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Projecting the Summer Climate of Mainland China in the Middle 21st Century: Will the Droughts in North China Persist?
21世纪中叶的中国大陆气候:华北干旱还会持续吗

LI Shuanglin,
李双林

大气和海洋科学快报 , 2008,
Abstract: Since no consensus has been reached in previous studies about how the summer climate in China will evolve in the first half of the 21st century, this issue is addressed here through sensitivity experiments by forcing an atmospheric general circulation model (AGCM), the Geophysical Fluid Dynamics Laboratory (GFDL)’s Atmospheric Model Version 2.0 (AM2) with projected sea surface temperature (SST) trend. A total of two SST trends from the Intergovernmental Panels on Climate Change (IPCC) Special Report on Emissions Scenario (SRES) A1B are used. The two trends are from two coupled climate system models, the National Center for Atmospheric Research (NCAR) Community Climate System Model Version 3.0 (CCSM3) and the GFDL Climate Model Version 2.0 (CM2), respectively. Results consistently suggest a substantial warming and drying trend over much of China, with a surface air temperature increase of 1.0-2.0oC and a 10%-20% decrease in rainfall. Exceptions are the areas from northwestern China to western North China as well as the southern Tibetan Plateau, which are projected to be wetter with a rainfall anomaly percentage increase of 10%-50%. The drying in eastern North China has not been documented to date but appears to be reasonable. Physically, it is attributed to anomalous northeasterly winds at the rear of a low-level cyclone over the South China Sea, the Philippines and the subtropical western North Pacific. These conditions, which govern the climate of eastern China, are forced by the northward shift of convection over warm waters due to additional warming.
The nature of the rainfall onset over central South America
GONZáLEZ, M.;VERA, C. S.;LIEBMANN, B.;MARENGO, J. A.;KOUSKY, V.;ALLURED, D.;
Atmósfera , 2007,
Abstract: the objective of this work is to provide a detailed description of the onset of the south american monsoon based on precipitation observations available over tropical and subtropical south america. the analysis was also performed using outgoing longwave radiation (olr) data in order to assess the ability of this particular dataset to reproduce the main features associated with precipitation evolution during austral spring. results show that both olr and precipitation data agree in describing the progression of convection from the northwest and southeast into central brazil by the beginning of october. moreover the assessment of available methods to identify onset dates shows that the method of kousky (1988), based on the olr evolution, provides the onset date in most of south america, without regionally adaptation, as the methods based on rainfall generally require. composite fields show that rainfall in central brazil begins with moderate rates, which are still lower than those observed over the northwestern and southeastern tropical regions. after the rainfall jump, that on average occurs three pentads later than the onset of rainfall, precipitation rates increase over central brazil and similar rates are observed over the entire tropical region. it is suggested that transient activity, which occurs around the onset period when the atmospheric mean conditions are getting more unstable as they approach summer-like conditions, is the one that imprints a rainfall-jump feature in the precipitation evolution. the character of changes in the precipitation rate, as the rainy season develops, provides complementary information that can be used together with onset date.
Simulated Change in the Interannual Variability of South Asian Summer Monsoon in the 21st Century

FU Yuanhai,LU Riyu,

大气科学进展 , 2010,
Abstract: This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO--monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change (IPCC) scenarios A1B and A2, respectively, by analyzing the simulated results of twelve Coupled Model Intercomparison Project Phase 3 (CMIP3) coupled models. The dynamical monsoon index (DMI) was adopted to describe the interannual variability of South Asian summer monsoon, and the standard deviation (SD) was used to illustrate the intensity of interannual variability. It was found that most models could project enhanced interannual variability of monsoon in the 21st century. The multi-model ensemble (MME) results showed increases in the interannual variability of DMI: 14.3% and 20.0% under scenarios A1B and A2, respectively. The MME result also showed increases in the rainfall variability are of about 10.2% and 22.0% under scenarios A1B and A2. The intensification of interannual variability tended to occur over the regions that have larger variability currently; that is, ``the strong get stronger'. Another finding was that ENSO--monsoon relationships are likely to be enhanced in the 21st century. The dynamical component of the monsoon will be more closely correlated to ENSO in the future under global warming, although the ENSO--summer rainfall relationship cannot be reasonably projected by current models. This suggests that the South Asian summer monsoon is more predictable in the future, at least dynamically.
Projected change in the relationship between East Asian summer rainfall and upper-tropospheric westerly jet
Yi Dai,RiYu Lu
Chinese Science Bulletin , 2013, DOI: 10.1007/s11434-012-5540-1
Abstract: The authors analyzed the interannual variability in summer precipitation and the East Asian upper-tropospheric jet (EAJ) over East Asia under the Historical and Representative Concentration Pathways Scenarios (RCPs, including RCP4.5 and RCP8.5), using outputs of 17 Coupled Model Intercomparison Project phase 5 (CMIP5) coupled models. The analyzed results indicate that the models can reasonably reproduce relatively stronger interannual variability in both East Asian summer rainfall (EASR) and EAJ. These models can also capture the relationship between the rainfall anomaly along the East Asian rain belt and meridional displacement of the EAJ. Projected results suggest that the interannual variabilities in precipitation along the East Asian rain belt and in the EAJ are enhanced under the scenarios RCP4.5 and RCP8.5 in the 21st century, which is consistent with the previous studies. Furthermore, it is found that the relationship between the East Asian rainfall and the meridional displacement of the EAJ is projected to be stronger in the 21st century under the global warming scenarios, although there are appreciable discrepancies among the models.
The spring soil moisture and the summer rainfall in eastern China
ZhiYan Zuo,RenHe Zhang
Chinese Science Bulletin , 2007, DOI: 10.1007/s11434-007-0442-3
Abstract: The relation between the soil moisture in spring and the rainfall in summer in eastern China is investigated. Results show that the summer rainfall in eastern China is closely related to the spring soil moisture in the area from North China to the lower reaches of Yangtze River (NCYR). When spring soil moisture anomalies over NCYR are positive, the summer precipitation exhibits positive anomalies in Northeast China and the lower reaches of Yangtze River, and negative anomalies in southern China and North China. The higher soil moisture over NCYR cools land surface and reduces the land-sea temperature gradient, which weakens East Asian summer monsoon. The western Pacific Subtropical High (WPSH) is located to the south and shifts westward, resulting in more rainfall in the lower reaches of Yangtze River and less in southern China and North China.
Variability and Trends of Summer Monsoon Rainfall over Bangladesh  [PDF]
MN Ahasan,Md AM Chowdhary,DA Quadir
Journal of Hydrology and Meteorology , 2010, DOI: 10.3126/jhm.v7i1.5612
Abstract: In this paper, the updated rainfall data of 50 years (1961-2010) for 30 selected rain gauge stations of Bangladesh have been used. The data were analyzed to investigate the variability and trends of summer monsoon (June- September) rainfall over Bangladesh. The possible teleconnection of monsoon rainfall variability with ENSO has also been investigated. Annual profile of the station mean monthly rainfall of Bangladesh shows a unimodal pattern with high rainfall between June-September (monsoon season) with highest in July and low rainfall between December – February with lowest in January. All Bangladesh mean summer monsoon rainfall is 1769.14 mm, standard deviation 209.16 mm (coefficient of variance 11.82 %) and annual country average rainfall is 2456.38 mm. Summer monsoon rainfall widely varies over the geographical areas with lowest in central-western part and highest in southeastern part with next highest in northeastern part of the country. The trend analysis shows that the trend of the country average monsoon rainfall is decreasing (-0.53 mm/year). The spatial distribution of the trend values indicates that the summer monsoon rainfall exhibits increasing trends at the rate of 5-6 mm/year in the NW region and 3-4 mm/ year in the south-central and extreme SE region. The eastern region exhibits decreasing trends of about -2 to -7 mm/year with highest (-6 to -7 mm/year) in the east-central part. The time series plot of country average summer monsoon rainfall shows the inter-annual variability in the timescales of 2-3 years and 4-6 years. The time series of 5 year moving average reveals existence of low frequency variability of timescales of 9-14 years. The time series of Bangladesh monsoon rainfall shows that there were 11 strong monsoon years and 8 weak monsoon years within the periods of 1961-2010 (50 years). The analysis of the decadal mean rainfall shows that the decades 1961-1970 and 1981-1990 were wet and the decades 1971-1980, 1991-2000 and 2001-2010 were dry. Floods in Bangladesh result from the excess rainfall occurring both inside and outside the country. Summer monsoon rainfall is characterized by active and weak (break) spells, which are associated with the fluctuation of monsoon rainfall in the time scales of 20-25 and 40-50 days. Such fluctuations are caused due to north-south movement of the monsoon trough. The fluctuations in the time scales of 4-7 and 10-14 days are associated with the formation of low pressure systems over the head Bay. The possible atmospheric teleconnections of summer monsoon rainfall with ENSO have also been
EXCESS RAINFALL IN THE SUMMER 2011, RISK PHENOMENON IN TRANSYLVANIA
NICOLAE RUSAN,ADRIAN PA?OL
Aerul ?i Apa : Componente ale Mediului , 2012,
Abstract: Excess rainfall in the summer 2011, risk phenomenon in Transylvania, highlight precipitation quantities that in the warm season become more abundant due to general circulation intensity of the atmosphere, as well as to the increasing role of thermal convection that develops in unstable air masses, which is also reflected in the amount of precipitation. In summer months, the most abundant rainfall falls due to thermal convection in most cases. Excess rainfall may be present in any season of the year.They are emphasized by the largest amounts of annually, monthly precipitation, by the absolute maximum amounts of precipitation in 24 hours, by the frequency of heavy rains and the days that exceed 10 l /m2. We can say that the excess rainfall often lead to destruction and unimaginable damage.
Arctic dipole anomaly and summer rainfall in Northeast China
BingYi Wu,RenHe Zhang,D’Arrigo Rosanne
Chinese Science Bulletin , 2008, DOI: 10.1007/s11434-008-0229-1
Abstract: A dipole structure anomaly in summer Arctic atmospheric variability is identified in this study, which is characterized by the second mode of empirical orthogonal function (EOF) analysis of summer monthly mean sea level pressure (SLP) north of 70°N, accounting for 12.94% of the variance. The dipole anomaly shows a quasi-barotropic structure with opposite anomalous centers over the Canadian Arctic and the Beaufort Sea and between the Kara Sea and the Laptev Sea. The dipole anomaly reflects alternating variations in location of the polar vortex between the western and eastern Arctic regions. The positive phase of the dipole anomaly corresponds to the center of the polar vortex over the western Arctic, leading to an increase in summer mean rainfall in Northeast China. The dipole anomaly has a predominant 6-year periodicity, and shows interdecadal variations in recent decades.
Trend Analysis of Water Pollutant at Summer Rainfall Season  [PDF]
Youngshin Lee, Sanghee Shin
Journal of Environmental Protection (JEP) , 2014, DOI: 10.4236/jep.2014.54026
Abstract:

This study, with Hongdong Reservoir, is intended to evaluate the changes in water quality in the lake before and after rainfall in summer. Various non-point source pollutions are scattered around the reservoir, and to determine the pollution level by pollution source, samples were taken at the same point before rainfall (1st), during rainfall (2nd) and after rainfall (3rd) and concentration was measured. Pollutant concentration curve at the measuring points (HDS1, HDS2, HDS3) appeared to be similar with the hydrological curve. When comparing the concentration immediately before rainfall with event mean concentration (EMC), SS and COD were 4 - 59 times and 1 - 4 times, respectively. However, when it comes to total nitrogen (T-N), concentration arrived at the reservoir stayed the range of 1.3 - 12.0 mg/L in all 3 cases without significant variation, which indicated that total nitrogen load is critical when arriving at the reservoir, irrespective of rainfall, and thus it’s necessary to consider non-point source pollution runoff also in addition to point source pollution when developing the water quality improvement measures in reservoir.

Significant relationship between spring AO and the summer rainfall along the Yangtze River
Daoyi Gong,Jinhong Zhu,Shaowu Wang
Chinese Science Bulletin , 2002, DOI: 10.1360/02tb9212
Abstract: The influence of spring AO on the summer rainfall along the Yangtze River is investigated. The long-term rainfall observations are filtered to remove the low-frequency variations longer than 10 years. The inter-annual components show a high correlation to AO in the last hundred years. The strongest correlation appears for May AO and summer rainfall with a value of 0.39, significant above the 99% confidence level. Associated with one standard deviation stronger May AO index, the rainfall over the Yangtze River to the southern Japan decreases by about 3%-9%, while, at the same time increases by about 3%–6% in the northern China and far-eastern Russia. The coherent changes in rainfall are significantly related to the East Asian summer jet stream in the upper troposphere. When there is stronger AO in spring, the jet stream tends to move polarward in summer, and leads the rainfall-belt to move northward too. That gives rise to a drier condition in the Yangtze River valley, wetter anomalies in northern China. This signal would be helpful for the summer rainfall prediction in China.
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