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Using monthly data from 19 meteorological stations in Guangxi Zhuang Autonomous region from 1961 to 2020, this study calculated the standardized precipitation evapotranspiration index (SPEI) based on the Penman-Monteith evapotranspiration model (SPEI_PM). The temporal and spatial variation of meteorological drought were analyzed via linear tendency estimation, and Mann-Kendall trend test. The correlation between El Niño-Southern Oscillation (ENSO) and meteorological drought in Guangxi was also explored by cross-correlation function, cross wavelet transform and wavelet coherence. The values for summer, autumn, and annual SPEI_PM from 1961 to 2020 exhibited a significant linear trend of increasing wetness over time. Annual and seasonal droughts throughout the region were predominately mild and moderate, with less frequent severe and extreme droughts. Spring droughts were concentrated in the central part of the region, summer droughts in the southwest, autumn droughts in the southeast and northeast, and winter droughts spread throughout the region. Annual droughts were concentrated in the northeast. The rate of drought occurrence as measured by the stations in Guangxi exhibited a distinctly chronological character. Large-scale droughts (especially severe and extreme droughts) across the entire region occurred most often in the 1960s, 1970s, and 2000s. The impact of ENSO on the meteorological drought in Guangxi was characterized by spatial heterogeneity. Correlation between the ocean Niño index (ONI) and meteorological drought was highest in the northeast and southeast, as well as the northwest. There was no significant correlation between drought and ONI in coastal areas and most southwestern parts of the region. As a typical example from meteorological stations in northeastern Guangxi, SPEI-3 and ONI at the Guilin Meteorological station showed interannual oscillation cycles of 16-48 months in the period 1962-1976, and 12-64 months in the period 1990-2019. These results can serve as a useful reference for future drought forecasting and assessment in Guangxi. [ABSTRACT FROM AUTHOR]

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Copyright of China Rural Water & Hydropower is the property of China Rural Water & Hydropower Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Extreme weather and climate events caused by El Niño have significant impacts on socio-economic conditions and the safety of people’s lives and properties.Between 2014 and 2016， a super El Niño event occurred， leading to frequent extreme weather and climate events worldwide.This study focuses on the Indochina Peninsula region and explores the potential reasons for abnormally decreased precipitation in April 2016， against the backdrop of the super El Niño event.The research utilizes monthly observations and reanalysis data of sea temperatures， precipitation， wind fields， and specific humidity to investigate circulation patterns and abnormal moisture transport.The results indicate that in April 2016， the ICP experienced anomalous sinking currents due to the influence of a developing and robust Western North Pacific Anti-Cyclone and subtropical high-pressure systems.These conditions hindered moisture convergence necessary for precipitation formation.Furthermore， through dynamic diagnostic analysis， the study finds that the product of the Nino3.4 index and the zonal gradient of SST anomalies （GSSTA） between the equatorial East Indian Ocean and the equatorial Western Pacific Ocean effectively indicates the super El Niño event.Additionally， the modulation of nonlinear moisture advection over the ICP plays a vital role in the abnormally low precipitation in the region in April.During the 2015/2016 El Niño event， conflicting wind patterns emerged between the easterly winds on the southern side of the WNPAC and the anomalous westerly moisture transport guided by GSSTA.This conflict weakened the moisture transport from the Pacific Ocean and the Bay of Bengal to the ICP.Over the ICP， most of the moisture exhibited a pattern of being less in the south and more in the north， with higher levels in the east and lower in the west.This led to moisture divergence， which was unfavorable for precipitation formation.In summary， this study emphasizes the significant influence of a super El Niño event on extreme weather and climate events， particularly focusing on the abnormally decreased precipitation over the Indochina Peninsula in April 2016.By examining circulation patterns and moisture transport anomalies， the research contributes to understanding the underlying causes and dynamics of these events.The findings have implications for future weather predictions， climate change assessments， and the development of effective strategies to mitigate the impacts of extreme weather events in the Indochina Peninsula region.In April 2016， under the combined action of the Bay of Bengal anomalous anticyclonic and the Western North Pacific Anti-Cyclone， the Indochina Peninsula convection was suppressed， and the warm and wet air was transported to South China under the guidance of the anomalous south wind.

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Wildland Fire Science is the property of Journal of Wildland Fire Science Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The universal time (UT1-UTC) and length of day change (ΔLOD) are two parameters that describe the Earth's rotation rate variations. UT1-UTC is typically used in space projects, whereas ΔLOD is used for scientific investigations. Therefore, studying the variations between the two parameter sequences is very important. In this study, we reviewed the Earth's rotation rate over the last five decades and revealed an abnormal phenomenon in UT1-UTC. Since May 2020, the Earth's rotation has reversed from a deceleration trend to an acceleration trend. Besides, we used ΔLOD to find the possible geophysical contributors and focused on the climate-related contributions. Results revealed that the interannual LOD exhibited a notable degree of consistency with ENSO indices after using the Difference+FDSR method to remove the internally and externally induced signals. Notably, two La Nina with intermediate strength and the beginning of a closely followed third trough were detected in the last three years. The contributions of these events to the latest rotation acceleration are approximately 9%.

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It is a great significance to improve the understanding of spring continuous rain and to prevent and reduce disasters by studying the change rule of spring continuous rain over the Anhui province in recent decades and its relationship with El Niño/La Niña events. Based on the daily rainfall and sunshine hours at 77 stations in the Anhui province and the NCEP/NCAR reanalysis dataset,the variation characteristics of spring continuous rain over the Anhui province is studied and the possible impacts from different types of El Niño/La Niña decaying different years is discussed with the methods of EOF,composition analysis,and etc. The days,the frequency,and the longest days of spring continuous rain over the Anhui province during the past 58 years show similar distribution characteristics with less in the north,more in the south,and maximum in the south of Jiangnan. The number of spring continuous rainy days has an obvious decreasing trend and decreases by 1.0 day for every 10 years on average. The spatial distribution of continuous rain days includes two patterns: consistency in all areas and contrary in the north and south. The number of spring continuous rainy days over the Anhui province is more (less) during the years with eastern pattern El Niño (La Niña) decaying,and is less during the years with central pattern El Niño/La Niña decaying. During the years with eastern pattern El Niño (La Niña) decaying,the West Pacific subtropical high (WPSH) is obviously stronger (weaker) and abnormally northward (southward),and the high pressure in the Sea of Japan is obviously stronger. In addition,there is a pattern of two ridges-one trough (one trough-one ridge) for 500 hPa geopotential height at the mid-high latitudes of Eurasia. The high ridge (low trough) over the Ural mountains and the low trough over the Lake Baykal are evident. In the meantime,the cold air from the bottom (front) of the trough (ridge) continues flowing southward,converging continuously with the southwest warm (northeast cold) air low from the Western North Pacific anomalous anticyclone (cyclone) over the Jianghui area,which leads to more (less) spring continuous rain over Anhui province. During the years with central pattern El Niño decaying,the WPSH is abnormally stronger and southwestward,and the low trough over the outer Xing' an Mountain is evident. During the years with central pattern La Niña decaying,there is anomalous cyclonic circulation over the West Pacific and the Lake Baykal,and northerly wind prevails over the Jianghuai area,which leads to less spring continuous rain over the Anhui province.

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Copyright of Journal of Irrigation & Drainage is the property of Journal of Irrigation & Drainage Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Reference crop evapotranspiration (ET0 ) can fully represent the evapotranspiration capacity in areas, such as efficient water-saving irrigation in agriculture. Most studies have typically conducted sensitivity analyses of changing ET0 in the local meteorological factors, without considering the remotely correlated effects of large-scale climate variability on ET0 . Large-scale climate variability generated by the ocean is a significant driver of global and regional climate change, indicating the nonnegligible impact on the evolution pattern of ET0 . However, it is still lacking in the influence of large-scale climate variability on ET0, leading to the inaccurate attribution of ET0 changes. Therefore, this study aims to explore the relationships between the large-scale climate variability of El Niño Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO) with the ET0 variability characteristics in Xinjiang region. The daily meteorological data and climate variability indices were collected from 84 meteorological stations using multiple linear regression and Cramer's mutation test. The results indicate that the ET0 showed a decreasing trend from 1960 to 2020, with an average decreasing rate of 0.75 mm/a; the year 1998 was the mutation of the ET0, and the ET0 showed an obvious decreasing trend from 1960 to 1997, with an average decreasing rate of 2.50 mm/a, and then turned to an outstandingly increasing trend from 1998 to 2020, with an average increasing rate of 3.18 mm/a. The multivariate linear correlation results show that the ET0 was negatively correlated with the RH with a regression coefficients of −0.46, and positively correlated with the U, T, and Rn with regression coefficients of 0.95, 0.36, and 0.20, where the changes of ET0 were mainly dominated by the changes of U. On the seasonal scale, the interannual variation trend of ET0 in the four seasons was more consistent with the annual cumulative ET0 variation trend, which decreased at the rate of 0.01, 0.54, 0.23, and 0.01 mm/a in spring, summer, autumn, and winter, respectively, whereas, the trend change in the spring, summer, and autumn seasons occurred in the mid1990s, respectively. PDO was the main variable affecting the trend shift of ET0, where the regression coefficients between the two was -0.34. There was also a significant negative correlation of U with PDO and AMO, with regression coefficients of −0.31 and −0.34, respectively. The PDO was shifted from a positive to a negative phase in 1998, resulting in the wind speed shifting from a downward to an upward trend, which in turn led to the trend shift of ET0 in the Xinjiang region in 1998. The shift of AMO from a negative to a positive phase strengthened the trend change of wind speed, while the effects of ENSO and IOD on wind speed were relatively weak. The negative phase of PDO was achieved in the spatial regression of sea surface temperature (SST) with ET0, which further verified the influence of PDO on the trend shift of ET0 in the Xinjiang region of western China. [ABSTRACT FROM AUTHOR]

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Copyright of Reviews of Geophysics & Planetary Physics is the property of Editorial Office of Reviews of Geophysics & Planetary Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Data Acquisition & Processing / Shu Ju Cai Ji Yu Chu Li is the property of Editorial Department of Journal of Nanjing University of Aeronautics & Astronautics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the hourly precipitation data from 2005 to 2021 at the 91 meteorological stations and Oceanic Niño Index in Guangxi in rain season, the spatial and temporal distribution characteristics of extreme short-time heavy rainfall are analyzed. The results show that: (1) In most parts of Guangxi, the intensity of extreme short-time heavy rainfall ranges from 40 to 70 mm·h-1. The highest intensity and frequency of extreme heavy rain are seen in the coastal areas, while the lowest intensity is seen in northern inland regions with more frequent heavy rain. (2) The number of extreme short-time heavy rainfall per year continues to rise. In May and June, the frequency of these events is the highest and the little monthly change of the heavy rainfall intensity has been observed. (3) The diurnal variation curve of the incidence of extreme heavy precipitation appears to be bimodal with peaks during 04∶00 BT-05∶00 BT and 05∶00 BT-06∶00 BT. The intensity of this kind of rainfall varies from 50 to 55 mm per hour with little variation in amplitude in different hours. (4) The spatial distribution characteristics of extreme short-time heavy rainfall is not only closely related to the terrain features, but also associated with the South China Sea summer monsoon onset and El Niño/La Nina event. (5) It is shown that there is a positive correlation between the Oceanic Niño Index of previous autumn and the frequency of extreme short-time heavy rainfall.

Based on the monthly mean sea surface temperature(SST) data and the reanalysis data over the period of 1958-2018, we have investigated the interdecadal variation of the thermal response characteristics of the Indian Ocean, the South China Sea, and the Maritime Continent to the El Nino-South-We have also investigated the interdecadal variation of the physical process for the circulation response features over the subtropical northwestern Pacific Ocean to ENSO events. During the evolution of the ENSO events, the SST in different areas of the tropical Indian Ocean and adjacent waters presents various features in terms of both maximum lag-response and duration of prominent lag-response to the SST anomalies in the equatorial central-eastern Pacific. The prominent lag-response of the SST in the tropical northern Indian Ocean, the Maritime Continent, and the South China Sea can last until the following summer of ENSO. Both the evolution features of the ENSO events and the lag response features of SST in the tropical Indian Ocean and the Maritime Continent to ENSO experienced obvious interdecadal changes in the early 1980s and early 2000s. Compared with the first and the third periods, the duration and strength of ENSO events were longer and stronger in the second period, respectively, accompanied by slower significant response of the SST in the tropical southern and northern Indian Oceans. The SST in the Maritime Continent experienced noticeable interdecadal changes alternatively in the significant lag-response and the less significant lag-response to ENSO, with a longer duration of the noteworthy response in the last period than in the first one. The impact process of the ENSO on the summer circulation over the subtropical East Asia, via the lag-response of the SST in the tropical Indian Ocean and adjacent waters, also shows interdecadal changes. The SST in the Maritime Continent, the tropical northern Indian Ocean and the equatorial central-eastern Pacific can be recognized as the key factors in different periods, which may induce the anomalous summer circulation over the subtropical East Asia, and then further affect the summer climate in East Asia. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Geodesy & Geodynamics (1671-5942) is the property of Editorial Board Journal of Geodesy & Geodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Based on the daily precipitation data at the 83 national automatic weather stations over Jiangxi Province in spring (March to May) from 1961 to 2018 and the diurnal reanalysis data from NCEP/NCAR, we have performed an analysis on the characteristics of atmospheric circulation for the spring precipitation anomalies in Jiangxi and its response to ENSO events. The results show that in the years with abnormally more precipitation in spring in Jiangxi, as the mid-and high-latitudes in the middle layer 500 hPa is affected by the Eurasian circulation (EU type), the blocking high near the Ural Mountains is active, and both the low trough in the Baikal Lake area and the Western Pacific subtropical high (hereinafter referred to as WPSH) are stronger than the climatic mean state, which is conductive to the writhe of cold air from the north to south and southerly warm and wet airflow in Jiangxi. In addition, the western Pacific region in east of the Philippines in the low-level 850 hPa is controlled by the anomalous anticyclone circulation, causing the enhancement of water vapor transport from the South China Sea to Jiangxi. While the atmospheric circulation characteristics in the years with abnormally less precipitation in spring in Jiangxi are opposite to those in the above years with abnormally more precipitation. Moreover, ENSO is an important forcing signal affecting the spring precipitation in Jiangxi. In the year of El Niño (La Niña) decay, the WPSH at low level 850 hPa in East Asia in spring is stronger (weaker), which is (isn' t) favorable for the transportation of water vapor from the South China Sea to Jiangxi. More (less) precipitation in Jiangxi is due to the dynamic uplift formed by convergence (divergence) in the low-level and divergence (convergence) in the upper level 200 hPa.

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Based on precipitation data at Anhui meteorological stations and NCEP reanalysis data, in this paper we analyze the characteristics and the causes of Meiyu climate anomaly in Anhui Province in 2020, and evaluate the skill of climate prediction and the effectiveness of prediction precursor signals. The main conclusions are as following. (1) In Anhui Province, Meiyu onset date was June 2 and outset date was August 1. Meiyu duration was 60 days. Meiyu precipitation was 1 057 mm in South along the Yangtze River and 810 mm between Yangtze River and Huaihe Rive, and the rainfall intensity in many places reached the historical extreme value in 2020. On the whole, the length of Meiyu period, the wide coverage, the large amount of accumulated rainfall and the intensity of Meiyu reached the top level since 1961. (2) The main reason for the abnormal Meiyu is that the blocking high is active near the Ural Mountain and the East Siberian-Okhotsk Sea from June to July. The EAP wave train on the 500 hPa geopotential height anomaly field along the East Asian coast is obvious. The summer monsoon is weak. The Western Pacific Subtropical High is abnormally strong and located too far to west and south, which is conducive to the convergence of cold and warm air in Anhui Province. The water vapor transport from the west side of the subtropical high to the province is extremely strong. The reason for the longer Meiyu period is that the ridge line of subtropical high is northward in June and southward in July, which leads to the early onset and late demise of Meiyu. (3) In the previous winter and spring, there was a weak El Niño event in the equatorial central Pacific Ocean. Although the indication of ist influence on Meiyu in Anhui Province is not clear, the response signal is that the Indian Ocean SST and subtropical high are abnormally warm and strong. According to historical statistics, if the equatorial Middle East Pacific Ocean is basically in El Niño state in previous winter, the probability of more intensive Meiyu in these years is very high. Therefore, the Indian Ocean SST and Western Pacific Subtropical High response factors can be used as the starting points to improve the prediction ability of Meiyu in weak El Niño years.

During the summer of 2016 and 1998 in the context of the decaying phase of the super El Niño event,the three persistent heavy rainfall events occurred in the middle and lower reaches of the Yangtze River from June 19 to July 7 in 2016 (hereinafter referred to as during the period of 2016),from June 12 to 27 (hereinafter referred to as during the period Ⅰ of 1998) in 1998, and from July 17 to August 2 (hereinafter referred to as during the period Ⅱ of 1998) in 1998, which brought great challenges to the national flood control business. Based on daily precipitation at 2407 meteorological observation stations in mainland China,daily reanalysis atmospheric data from NCEP/NCAR and other data,we have conducted a comparative analysis of the similarities and differences of summer persistent heavy rainfall and associated atmospheric circulation characteristics in the middle and lower reaches of the Yangtze River between 2016 and 1998. Results are as follows. (1) The persistent heavy rainfall belt is the northernmost during the period of 2016 and the southernmost during the period Ⅰ of 1998 among the three events,while the rainfall intensity during the period of 2016 is roughly the same as that during the period Ⅰ of 1998, and it for both periods is stronger than that for the period Ⅱ of 1998. (2) There are many similarities in the atmospheric circulation characteristics during the three periods of persistent heavy rainfall. For example,there exist low troughs near the eastern coast of China,the Northwest Pacific Subtropical High (NWPSH) and South Asia High (SAH) are larger in range and stronger in intensity than normal,and the intensity of the upper westerly jet (UWJ) and low southwest jet and the easterly water vapor transport along the south side of the NWPSH are also stronger than normal. (3) The significant differences in the atmospheric circulation during the three periods of persistent heavy rainfall events are that the low trough near the coastal of eastern China during the persistent heavy rainfall of 2006 (1998) is shallow (deep). When upper-level divergence zone between the north sides of NWPSH and SAH ridge lines and the south sides of westerly jet belt,low-level jet belt and shear line with convergence,and Australian High in the southern hemisphere are northerly (southerly) in position,the persistent heavy rainfall zones are also northerly (southerly). NWPSH,SAH,and upper-level westerly jet during the period of 2016 and the period Ⅰ of 1998 are significantly stronger than those during the period Ⅱ of 1998. The rainfall intensity in the former two periods is also greater than that in the later period.

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Summer rainstorms occur frequently in Beijing-Tianjin-Hebei region. As one of the key factors affecting the formation of heavy rain,precipitable water vapor has been recognized as highly correlated with the Global Navigation Satellite Systems Zenith Tropospheric Delay (GNSS ZTD). In this study,the time series of GNSS ZTD and their response to El Niño events were analyzed based on GNSS observations in Beijing-Tianjin-Hebei region. Fast Fourier transform and wavelet transform were used to carry out GNSS ZTD timing sequence analysis from frequency domain and time domain,and the time sequence of GNSS ZTD with different periodicity was compared with the Eastern-Pacific types of El Niño index (IEP) and the Central-Pacific types of El Niño index (ICP) . The results showed that there was a corresponding relationship between the abnormal period of GNSS ZTD and El Niño events. Specifically,the GNSS ZTD was positively correlated with IEP, and significantly negatively correlated with ICP . Under the influence of IEP, the GNSS ZTD increased in seasonal cycle,but decreased in monthly cycle and half-monthly cycle. While under the influence of ICP, the GNSS ZTD decreased in seasonal cycle,monthly cycle,and half-monthly cycle. The above results can provide reference for regional GNSS ZTD variation analysis,and provide a reliable basis for sensing El Niño events with precipitable water vapor. [ABSTRACT FROM AUTHOR]

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Applied Ecology / Yingyong Shengtai Xuebao is the property of Chinese Journal of Applied Ecology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, the gravity recovery and climate experiment (GRACE), altimetry, ARGO, TRMM (tropical rainfall measurement mission) data and multivariate ENSO index (MEI) from January 2005 to December 2016 are adopted to analyze the effects of ENSO on the Western Pacific and its coastal areas, from the aspects of sea level, oceanic mass, steric and the terrestrial water storage change. During the GRACE data processing, we remove the effect of tectonic signals, and use an iterative forward model- ing method to recover time-varying signal. The result shows, the changes in the Western Pacific mean sea level (WPMSL) in response to ENSO are as follows: The sea level is lower during El Niño and higher dur- ing La Niña; in particular, during 2014—2016 El Nino, the WPMSL dropped by nearly 26.2 mm. The ste- ric change is the dominant factor affecting the nonseasonal anomalies of the WPMSL. The nonseasonal anomalies of water storage in Australia and Indochina Peninsula also respond well to the ENSO, and the correlation coefficients with the MEI are －0.61 (lag three months) and －0.65 (lag eight months). The re- sponse of the Yangtze River basin to ENSO is mainly in the middle and lower basin, 2014—2016 El Niño caused the water storage in the Yangtze River basin to reach the maximum value in recent years. [ABSTRACT FROM AUTHOR]

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The flood disasters caused a great loss of life and property in Yangtze River Basin during June-July of 2016. Meiyu became one of the main causes of flood disasters due to the frequency, long duration and high intensity. In this study, chronology of extreme Meiyu events since 1736 was reconstructed derived from Chinese historical documents and the observational data. Furthermore, the long-term variation characteristics of extreme Meiyu events and relationships between extreme Meiyu and El Niño events were analyzed. The general circulation patterns were diagnosed to explain how El Niño influenced extreme Meiyu. The results show that there were 44 extreme Meiyu events (including 21 mega-Meiyu events) from 1736 to 2016.The most frequent occurrences of extreme Meiyu events were detected during 1901-1920 and 1991-2000. There were 21 mega-Meiyu events over the past 300 years, and the intensity was similar to that of 2016. It is found that the closely corresponding relationships existed between extreme Meiyu events and El Niño in this period. For example, 37 of total 44 extreme Meiyu events occurred in the El Niño or their following years, and 16 of total 21 mega-Meiyu events occurred with El Niño episodes. In the El Niño years, the meridional circulations were intensified over the mid-latitudes.The water vapor transported westerly and northerly to the mainland of China.A great amount of water vapor from south and the cold air from high latitudes intersected in the Mid-lower Reaches of the Yangtze River, which led to continuous precipitation. Moreover, in the El Niño following years, there was a steady subtropical high system at low latitudes. The transportation path of vapor was northerly, and then the vapor fluxes increased in Yangtze River Basin. The extreme Meiyu events occurred easier under this circulation background. [ABSTRACT FROM AUTHOR]

The differences of oceanic and atmospheric circulation anomalies between 2015 and 2016 are analyzed and their impacts on summer precipitation in China are investigated in this paper, by using the monthly precipitation data of 160 stations in China and NCEP/NCAR monthly data. The results show that the distribution of summer precipitation anomalies are obviously different in 2015 and 2016. The summer precipitation anomalies are less over North China,but more over South China in 2015. Compared with 2015, the summer precipitations increase obviously, especially Chinese north region, with a meridian rain belt in 2016. The abnormal sea surface temperature (SST) in 2015 is corresponding to the development year of El Nino, warm phase of basin- wide SSTA variation in the tropical Indian Ocean(IOBW) and positive phase of Tropical Indian Ocean Dipole(TIOD), while the SST in 2016 shows the ending year of El Nino, warm phase of IOBW and negative phase of TIOD. In 2015, the western Pacific subtropical high is stronger and southward than normal affected by SST anomalies in the tropical Indian- Pacific Ocean. The actions jointed with active cold airs and southward westerly jet axis result in the less precipitation over Chinese north region and more precipitation over Chinese south region. In 2016, El Nino decay and negative TIOD lead the subtropical high northward, and the battery charge caused by warm IOBW lead subtropical high stronger. The northward and stronger subtropical high meeting weak cold air and northward westerly jet axis, cause more precipitation in the middle and lower reaches of Yangtze River and its north region. [ABSTRACT FROM AUTHOR]

Based on the data of drought and flood disasters in Northeast China during 1751 to 2000, the characteristics of drought and flood disasters are analyzed. The relationship between the meteorological factors and the drought and flood disasters has been established, and three methods for forecasting the trends of floods and droughts, which are the transition probability, the phase of the sun activities and El Nino, are proposed. The future trends of drought and flood disasters for the period of 2001 to 2010 are forecasted. The results are summarized as follows: The drought and flood disasters in the 20th century are more serious than before, especially the times of the drought disasters have increased obviously than those in the 19th century. There will be more than 2 drought disasters and 1-2 flood disasters in Northeast China for the period of 2001-2010 and the critical period of flood disasters will be in about 2007. It has been proven to be an effective reference for guiding the practical flood hazard control and mitigation in Northeast China. [ABSTRACT FROM AUTHOR]

Regional meteorological conditions and emissions reduction are closely related to air quality. China has a monsoonal climate and regional meteorological conditions are significantly impacted by interannual climate variability. The objective of this study was to evaluate the contributions of meteorological conditions and emissions reduction to regional improvements in air quality. Trend analyses of key meteorological factors and air pollution for the Beijing-Tianjin-Hebei region, Chengdu-Chongqing region, Yangtze River Delta, and Pearl River Delta urban agglomeration areas were performed for the period from 2001 to 2018, and K-Nearest Neighbor (KNN) models were constructed for each calendar year. The analysis showed that approximately half of the years between 2001 and 2018 experienced abnormal global-scale climate conditions, i.e., El Niño and La Niña. Both emissions reduction and climate changes contributed to the improvement of air quality during the study period. The contribution of meteorological conditions to air quality improvement under abnormal climate conditions was 51% compared to 30% under normal climate conditions in the Beijing-Tianjin-Hebei region; for the Yangtze River Delta and Pearl River Delta regions, meteorological conditions contributed approximately 50% to the improvement of air quality under both abnormal and normal climate conditions. In addition, the contribution of emissions reduction to air quality improvement was higher in the study areas during 2015-2018 compared to 2001-2012. This indicates that emissions reduction has played an increasingly important role in air quality improvements largely due to the implementation of a variety of emission control measures. However, the contribution of meteorological conditions to air quality improvement cannot be ignored.

The ENSO events affect climate and fire danger of China. It would be helpful for improving fire danger forecast to understand the impacts of ENSO events on fire weather for various ecological zones in the country. We calculated the fire weather index (FWI) using the daily climatic dataset (V3.0) of international exchange weather stations in China during 1951-2016. The burned areas in forests for each ecological zone in 2001-2016 were derived from MODIS fire products. Temperature, precipitation, FWI and burned areas in fire season were estimated for each ecological zone by ENSO events (weak, medium, strong, and super strong El Niño events and weak, medium, and strong La Niña events). The results showed that there were 19 El Niño events and 14 La Niña events during 1950-2016. The average daily maximum temperature of the spring fire season increased significantly in the northwestern region with the influence of strong or super strong El Niño event, while the temperature reduced significantly in the medium El Niño event for mid-temperate semi-arid grassland. Precipitation in fire season generally increased in El Niño events in southern and southwestern forest regions. It would be reduced in most areas affected by the low and medium intensity La Niña event, but be increased during the strong La Nina event. The fire weather indices of southern forest regions decreased due to the weak El Niño event. The FWI of the northern forest regions increased with the strong or super strong El Niño event, and reduced in the southern and southwestern forest areas. There was a significant spatial difference on the FWI for some ecological zones with the impacts of the El Niño/La Niña events. The burned areas showed a consistent change trend with seasonal severity rating (SSR) during 2001-2016 when the SSR changed significantly for the regions of deciduous broad-leaved forest in humid/semihumid areas of warm temperate zone, broad-leaved forest in the middle north subtropical humid areas, and broad-leaved forest in tropical and subtropical humid areas. The burned areas in the rest regions were not affected by the ENSO events.