Precipitation In Southern China Research Articles

Skillful prediction of boreal winter-spring seasonal precipitation in Southern China based on machine learning approach and dynamical ENSO prediction

Skillful prediction of boreal winter-spring seasonal precipitation in Southern China based on machine learning approach and dynamical ENSO prediction

Using machine learning to analyze the changes in extreme precipitation in southern China

Convolutional neural network (CNN) is applied to identify the extreme precipitation events (EPEs) in southern China and the physical contributions are quantified for the changes in extreme precipitation in recent decades. The CNN correctly identifies about 96% of the observed EPEs based on the given large-scale atmospheric circulation. The discrimination made by the neural network is revealed by using the layer-wise relevance propagation method. The CNN is inclined to classify the circulation pattern as an extreme precipitation circulation pattern (EPCP), when a deep cyclonic anomaly and intense horizontal pressure gradient appear over southern China at the lower and middle troposphere. The extreme precipitation amount decreases during April and May (AM) and increases in June to August (JJA) after the early-1990s. Result of the quantitative partitioning analysis indicates that the dynamic and thermodynamic effects respectively contribute 297.6% and −234% to the reduction of extreme precipitation in AM. The decline in EPCP frequency dominates the decrease in EPEs. In JJA, the increased extreme precipitation after the early 1990s is attributed to both the interdecadal increase in the EPCP frequency and the increasing trend in the atmospheric moisture. The dynamic and thermodynamic changes play almost equal roles in the increased extreme precipitation in JJA.

Anthropogenic Influences on Extremely Persistent Seasonal Precipitation in Southern China during May–June 2022

Abstract Precipitation in southern China during April–June 2022 was the highest since 1961. Anthropogenic forcing has reduced the probability of 2022-like Rx30day precipitation by about 45% based on CMIP6 simulations.

Intraseasonal variation in extreme precipitation in southern China during winter 2015/16, and its precursors

Extremely heavy rainstorms occurred over southern China during the winter of 2015/16, with record-breaking rainfall in the cold season. These extraordinary rainfalls were featured by pronounced intraseasonal variation in terms of both meridional displacement and amount of heavy precipitation. The main rain belt meandered around the lower reaches of the Yangtze River during December 2015, and then penetrated southward to the Pearl River basin with a dramatic increase in rainfall amount during January 2016. The intraseasonal features of heavy rainfall cannot be well explained by the quasi-steady El Niño condition, but are possibly governed by the circulation modulations at different latitudes. The transition of anomalous height from low to high over the Urals brought strong cold air outbreaks and therefore southward displacement of the main rain belt. This transition together with increased southwesterly flows in front of the deepened India-Burma trough led to strong moisture convergence and thus torrential rains during January 2016. These circulation transitions might be related to certain changes in the preceding ocean conditions. A negative Arctic sea-ice anomaly to the west of 90°E persisted throughout the winter, while the previously excessive Arctic sea ice over east of 100°E vanished in November 2015. This conversion from dipole to monopole structure of sea-ice anomalies could favor the development of the Ural highs and enhancement of cold air intrusion from the expanded Siberian highs. Additionally, the deepened India-Burma trough and further intensified southwesterly flows might be related to the warming sea surface temperature over the tropical Indian Ocean.

Anthropogenic Influence on 2022 Extreme January–February Precipitation in Southern China

Abstract The precipitation in January–February 2022 in southern China was the second-largest amount since 1961. Anthropogenic influence reduced the likelihood of extreme events like 2022 by about 50% (55%) in HadGEM3 (CMIP6).

Global Cooling‐Driven Summer Monsoon Weakening in South China Across the Eocene‐Oligocene Transition

AbstractRecent research has suggested that East Asia has experienced a prevailing monsoon climate since the Eocene. However, there is little knowledge about the development of the East Asian monsoon system before the Miocene, particularly in southern China, due to a lack of well‐dated continuous sediment records. Here, we present new magnetic proxy records from International Ocean Discovery Program Site U1501 in the northern South China Sea. We conducted rock magnetic experiments, made scanning electron microscopy observations and performed diffuse reflectance spectrum analysis on the late Eocene‐early Oligocene core sediments. The magnetic signal of the sediments is dominated by detrital magnetite and titanomagnetite formed during the silicate weathering and erosion processes, which were used to infer the evolution of summer monsoon precipitation in southern China. Our results along with geochemical and clay mineral data from Site U1501 strongly indicate that the East Asian summer monsoon generally weakened across the Eocene‐Oligocene transition. This change was linked to coeval global cooling rather than tectonic processes. Prior to the Eocene‐Oligocene transition, the summer monsoon intensified, likely due to the latest Eocene warming event caused by the enhancement of the Atlantic Meridional Overturning Circulation, which may have preconditioned the Earth system for the greenhouse‐to‐icehouse transition.

Diversity on the Interannual Variations of Spring Monthly Precipitation in Southern China and the Associated Tropical Sea Surface Temperature Anomalies

Diversity on the Interannual Variations of Spring Monthly Precipitation in Southern China and the Associated Tropical Sea Surface Temperature Anomalies

Summer Extreme Precipitation in Southern China from the Perspective of Moisture Static Energy

Abstract The extreme precipitation (EP) in the early and late rainy seasons in Southern China is investigated from the perspective of moist static energy (MSE). At the synoptic time scale, the EP is accompanied by the charge–discharge paradigm of the vertically integrated MSE (〈MSE〉); the positive 〈MSE〉 anomaly reaches the peak one day before EP and decreases quickly during the event. The charge–discharge paradigm of 〈MSE〉 is dominated by the horizontal and vertical advection, respectively. However, synoptic systems responsible for the 〈MSE〉 charge in the early and late rainy seasons are different due to the different horizontal distributions of climatological MSE in the lower troposphere caused by the northward migration of solar radiation and the monsoon system. At the interannual time scale, more EP in the early (late) rainy season is associated with the higher seasonal-mean 〈MSE〉 that can be caused by the anomalous anticyclone (cyclone) in the western North Pacific induced by the SST anomalies in the tropical Indian Ocean and central North Pacific (the tropical Pacific). The multimodel ensemble mean of CMIP6 models reproduces well the observed 〈MSE〉–EP relationship in both the historical and Shared Socioeconomic Pathway 5–8.5 (SSP5–8.5) runs. Moreover, the mean state of 〈MSE〉 increases in the SSP5–8.5 compared to historical runs along with more frequent occurrence of EP events. Hence, 〈MSE〉 can serve as a useful metric for studying EP in Southern China at various time scales.

Regional difference in precipitation seasonality over China from CMIP6 projections

AbstractBased on historical simulations and projections under two scenarios of the Shared Socioeconomic Pathways (SSP2‐4.5 and SSP5‐8.5) provided by 32 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we investigate the future precipitation seasonality changes over China by two indices, the dimensionless seasonality index (DSI) and the relative seasonality index (SI), and the associated physical mechanisms by moisture budget diagnosis. The results show that relative to the baseline period 1995–2014, the DSI is enhanced across almost all of China at the end of the 21st century, with stronger magnitudes in southeastern China and the southern Tibetan Plateau and weaker magnitudes in northwestern China, and national‐mean enhancements are 15% (7%–21%) and 23% (15%–29%) for the multimodel median (25th–75th percentile range across models) under the SSP2‐4.5 and SSP5‐8.5 scenarios, respectively. Projected SI changes show large regional differences, with decreases in northern China and increase in southern China, leading to little change for the national mean. The DSI and SI changes are associated with uneven distributions of changes in absolute amounts and relative proportions of precipitation among seasons, respectively. Further analysis reveals that the contributions of different moisture budget terms to precipitation changes vary across seasons, resulting in changes in the seasonal distribution of precipitation and thus the DSI and SI changes. Specifically, the thermodynamic component of vertical moisture advection primarily determines the greater magnitude of increased precipitation in summer than in winter in most of China, resulting in the DSI change. The reduction in residual term dominates the diminished winter precipitation in southern China, leading to more precipitation concentrated in summer for given annual precipitation and thus the intensification in SI, while the opposite holds true in northern China.

Linkage between the Asian-Pacific Oscillation and winter precipitation over southern China: CMIP6 simulation and projection

Based on the simulations of 30 CMIP6 models, this paper evaluates their performance in simulating the linkage between the winter Asian-Pacific Oscillation (APO) and precipitation over southern China (SC). Results show that 12 out of the 30 models can reproduce well the observed inverse relationship featuring a positive APO phase corresponding to a decrease in SC precipitation. Associated with the positive APO phase, an anomalous anticyclonic circulation dominates the southern part of Asia in the upper troposphere, and an anomalous cyclonic circulation prevails particularly in the lower troposphere of the South China Sea and the Malay Archipelago. Accordingly, the East Asian westerly jet (EAWJ) shifts northward, and low-level northeasterly anomalies appear over SC, which yield anomalous descending motion and water vapor flux divergence in SC, respectively, hence decreasing the in-situ precipitation. Using the ensemble of the 12 models, the future relationship between the winter APO and SC precipitation under the SSP5-8.5 scenario was further projected. The projection indicates that the APO connection with SC precipitation will still be significant, but weakened slightly, during the second half of the 21st century as compared to the present. Such a weakening may result from the weaker linkage between SC precipitation and the meridional displacement of the EAWJ.

Effects of the Trends in Spring Sensible Heating over the Tibetan Plateau during Different Stages on Precipitation in China

The spring sensible heating (SSH) over the Tibetan Plateau (TP), which can significantly affect the precipitation in China, has experienced three different stages of change, showing significant increasing (1961–1979, Stage I), decreasing (1980–2002, Stage II), and increasing (2003–2014, Stage III) trends. In this study, the impact of these different trends in TP SSH on spring precipitation (SPR) in China and their possible mechanisms are investigated, based on observations and the reanalysis product. In Stage I, the SPR represents a contrasting north-south pattern associated with the increasing TP SSH, showing increasing trends over southern China and decreasing trends over central and northern China. Further, the spatial distribution of SPR trends shows a contrasting east-west pattern in Stage II. That is, persistent weakening TP SSH plays a more crucial role in increasing and decreasing SPR over southwestern and southern China, respectively. However, compared with the significant trend in SPR in Stage III, the regulation of TP SSH on SPR weakens significantly. Dynamically, the increasing TP SSH in Stage I can strengthen the subtropical westerly jet in the upper layer, simultaneously configured with an anomalous cyclone in northeastern China, which deepens the East Asian trough. Thus, anomalous convergence in the upper layer occurs over central and northern China, favoring the downdraft. It then causes more cold and dry air to move southward in the lower troposphere, which then encounters the warm and wet southwest airflows, boosting the updraft over southern China. In Stage II, regression analysis shows that if the TP SSH increases, an anomalous cyclone in the middle and upper troposphere occurs over the western TP, causing the downdraft and less precipitation over southwestern China, while a cyclone in the lower troposphere occurs over the western North Pacific and extends to southern China, promoting the ascending motions and more precipitation in southern China. However, in this stage, TP SSH actually weakens, thus contributing to more precipitation over southwestern China and less precipitation over southern China.

Impact of changes in refractive indices of secondary organic aerosols on precipitation over China during 1980–2019

Secondary organic aerosols (SOAs), which include both colorless and colored carbonaceous aerosols, represent a major type of aerosol globally. Previous studies have reported that colored aerosols drive the well-known precipitation changes over southern China called the south-flood north-drought (SFND). Considering the highest concentration of SOA in China, SOAs can cause fluctuations in the precipitation system over China. However, studies on the climatic effects of SOAs over East Asia are scarce owing to the chemical complexity of SOAs and high computational cost. Therefore, to investigate the effect of SOAs on the precipitation change over China, we implemented an SOA scheme using empirical parameters in the chemistry-climate model. We performed a control and two sensitivity simulations depending on the difference in refractive indices of SOAs to elucidate the effects of light absorption by SOAs on precipitation. Our results suggest that strong light absorption by SOAs strengthens the convective precipitation over southern China following the enhancement of atmospheric stability with a secondary circulation effect. However, the surface temperature changes caused by SOAs shift the jet core if weak light absorption by SOAs is assumed, causing a strong downdraft in the mid-troposphere and decreasing humidity over south-eastern China. Therefore, precipitation was significantly reduced over southern China. Our results show that light-absorbing SOAs have had a significant impact on precipitation in southern China for the past few decades. Furthermore, the apparent difference in mechanisms of precipitation change between strong and weak light absorption by SOAs suggests the importance of choosing suitable refractive indices for SOAs in the climate–atmospheric chemistry model.

Soil moisture-constrained East Asian Monsoon meridional patterns over China from observations

As an internal forcing of the earth climate system, soil moisture (SM) significantly influences the water and energy cycle by controlling evapotranspiration and terrestrial solar energy. The current study used observed precipitation, remotely sensed SM, and reanalysis of atmosphere and land parameters to assess the East Asian Monsoon (EAM) precipitation variability due to meridional SM oscillations across China. A generalized linear method, namely coupled manifold technique (CMT) for assessing the reciprocal forcing between two climate fields and numerical simulations are applied to SM and EAM precipitation. We find that the EAM precipitation interannual variability between north and south China significantly correlates with SM meridional oscillation. The CMT results further showed that SM forcing has a significant (99% confidence) influence on the EAM precipitation explaining about 0.40 of the variance ratio in north and south China. The EAM and SM composite analysis show that the wetter (drier) north (south) oscillates the EAM precipitation over the north (south) of China and vice versa due to SM thermal controls. We then used control and sensitivity simulations with SM observations to further validate the findings implying that SM can potentially improve the interannual EAM forecast skills. The model results show that a wetter (drier) north (south) results in negative (positive) sensible heat (latent heat) anomalies that impact the boundary layer and propagate to change the meridional atmospheric heating profile. When positive (negative) SM anomalies exist over northern (southern) China, the zonal easterlies and extratropical westerlies move to north China causing above-normal precipitation that descends into southern China, suppressing subtropical westerlies and precipitation in southern China. On the contrary, a dry (wet) north (south) favors intensified subtropical westerlies and precipitation in southern China. The findings have dire implications for the water and energy cycle of the region in the projected wetting and drying patterns of the north (south).

The spatial-temporal patterns of East Asian climate in response to insolation, CO2 and ice sheets during MIS-5

Marine Isotope Stage (MIS) 5, between about 130 and 70 ka BP, is characterized by climate oscillations consisting of three interstadials and two stadials. Many climate simulations have been performed for the warmest MIS-5e period, but few has been made to cover the entire MIS-5 to investigate the climate variability during this long period. In this study, two sets of snapshot simulations by a step of 2 ka covering the whole MIS-5 period are performed with the model HadCM3 to investigate the relative impacts of insolation, CO2 and Northern Hemisphere ice sheets on the East Asian climate variability. Our results show that precipitation and temperature in different subregions in East Asia have different sensitivity to astronomical forcing, CO2 and ice sheets, in particular when seasonal and mean annual changes are concerned. The variability of temperature and precipitation within MIS-5 is mainly controlled by precession but their magnitudes are modulated by CO2 and ice sheets. The impact of ice sheets on summer precipitation vary between subregions and is sensitive to ice sheet configurations and background insolation. The summer precipitation in southern China is more sensitive to ice sheets than in northern China. Moisture budget analysis show that insolation and CO2 affect the summer precipitation by the dynamic and thermodynamic processes, respectively, and the impact of ice sheets is mainly through the vertical dynamic processes which is strongly associated with the ice sheet-induced wave train at the hemisphere scale.

Spatiotemporal Variability of the Southern Second Mode and Its Influence on June Precipitation in Southern China

AbstractBased on the Empirical Orthogonal Functions decomposition of the Sea level pressure (SLP) anomalies over the southern extratropic, the second pattern is defined as a southern second mode (SMD2), and its corresponding principal component is named the southern second mode index. The most significant feature of SMD2 is the seesaw pattern of SLP, which indicates the opposite phase of the Amundsen Low and surroundings. The spatial mode of EOF2 varies in different months but EOF2 in March is most similar to SMD2. This study shows that the March SMD2 is negatively associated with the June precipitation in southern China. The mechanisms can be briefly summarized as follows: The March SMD2 is negatively correlated with sea surface temperature (SST) in the midlatitude. Surface wind changes can affect surface heat flux and heat transport, leading to the SST changes. The SST anomaly acts as the “oceanic bridge” to preserve the March SMD2 signal and persists into late summer. The key area of SST is associated with Maritime Continent convective activity anomalies, which can excite and maintain the Pacific‐Japan pattern resulting in precipitation anomalies in south China. Through sea‐air interactions, the SMD2 can affect the precipitation in southern China across seasons. This work is expected to provide a new perspective for forecasting summer precipitation in southern China.

Evaluating and projecting of climate extremes using a variable-resolution global climate model (VR-CESM)

Increasing risk of many natural hazards including floods, wildfires, and reduction of agricultural production are often due to extreme climate events such as heavy precipitation, heat waves and drought. In this study, the variable-resolution Community Earth system model (VR-CESM) was used to investigate potential changes in extreme climate events at refined-resolution (14 km) in the western U.S. and eastern China. The model performance for simulating climate extremes is evaluated by various extreme metrics and assessed against the PRISM reference dataset in the U.S. VR-CESM is also compared with other models at different resolutions, including the uniform coarser resolution model CESM with the same physical parameterization, and HadGEM2-WRF, one RCM in the CORDEX-NA ensembles with the same SST forcing as the GCMs. Among those precipitation extreme metrics, VR-CESM simulates the short-term daily metrics (e.g., 95th percentile precipitation) in the western U.S. well (with greater uncertainties in the Sierra Nevada and Cascade Mountains), but underestimates the long-term metrics (e.g., number of dry years) during the historical period. For temperature extremes, VR-CESM also overestimates the number of hot temperature extremes in California’s Central Valley and southwestern desert regions; this is consistent with the warm seasonal average JJA biases. In model intercomparisons, VR-CESM has smaller biases than CESM and HadGEM2-WRF for both extreme precipitation and temperature events. Additionally, the Palmer Drought Severity Index (PDSI) for all models is simulated at four watersheds and compared to the PRISM reference dataset with statistical testings for their similarities. Under RCP8.5 through 2050, VR-CESM projects stronger and more frequent extreme precipitation in the mountains and hot events in the deserts of the western U.S., with more wet periods in California as indicated by PDSI. In another VR-CESM refined-resolution region in China, VR-CESM projection indicates an increase in strength and magnitude of extreme precipitation in southern China and hot temperature extremes in eastern China. Geographic heterogeneity in PDSI projections is also evident as the North China Plain is projected to have more dry periods while the Three Gorges Basin is projected to not change much. This study demonstrates that the analysis of multiple extreme metrics is essential to provide an adequate understanding of how extremes may change in the future in a particular place.

Effects of Low-Frequency Oscillation at Different Latitudes on Summer Precipitation in Flood and Drought Years in Southern China

Based on the daily precipitation data from 753 meteorological stations provided by the National Meteorological Information Center (China) and the daily reanalysis data from NCEP/NCAR and ERA5 during the period from 1980 to 2020, the low-frequency (LF) precipitation characteristics of the typical summer flood and drought years in southern China and their relation to the LF atmospheric circulation at different latitudes are compared and analyzed, and extended-range forecasting signals are given. The results show that: (a) In both flood and drought years, summer precipitation in southern China is controlled by 10–20 day oscillation (quasi-biweekly oscillation, QBWO); (b) LF convection is active in southern China in both flood and drought years, but the convective center is southward in flood years, and the vertical meridional circulation is stronger. The key circulation systems of 500 hPa LF height field in flood and drought years include LF “two ridges and one trough” and LF “+”, “−”, “+” East Asia Pacific (EAP) teleconnection wave train in mid-high latitudes of Eurasia. However, the “two ridges and one trough” in flood years are more westward and meridional than in drought years, and the LF Subtropical High is stronger and more extensive, with more significant westward extension; (c) In flood (drought) years, there is northerly and then westerly (central westerly) dry-cold, northeasterly wet-cold, southwesterly (none), and southeasterly (including southerly across the equator) wet-warm water vapor channels. The sources of dry and wet cold air in flood (drought) years are located near Novaya Zemlya (the eastern West Siberian Plain), the Yellow Sea, and the Bohai Sea (Sea of Japan). Additionally, the sources of wet-warm water vapor include the Arabian Sea, the Bay of Bengal, the western Pacific Ocean, and the sea area of northeastern Australia (the western Pacific Ocean and the northern sea area of Australia); and (d) The LF predictive signals of outgoing longwave radiation (OLR) appear on −11 days, while the signals of the 500 hPa height field are on −9 days. There are both westward and eastward propagation predictive signals in flood years, and only westward spread signals in drought years.

Local and non‐local atmospheric effects of abnormal soil moisture over Indochina during May and June

AbstractIndochina is one of the key areas affecting the East Asian summer monsoon and its thermal condition can modulate the prevailing wind and water vapour transport, especially in the early stages of establishment of the summer monsoon. Previous studies emphasized the climatic effect of the seasonal‐averaged soil moisture (SM), but the subseasonal effects of land surface processes over Indochina are not clear yet. This study investigated the subseasonal effect of SM in Indochina on precipitation in southern China (SC) during May and June together with its relevant mechanism based on both statistical analysis and numerical experiments. Results show that increased SM in Indochina in May is closely associated with increased local (Indochina) precipitation and suppressed non‐local (SC) precipitation in June. The positive SM anomaly over Indochina can persist from May to June, cooling the atmosphere and increasing the specific humidity in the lower troposphere. Meanwhile, the potentially unstable lower troposphere and the ascending motion over Indochina result in strengthened upward moisture advection and condensational heating, which are conducive to forming an abnormal cyclonic circulation and increased precipitation over Indochina. To the northeast, an easterly wind anomaly appears in SC, leading to weakened moisture transport and decreased precipitation. When the SM decreases over Indochina, the opposite results are obtained. Moreover, through increasing and decreasing SM in Indochina in May, numerical experiments showed similar results to those of reanalysis data and further indicated that the moist and thermal processes of the SM anomaly over Indochina play distinct roles in affecting the atmosphere and regional precipitation. The moisture process mainly influences local precipitation, whereas the thermal process can change the precipitation non‐locally. This study highlights the significant local and non‐local impacts of SM in Indochina and could contribute to understanding the physical mechanisms of SM effects.

Amplifying subtropical hydrological transition over China in early summer tied to weakened mid-latitude synoptic disturbances

The rainy season over southern China (SC) begins with the onset of the South China Sea monsoon around mid-May. We demonstrate here that the SC precipitation exhibits a notable drying (wetting) trend prior to (after) the monsoon onset, leading to a more abrupt thus amplified hydrological transition over SC in early summer. The contrasting precipitation trends are largely driven by the recent decline in mid-latitude synoptic eddy activity. Weakened mid-latitude synoptic disturbances suppress SC frontal activities before the monsoon onset, facilitating the drying trend, and enhance the spatial stationarity of the SC monsoonal front after the monsoon onset, leading to the wetting trend. CMIP6 models in general fail to capture the contrasting trends between the two periods. In models where both the trends in precipitation and mid-latitude synoptic eddy activity are well captured, the amplification of the hydrological transition over SC is projected to continue well into the late 21st century. Our results highlight the footprints of hemispheric-scale climate change in regional hydroclimate and the obvious challenges faced by climate models in capturing such footprints.

Impact of Soil Freezing‐Thawing Processes on August Rainfall Over Southern China

AbstractThe impact of soil freezing‐thawing processes on August rainfall in Southern China (SC) during 1979–2008 and related physical mechanisms are investigated using the coupled land‐atmosphere model Grid‐Point Atmospheric Model version 2.0—Community Land Model version 2.0 (GAMIL2.0‐CLM2.0). The moisture‐budget analysis is employed to quantify the contributions of different factors to the change of precipitation in SC. The results indicate that the vertical moisture advection and its dynamic component play an essential role in the long‐term trends of August rainfall. The possible physical mechanism is that the model which includes the supercooled water simulates much higher soil/air temperature in August, especially in the north of 40°N, which is not only weakened the meridional thermal contrast but also induced an anomaly “north high–south low” circulation pattern in the middle and high latitude of Eurasia. Both resulted in the 200 hPa zonal winds weakening, and 850 hpa northerly wind southward moved. Meanwhile, a convergence anomaly cyclone is initiated in the lower troposphere over SC regions, accompanied by enhanced ascending and strong moisture flux convergence, which is beneficial to the increased precipitation. This study provides a new interpretation of the “southern flooding” during 1979–2008 from the point of frozen soil changing.