Impact of Anthropogenic Aerosols on Summer Precipitation in the Beijing–Tianjin–Hebei Urban Agglomeration in China:Regional Climate Modeling Using WRF-Chem

The WRF model with chemistry(WRF-Chem) was employed to simulate the impacts of anthropogenic aerosols on summer precipitation over the Beijing–Tianjin–Hebei urban agglomeration in China. With the aid of a high-resolution gridded inventory of anthropogenic emissions of trace gases and aerosols, we conducted relatively long-term regional simulations,considering direct, semi-direct and indirect effects of the aerosols. Comparing the results of sensitivity experiments with and without emissions, it was found that anthropogenic aerosols tended to enhance summer precipitation over the metropolitan areas. Domain-averaged rainfall was increased throughout the day, except for the time around noon. Aerosols shifted the precipitation probability distribution from light or moderate to extreme rain. Further analysis showed that the anthropogenic aerosol radiative forcing had a cooling effect at the land surface, but a warming effect in the atmosphere. However, enhanced convective strength and updrafts accompanied by water vapor increases and cyclone-like wind shear anomalies were found in the urban areas. These responses may originate from cloud microphysical effects of aerosols on convection, which were identified as the primary cause for the summer rainfall enhancement.     

Numerical Study of the Effect of Anthropogenic Aerosols on Spring Persistent Rain over Eastern China

The eff ect of anthropogenic aerosols on the spring persistent rain （SPR） over eastern China is investigated by using a high-resolution Community Atmosphere Model version 5.1 （CAM5.1）. The results show that the SPR starts later due to anthropogenic aerosols, with a shortened duration and reduced rainfall amount. A reduction in air temperature over the low latitudes in East Asia is linked to anthropogenic aerosols;so is a weakened southwesterly on the north side of the subtropical high. Meanwhile, air temperature increases signifi cantly over the high latitudes. This north-south asymmetrical thermal eff ect acts to reduce the meridional temperature gradient, weakening the upper-level westerly jet over East Asia and the vertical motion over southeastern China. As a result, the SPR is reduced and has a much shorter duration. The indirect eff ect of anthropogenic aerosols also plays an important role in changing the SPR. Cloud droplet number concentration increases due to anthropogenic aerosols acting as cloud condensation nuclei, leading to a reduction in cloud eff ective radius over eastern China and a reduced precipitation effi ciency there.     

THE APPLICATION OF ASSIMILATED AIRCRAFT DATA IN SIMULATING A HEAVY RAIN OVER SOUTH CHINA IN JUNE 2005

Regular and irregular observational data are used to analyze and simulate a torrential rain over the south of China on 18 – 24 June 2005. Since the regular data cannot depict the rainfall system fully, GRAPES model is used to simulate this process. Different data are assimilated for 12 hours by its simulating system and different analysis data are obtained. In order to analyze how well the model forecast has been improved with the addition of assimilated aircraft data, these different analysis data are used as the first-guess data to conduct two control numerical simulation tests. From these tests, it is proved that the model that adds aircraft assimilation data can simulate the main region of precipitation, which is more consistent with the observed precipitation than the model that does not, and that the accuracy rate is also improved. These numerical simulation tests not only show that it is necessary and capable to improve the modeling of this torrential rain process by using aircraft data, but also lays the foundation for forecasting heavy rains in the south of China based on aircraft data.     

THE ANALYSIS OF MECHANISM OF IMPACT OF AEROSOLS ON EAST ASIAN SUMMER MONSOON INDEX AND ONSET

RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols(dust, sea salt,sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon(EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM.The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25° N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced,especially in North and Southwest China where the value of moisture flux divergence increases.     

Changes in Summer Persistent Precipitation over the Middle–Lower Reaches of the Yangtze River and Associated Atmospheric Circulation Patterns

Persistence is an important property of precipitation and its related impacts. However, changes in persistent precipitation and the possible underlying mechanisms in the context of global warming have not yet been discussed in sufficient depth. In this study, the changes in persistent precipitation in summer and related atmospheric circulation patterns over the middle–lower reaches of the Yangtze River(MLRYZR)—a typical monsoon region frequently hit by consecutive rainfall events—are analyzed based on observed daily precipitation and NCEP/NCAR reanalysis data from 1961 to 2019. The results reveal that persistent precipitation events(PPs) tend to happen in a more persistent way, with increased frequency and intensity in the MLRYZR region. Mechanism analyses show that persistent precipitation has happened along with simultaneous enhancement of some large-scale atmospheric circulation patterns,including the Lake Baikal blocking(BB), the Okhotsk Sea blocking(OB), and the western Pacific subtropical high(WPSH). Such enhanced anomalous circulation patterns could persistently reinforce the convergence and supply of water vapor in the MLRYZR region, contributing to the increase in PPs in this region. Based on the above results, we are able to offer some new insights into the long-term changes in precipitation structure and the possible causes. This study is also expected to support attribution studies on regional precipitation changes in the future.     

Changes in Persistent and Non-Persistent Flood Season Precipitation over South China During 1961-2010

The characteristics and possible causes of changes in persistent precipitation（PP） and non-persistent precipitation（NPP） over South China during flood season are investigated using daily precipitation data from 63 stations in South China and NCEP/NCAR reanalysis data from 1961 to 2010. This investigation is performed using the Kendall＇s tau linear trend analysis, correlation analysis, abrupt climate change analysis, wavelet analysis, and composite analysis techniques. The results indicate that PP dominates total precipitation over South China throughout the year. The amounts of PP and NPP during flood season vary primarily on a 2–5-yr oscillation. This oscillation is more prominent during the early flood season（EFS; April–June）. NPP has increased significantly over the past 50 years while PP has increased slightly during the whole flood season. These trends are mainly due to a significant increase in NPP during the EFS and a weak increase in PP during the late flood season（LFS; July–September）. The contribution of EFS NPP to total flood season precipitation has increased significantly while the contribution of EFS PP has declined. The relative contributions of both types of precipitation during LFS have not changed significantly. The increase in EFS NPP over South China is likely related to the combined efects of a stronger supply of cold air from the north and a weaker supply of warm, moist air from the south. The increase in NPP amount may also be partially attributable to a reduction in the stability of the atmosphere over South China.     

Effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency during a torrential rainfall event in China

The effects of vertical wind shear, radiation and ice microphysics on precipitation efficiency （PE） were investigated through analysis of modeling data of a torrential rainfall event over Jinan, China during July 2007. Vertical wind shear affected PE by changing the kinetic energy conversion between the mean and perturbation circulations. Clou~radiation interaction impacted upon PE, but the relationship related to cloud radiative effects on PE was not statistically significant. The reduction in deposition processes as- sociated with the removal of ice microphysics suppressed efficiency. The relationships related to effects of vertical wind shear, radiation and ice clouds on PEs defined in cloud and surface rainfall budgets were more statistically significant than that defined in the rain microphysical budget.     

MULTIPLE TIME SCALE ANALYSIS OF CLIMATE VARIATION IN MACAU DURING THE LAST 100 YEARS

The multiple time scale climate changes are studied and calculated with statistical analysis and wavelet transformation on the basis of daily series of observed data over the period 1901-2007 in Macau.The result shows that statistically significant oscillations with 2 to 5 years of period generally exist in the series of climate variables(e.g.annual mean surface air temperature and precipitation as well as evaporation etc.),but with obvious locality in time domain.The variation of annual mean surface air temperature has a quasi 60-year period.The phases of the 60-year variation approximately and consistently match that of Atlantic Multidecadal Oscillation(AMO).The oscillations of seasonal mean surface air temperature in summer and winter have the periods of quasi 30-year and quasi 60-year,respectively.These two periods of oscillations have statistically significant correlation with Pacific decadal oscillation(PDO) and AMO,individually.The multidecadal variations of the precipitation of the annually first flood period and annual evaporation are dominated by periods of quasi 30-year and quasi 50-year,respectively.     

Detection, Causes and Projection of Climate Change over China： An Overview of Recent Progress

This article summarizes the main results and findings of studies conducted by Chinese scientists in the past five years.It is shown that observed climate change in China bears a strong similarity with the global average.The country-averaged annual mean surface air temperature has increased by 1.1℃over the past 50 years and 0.5-0.8℃over the past 100 years,slightly higher than the global temperature increase for the same periods.Northern China and winter have experienced the greatest increases in surface air temperature.Although no significant trend has been found in country-averaged annual precipitation, interdecadal variability and obvious trends on regional scales are detectable,with northwestern China and the mid and lower Yangtze River basin having undergone an obvious increase,and North China a severe drought.Some analyses show that frequency and magnitude of extreme weather and climate events have also undergone significant changes in the past 50 years or so. Studies of the causes of regional climate change through the use of climate models and consideration of various forcings,show that the warming of the last 50 years could possibly be attributed to an increased atmospheric concentration of greenhouse gases,while the temperature change of the first half of the 20th century may be due to solar activity,volcanic eruptions and sea surface temperature change.A significant decline in sunshine duration and solar radiation at the surface in eastern China has been attributed to the increased emission of pollutants. Projections of future climate by models of the NCC(National Climate Center,China Meteorological Administration)and the IAP(Institute of Atmospheric Physics,Chinese Academy of Sciences),as well as 40 models developed overseas,indicate a potential significant warming in China in the 21st century,with the largest warming set to occur in winter months and in northern China.Under varied emission scenarios,the country-averaged annual mean temperature is projected to increase by 1.5-2.1℃by 2020,2.3-3.3℃by 2050, and by 3.9-6.0℃by 2100,in comparison to the 30-year average of 1961 1990.Most models project a 10% 12% increase in annual precipitation in China by 2100,with the trend being particularly evident in Northeast and Northwest China,but with parts of central China probably undergoing a drying trend.Large uncertainty exists in the projection of precipitation,and further studies are needed.Furthermore,anthropogenic climate change will probably lead to a weaker winter monsoon and a stronger summer monsoon in eastern Asia.     

REGIONAL CHARACTERISTICS OF SUMMER PRECIPITATION ANOMALIES OVER CHINA

The regional characteristics of precipitation anomalies of total summer precipitation of June,July and August and individual monthly precipitation are analyzed by using the method of VarimaxEOF and correlation analysis.The data set used is the precipitation of a 5°Lat.×5°Long.spatialuniform network over China in the period of 1959 to 1994.The analysis of total summer precipitation shows that the most significant regionalcharacteristic is the existence of negative correlation in precipitation anomalies between the lowerreaches of the Changjiang River and the Huaihe River Valley(the LRCH region)and the middlereaches of the Huanghe River Valley(the MRH region),and between the LRCH region and SouthChina.The precipitation anomaly over the Sichuan Basin is negatively correlated with that overeastern part of Qinghai-Xizang Plateau and that over the LRCH region.The regionalcharacteristics of summer precipitation anomalies in western China are that there exists negativecorrelation between the summer precipitation anomalies over the southern part of the central andeastern Qinghai-Xizang Plateau and that over its northern part.There also exists positivecorrelation between the southern part of the central and eastern Qinghai-Xizang Plateau and theeastern part of North China and the southern part of Northeast China.The above spatialcorrelation modes have significant periods of about 3 years and ten years.The analysis of themonthly precipitation shows that in June there exists positive correlation among the precipitationanomalies over the LRCH region,the eastern part of North China and Northeast China.In July,the precipitations in the MRH region and the LRCH region are negatively correlated.The regionalcharacteristic of precipitation anomalies in August is very similar to that of the total summerprecipitation anomalies.     

THE SPATIOTEMPORAL CHARACTERISTICS OF LIGHT RAIN DAYS AND LOW CLOUD COVER UNDER HEAVY POLLUTION OVER SOUTH CHINA

By using the data set of light rain days and low cloud cover at 51 stations in South China (SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows: (1) The trends of light rain days and low cloud cover over SC are opposite (light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area. (2) The regression coefficients of light rain days and low cloud cover during 1960–2005 are 4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level. (3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter. (4) There are two regions with large values of aerosol optical depth (AOD), which distribute in central and southern Guangxi and Pearl River Delta (PRD) of Guangdong, and the value of AOD in PRD is up to 0.7. The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.     

MM5 Simulations of the China Regional Climate During the LGM. Ⅱ： Influence of Change of Land Area,Vegetation, and Large-scale Circulation Background

Using a regional climate model MM5 nested to an atmospheric global climate model CCM3, a series of simulations and sensitivity experiments have been performed to investigate the relative LGM climate response to changes of land-sea distribution, vegetation, and large-scale circulation background over China. Model results show that compared with the present climate, the fluctuations of sea-land distribution in eastern Asia during the LGM result in the temperature decrease in winter and increase in summer. It has significant impact on the temperature and precipitation in the east coastal region of China. The impact on precipitation in the east coastal region of China is the most significant one, with 25%-50% decrease in the total precipitation change during the LGM. On the other hand, the changes in sea-land distribution have less influence on the climate of inland and western part of China. During the LGM, significant changes in vegetation result in temperature alternating with winter increase and summer decrease, but differences in the annual mean temperature are minor. During the LGM, the global climate, i.e., the large-scale circulation background has changed significantly. These changes have significant influences on temperature and precipitation over China. They result in considerable temperature decreases in this area, and direct the primary patterns and characteristics of temperature changes. Results display that, northeastern China has the greatest temperature decrease, and the temperature decrease in the Tibetan Plateau is larger than in the eastern part of China located at the same latitude. Moreover, the change of large-scale circulation background also controls the pattern of precipitation change. Results also show that, most of the changes in precipitation over western and northeastern parts of China are the consequences of changing large-scale circulation background, of which 50%-75% of precipitation changes over northern and eastern China are the results of changes in large-scale circulation backgrou     

OBSERVATION RESEARCH FOR THE MEASURING RAINFALL CAPACITY OF TRMM/TMI-85.5G BASED ON PRECIPITATION DATA DURING THE HEAVY RAIN EXPERIMENT IN SOUTHERN CHINA

The capacity of Tropical Rainfall Measuring Mission (TRMM) Satellite for measuring rainfall was examined by using TMI-85.5 GHz microwave image data and precipitation data during a heavy rainfall experiment in southern China. From comparisons with the distribution of rain amount in an hour with BB T of 85.5 GHz microwave, it is clear that the center of heavy rain corresponds with an area of low BB T value. The location and shape of BB T distribution is similar to that of precipitation, and the larger the rainfall rates, the lower the BB T . A statistic analysis shows that the correlation coefficients between BB T and rain rates is negative and significant. Especially, when the rain rate is over 7 mm/h, the correlation degree between BB T and rain rates is more significant. The results shows that TRMM/TMI-85.5 G has great ability to measure convective heavy rain.     

Numerical Assessing Experiments on the Individual Component Impact of the Meteorological Observation Network on the ＂July 2000＂ Torrential Rain in Beijing

In an effort to assess the impact of the individual component of meteorological observations (ground-based GPS precipitable water vapor,automatic and conventional meteorological observations) on the torrential rain event in 4-5 July 2000 in Beijing (with the 24-h accumulated precipitation reaching 240 mm),24-h observation system experiments are conducted numerically by using the MM5/WRF 3DVAR system and the nonhydrostatic MM5 model.Results indicate that,because the non-conventional GPS observations are directly assimilated into the initial analyses by 3DVAR system,better initial fields and 24-h simulation for the severe precipitation event are achieved than those under the MM5/Litter_R objective analysis scheme. Further analysis also shows that the individual component of meteorological observation network plays their special positive role in the improvement of initial field analysis and forecasting skills.3DVAR scheme with or without radiosonde and pilot observation has the most significant influence on numerical simulation,and automatic and conventional surface meteorological observations rank second.After acquiring the supplement information from the other meteorological observations,the ground-based GPS precipitable water vapor data can more obviously reflect initial field assimilation and precipitation forecast.By incorporating the ground- based GPS precipitable water vapor data into the 3DVAR analyses at the initial time,the threat scores (TS) with thresholds of 1,5,10,and 20 mm are increased by 1%-8% for 6- and 24-h accumulated precipitation observations,respectively.This work gives one helpful example that assesses the impact of individual component of the existing meteorological observation network on the high influence weather event using 3DVAR numerical system.     

Continuous Measurement of Number Concentrations and Elemental Composition of Aerosol Particles for a Dust Storm Event in Beijing

A continuous measurement of number size distributions and chemical composition of aerosol particles was conducted in Beijing in a dust storm event during 21-26 March 2001. The number concentration of coarse particles （ 〉2μm） increased more significantly than fine particles （ 〈2μm） during the dust storm due to dust weather, while the anthropogenic aerosols collected during the non-dust-storm period tended to be associated with fine particles. Elemental compositions were analyzed by using proton-induced X-ray emission （PIXE）. The results show that 20 elements in the dust storm were much higher than in the non-dust-storm period. The calculated soil dust concentration during the dust storm was, on average, 251.8μg m^-3, while it was only 52.1μg m^-3 on non-dust-storm days. The enrichment factors for Mg, A1, P, K, Ca, Ti, Mn, Fe, C1, Cu, Pb, and Zn show small variations between the dust storm and the non-dust-storm period, while those for Ca, Ni and Cr in the dust storm were much lower than those in the non-dust-storm period due to significant local emission sources. A high concentration and enrichment factor for S were observed during the dust storm, which implies that the dust particles were contaminated by aerosol particles from anthropogenic emissions during the long-range transport. A statistical analysis shows that the elemental composition of particles collected during the dust storm in Beijing were better correlated with those of desert soil colleted from desert regions in Inner Mongolia. Air mass back-trajectory analysis further confirmed that this dust storm event could be identified as streaks of dust plumes originating from Inner Mongolia.     

Study on climatic characteristics of China-influencing tropical cyclones

Analysis of the climatic characteristics of the tropical cyclones that affect China yields several interesting features. The frequency of these tropical cyclones tended to decrease from 1951 to 2005, with the lowest frequency in the past ten years. The decrease in the frequency of super typhoons is particularly significant. The main season of tropical cyclone activities is from May to November, with an active period from July to September. There are three obvious sources of these tropical cyclones and they vary with seasons and decades. Their movement has also changed with seasons. On average, these tropical cyclones affect China for 5.6 months annually and the period of influence decreases in the past decades. An analysis of daily data indicates that the days of typhoon influence are shorter in winter and spring and longer in summer. The frequency of tropical cyclones is the largest over southeastern China, decreasing northwestward. Taiwan is the region that is affected by tropical cyclones most frequently. The average annual precipitation associated with tropical cyclones has also decreased gradually northwestward from southeastern China.     

Climate Change in the Subtropical Jetstream during 1950–2009

A study of six decades(1950–2009) of reanalysis data reveals that the subtropical jetstream(STJ) of the Southern(Northern) Hemisphere between longitudes 0°E and 180°E has weakened(strengthened) during both the boreal winter(January,February) and summer(July, August) seasons. The temperature of the upper troposphere of the midlatitudes has a warming trend in the Southern Hemisphere and a cooling trend in the Northern Hemisphere. Correspondingly, the north–south temperature gradient in the upper troposphere has a decreasing trend in the Southern Hemisphere and an increasing trend in the Northern Hemisphere, which affects the strength of the STJ through the thermal wind relation. We devised a method of isotach analysis in intervals of 0.1 m s-1in vertical sections of hemispheric mean winds to study the climate change in the STJ core wind speed, and also core height and latitude. We found that the upper tropospheric cooling of the Asian mid-latitudes has a role in the strengthening of the STJ over Asia, while throughout the rest of the globe the upper troposphere has a warming trend that weakens the STJ. Available studies show that the mid-latitude cooling of the upper troposphere over Asia is caused by anthropogenic aerosols(particularly sulphate aerosols) and the warming over the rest of the global mid-latitude upper troposphere is due to increased greenhouse gases in the atmosphere.     

Direct Radiative Forcing of Anthropogenic Aerosols over Oceans from Satellite Observations

Anthropogenic aerosols play an important role in the atmospheric energy balance. Anthropogenic aerosol optical depth (AOD) and its accompanying shortwave radiative forcing (RF) are usually simulated by nu- merical models. Recently, with the development of space-borne instruments and sophisticated retrieval algorithms, it has become possible to estimate aerosol radiative forcing based on satellite observations. In this study, we have estimated shortwave direct radiative forcing due to anthropogenic aerosols over oceans in all-sky conditions by combining clouds and the Single Scanner Footprint data of the Clouds and Earth’s Radiant Energy System (CERES/SSF) experiment, which provide measurements of upward shortwave fluxes at the top of atmosphere, with Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud products. We found that globally averaged aerosol radiative forcing over oceans in the clear-sky conditions and all-sky conditions were -1.03±0.48 W m-2 and -0.34 ±0.16 W m-2, respectively. Direct radiative forcing by anthropogenic aerosols shows large regional and seasonal variations. In some regions and in particular seasons, the magnitude of direct forcing by anthropogenic aerosols can be comparable to the forcing of greenhouse gases. However, it shows that aerosols caused the cooling effect, rather than warming effect from global scale, which is different from greenhouse gases.     

Current Status and Future Challenges of Weather Radar Polarimetry: Bridging the Gap between Radar Meteorology/Hydrology/Engineering and Numerical Weather Prediction

After decades of research and development, the WSR-88 D(NEXRAD) network in the United States was upgraded with dual-polarization capability, providing polarimetric radar data(PRD) that have the potential to improve weather observations,quantification, forecasting, and warnings. The weather radar networks in China and other countries are also being upgraded with dual-polarization capability. Now, with radar polarimetry technology having matured, and PRD available both nationally and globally, it is important to understand the current status and future challenges and opportunities. The potential impact of PRD has been limited by their oftentimes subjective and empirical use. More importantly, the community has not begun to regularly derive from PRD the state parameters, such as water mixing ratios and number concentrations, used in numerical weather prediction(NWP) models.In this review, we summarize the current status of weather radar polarimetry, discuss the issues and limitations of PRD usage, and explore potential approaches to more efficiently use PRD for quantitative precipitation estimation and forecasting based on statistical retrieval with physical constraints where prior information is used and observation error is included. This approach aligns the observation-based retrievals favored by the radar meteorology community with the model-based analysis of the NWP community. We also examine the challenges and opportunities of polarimetric phased array radar research and development for future weather observation.     

EFFECT OF TROPICAL CYCLONE PRECIPITATION ON ALLEVIATING THE DROUGHT SITUATION IN THE SOUTHEAST COASTAL REGIONS OF CHINA DURING SUMMER AND AUTUMN: USING THE IMPROVED OBJECTIVE SYNOPTIC ANALYSIS TECHNIQUE

To quantitatively study the role of tropical cyclone precipitation (TCP) on alleviating the drought in the southeast coastal region of China (SCR) during summer and autumn, the objective synoptic analysis technique (OSAT), improved for consistency and rationality, was used to separate the TCP data on the summers and autumns of 1963–2005 on the basis of daily precipitation data from stations and tropical cyclone best track data. After defining the season drought index, the actual drought distribution and the assumed drought distribution without TCP were acquired. The results showed that within 1 000 km from the southeast coastline of China, TCP accounted for 11.3% of natural precipitation (NP). Without TCP, the drought index in the SCR during summer would have increased from 0.2 to 0.6 or even above 1.0 in some regions whereas the drought index during autumn would have increased from 0.4 to 0.6 or above 1.2 in some regions. The impact of TCP on drought decreases progressively from the southeast coastline to the inland regions. The TCP proportion (TCPP) showed a significant negative correlation with the drought index in many regions of the southeast, and the significant region is wider in autumn than in summer. TCP relieved the drought most significantly within a range of 0–500 km from the southeast coastline. This drought relief showed different characteristics for the interannual variability in summer and autumn, and the cross wavelet transform indicated that the impact of TCP on drought mainly lies in 2–4-year time scales. In particular, there was a significant effect during the summers of 1977–1985 and in the autumns following that of 1985. Therefore, TCP has indeed largely alleviated drought in the SCR during summer and autumn.