), late withdrawal (around 1 August), and intense rainfall during the mei-yu season. The precipitation in the early onset and late withdrawal stages contributed more than half of the total mei-yu-period precipitation over the mei-yu regions in 2020. In this study, the authors explored the dominant remote forcing of the mei-yu early onset and late withdrawal to understand the mechanisms of this super mei-yu. The early onset can mainly be attributed to an early northward-shifted East Asian jet stream (EAJS). The late withdrawal mainly resulted from the stagnant EAJS and the western North Pacific subtropical high (WPSH) during 10 July to 1 August. Specifically, North Atlantic sea surface temperature anomalies (SSTAs) excited a Rossby wave, which was steered by atmospheric anomalies related to the western North Pacific SSTAs, causing the early northward-shifted EAJS and generating an early onset. The record-breaking warm SSTAs over the North Indian Ocean to South China Sea and the reduced sea-ice concentration (SIC) over the Laptev–East Siberian Sea played important roles in causing the stagnant WPSH and EAJS during July, which led to the late withdrawal. Meanwhile, the SIC anomalies may have caused the inhomogeneous rainfall distribution in the mei-yu regions. Furthermore, projection results suggest that the probability of a late mei-yu withdrawal similar to the 2020 case will increase in the future. Finally, potential predictors of an extreme mei-yu are discussed.摘要2020年发生在江淮流域, 朝鲜半岛和日本南部 (简称梅雨区) 的暴力梅造成了巨大的人员伤亡和经济损失. 此次暴力梅的主要特征为: 入梅早 (6月1日) , 出梅晚 (8月1日) 以及较强的梅雨期降水. 2020年异常早入梅和晚出梅时期的降水占梅雨期总降水的一半以上. 因此, 为了深入解析2020暴力梅的机制, 本文将分析2020异常早入梅和晚出梅的主导遥强迫机制. 研究表明, 东亚急流提前北跳是造成入梅偏早的主要原因, 而西北太平洋副热带高压 (西太副高) 的作用并不显著. 具体来说, 5月北大西洋海表温度 (SST) 异常激发出东传的罗斯贝波, 同时西北太平洋的暖SST异常改变该罗斯贝波的传播. 进而在两者共同的作用下造成东亚急流的提前北跳, 并导致入梅偏早. 2020年7月破纪录的北印度洋-南海SST暖异常和拉普特夫-东西伯利亚海的海冰密集度 (SIC) 的偏少阻止西太副高和东亚急流的北跳.推迟北跳的西太副高和东亚急流有利于梅雨降水增多, 最终导致出梅偏晚. 同时SIC异常可能是梅雨雨带偏北的原因. 此外, 预估结果表明, 类似于2020出梅偏晚的概率在未来将会增加. 最后, 本文也探讨了暴力梅的潜在预测因子.

Evaluation of All-Sky Assimilation of FY-3C/MWHS-2 on Mei-yu Precipitation Forecasts over the Yangtze-Huaihe River Basin

Evaluation of All-Sky Assimilation of FY-3C/MWHS-2 on Mei-yu Precipitation Forecasts over the Yangtze-Huaihe River Basin

Longer Time-Scale Variability of Atmospheric Vertical Motion over the Tibetan Plateau and North Pacific and the Climate in East Asia

The vertical motion of air is closely related to the amount of precipitation that falls in a particular region. The Tibetan Plateau and the North Pacific are important determinants of the East Asian climate. We use climate diagnosis and statistical analysis to study the vertical motion of the air over the North Pacific and Tibetan Plateau and the relationship between the vertical motion of air over them and the climate in East Asia. Here we show that there is a downward movement of air over the Tibetan Plateau during the winter, with a maximum velocity of downward movement at 500 hPa, whereas there is an upward movement of air with a maximum velocity of upward movement at 600 hPa during the summer. Precipitation in East Asia has a significant negative correlation (The correlation coefficient exceeds −0.463 and confidence level is greater than 99%) with the vertical motion of air over the Tibetan Plateau and the North Pacific during both the winter and summer. There is also a negative correlation of precipitation in the region south of the Yangtze River with the vertical motion of air over the Tibetan Plateau in winter, whereas the area of negative correlation to the vertical motion of air over the North Pacific in winter is located to the east of the Tibetan Plateau and the Yangtze–Huaihe river basin. The research results provide a climatic framework for the vertical motion of air over both the Tibetan Plateau and the North Pacific.

Impact of radar data assimilation on a squall line over the Yangtze–Huaihe River Basin with a radar reflectivity operator accounting for ice‐phase hydrometeors

AbstractA radar reflectivity observation operator with ice‐phase hydrometeors was employed for the assimilation of the real radar observations of a squall line on June 14, 2009, over Anhui and Jiangsu provinces in China. The three‐dimensional variational (3DVAR) data‐assimilation system along with the Weather Research and Forecasting (WRF) model was applied. The impact of assimilating radar radial velocity and reflectivity is investigated by analysing the meteorological conditions for different stages of the squall line. The results show that the radar data‐assimilation experiments adjust and improve the initial fields to some extent for the squall line with the cycling data‐assimilation strategy. The analysed and predicted radar composite reflectivity is significantly improved with the use of the ice‐phase hydrometeors observation operator. The improvements are illustrated in terms of the wind fields for both the surface and upper level, the radar reflectivity, the surface perturbation potential temperature and the surface perturbation pressure. In addition, the forecast skills of the precipitation are improved noticeably for both the location and the intensity after using the ice‐phase hydrometeors radar observation operator.

Attribution of Persistent Precipitation in the Yangtze-Huaihe River Basin during February 2019

In February 2019, a month-long persistent precipitation event occurred in the Yangtze-Huaihe River basin. The geopotential height field that affected the duration of this frontal rainfall was divided into a high-latitude part and a low-latitude part for analysis. In the high-latitude part, a two-wave structure led to quasi-stationary circulation, and the change of both the blocking high pressure and Arctic Oscillation phase caused cold air to invade South China continuously and changed the frontal position. In mid-to-low latitudes, the persistent precipitation showed quasi-biweekly oscillation characteristics. The so-called “subtropical high-precipitation-anticyclone” (SHPA) feedback mechanism blocked the circulation systems in the mid-to-low latitudes and provided a continuous supply of water vapor for precipitation. As for the effect of sea surface temperature, the western North Pacific anomalous anticyclone stimulated by El Nino strengthened the intensity of the southerly wind and provided support for the redevelopment of the anticyclone system in the SHPA feedback mechanism. The sea surface temperature anomaly in the South China Sea provided sensible heating for precipitation, and convergent rising airflow was conducive to the occurrence of precipitation. Additionally, the SHPA mechanism provides a reliable basis for the prediction of persistent precipitation in winter in the mid-to-low latitudes.

Towards influence of Arabian Sea SST anomalies on the withdrawal date of Meiyu over the Yangtze-Huaihe River basin

Prediction of Meiyu withdrawal date (MWD) over the Yangtze-Huaihe River basin (YHRB) around mid-July has aroused extensive concern recently because of the profound socioeconomic and academic importance. However, relatively few researches have been carried out to identify the potential predictability source that can physically contribute to the Meiyu retreat over the YHRB, which exhibits profound year-to-year variations. This study identifies that the later-than-normal Meiyu withdrawal is preceded by the significant tropical June Arabian Sea (AS) surface sea surface (SST) warming on the interannual timescale. Analyses of possible mechanisms suggest that a striking quasi-barotropic “north-low–south-high” meridional seesaw pattern (i.e. PJ-like pattern) over the Northeast Asian–western North Pacific sector in July favors the transport and convergence of warm-moist water vapor and cold-dry air mass over the YHRB, inducing abundant in situ precipitation and thereby maintaining the Meiyu rainband. Under such a background, the Meiyu termination over the YHRB is delayed. Moreover, dynamical diagnoses and numerical model simulations indicate that the warmer-than-normal AS, which persists from June to the following July, can induce a notable localized low-level cyclonic anomaly via a Rossby-wave-like Matsuno–Gill-type atmospheric response. This cyclonic anomaly can further stimulate a large-scale atmosphere bridge stretching across South Asia and propagating poleward into Northeast Asia, which modulates the aforementioned downstream MWD-related atmospheric conditions continuously. Therefore, AS SST warming can remotely regulate and maintain the July Meiyu rainband through inducing a major direct forcing for the later Meiyu withdrawal over the YHRB, namely the East Asian coastal “north-low-south-high” meridional teleconnection. These results indicate and demonstrate the possible source of predictability for Meiyu withdrawal. This work may help improve forecasting of the withdrawal timing of Meiyu over the YHRB through more accurate predictions of SST over the AS region.

Relationships Between Jianghuai Meiyu Anomaly and the Collaborative Evolution of Wave Trains in the Upper and Lower Troposphere in Mid-July of 2020

Based on the ECMWF reanalysis dataset (ERA5), SST , OLR and the daily precipitation data, the relationship between the Meiyu anomaly in the Yangtze-Huaihe river basin (YHB) and the collaborative evolution of wave trains in the upper and lower troposphere in the mid-July of 2020 is analyzed. The results show that the key circulation background for the long-lasting Meiyu season in the summer of 2020 is the coexistence and collaborative evolution of the Silk-Road (SR) wave train in the upper troposphere and the – + Pacific-Japan (PJ) wave train in the middle-lower troposphere, which is in favor of the movement towards each other of the South Asia high (SAH) and the western Pacific subtropical high (WPSH), resulting in the upper-level divergence over the YHB where is the right side of the jet entrance area. The WPSH strengthens and extends westward, transporting abundant water vapor to the YHB from the Western Pacific and South China Sea. Meanwhile, the meridional circulation develops at the middle and high latitudes, which is in favor of cold-dry air and warm-moist air strongly interact over the YHB, leading to the long-lasting Meiyu season. The coordinative evolution of the SR and PJ wave trains not only affects the persistence and intensity of precipitation in the YHB, but also can be regarded as a precursor signal for the occurrence of persistent heavy rainfall to some extent. The wave-activity flux dispersing eastward along the upper-level jet is beneficial to the development and maintenance of the SR wave train, and the poleward dispersing wave-activity flux is related to the development and maintenance of the PJ wave train. Additionally, along with the weakening El Nino in 2019, the anomalous convection caused by the warm SST in the Western Pacific warm pool is conducive to the formation and maintenance of the PJ wave train. The abnormal convection caused by the warm SST in the Indian Ocean and the east coast of the tropical Atlantic may affect the SR wave train. These are also one of the reasons for the long Meiyu season in 2020.

Dynamical downscaling simulation of the East Asian summer monsoon in a regional Climate‐Weather Research and Forecasting model

AbstractA regional Climate‐Weather Research and Forecasting (CWRF) model with a 30‐km horizontal resolution was applied to simulate the East Asian summer monsoon (EASM) and climate in China from 1980 to 2016. As compared with observations and reanalysis data, the model can reasonably reproduce the spatial distributions of the climatological mean atmospheric circulation and water vapour transport in East Asia, as well as the seasonal advance and retreat of EASM and rain bands. The correlation coefficient between the EASM circulation index in the simulation and reanalysis is .97. The model can well represent the geographic distributions of summer mean temperature and precipitation over most of China. However, model biases still exist, in particular the skill in the Yangtze–Huaihe River basin is relatively low. The simulated climatological mean temperature and precipitation deviations from observations may be related to the model's systematic circulation biases, with a thicker lower troposphere (i.e., higher temperature between 500 and 1,000 hPa) over most of China (except for the south and southwest) and a thinner one over the coastal oceans in summertime. Compared with the reanalysis, the model overestimates the land‐ocean thermal contrast, which causes the South Asian High shifted to the north and east, as well as the subtropical high and tropical convective activity located further north and persisted longer. Consequently, more water vapour transports northward, leading to more precipitation over North China–Northeast China and less precipitation over the Yangtze and Huaihe River basin. Therefore, the enhanced land‐ocean thermal contrast may be a major factor for the stronger EASM in the model, and corresponding precipitation and temperature biases in China. This analysis provides important information for further improving model performance in EASM simulation.

Sub-daily soil moisture estimate using dynamic Bayesian model averaging

Accurate estimation of soil moisture (SM) from satellite products and model simulations at sub-daily timescale remains a challenge. This study proposes a general dynamic Bayesian model averaging (BMA) framework for merging sub-daily model products. Compared to the traditional BMA method, this study introduces adaptive weights (dynamically variant with time) for BMA members. Based on the previous evaluation work, a subset of model products is selected from eight model products as BMA members. The dynamic BMA experiment is performed for the surface SM (0–10 cm) model products at sub-daily (6-h) timescale in 2017 over the Yangtze-Huaihe river basin. The results are compared with the automatic SM observations (ASMOs) with unprecedented high spatial and temporal resolution (up to 7 stations within a 104 km2 pixel; hourly). Because weather pattern and model performance change over time, the determination of an optimal training period is critical to obtain adaptive BMA weights for rapid weather regime changes. The sensitivity of training length (days) is then examined, and the optimum data length used in the BMA training period proves to be about 80 days. With deterministic and probabilistic verification metrics, the dynamic BMA estimated SM is comprehensively evaluated against the ASMOs, eight global model products, and the CMA’s (China Meteorological Administration) regional Land Data Assimilation System (CLDAS) product. To better compare the probability distribution of different products, the cumulative distribution function (CDF) consistency histogram and a more objective metric consistency deviation (CD) are proposed to diagnose the consistency of two SM CDFs (e.g., the BMA estimated and the observed CDF). In terms of both the deterministic (the Kling-Gupta efficiency, correlation, system bias, and bias adjusted root-mean square error) and probabilistic verification methods (CD, QQ-plots, and reliability), the dynamic BMA estimated SM outperforms any BMA members and even the benchmark product CLDAS. This study demonstrates that the dynamic BMA framework provides a new solution for merging SM model products. The merged SM and the BMA combined probability distribution can be further used for drought monitoring and prediction.

Pollen-vegetation/land use relationships in southeastern China: Complexity and applicability for paleoenvironmental reconstruction

Fossil pollen, as a key indicator of vegetation landscapes, can provide abundant information of long-term land use dynamics. However, pollen-vegetation relationships are complex, and the relevant studies are rare in the large sedimentary basins associated with strong human disturbances. This study aims to investigate the pollen-vegetation/land use relationships at a large regional scale, and to supplement reference for more accurate paleoenvironmental reconstruction in the future. A total of 124 modern pollen samples were collected from 66 lakes in the Yangtze-Huaihe River Basin (YHRB), southeastern China. We conducted a contrastive analysis of both pollen and land use data in different spatial extents and categories. Our results reveal that the pollen assemblages of the YHRB are dominated by both arboreal and herbaceous taxa, such as Pinus, Quercus, Pterocarya, Juglans, Poaceae, Artemisia, Cruciferae, Chenopodiaceae, Compositae, and Humulus. The spatial differences of pollen assemblages in the YHRB are obvious, resulted from the confounded effects of natural environment and human disturbance. Hydrologic process plays a key role in pollen dispersal and deposition in the YHRB. Waterborne pollen is an important component of the lacustrine pollen assemblages, and fern spores and total pollen concentration can be used to indicate the degree of hydrologic process. The main source of lacustrine pollen here generally derives from sub-basins, and the source area is about 80 km. Anthropogenic impact is another significant factor determining the pollen-vegetation relationships in the YHRB. Cereal and anthropochore pollen as well as pollen diversity indexes are ideal indicators of agricultural activities. We suggest that the 4 types of estimated pollen/land-use ratios in this study, covering forest, farmland, rural land, and wetland could be used as a reference for reconstructing past land cover. Our study also demonstrates the existing problems and the potential improvements for the further studies on pollen-based paleoenvironmental reconstruction.

Projection and possible causes of summer precipitation in eastern China using self-organizing map

Self-organizing map (SOM) is used to simulate summer daily precipitation over the Yangtze–Huaihe river basin in Eastern China, including future projections. SOM shows good behaviors in terms of probability distribution of daily rainfall and spatial distribution of rainfall indices, as well as consistency of multi-model simulations. Under RCP4.5 Scenario, daily rainfall at most sites (63%) is projected to shift towards larger values. For the early 21st century (2016–2035), precipitation in the central basin increases, yet decreases occur over the middle reaches of the Yangtze River as well as a part of its southeast area. For the late 21st century (2081–2100), the mean precipitation and extreme indices experience an overall increase except for a few southeast stations. The total precipitation in the lower reaches of the Yangtze River and in its south area is projected to increase from 7% at 1.5 °C global warming to 11% at 2 °C, while the intensity enhancement is more significant in southern and western sites of the domain. A clustering allows to regroup all SOM nodes into four distinct regimes. Such regional synoptic regimes show remarkable stability for future climate. The overall intensification of precipitation in future climate is linked to the occurrence-frequency rise of a wet regime which brings longitudinally closer the South Asia High (eastward extended) and the Western Pacific Subtropical High (westward extended), as well as the reduction of a dry pattern which makes the two atmospheric centers of action move away from each other.

A Lagrangian Analysis of Water Vapor Sources and Pathways for Precipitation in East China in Different Stages of the East Asian Summer Monsoon

AbstractThe Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) platform is used to simulate Lagrangian trajectories of air parcels in East China during the summer monsoon. The investigation includes four distinct stages of the East Asian summer monsoon (EASM) during its seasonal migration from south to north. Correspondingly, the main water vapor channel migrates from the west Pacific Ocean (PO) for the premonsoon in South China (SC) to the Indian Ocean (IO) for the monsoon in SC and in the Yangtze–Huaihe River basin, and finally back to the PO for the terminal stage of monsoon in North China. Further calculations permit us to determine water vapor source regions and water vapor contribution to precipitation in East China. To a large extent, moisture leading to precipitation does not come from the strongest water vapor pathways. For example, the proportions of trajectories from the IO are larger than 25% all of the time, but moisture contributions to actual precipitation are smaller than 10%. This can be explained by the large amount of water vapor lost in the pathways across moisture-losing areas such as the Indian and Indochina Peninsulas. Local water vapor recycling inside East China (EC) contributes significantly to regional precipitation, with contributions mostly over 30%, although the trajectory proportions from subregions in EC are all under 10%. This contribution rate can even exceed 55% for the terminal stage of the monsoon in North China. Such a result provides important guidance to understand the role of land surface conditions in modulating rainfall in North China.

The Relationship Between Abnormal Meiyu and Medium-Term Scale Wave Perturbation Energy Propagation Along the East Asian Subtropical Westerly Jet

The East Asian subtropical westerly jet (EASWJ) is one of the most important factors modulating the Meiyu rainfall in the Yangtze-Huaihe River Basin, China. This article analyzed periods of the medium-term EASWJ variation, wave packet distribution and energy propagation of Rossby waves along the EASWJ during Meiyu season, and investigated their possible influence on abnormal Meiyu rain. The results showed that during the medium-term scale atmospheric dynamic process, the evolution of the EASWJ in Meiyu season was mainly characterized by the changes of 3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves. The strong perturbation wave packet and energy propagation of the 3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves are mostly concentrated in the East Asian region of 90°-150°E, where the two wave trains of perturbation wave packets and wave-activity flux divergence coexist in zonal and meridional directions, and converge on the EASWJ. Besides, the wave trains of perturbation wave packet and wave-activity flux divergence in wet Meiyu years are more systematically westward than those in dry Meiyu years, and they are shown in the inverse phases between each other. In wet (dry) Meiyu year, the perturbation wave packet high-value area of the 10-15 d low-frequency variability is located between the Aral Sea and the Lake Balkhash (in the northeastern part of China), while over eastern China the wave-activity flux is convergent and strong (divergent and weak), and the high-level jets are strong and southward (weak and northward). Because of the coupling of high and low level atmosphere and high-level strong (weak) divergence on the south side of the jet over the Yangtze-Huaihe River Basin, the low-level southwest wind and vertically ascending motion are strengthened (weakened), which is (is not) conducive to precipitation increase in the Yangtze-Huaihe River Basin. These findings would help to better understand the impact mechanisms of the EASWJ activities on abnormal Meiyu from the perspective of medium-term scale Rossby wave energy propagation.

Estimation of ecosystem services value based on land use and cover change information derived from remote sensing data

It is an effective method to study the value change of ecological services based on land use and cover change information. This paper analyzed the land use and cover change information in the research area, which is based on the remote sensing images and social statistics data of 2005, 2010, and 2015, and then, quantitative estimation of the ecosystem service value was performed. Yangtze-Huaihe river basin, China is a fragile ecological area, which is selected as the research area. During 2005-2015, the area of cultivated land and construction land was the main land use types in the study area, the land use and cover change in the study area were obvious, which was characterized by the increasing of construction land area and the decreasing of cultivated land area, and the total ecosystem services value in the research area has been decreasing continuously, the value from 34.376 billion yuan in 2005 to 26.161 billion yuan in 2015.