Yangtze-Huai River Basin Research Articles

Influence of aerosol forcing on the seasonal march of East Asia summer monsoon

Focusing on the anthropogenic aerosols effects on the East Asian Summer Monsoon (EASM) progression, we found that aerosols delay the northward progression of EASM by one pentad in the south of the middle-lower reaches of the Yangtze River (PD1: pentads 25-35) and the North-Northeast China (PD3: pentads 38-42). However, aerosols have minimal impact on the seasonal march of EASM over the Yangtze-Huai River basin (PD2: pentads 36-37). In PD1 and PD3, aerosols reduce sea-land temperature differences. Also, a southward shift in the westerly jet causing lower-level north winds, which weakens the EASM in PD3. The delayed EASM progress shows its weakness in PD1 and PD3. While in PD2, EASM intensity weakens without affecting its northward progression. Aerosols, though affecting the position and intensity of Western Pacific Subtropical High, minimally influence its northward movement speed, hence no effect on the seasonal march of EASM in PD2.

Impact of May atmospheric latent heating over the Southeast Asian low-latitude highlands on interannual variability in the Meiyu onset date

The Yangtze-Huai River Basin (YHRB) is an economically developed area and one of the most densely populated regions in China. Based on ERA5 reanalysis and Meiyu monitoring data, this study investigates the relationship between interannual variability in atmospheric latent heating (LH) over the Southeast Asian low-latitude highlands (SEALLH) during early summer and the Meiyu onset date (MOD) in the YHRB. The mean MOD is 9 June, with a quasi-6-year interannual oscillation period. A stronger early summer LH over the SEALLH coincides with earlier MOD; below 500 hPa, LH increases with height and drives an anomalous southwesterly airflow from the Bay of Bengal (BOB) to the SEALLH via β effects. Circulation over the western North Pacific (WNP) is dominated by an anomalous anticyclone, causing the WNP subtropical high (WNPSH) to extend westward and northward. Continuous positive LH anomalies over the SEALLH cause anomalous southwesterly winds to transport moist enthalpy air masses from low latitudes into the YHRB, resulting in abnormal convergence there. Favorable dynamic and thermal conditions drive enhanced precipitation over the YHRB, eventually leading to a MOD that is 13 days earlier than that during periods when early summer LH is relatively weak over the SEALLH. This result potentially supports our capacity to predict the Meiyu in the YHRB.

Predictability of Extremely Pluvial Winters Over the Yangtze–Huai River Basin in China

AbstractIn the 2018–2019 winter, an unprecedented pluvial event occurred in the Yangtze‐Huai River Basin (YHRB), which is one of the most developed areas in China. This was a record over the past 40 years. Other notable events during this period were the events of the 2002–2003, 1997–1998, and 1989–1990 winters. This study aims to examine the ability of the Scale Interaction Experiment‐Frontier (SINTEX‐F) to predict these extremely pluvial winters and its predictability source. Extreme precipitation events in the 2018–2019 and 1997–1998 winters were reasonably well predicted 1 month earlier by the ensemble seasonal prediction system from deterministic and probabilistic perspectives. In contrast, the predictions of extremely pluvial winters in 2002–2003 and 1989–1990 were less skillful in some parts of the YHRB. The analysis of co‐variability of inter‐member anomalies suggested that the SST anomalies in the tropical western Indian Ocean (IO) and the tropical Pacific Ocean were responsible for the predictions of the 2018–2019 and 1997–1998 winters through increased low‐level moisture convergences in the YHRB as well as wave trains along the upper westerly jet. Limited performance in predicting the 2002–2003 and 1989–1990 events might be due to less accurate prediction of low‐level circulation around the YHRB associated with the SST anomalies in the tropical eastern IO, western IO, and the Pacific, respectively. Besides, atmospheric internal variability as well as model biases may also limit the deterministic prediction skills.

Convection Initiation During the Meiyu Environment in the Yangtze‐Huai River Basin of China

AbstractConvection is the main contributor to heavy rainfall over China's Yangtze‐Huai River Basin (YHRB) during Meiyu season; however, the mechanisms of convection initiation (CI) associated with the Meiyu front are still not well understood. In this study, a large set of 86,099 CI events, identified from composite reflectivity data in YHRB over six Meiyu seasons, were used to investigate the characteristics of the spatiotemporal distribution of CI in YHRB. The result showed that the overwhelming majority of CI events (∼90%) occurred in the region of existing stratiform clouds. Meanwhile, CI tended to concentrate in mountainous areas and exhibited two triggering modes. By relating the CI events with an objective analysis of ERA5 reanalysis data, it was also revealed that the characteristics of CI occurrence varied with patterns of Meiyu circulation and their interactions with local topography, and the warm air advection pattern dominated the Meiyu CI. We further illustrated that CI on the plains occurred with a morning peak corresponding to environments of high 0–3 km shear (SHR3) and low most unstable convective available potential energy (MUCAPE), while the CI near or over mountains had an afternoon peak corresponding to low SHR3 and high MUCAPE environments.

Identification of Meiyu process and spatiotemporal characteristics of different precipitation levels during the Meiyu period over the Yangtze-Huai River Basin

Identification of Meiyu process and spatiotemporal characteristics of different precipitation levels during the Meiyu period over the Yangtze-Huai River Basin

Reconstructed springtime (March–June) precipitation tracked by tree rings dating back to 1760 CE in the Qinling-Bashan mountainous area

In recent decades, considerable advances have been made in dendroclimatic reconstruction in the eastern monsoon region of China. However, understanding of long-term hydroclimatic changes has not been comprehensive due to the complexity of the regional geography in China's north-south transitional zone. Growth-climate response analysis indicated that springtime precipitation is the main factor limiting the radial growth of pine trees in the Qinling-Bashan mountainous area. Based on the three tree ring chronologies distributed in the southeast of Shaanxi Province, we developed a March–June precipitation reconstruction spanning 1760–2020 CE for the Qinling-Bashan mountainous area. Precipitation reconstruction accounts for 40.6% of the total precipitation variance during the instrumental period 1955–2016. Spatial correlation analysis indicated that the precipitation reconstruction recorded similar common precipitation signals for the eastern Qinling Mountains and the Yangtze-Huai River Basin. The results of the superposed epoch analysis (SEA) revealed that low precipitation was one of the main causes of severe drought and locust plague events. The preliminary synoptic climatology analysis showed that our reconstructed precipitation is closely linked to the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) variability.

Monitoring Post-Flood Recovery of Croplands Using the Integrated Sentinel-1/2 Imagery in the Yangtze-Huai River Basin

The increasingly frequent flooding imposes tremendous and long-lasting damages to lives and properties in impoverished rural areas. Rapid, accurate, and large-scale flood mapping is urgently needed for flood management, and to date has been successfully implemented benefiting from the advancement in remote sensing and cloud computing technology. Yet, the effects of agricultural emergency response to floods have been limitedly evaluated by satellite-based remote sensing, resulting in biased post-flood loss assessments. Addressing this challenge, this study presents a method for monitoring post-flood agricultural recovery using Sentinel-1/2 imagery, tested in three flood-affected main grain production areas, in the middle and lower Yangtze and Huai River, China. Our results indicated that 33~72% of the affected croplands were replanted and avoided total crop failures in summer 2020. Elevation, flood duration, crop rotation scheme, and flooding emergency management affect the post-flood recovery performance. The findings also demonstrate rapid intervention measures adjusted to local conditions could reduce the agricultural failure cost from flood disasters to a great extent. This study provides a new alternative for comprehensive disaster loss assessment in flood-prone agricultural regions, which will be insightful for worldwide flood control and management.

Seasonal Amplitude of Water Storage Variations of the Yangtze–Huai Plain Lake Group: Implicaion for Floodwater Storage Capacity

Lakes are of significant importance in regulating floods and providing water sources. The seasonal water storage variations for the plain lake group in the Yangtze–Huai River Basin (YHRB) are significant for alleviating flood pressure and regulating runoff. However, to date, the seasonal amplitude of lake water storage variations and its capacity of buffering floodwater in the YHRB is not quantified well and remains to be investigated comprehensively. To advance the understanding of such a critical scientific issue, the water level data of the plain lake group (area>100 km2, 29 lakes) in the YHRB is collected from multi-source data between 1990 and 2020. Using lake inundation area obtained from Global Surface Water and water level variations, water storage dynamics for the plain lake group are quantified. Furthermore, this study also uses the Gravity Recovery and Climate Experiment (GRACE) products to analyze the terrestrial water storage anomalies (TWSA) in the whole basin. The results indicate that the seasonal amplitude of water level change and water storage variation of the plain lake group are 2.80 ± 0.71 m and 37.38 ± 14.19 Gt, respectively. Poyang and Dongting Lakes, two lakes that maintain the natural connection with the Yangtze River, have the most substantial seasonal amplitude in the hydrological situation. The amplitude in water level and water storage in Poyang Lake is 9.53 ± 2.02 m and 14.13 ± 5.54 Gt respectively, and that in Dongting Lake is 7.39 ± 1.29 m and 7.31 ± 3.42 Gt respectively. The contribution of seasonal variation of water storage for large plain lakes to TWSA in the YHRB is approximately 33.25%, fully reflecting these lake’s imperative position in the YHRB. This study is expected to enhance the scientific understanding of the seasonal hydrologic regime for the large lakes in the YHRB and contribute to the management of flood risks and water resources in East China.

Anomalous Features of Extreme Meiyu in 2020 over the Yangtze-Huai River Basin and Attribution to Large-Scale Circulations

Anomalous Features of Extreme Meiyu in 2020 over the Yangtze-Huai River Basin and Attribution to Large-Scale Circulations

A 33-yr Mei-Yu-Season Climatology of Shear Lines over the Yangtze–Huai River Basin in Eastern China

AbstractA 33-yr climatology of shear lines occurring over the Yangtze–Huai River basin (YHSLs) of eastern China during the mei-yu season (i.e., June and July) of 1981–2013 is examined using the daily ERA-Interim reanalysis data and daily rain gauge observations. Results show that (i) nearly 75% of the heavy-rainfall days (i.e., >50 mm day−1) are accompanied by YHSLs, (ii) about 66% of YHSLs can produce heavy rainfall over the Yangtze–Huai River basin, and (iii) YHSL-related heavy rainfall occurs frequently in the south-central basin. The statistical properties of YHSLs are investigated by classifying them into warm, cold, quasi-stationary, and vortex types based on their distinct flow and thermal patterns as well as orientations and movements. Although the warm-type rainfall intensity is the weakest among the four, it has the highest number of heavy-rainfall days, making it the largest contributor (33%) to the total mei-yu rainfall amounts associated with YHSLs. By comparison, the quasi-stationary type has the smallest number of heavy-rainfall days, contributing about 19% to the total rainfall, whereas the vortex type is the more frequent extreme-rain producer (i.e., >100 mm day−1). The four types of YHSLs are closely related to various synoptic-scale low-to-midtropospheric disturbances—such as the southwest vortex, low-level jets, and midlatitude traveling perturbations that interact with mei-yu fronts over the basin and a subtropical high to the south—that provide favorable lifting and the needed moisture supply for heavy-rainfall production. The results have important implications for the operational rainfall forecasts associated with YHSLs through analog pattern recognition.

Event-based extreme precipitation in Central-Eastern China: large-scale anomalies and teleconnections

Event-based extreme precipitation (EEP), defined as an extreme precipitation event (no less than 1 mm for continuous days) having at least one daily precipitation exceeding the 90th percentile, are categorized into three types according to the time distribution pattern (TDP) of extreme precipitation: daily intense precipitation appearing only at the first half of event (TDP1), at both the first and second halves (TDP2), and only at the second half of event (TDP3). This study focuses on the TDP1 and TDP2 types, which occur much more frequently in the central-eastern China and investigates associated distinguishing large-scale teleconnection patterns. The TDP1 events dominantly occur in mid-to-late spring, which are associated with the Silk Road pattern (SRP) wave train manifested from western Europe to northwest Pacific along the subtropical westerly jet. The tripolar sea surface temperature (SST) anomalous pattern over the North Atlantic Ocean, i.e., low SST anomalies in the Azores Islands, two high SST anomalies over the Greenland and subtropical North Atlantic are mainly attributed to force the SRP wave. Meanwhile, the enhanced northwestward moisture transport from the South China converges with the southeastward moisture transport related to the SRP from the North China, resulting in the TDP1 extreme precipitation events over the central-eastern China. The TDP2 events are closely conjunction with the Meiyu precipitation in the Yangtze-Huai River basin in summer. During the TDP2 events, the East Asia/Pacific (EAP) teleconnection is exhibited along the East Asia coasts, which is triggered by the anomalous convection in the western North Pacific. An anomalous anticyclone related to the EAP teleconnection contributes to the westward stretch of the western Pacific subtropical high, providing significant enhanced moisture transportation toward the Yangtze-Huai River basin. Correspondingly, the meridional gradient of the equivalent potential temperature $$\theta_{e}$$ is intensified and favored of forming Meiyu front precipitation. This study highlights the definition of EEP event emphasizing the TDP of extreme precipitation and distinguished features of occurring seasons and large-scale circulations associated with the two dominant types of EEP events.

Quantitative Analysis of Water Vapor Transport during Mei-Yu Front Rainstorm Period over the Tibetan Plateau and Yangtze-Huai River Basin

There are continuous precipitation systems moving eastward from the Tibetan Plateau to the middle and lower reaches of the Yangtze-Huai River during the Mei-yu period. We selected 20 typical Mei-yu front precipitation cases from 2010 to 2015 based on observational and reanalysis data and studied the characteristics of their environmental fields. We quantitatively analyzed the transport and sources of water vapor in the rainstorms using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT_4.9) model. All 20 Mei-yu front precipitation cases occurred in a wide region from the Tibetan Plateau to the Yangtze-Huai River. The South Asian high and upper level jet stream both had strong intensities during the Mei-yu front rainstorm periods. Heavy rainfall mainly occurred in the divergence zone to the right of the high-level jet and in the convergence zone of the low-level jet, where strong vertical upward flows provided the dynamic conditions required for heavy rainfall. The water vapor mainly originated from the Indian Ocean, Bay of Bengal, and South China Sea. 52% of the air masses over the western Tibetan Plateau originated from Central Asia, which were rich in water vapor. The water vapor contribution at the initial position was only 41.5% due to the dry, cold air mass over Eurasia, but increased to 47.6% at the final position. Over the eastern Tibetan Plateau to the Sichuan Basin region, 40% of the air parcels came from the Indian Ocean, which was the main channel for water vapor transport. For the middle and lower reaches of the Yangtze River, 37% of the air parcels originated from the warm and humid Indian Ocean. The water vapor contribution at the initial position was 38.6%, but increased to 40.2% after long-distance transportation.

Dominant variation modes associated with Yangtze–Huai River Basin summer heavy rainfall events

ABSTRACTThe Yangtze–Huai River Basin (YHRB) always suffers from anomalously heavy rainfall during the warm season, and has been well explored as a whole area during the past several decades. In thi...

Relationship between the onset date of the Meiyu and the South Asian anticyclone in April and the related mechanisms

The onset date of the Meiyu has attracted extensive attention because it marks the beginning of the rainfall season in the Yangtze-Huai River basin (YHRB). In this study, the relationship between the onset dates of the Meiyu and its precursors is investigated; and the South Asian anticyclone (SAA) in April, which is generated by atmospheric apparent sources over South Asia, is introduced. The results show that years with stronger SAA in April are concurrent with earlier onsets of the Meiyu and increased precipitation in June over the YHRB and vice versa. The mechanisms involved in this relationship are further investigated. The SAA emerges in early April, and moves eastward to the western North Pacific (WNP) in the late pentad of April due to the abrupt zonal energy transport, leading to anomalous divergence in the upper troposphere over the WNP. The divergence anomaly enhances ascending motion in situ due to Ekman pumping, leading to an anomalous cyclone at lower levels over this region. Due to the southward-moving ascending motion and the presence of the lower tropospheric cyclone in the fourth pentad of May, the precipitation moves southward to the Philippine Sea (PHS). The associated stronger convection over the PHS further triggers a meridional overturning pattern, which develops into the Pacific-Japan like pattern (PJ-like pattern). The PJ-like pattern persists from the end of May to the beginning of June, which promotes the earlier onset of the Meiyu. In addition, due to the increased heating associated with the abundant precipitation over the PHS around the fourth pentad of May, the Western Pacific subtropical high (WPSH) shifts northward earlier. Ultimately, the earlier establishment of the PJ-like pattern and the earlier northward shift of the WPSH cause stronger-than-normal southwesterly flows and additional water vapor transport to the YHRB, leading to the advanced onset of the Meiyu and additional precipitation in June.

Effects of Different Configurations of the East Asian Subtropical and Polar Front Jets on Precipitation during the Mei-Yu Season

Abstract Observational analysis indicates that the East Asian jet stream consists of two separate branches: the East Asian subtropical jet (EASJ) and the East Asian polar front jet (EAPJ). The impacts of different intensity configurations of the EASJ and EAPJ on precipitation during the mei-yu season are investigated using the NCEP–NCAR Reanalysis Project (NNRP) dataset and daily gauge observations in East China. The intensity and location of precipitation are associated with different configurations of the EASJ and EAPJ. Precipitation intensity increases with intensification of the EASJ and EAPJ. The rainband is located to the north of the mei-yu region when the EASJ intensifies and the EAPJ weakens. Further analyses indicate that the intensity changes of the EASJ and EAPJ are linked to the cold and warm airmass activities. For cases with strong EASJ and EAPJ, both the warm-moist and cold air masses are active. When the warm-moist and cold air masses meet near 30°N, abundant precipitation occurs in the Yangtze-Huai River basin (YHRB). For cases with weak EASJ and EAPJ, both the cold and warm-moist air masses are inactive, and no significant precipitation occurs in the YHRB. For cases with strong EASJ and weak EAPJ, the warm-moist air mass moves northward while the cold air mass is weak. Precipitation concentrates to the north of YHRB. For cases with weak EASJ and strong EAPJ, cold air extends farther south while the warm-moist air mass is inactive. Precipitation occurs to the south of YHRB.

Numerical Simulation of the Heavy Rainfall in the Yangtze-Huai River Basin during Summer 2003 Using the WRF Model

AbstractIn this study, a 47-day regional climate simulation of the heavy rainfall in the Yangtze-Huai River Basin during the summer of 2003 was conducted using the Weather Research and Forecast (WRF) model. The simulation reproduces reasonably well the evolution of the rainfall during the study period's three successive rainy phases, especially the frequent heavy rainfall events occurring in the Huai River Basin. The model captures the major rainfall peak observed by the monitoring stations in the morning. Another peak appears later than that shown by the observations. In addition, the simulation realistically captures not only the evolution of the low-level winds but also the characteristics of their diurnal variation. The strong southwesterly (low-level jet, LLJ) wind speed increases beginning in the early evening and reaches a peak in the morning; it then gradually decreases until the afternoon. The intense LLJ forms a strong convergent circulation pattern in the early morning along the Yangtze-Huai Ri...

Low-Level Jets over Southeast China: The Warm Season Climatology of the Summer of 2003

AbstractThe southwesterly low-level jet (LLJ) over southeast China in the summer of 2003 is analyzed in this study. The analysis is based on the National Centers for Environmental Prediction (NCEP) Final (FNL) operational global analysis data on 1.0×1.0-degree grids at 6-h intervals. The major criteria for choosing the LLJ included the following: a maximum wind speed equal to or greater than 12.0 m s–1, a wind direction of between 180° and 270°, and the height of wind maximum at 900–700 hPa, not confined to single pressure level. The results show that the LLJs over southeast China dominate at 850 and 800 hPa. These LLJs are closely associated with the topography of this area and tend to locate regions with large terrain gradients, including the northeastern and eastern Yunnan-Guizhou Plateau. Under the influence of mid-latitude westerly winds, the LLJs above 750 hPa move northward to the Yangtze-Huai River Basin. Compared to the ten-year (2000–2009) mean climate conditions, the LLJs in the warm season of ...

Probabilistic Projections of Climate Change over China under the SRES A1B Scenario Using 28 AOGCMs

Probabilistic projection of climate change consists of formulating the climate change information in a probabilistic manner at either global or regional scale. This can produce useful results for studies of the impact of climate change impact and change mitigation. In the present study, a simple yet effective approach is proposed with the purpose of producing probabilistic results of climate change over China for the middle and end of the twenty-first century under the Special Report on Emissions Scenarios A1B (SRES A1B) emission scenario. Data from 28 coupled atmosphere–ocean general circulation models (AOGCMs) are used. The methodology consists of ranking the 28 models, based on their ability to simulate climate over China in terms of two model evaluation metrics. Different weights were then given to the models according to their performances in present-day climate. Results of the evaluation for the current climate show that five models that have relatively higher resolutions—namely, the Istituto Nazionale di Geofisica e Vulcanologia ECHAM4 (INGV ECHAM4), the third climate configuration of the Met Office Unified Model (UKMO HadCM3), the CSIRO Mark version 3.5 (Mk3.5), the NCAR Community Climate System Model, version 3 (CCSM3), and the Model for Interdisciplinary Research on Climate 3.2, high-resolution version [MIROC3.2 (hires)]—perform better than others over China. Their corresponding weights (normalized to 1) are 0.289, 0.096, 0.058, 0.048, and 0.044, respectively. Under the A1B scenario, surface air temperature is projected to increase significantly for both the middle and end of the twenty-first century, with larger magnitude over the north and in winter. There are also significant increases in rainfall in the twenty-first century under the A1B scenario, especially for the period 2070–99. As far as the interannual variability is concerned, the most striking feature is that there are high probabilities for the future intensification of interannual variability of precipitation over most of China in both winter and summer. For instance, over the Yangtze–Huai River basin (28°–35°N, 105°–120°E), there is a 60% probability of increased interannual standard deviation of precipitation by 20% in summer, which is much higher than that of the mean precipitation. In general there are small differences between weighted and unweighted projections, but the uncertainties in the projected changes are reduced to some extent after weighting.

Analysis of the Baiu Precipitation and Associated Circulations Simulated by the MIROC Coupled Climate System Model

The major features of Baiu simulated by the climate model (MIROC_Hires) are examined by analyzing the differences between simulations and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data during 1981–2000, focusing on the evaluation of the model performances in reproducing the Baiu precipitation climatology as well as the associated 3-dimensional circulation systems, the relationship with Indian Summer Monsoon (ISM) and the configuration of upper and lower level jets. The results show that the model can reproduce heavy precipitation centers over the Yangtze-Huai River Basin during the Baiu period. The horizontal and vertical structures of the circulation systems during the Baiu period are also well simulated, such as an intensive meridional gradient of moisture and it’s equivalent potential temperature, the strong low-level southwesterly flow in the lower troposphere over East China, the location of the westerly jet in the upper troposphere, the strong ascending motion over heavy rainfall area (HRA) and compensatory descending motion over the northern and southern sides of HRA. However, obvious discrepancies occur in the overestimated precipitation over southeastern China during the Baiu period. In addition, our study suggests that the biases of the ISM and the configuration of upper and lower level jet results in deficiencies in the evolution of Baiu. The simulated onset of ISM is one pentad later than the reanalysis data, while the onset day of simulated Baiu is one pentad later than the reanalysis data, as well. The simulation showed southward shifting of the upper level jet and the stronger, lower level jet. These location and intensity biases essentially favor excess precipitation in southeastern China. Therefore, it is necessary for the coupled model to improve the configuration of upper and lower level jets in simulating the Baiu.