North China Rainfall Research Articles

Impact of the thermal contrast between the Arabian Sea and the Iranian Plateau on the interannual variability of the East Asian summer monsoon

Abstract The land–sea thermal contrast is known to have a significant impact on the atmospheric circulation. We investigated the influence of the thermal contrast between the Arabian Sea (AS) and the Iranian Plateau (IP) on the interannual variability of the East Asian summer monsoon (EASM). It is found that the thermal distribution of AS–IP exhibits a fixed dipole mode. When the apparent heat over AS (IP) is higher (lower) than normal, summer rainfall is abundant over the mid- and lower reaches of the Yangtze River and Japan with the adjacent maritime regions. By contrast, there is lower rainfall in North China and the coastal regions of South China. We attribute this phenomenon to the propagation of mid-latitude Rossby waves, which play a crucial role in regulating the atmospheric circulations on East Asia and the Northwest Pacific. Significant anomalies in the transport of water vapor were seen in our statistical analyses and were partly reproduced by the Linear Baroclinic Model and Weather Research and Forecasting model experiments. The anticipated outcomes of this research will help to identify another factor related to the variability of the EASM, and provide a scientific basis for understanding the distribution and interaction of thermal anomalies on the plateau system and the Indian Ocean.

Ridge planting increases the rhizosphere microbiome diversity and improves the yield of Pinellia ternata (Thunb.) Breit in North China.

Pinellia ternata (Thunb.) Breit is an important traditional Chinese medicine. In North China, conventional flat planting of P. ternate is prone to root rot during the rainy season, leading to severe yield loss. Variations in planting patterns (e.g., ridge planting) can effectively alleviate this situation. However, the relationship between planting patterns and the changes induced by rhizosphere microbiome still needs to be determined. In this study, we clarified the effect of ridge planting on the yield of P. ternata and rhizosphere microbial community using high-throughput amplicon sequencing of 16S rRNA. Field experiments showed that ridge planting could increase the yield of P. ternata by 72.69% compared with flat planting. The high-throughput sequencing results demonstrated that fungal and bacterial communities in rhizosphere siols of flat and ridge planting showed obvious difference in diversity, structure, relative abundance, and community composition. The fungal phyla Zygomycota, Basidiomycota, Glomeromycota, and the bacterial phyla Chlamydiae, Tenericutes, and Hydrogenedentes were present in a higher relative abundance in the rhizosphere of ridge planting. Adonis multivariate analysis of variance results showed that 29 bacterial genera were significantly up/down-regulated, and only 4 fungal genera were changed considerably in ridge planting soil, indicating that the bacterial community composition varied significantly between the two treatments. Correlation analysis revealed that the yield of P. ternata was positively correlated with fungal genera Emericellopsis while negatively correlated with bacterial genera Acetobacter, Iamia, and fungal genera Thielavia. Overall, this study showed that ridge cropping significantly impacts the diversity and composition of the rhizosphere microbiome. It creates an environment favorable for crop growth and can be an effective planting strategy for P. ternata in areas with irrigation and high monsoon rainfall in North China.

Enhanced rainfall in North China in July 2021: Role of the North Pacific SST gradient

The rainfall over North China (NC) in July 2021 was the most since 1980, and coincided with a meridional gradient of sea surface temperature anomaly (MGSSTA) in the Pacific. The present study shows that the gradient between the positive sea surface temperature anomaly (SSTA) over the northwestern Pacific and the negative SSTA over the tropical central Pacific was the main reason for the enhanced rainfall in NC in July 2021 because of its influence on the anomalous northward movements of the western North Pacific anticyclone (WNPAC) and its southern cyclone. The associated easterly wind anomalies along the southern flank of the WNPAC converged with the anomalous easterly along the north flank of the anomalous cyclone, transporting more moisture from south to NC. Meanwhile, the MGSSTA likely induced an anomalous reversed Hadley circulation accompanied by distinct southerly wind anomalies in the low troposphere. These anomalies favored a strong monsoon circulation, which is often accompanied by a rain band in a more northern location.摘要2021年7月, 华北地区的降水量突破1980年以来的极值, 这与太平洋海温异常的经向梯度相吻合. 研究表明, 西北太平洋正海温异常与热带中太平洋负海温异常之间的梯度是2021年7月华北地区降水异常偏多的主要原因, 该梯度使得西北太平洋反气旋及其南部的气旋北移, 汇合的偏东风将大量水汽从海洋输送到华北地区, 使得华北地区降水偏多. 同时, 太平洋海温异常的经向梯度可能在对流层低层触发异常的反向哈德利环流, 伴随着南风异常, 使得季风环流增强, 雨带偏北.

Links Between Orbital Forcing, Antarctic Ice Volume, and the East Asian Hydrological Cycle Over the Pliocene

AbstractRevealing the evolution of monsoonal intensity through the Pliocene on orbital timescales is of potential utility for providing insights into the response of Asian monsoons to future high pCO2 scenarios. Here, we report a continuous Pliocene cyclostratigraphic record from lake deposits of the Xinding Basin, Shanxi Graben, North China, and reconstruct the regional hydrological cycle from this location during ∼5.2 to 2.56 Ma. Our results show that regional hydrological cycling was consistently dominated by long‐and short‐eccentricity (405‐and 100‐kyr) forcing over the Pliocene. Gamma‐ray (GR) data (reflecting hydrodynamic changes) show strengthened 100‐kyr eccentricity power after ∼3.5 Ma, whereas 100‐kyr eccentricity power preserved in magnetic susceptibility (MS; interpreted as a proxy of pedogenesis and magnetic mineral dissolution) slightly weakened after ∼3.5 Ma. This orbital power transition at the 100‐kyr eccentricity scale may link to expansion of Antarctic ice volume after ∼3.5 Ma, which enhanced East Asian summer monsoon intensity and thus increased summer rainfall in North China, resulting in changes to hydrological cycling and the expression of eccentricity climate forcing in East Asian basins. In addition, our results demonstrate that the orbital configuration at ∼4.2–4.4 Ma could have been a contributory factor in strengthening the intensity of the East Asian summer monsoon at this time.

Unprecedented July Rainfall in North China in 2021: Combined Effect of Atlantic Warming and Arctic Sea‐Ice Loss

AbstractRecord‐breaking July‐mean precipitation hit North China in 2021, resulting in huge economic losses and human casualties. The prevailing easterlies over the southern flank of a remarkable anomalous anticyclone centered over the Kuril Islands transported sufficient water vapor into North China, resulting in persistent downpours on the windward side of the North China Plain. The anomalous anticyclone was a portion of the Eurasian Rossby wave trains. The record‐high Atlantic sea surface temperature anomalies induced the Rossby wave trains, which ended with an anomalous anticyclone over the Kuril Islands; meanwhile, the record‐low sea‐ice concentration over the Laptev–East Siberian Seas reinforced the anomalous anticyclone. Therefore, the combined effect of Atlantic and Arctic thermal forcings caused the record‐breaking July‐mean rainfall in North China in 2021. Using these two boundary layer forcings as independent predictors to run a multiple regression model produced encouraging hindcasting skills.

Water vapour multi-vortex structure under the interactions of typhoons and mid-low latitude systems during extreme precipitation in North China

With diverse atmospheric circulation and complex mechanisms, typhoon remote rainstorms (TRR) are closely related to a variety of mid-low latitude systems. The anomalous signatures in such processes can improve forecasting heavy rainfall associated with typhoons and fill the gaps in current physical conceptual models of TRR. Using the optimal typhoon path dataset, ground observation data, and the National Centres for Environmental Prediction (NCEP) reanalysis dataset, the impact of anomalous water vapour transport on excessive rainfall in North China is investigated. The vector empirical orthogonal function (VEOF) analysis is applied to typhoon precipitation events from 1970 to 2021, and three major modes are extracted to reflect the anomalous water vapour transport for typhoon precipitation. Mode 1 reflects a moisture circulation pattern in North China due to the coexistence of typhoons and remote and direct precipitation, with the highest probability of heavy precipitation. The differences in remote precipitation areas and intensities are attributed to the location of typhoons in the western North Pacific and the shifting of the subtropical high ridge. To characterise the water vapour transport circulation of TRR in North China, we proposed the ‘multi-vortex’ idea. The transmission of the multi-vortex ensures a continuous supply of TRR water vapour, and the enhancement of the multi-vortex is significantly linked to the enhancement of remote precipitation. Three extreme northern rainstorms, 75·8 Henan, 7·21 Beijing, and 7·20 Zhengzhou rainstorms, have anomalous multi-vortex water vapour convergence, similar to Mode 1. The mechanism of water vapour driven by multi-vortex in the three severe rainstorm events is more extreme than in usual TRR events in North China. The stronger Indian low vortex and relatively southerly subtropical highs can intensify the southwest branch of the double water vapour transport branch, whereas the strengthening of typhoons in the western North Pacific facilitates water vapour transport through the channel on the southwestern side of the subtropical highs and then transports it to key rainstorm areas, promoting TRR development. Therefore, the combination of subtropical highs, typhoons, and the anomalous multi-vortex structure may help in the establishment of key indicators of extreme precipitation in North China.

Coupling of the ecosystems in North China with the East Asian summer monsoon rainfall during the Holocene

The influence of Holocene East Asian Summer Monsoon (EASM) rainfall on ecosystems over northern China remains controversial: delay or synchronization. Here we present Holocene quantitatively reconstructed temperature and salinity records based on alkenone proxies in the Dali Lake from northern China. Our data indicate that the Dali Lake was significantly diluted to a freshwater lake (0.8 ± 0.4 g/L) during ∼11.4–3.8 cal ka BP, relative to the modern brackish state. From the early Holocene (before 8.0 cal ka BP) to the middle Holocene (8.0–5.0 cal ka BP), the average salinity value of Dali Lake decreased by ∼0.3 g/L (ca. 30%), but our reconstructed temperature record shows an increase of ∼2.1 °C. In the context of climate warming, the evaporation was enhanced, and thus the decline in salinity is attributed to the increased precipitation, indicating a mid-Holocene EASM rainfall maximum. After comparing our reconstruction with vegetation data, we proposed that the stable and abundant EASM rainfall promoted the forest expansion and vegetation recovery over northern China during the mid-Holocene, suggesting the coupling of ecosystems and EASM rainfall in North China.

Warmer SSTs in the Equatorial Eastern Pacific Delay the Seasonal March of the Asian–Pacific Summer Monsoon Onset

Abstract This study investigates the impact of El Niño–Southern Oscillation (ENSO) on the seasonal evolution of the Asian–Pacific summer monsoon. The results show that during the summers when the SSTs in the equatorial eastern Pacific are above normal (i.e., during developing El Niño), the seasonal march of the Asian–Pacific summer monsoon is delayed. Specifically, the stepwise northeastward extension of the western North Pacific monsoon and the northward migration of East Asian and Indian monsoon are all delayed, resulting in rainfall deficiency in the western North Pacific and India, and more rainfall in the Yangtze River valley but less rainfall in North China due to the delayed northward migration and resultant prolonged rainy season in the Yangtze River valley. In addition, the seasonal march of the Asian upper-tropospheric westerly jet, which is mainly characterized by the northward migration during the monsoon development, is also delayed, concurrent with the delayed march of monsoonal rainfall. During La Niña summers, however, the seasonal march of the monsoon and Asian jet does not exhibit clear variations, suggesting asymmetrical impacts between El Niño and La Niña. Furthermore, we explain these variations in the seasonal evolution of rainfall and jet and the asymmetrical impacts between El Niño and La Niña through the variations in tropical tropospheric temperatures and the resultant changes in meridional temperature gradient. Significance Statement The seasonal march of the Asian–Pacific summer monsoon exhibits large spatial and temporal variations, but shows some regular features such as stepwise northward migrations. The impacts of ENSO on the seasonal evolution of the components of Asian–Pacific summer monsoon have been shown in previous studies. However, there have been remarkable uncertainties in the previous results, and more emphasis has been put on the impacts of preceding ENSO. This study starts from El Niño and La Niña summers to reduce uncertainty caused by defining the seasonal march of the monsoon, and includes the variations in circulations that correspond well to monsoonal rainfall, making the conclusions more reliable.

The Effect of Rainfall on Aquatic Nitrogen and Phosphorus in a Semi-Humid Area Catchment, Northern China.

The impact of rainfall on water quality may be more important in semi-arid regions, where rainfall is concentrated over a couple of months. To explore the impact of rainfall changes on water quality, e.g., nitrogen (TN) and phosphorous (TP), the diversion from Luan River to Tianjin Watershed in the northern semi-humid area was selected as the study area. TN and TP concentrations in rivers and the Yuqiao Reservoir during the three-year high-flow season (2019–2021) were analyzed. The response relationship and influencing factors among the watershed’s biogeochemical process, rainfall, and water quality were clarified. The results showed that rainfall in the high flow season mainly controlled the river flow. The concentration of TN and TP in the inflow rivers is regulated by rainfall/flow, while the concentration of TN and TP in the water diversion river has different variation characteristics in the water diversion period and other periods. The lowest annual concentrations of TN and TP were observed in the normal year, while the highest annual concentration was observed in the wet year, indicating that the hydrological process drove the nutrient transport in the watershed. For the tributaries, the Li River catchment contributed a large amount of N and P to the aquatic environment. For the reservoir, the extreme TN concentrations were the same as the tributaries, while the extremes of TP concentrations decreased from the dry year to wet year, which was in contrast to the tributaries. The spatial variation of TN and TP concentrations in the reservoir showed that the concentration decreased following the flow direction from the river estuary to the reservoir outlet. Considering climate change, with the increase of rainfall in North China in the future, the TN and TP transport fluxes in the watershed may continue to increase, leading to the nitrogen and phosphorus load of the downstream reservoir. To ensure the impact of the increase of potential N and P output fluxes in the watershed on the water quality of the reservoir area, it is necessary to strengthen the effective prevention and control of non-point source pollution in the watershed.

The strengthening relationship between summer rainfall over North China and PDO since the mid-2000s

The interdecadal change of the summer (July–August) rainfall over North China (SRNC) is of great concern to the climate research community. Based on the sliding correlation and interdecadal difference analysis, the interdecadal change of SRNC was studied. Results show a significantly wetter period of SRNC since the mid-2000s, which was associated with strengthening negative relationship between SRNC and PDO. PDO affected the SRNC through the jet stream in the upper-level and the East Asia–Pacific (EAP) teleconnection pattern. In the negative phase of the PDO since the mid-2000s, the contractive upper-level jet stream in the west of North China resulted in the abnormal updraft over the southern region of North China. Meanwhile, the positive phase of the EAP teleconnection pattern brought warm and wet southeast flow entering North China from its eastern boundary, both bringing more rainfall in North China. The abnormal water vapor transport from the western Pacific was very different from that accompanying the East Asian summer monsoon.

Comparison of Two Kinds of Momentum Control Variables in 3DVAR During Assimilating Low-resolution Observations in a Convective-scale Model: a Case Study of Torrential Rainfall in North China

Comparison of Two Kinds of Momentum Control Variables in 3DVAR During Assimilating Low-resolution Observations in a Convective-scale Model: a Case Study of Torrential Rainfall in North China

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.

Case studies of atmospheric rivers over China and Australia: new insight into their rainfall generation

While the Australia–Asian (A-A) monsoon is a prominent feature of weather and climate in China and Australia, there are significant differences in their dominant weather patterns and climate drivers. In order to explore different characteristics of atmospheric rivers (ARs) affecting weather and climate in these two countries, this paper compares two typical AR events that occurred in the boreal summer (austral winter) in 2016. The event in China produced record-breaking rainfall in North China, whereas the event in Australia was accompanied by a classic Northwest Cloud Band (NWCB) and produced a rainfall belt across the continent. Using global reanalysis products and ground-based observational data, we analysed the synoptic backgrounds, vertical structures, water vapour sources and relationship between ARs and cloud distributions. In both China and Australia, heavy precipitation was triggered by strong water vapour transport by ARs ahead of midlatitude frontal systems. The main differences between these two AR events and their associated rainfall effectiveness were that (i) the AR intensity in the Asian summer monsoon was stronger than that in the austral winter season over Australia; (ii) the centre of AR maximum moisture transport in China was around 850 hPa, whereas in Australia, it was located at around 700 hPa; and (iii) the AR-induced rainfall was heavier in China than in Australia. These differences were caused by numerous factors, including a lack of topographic influence, a dry climate background in Australia, and different interactions between warm and moist air conveyed by ARs from the tropics with cold air from the midlatitudes. We paid particular attention to the relationship between the Australian AR and its associated cloud structure and rainfall to understand precipitation efficiency of the NWCB. In addition, we assessed the forecast skills of an Australian numerical weather prediction system (ACCESS-APS2) for the two events with different lead times. The model produced reasonable forecasts of the occurrence and intensity of both AR events several days in advance, and the AR forecast skill was better than its forecasts of rainfall location and intensity. This demonstrates the value of using AR analysis in guiding extreme rainfall forecasts with longer lead time.

Asymmetric impact of East Asian jet’s variation on midsummer rainfall in North China and Yangtze River Valley

Variations of East Asian subtropical westerly jet (EAWJ) have a close relationship with the midsummer rainfall anomalies in Yangtze River Valley (YRV) and North China (NC). The present study shows that the relationship is asymmetric. When EAWJ is located north (south) of its median position for 1979–2013, EAWJ’s southward displacement is associated with the increased (decreased) rainfall anomalies in NC and no obvious (increased) rainfall anomalies in YRV; and vice versa. The mechanism is as follows. EAWJ’s southward displacement is associated with northward flow anomalies over NC and YRV, when EAWJ is located north of the median position. The associated moisture convergence and warm advection anomalies over NC cause increased rainfall anomalies in NC, while rainfall anomalies in YRV are weak due to the weak thermal advection and water vapor convergence/divergence anomalies. When EAWJ is located south of the median position, anomalous southwestward and eastward flow are observed over NC and YRV, respectively, associated with EAWJ’s southward displacement. The resultant cold advection anomalies over NC cause decreased rainfall anomalies in NC, while the resultant anomalous warm advection and moisture convergence over YRV cause positive rainfall anomalies in YRV. The asymmetric circulation changes responsible for the asymmetric rainfall changes in YRV&NC are quasi-barotropic, implying that EAWJ is among the large-scale environmental forcings for the asymmetric rainfall variability in NC&YRV.

Improving the prediction skill for China summer rainfall through correcting leading modes in Beijing Climate Center's Climate System Model

In this study, the performance of Beijing Climate Center's Climate System Model (BCC_CSM) is analysed in terms of China summer rainfall prediction, especially its capability to reproduce the spatial structure and temporal variation of the leading modes of empirical orthogonal function decomposition. Results show that the BCC_CSM has predictability for the summer mean rainfall pattern, namely, reproducing more rainfall in South China and maritime area, and less rainfall in North China and inland area. The model can reproduce the spatial pattern of the first two leading modes of observed summer rainfall; however, it fails to show correct interannual variability of the first two principle components, which may lead to a low skill in summer rainfall anomaly prediction over most parts of China. The leading mode‐based correction (LMC) method is then applied for the post processing procedure to correct prediction errors. Cross validation confirms that the LMC method can integrate the historical spatial pattern information of observed summer rainfall with the original model prediction, making the corrected model output better reflect spatial structure of the leading modes and their interannual variation. Compared with the original model output, the positive temporal correlation coefficient area for the corrected China summer rainfall anomalies is thus increased, and the average spatial correlation coefficient during 1991–2015 is improved from −0.01 before the correction to 0.17. The LMC method shows its potential for improving the prediction skill of BCC_CSM, which can be used in operational prediction.

Optimizing planting date and supplemental irrigation for potato across the agro-pastoral ecotone in North China

Abstract Adjusting planting date along with supplemental irrigation is widely used to improve potato yield in the agro-pastoral ecotone (APE) with high variability of limited rainfall in North China. Optimal planting date and supplemental irrigation time for potato differed greatly with climate and soil conditions, and were not fully investigated via field experiments. In this study, using APSIM-Potato model carefully calibrated and validated with two-years serial planting experimental data, the individual and coupled impacts of planting date and supplemental irrigation time on yield and water productivity (PWP) of potato were quantified across the APE. APSIM-Potato performed well in simulating phenology, leaf area index (LAI), soil water dynamics, biomass of potato, and also captured the trend in potato yields under different planting dates. Based on the long-term simulations from 1981 to 2010, the optimal planting dates were May 10 (local normal planting date), May 20 and May 30 in the eastern, middle and western APE, respectively. Yield and PWP of potato could be increased by 12.5% and 7.0% in the middle APE, 23.3% and 18.3% in the western APE respectively, under the optimal planting date compared with the local normal planting date under rainfed condition. Supplemental irrigation (8-55 mm) from rainwater harvesting could increase potato yield by 3.5-35.2%, 6.9-41.8%, and 9.0-50.8% respectively, in the eastern, middle and western APE. The corresponding PWP could be enhanced by 1.2-22.7%, 6.7-30.8% and 4.5-33.7%, respectively. Combining the optimal planting date with better scheduling the maximal harvested rainwater could increase yield and PWP of potato by 36.8% and 23.4%, 69.2% and 49.2%, 64.3% and 48.8%, respectively for the eastern, middle and western APE, compared with the simulation results under the local normal planting dates and rainfed condition. The study suggested a large potential of increasing yield and PWP of potato across the APE by optimizing planting date and better scheduling the supplemental irrigation from rainwater harvesting.

Weakened Impact of the Indian Early Summer Monsoon on North China Rainfall around the Late 1970s: Role of Basic-State Change

Abstract Previous studies have found a link between north China and Indian rainfall during summer, with significantly increased rainfall in north China related to a stronger Indian summer monsoon. This link is weakened after the late 1970s, generally attributed to the reduced magnitude of interannual variability in the Indian summer rainfall. This study reveals a similar change in this rainfall link in early summer after the late 1970s. Related to a heavier Indian early summer rainfall, rainfall in north China enhances significantly before the late 1970s but not thereafter. The change in rainfall teleconnection is caused by the weakened impact on north China rainfall of a midlatitude wave train along the Asian jet in the upper troposphere. After the late 1970s, the portion of the wave train over East Asia displaces eastward, leading to an eastward shift in the associated ascending motion and, subsequently, enhanced rainfall from north China to the Yellow Sea. Moreover, the change in the midlatitude wave train is attributed to the change in the basic state over East Asia (i.e., a northward shift of the East Asian upper-tropospheric westerly jet after the late 1970s). The latter reduces stationary Rossby wavenumber and increases wavelength of the midlatitude wave train, leading to an eastward shift of the wave train over East Asia. Therefore, in this study a mechanism is proposed for the change in early summer, different from the previous mechanism for the entire summer period.

The East Asian summer monsoon variability over the last 145 years inferred from the Shihua Cave record, North China

The precipitation variability associated with the East Asian summer monsoon (EASM) has profound societal implications. Here, we use precisely dated and seasonally-resolved stalagmite oxygen isotope (δ18O) records from Shihua Cave, North China to reconstruct the EASM variability over the last 145 years. Our record shows a remarkable weakening of the EASM strength since the 1880s, which may be causally linked to the warming of the tropical Pacific and Indian Oceans. The δ18O record also exhibits a significant ~30-year periodicity, consistent with the instrumental, historical and proxy-based rainfall records from North China, plausibly driven by the Pacific Decadal Oscillation (PDO). Together, these observations imply that ~30-year periodicity is a persistent feature of the EASM, which remains significant with or without anthropogenic forcing. If indeed, the EASM rainfall in North China might decline significantly in the near future, which may affect millions of people in this region.

The impacts of the Indian summer rainfall on North China summer rainfall

Previous studies have indicated a connection between interannual variations of the Indian and North China summer rainfall. An atmospheric circulation wave pattern over the mid-latitude Asia plays an important role in the connection. The present study compares the influence of the above-normal and below-normal Indian summer rainfall on the North China summer rainfall variations. Composite analysis shows that the mid-latitude Asian atmospheric circulation and the North China rainfall anomalies during summer tend to be anti-symmetric in above-normal and below-normal Indian rainfall years. Analysis indicates that the Indian-North China summer rainfall relation tends to be stronger when larger Indian rainfall anomaly occurs during a higher mean rainfall period. The observed long-term change in the Indian-North China summer rainfall relationship cannot be explained by the impact of the El Nino-Southern Oscillation (ENSO). The present study evaluates the Indian-North China summer rainfall relationship in climate models. Analysis shows that the Indian-North China summer rainfall relationship differs largely among different climate models and among different simulations of a specific model. The relationship also displays obvious temporal variations in both individual and ensemble mean model simulations. This suggests an important role of the atmospheric internal variability in the change of the Indian-North China summer rainfall relationship.

Assessment of the Pacific decadal oscillation’s contribution to the occurrence of local torrential rainfall in north China

On 21–22 July 2012, torrential rains hit North China, with the daily precipitation record at Beijing station reaching 160.6 mm; this event is named the Beijing 7–21 case. This paper assesses the likelihood of the occurrence of local torrential rains, such as the Beijing 7–21 case, from the perspective of climate variability. In particular, the influence of the Pacific Decadal Oscillation (PDO) is assessed. There were five extreme events, with daily precipitation records equal to or larger than 160.6 mm, at Beijing station during the period 1951–2012; all of these events happened during negative phases of the PDO. The present analysis indicates that precipitation events more extreme than the Beijing 7–21 case should happen more than once per decade during negative phases of the PDO, but only about once every four decades during positive PDO phases. The negative phase of the PDO is found to be associated with a much greater probability of daily records of southerly winds in North China during summer. Strong southerly summer monsoons are deemed favorable for increasing the occurrence of local extreme rainfall over North China.