East Asian Summer Monsoon Index Research Articles

How the enhanced East Asian summer monsoon regulates total gross primary production in eastern China

Recognizing the relationship between gross primary production (GPP) and precipitation in eastern China, the East Asian Summer Monsoon (EASM) plays a crucial role in shaping GPP. Despite confirmation of the strong link between EASM and GPP, there remains a notable research gap in understanding the specific impact of the EASM on GPP in different regions of eastern China. Here we used simulations from Trends in Net Land–Atmosphere Carbon Exchanges (TRENDY) models from 1951 to 2010 and divided eastern China into five subregions for the study. We also used the New East Asian Summer Monsoon Index (NEWI) as a quantitative metric to distinguish between periods of strong and weak EASM. Building on this, this study aims to investigate the response of GPP in different subregions of eastern China. Regionally, under strengthened EASM years (1954, 1957, 1965, 1969, 1977, 1980, 1983, 1987, 1993 and 1998), East China experienced the most pronounced increase in GPP at 12 ± 21 (mean ± 1 sigma) gC m−2 mon−1 compared to the weak EASM years (1958, 1961, 1972, 1973,1978, 1981, 1985, 1994, 1997 and 2004). In contrast, Southwest China showed a decline in GPP at −4 ± 10 gC m−2 mon−1. Moreover, GPP also increased in Northeast and North China when EASM strengthened, while South China showed a decline in GPP. This indicated that GPP changed with monsoon intensity. According to the mechanism analysis, during strong EASM, there was intense moisture convergence through alterations in the atmospheric circulation field over East China and abundant precipitation, which further contributed to the increase in GPP. Downward solar radiation in Southwest China decreased with EASM enhancement, which suppressed GPP and hindered vegetation growth. Overall, the results highlight the importance of accurately predicting the impact of different EASM intensities of regional carbon fluxes.

Extreme precipitation stable isotopic compositions reveal unexpected summer monsoon incursions in the Qilian Mountains

Isotope composition and moisture sources of precipitation are important for understanding water cycles and reconstructing paleoclimate. Based on 15-years' precipitation stable Isotope composition (δ18O and δ2H) from four stations of the Qilian Mountains, we found unique δ18O and δ2H features associated with the incursion of the summer monsoon over the Qilian Mountains, northwestern China. In 12 of the 15 years, similar seasonal variations of δ18O and δ2H confirmed a dominant source of moisture from Westerly circulation, and higher intercepts of the local meteoric water line (LMWL) indicated strong recycling of continental moisture. However, in August 2016 and 2018, extremely low slopes and intercepts of the LMWL, and more negative δ18O and δ2H revealed substantial contributions of the Asian summer monsoon to precipitation of the Qilian Mountains, with extremely heavy precipitation in August 2016. The column moisture flux, land-sea thermal contrast, correlations of precipitation δ18O with East Asian Summer Monsoon Index and Westerlies Index, HYSPLIT modeling results and precipitation δ18O along backward trajectories confirmed incursions of the summer monsoon in August 2016 and 2018. Our redefining of the boundary of the summer monsoon region confirmed the summer monsoon incursion zone can extend to the west of longitude 96°E and north of latitude 40°N in strong monsoon years, corresponding to boundaries of monsoon incursions in the mid-Holocene. Temperature correlated with precipitation δ18O at monthly and shorter time scales, but not for whole seasons or at yearly scale, revealing that summer monsoon incursions are therefore more likely than changing temperature to explain the multi-year cycles in the Qilian Mountains ice archives. Continent-scale shifts in atmospheric circulation strongly influence water resources in the Qilian mountains, and may change in frequency as climate warms. This study therefore has important implications for understanding water resources in the Qilian mountains in the past and into the future.

Interpreting precipitation δ18O over eastern China for the Asian summer monsoon: Results from the last millennium simulations

AbstractThe Asian summer monsoon (ASM) plays a major role in the Asian climate system, affecting nearly half of the world's population. The oxygen isotopes of speleothem calcite (δ18Oc) records in China provide important insights into past ASM changes; however, it remains controversial whether the δ18Oc records over eastern China (EC) mainly reflect the Indian summer monsoon (ISM) or East Asian summer monsoon (EASM). In this study, we estimate the relationships between precipitation‐weighted oxygen isotopes (δ18Opw) and various ASM indices over the last millennium based on the isotope‐enabled Community Earth System Model. The δ18Opw in EC mainly characterizes the intensity of the ISM and, to some extent, reflects the meridional wind component of the EASM, but it has an opposite relationship with the zonal wind component of the EASM. Although the limitations of various EASM definitions lead to the contrary relations between the δ18Opw and EASM indices, the δ18Opw in EC is accompanied by consistent EASM footprints. Moreover, although the meridional wind‐based EASM indices are negatively correlated with δ18Opw over EC, the relationships are much weaker than that with the ISM indices. The widespread negative δ18Opw signals extending from the Indian Peninsula to East Asia are closely coupled with the low‐level circulation over the ISM region. When considering the relationship between the EASM and δ18Opw over EC, the positive contribution from the Northwest Pacific offset the negative contribution from the remote Indian Ocean, leading to the insignificant correlation between the EASM indices and δ18Opw over EC.

Impact of Long‐Distance Interaction Indicator (Monsoon Indices) on Spatio‐Temporal Variability of Precipitation Over the Mahanadi River Basin

AbstractThe variability of the Indian Summer Monsoon Rainfall (ISMR), lasting from June to September, has a major impact on the Indian economy and ecosystem. An attempt to assess the temporal fluctuation of ISMR with the long‐distance interaction indicators has been presented here. This also corroborates the argued statement of a weakening relationship between ISMR and Indian Summer Monsoon Index (ISMI) due to significant temporal fluctuation. Monsoon indices: the ISMI, East Asian Summer Monsoon Index (EASMI), South Asian Summer Monsoon Index (SASMI), and Western‐North Pacific Monsoon Index (WNPMI) have been studied to create a correlation, coherency, and teleconnection with the ISMR over the Mahanadi River basin (MRB) during 1948–2017. High‐resolution gridded precipitation data were employed to assess the statistical properties of the monsoon and to address the correlation, coherency, and teleconnection with the ISMR. Spearman's rank‐based correlation test, a non‐parametric Mann‐Kendall trend test, and Sen's slope have been used to assess the statistical properties of observed precipitation and the monsoon indices. Furthermore, wavelet transform coherence is used to detect transient correlations between ISMR and monsoon indices that have previously been uncorrelated. SASMI (ρ = 0.440) dominates ISMI (ρ = 0.422) as the most significant and influential long‐distance indicator with ISMR. The findings were reconfirmed on a sub‐basin scale, with the middle Mahanadi River Basin (MMRB) being the most significant and influential, whereas the upper Mahanadi River Basin and lower Mahanadi River Basin were the second and third most influential, respectively.

Influence of Spatial Dipole Pattern in Asian Aerosol Changes on East Asian Summer Monsoon

Abstract Since China implemented the Air Pollution Prevention and Control Action Plan in 2013, the aerosol emissions in East Asia have been greatly reduced, while emissions in South Asia have continued to increase. This has led to a dipole pattern of aerosol emissions between South Asia and East Asia. Here, the East Asian summer monsoon (EASM) responses to the dipole changes in aerosol emissions during 2013–17 are investigated using the atmosphere model of Community Earth System Model version 2 (CESM2). We show that decreases in East Asian emissions alone lead to a positive aerosol effective radiative forcing (ERF) of 1.59 (±0.97) W m−2 over central-eastern China (25°–40°N, 105°–122.5°E), along with a 0.09 (±0.07)°C warming in summer during 2013–17. The warming intensified the land–sea thermal contrast and increased the rainfall by 0.32 (±0.16) mm day−1. When considering both the emission reductions in East Asia and increases in South Asia, the ERF is increased to 3.39 (±0.89) W m−2, along with an enhanced warming of 0.20 (±0.08)°C over central-eastern China, while the rainfall insignificant decreased by 0.07 (±0.16) mm day−1. It is due to the westward shift of the strengthened western Pacific subtropical high, linked to the increase in black carbon in South Asia. Based on multiple EASM indices, the reductions in aerosol emissions from East Asia alone increased the EASM strength by almost 5%. Considering the effect of the westward shift of WPSH, the dipole changes in emissions together increased the EASM by 5%–15% during 2013–17, revealing an important role of South Asian aerosols in changing the East Asian climate.

Multi‐factor synergistic effects on summer precipitation in the Meiyu region of China

AbstractSummer precipitation in the Meiyu region of China arises from the synergy of multiple factors such as the East Asian summer monsoon (EASM), Western Pacific subtropical high (WPSH), the sea surface temperature (SST), etc. Based on an analysis of the key influencing factors of summer precipitation in the Meiyu region of China from 1961 to 2019, we selected five key factors: the EASM index (EXSMI), Western Pacific subtropical high area index and ridge line index (WPSH‐AI and WPSH‐RLI), Westerly Index (WI), and NAO index. These five indexes were then used to construct a multi‐factor synergy index (MFSI) by the weighted least‐square method. The results show that the MFSI was able to describe the characteristics of EASMI, WPSH, NAO, and the westerly circulation. It showed a good correlation with the temporal and spatial distribution of summer precipitation in the Meiyu region. In the strong (weak) MFSI years, the NAO index was low (high), the North Atlantic region presented a “+ − +” (“− + −”) three‐pole structure from south to north, the WI was low (high), the Siberian high pressure was weak (strong), the middle and high latitude Eurasia Mainland upper trough and ridge meridional decreased (increased). On the contrary, the precipitation increased (reduced). This index has a good indication of summer precipitation in the Meiyu region, which has important scientific significance and practical value for the prediction and prediction of precipitation in the Meiyu region of China.

Prediction Skill of GEFSv12 in Depicting Monthly Rainfall and Associated Extreme Events over Taiwan during the Summer Monsoon

Abstract The skillful prediction of monthly scale rainfall in small regions like Taiwan is one of the challenges of the meteorological scientific community. Taiwan is one of the subtropical islands in Asia. It experiences rainfall extremes regularly, leading to landslides and flash floods in/near the mountains and flooding over low-lying plains, particularly during the summer monsoon season [June–September (JJAS)]. In September 2020, NOAA/NCEP implemented Global Ensemble Forecast System, version 12 (GEFSv12), to support stakeholders for subseasonal forecasts and hydrological applications. In the present study, the performance evaluation of GEFSv12 for monthly rainfall and associated extreme rainfall (ER) events over Taiwan during JJAS against CMORPH has been done. There is a marginal improvement of GEFSv12 in depicting the East Asian summer monsoon index (EASMI) as compared to GEFS-SubX. The GEFSv12 rainfall raw products have been calibrated with a quantile–quantile (QQ) mapping technique for further prediction skill improvement. The results reveal that the spatial patterns of climatological features (mean, interannual variability, and coefficient of variation) of summer monsoon monthly rainfall over Taiwan from QQ-GEFSv12 are very similar to CMORPH than Raw-GEFSv12. Raw-GEFSv12 has an enormous wet bias and overforecast wet days, while QQ-GEFSv12 is close to reality. The prediction skill (correlation coefficient and index of agreement) of GEFSv12 in depicting the summer monsoon monthly rainfall over Taiwan is significantly high (>0.5) in most parts of Taiwan and particularly more during peak monsoon months, September, and August, followed by June and July. The calibration method significantly reduces the overestimation (underestimation) of wet (ER) events from the ensemble mean and probabilistic ensemble forecasts. The predictability of extreme rainfall events (>50 mm day−1) has also improved significantly.

Interdecadal to Multidecadal Variability of East Asian Summer Monsoon Over the Past Half Millennium

AbstractThe East Asian summer monsoon (EASM) plays a crucial role for ecosystems and societies in East Asia past, present, and future. However, substantial uncertainties remain regarding EASM variability on interdecadal to multidecadal timescales because of the short length of instrumental data in East Asia. This study extended the EASM circulation index in the modern meteorological studies to the paleoclimate over the past half‐millennium (1470–1998 CE) to reconcile the understanding of the EASM variability in paleoclimate and modern meteorological studies. The EASM index is reconstructed based on the common signal from the three main types of the proxy records (the tree rings, speleothems, and historical documentary data) related to EASM. The reconstructed EASM index captures the simultaneous changes of the “Meiyu precipitation” and the southwesterly anomalies in South China on interdecadal to multidecadal timescales, which is a dynamic pattern visible and well‐documented in the modern meteorology. Analysis of the reconstructed EASM index suggests that the interdecadal to multidecadal EASM variability is closely associated with the Pacific‐Japan teleconnection pattern, which acts as a bridge between the negative phase of the Pacific Decadal Oscillation and the anomalous anticyclonic circulation over the western North Pacific. It also indicates that the EASM variability over the recent 30 years (1992–2021 CE) falls within the range of natural variability over the past half‐millennium.

Spatiotemporal Variations of Extreme Precipitation in Wuling Mountain Area (China) and Their Connection to Potential Driving Factors

Changes in extreme precipitation have become a significant issue of regional disaster risk assessment and water resources management. Extreme precipitation variability is affected by multiple factors and shows disparities across different regions. Especially in mountain areas, geographic feature and local characteristics put more complexity and uncertainty on the changes of precipitation extremes. In this study, ten extreme precipitation indices of Wuling Mountain Area (WMA) during 1960–2019 have been used to analyzed the spatiotemporal variations of precipitation extremes. The relationships between extreme precipitation and potential driving factors, including geographic factors, global warming, local temperature, and climate indices, were investigated via correlation analysis. The results indicated that extreme precipitation tends to have a shorter duration and stronger intensity in WMA. Decreasing trends in R10mm, R20mm, R25mm, and the consecutive wet days (CWD) series account for 92%, 68%, 52%, and 96% of stations, while most stations in WMA have rising trends in Rx1day (68%), SDII (64%), R95p (72%), and R99p (72%). Significant abrupt changes in extreme precipitation indices mainly occurred in the 1980s–1990s. Geographic factors, local temperature, and climate indices exert different impacts on extreme precipitation. Longitude and elevation instead of latitude significantly affect extreme precipitation indices except for the maximum duration of wet spells. Global warming is likely to increase the intensity and decrease the duration of extreme precipitation, while the influence of local temperature is not exactly the same as that of global warming. The study reveals that summer monsoon indices are the dominant climate factor for variations of precipitation extremes in WMA. The correlation coefficient between extreme precipitation indices (such as Rx1day, R95p, R99p) and the East Asian summer monsoon index is around 0.5 and passed the significant test at the 0.01 level. The weakening of the summer monsoon indices tends to bring extreme precipitation with stronger intensity. The findings provide more understanding of the drivers and reasons of extreme precipitation changes in the mountain area.

Analysis of Extreme Temperature Variations on the Yunnan-Guizhou Plateau in Southwestern China over the Past 60 Years

Analysis of variations in 12 extreme temperature indices at 68 meteorological stations on the Yunnan-Guizhou Plateau (YGP) in southwestern China during 1960–2019 revealed widespread significant changes in all temperature indices. The temperature of the hottest days and coldest nights show significantly increasing trends, and the frequencies of the warm days and nights also present similar trends. The temperature of the coldest night has a significant and strong warming trend (0.38 °C/decade), whereas the frequency of frost days shows the fastest decrease (1.5 days/decade). Increases in the summer days are statistically significant, while a decreasing trend for the diurnal temperature range is not significant. Furthermore, there were significant differences in the changes of temperature indices between 1960–1989 and 1990–2019. Most parts of the YGP underwent significant warning, manifesting that the mountainous regions are relatively sensitive and vulnerable to climate change. The correlation coefficients between the temperature indices and various geographical factors (latitude, longitude, and height) reflect the complexity of regional temperature variability and indicate enhanced sensitivity of extreme temperatures to geographical factors on the YGP. It was also found that extreme temperatures generally had weaker correlations with the El Nino-Southern Oscillation, North Pacific Index, Southern Oscillation Index, North Atlantic Oscillation, and East Asian Summer Monsoon Index than with the South Asian summer monsoon index, Nino4 indices and Arctic Oscillation, and there were more insignificant correlations. Regional trends of the extreme temperature indices reflect the non-uniform temperature change over the YGP, which is due to the complex interaction between atmospheric circulation patterns and local topography. The results of this study have important practical significance for mitigating the adverse effects of extreme climatic changes, in particular for the YGP with its typical karst geomorphology and fragile ecological environment.

Differences in East Asian summer monsoon responses to Asian aerosol forcing under different emission inventories

Opposite anthropogenic aerosol emission trends in Asia can lead to different responses of the climate. Here, we examined the responses of the East Asian summer monsoon (EASM) to changes in Asian anthropogenic aerosol emissions during 2006–2014 using a global aerosol/atmospheric chemistry–climate coupled model (BCC_AGCM2.0_CUACE/Aero) with two sets of emission inventories: the Community Emissions Data System (CEDS) inventory adopted by the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the inventory developed at Peking University (PKU). The changes in Asian anthropogenic aerosol emissions during 2006–2014 between the two inventories were remarkably different, particularly in eastern China where completely opposite trends were observed (i.e., increase in the CEDS inventory, but significant reduction in the PKU inventory). The perturbation simulations with the Asian anthropogenic aerosol forcing from the two inventories showed opposite changes in aerosol optical depth, aerosol effective radiative forcing, cloud liquid water path, and total cloud cover in eastern China. The simulated ‘dipole-type’ changes (i.e., increase in India but decrease in China) in Asian aerosols and the resulting changes in local radiation budget under the PKU inventory were consistent with the corresponding observations. The summer surface temperatures over eastern China decreased by 0–0.4 K because of the Asian anthropogenic aerosol forcing under the CEDS inventory, while they increased by 0.1–0.8 K under the PKU inventory. The weakening of the EASM index caused by the Asian aerosol forcing under the PKU inventory was twofold greater than that under the CEDS inventory (−0.4 vs. −0.2). The Asian ‘dipole-type’ aerosol forcing contributed to the observed summer ‘southern drought and northern flood’ phenomenon in eastern China during 2006–2014. The slow ocean-mediated response to the regional ‘dipole-type’ aerosol forcing dominated the weakening of the EASM circulation and the precipitation changes in eastern China in the total response. This study further confirms that the biases in anthropogenic aerosol emissions over Asia can affect the CMIP6-based regional climate attribution.

Extreme precipitation variability across the Lancang‐Mekong River Basin during 1952–2015 in relation to teleconnections and summer monsoons

AbstractThe Lancang‐Mekong River Basin (LMRB) is home to ~70 million people whose life and livelihood are mostly dependent upon precipitation as the primary freshwater source. Hence, identifying potential oceanic–atmospheric drivers of regional precipitation variability is becoming increasingly important for the sustainable development of the LMRB. This study first investigated spatio‐temporal variability and trends in extreme precipitation characteristics (in terms of intensity, frequency, and duration) throughout the LMRB during 1952–2015, using gauge‐based gridded daily precipitation time series. Then, the associations between the historical extreme precipitation characteristics and seven teleconnection and five summer monsoon indices were explored. On the basin scale, no statistically significant (p < .05) trends were detected in annual extreme precipitation intensity, frequency, and duration indices. The number of wet days (R1mm) significantly increased in both the Mekong River Basin (MRB) and the Lancang River Basin (LRB), predominantly leading to longer wet spells in these two sub‐basins. Spatially, the relatively high extreme precipitation intensity and frequency indices, as well as consecutive wet days (CWD), significantly increased in the south, east, and northwest of MRB, while decreased in the west of MRB and the north of LRB. The intensity and frequency of historical extreme precipitations over the LMRB were most significantly correlated with the East Asian Summer Monsoon Index, North Atlantic Oscillation, and East Pacific/North Pacific pattern. However, the wet/dry spells showed the strongest associations with the Atlantic Multi‐decadal Oscillation/the Southern Oscillation Index on the interannual/decadal time scales (3–4/8–15 years) during 1986–1999/1968–2002, respectively.

Spatiotemporal changes and modulations of extreme climatic indices in monsoon-dominated climate region linkage with large-scale atmospheric oscillation

Spatiotemporal changes in six precipitation and five temperature extreme indices of Bangladesh and their linkage with nine ocean-atmospheric oscillation indices have been evaluated in this study to provide necessary information for adaptation planning and development of early warning systems. Daily maximum and minimum temperatures and precipitation for the period 1980–2017 recorded at 20 stations, homogeneously distributed over the country, were employed for this purpose. Modified Mann-Kendall (MMK) test was used to evaluate trends in weather extremes, and detrended fluctuation analysis (DFA) was employed to anticipate the possible continuation of existing trends in the future. The cross-wavelet transform (CWT) was used to evaluate the linkage of weather extremes with oscillation indices in the time-frequency domain. The results indicate an increase in hot extremes and a decrease in cool indices in Bangladesh. An increase in the continuous dry day (CDD) and one-day maximum precipitation (RX1day) was also observed, indicating gradual drying and more susceptibility to flash floods at the same time. DFA revealed the possible continuation of existing trends in temperature and precipitation indices. Almost all the climatic extreme indices of Bangladesh were found to follow periodic cycles with different frequencies. The hot extremes were significantly associated with five out of nine oscillation indices, including Atlantic Multidecadal Oscillation (AMO), Arctic Oscillation (AO), East Asian Summer Monsoon Index (EASMI), Sunspot, and South Asian Summer Monsoon Index (SASMI), while cool indices were linked with AMO only. Among the precipitation indices, only CDD was positively related to AO, El Niño Southern Oscillation (ENSO), and Southern Oscillation Index (SOI) and negatively associated with the Pacific Decadal Oscillation (PDO). Analysis of circulation patterns using reanalysis datasets explored that elevated summer geopotential height, no visible anticyclonic center, reduced high cloud cover, and enhanced low cloud covers contributed to increasing hot extremes in Bangladesh.

Index‐ and model‐dependent projections of East Asian summer monsoon in Coupled Model Intercomparison Project Phase 6 simulations

AbstractIn terms of five categories of East Asian summer monsoon (EASM) indices and one classic meridional wind index, we project the EASM intensity change over the 21st century using 27 global climate models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) under the mid‐range combined scenarios of Shared Socioeconomic Pathways and Representative Concentration Pathways (SSP2‐4.5). Results show that future changes in the EASM intensity are index‐ and model‐dependent. Relative to the reference period 1985–2014, the EASM intensity strengthens slightly based on the east–west thermal contrast indices but varies little as a whole based on the southwest monsoon indices over the 21st century, with large discrepancies among the models. However, it tends to weaken over time based on the other three categories of indices, including the north–south thermal contrast indices, the shear vorticity indices, and the South China Sea monsoon indices. In terms of the meridional wind index that directly measures the EASM circulation in the lower troposphere and holds valid under future global warming, the EASM intensity strengthens significantly over the 21st century as a consequence of increases in zonal and meridional land–sea thermal contrasts between the East Asian continent and the adjacent oceans of western North Pacific and South China Sea. There are certain relationships between the trends of the meridional wind index and other EASM indices. The projections are overall consistent between the ensemble means of all available 27 models and the 14 good models as selected according to their abilities to simulate the present EASM climatology, but with different magnitudes.

Improved decadal predictions of East Asian summer monsoon with a weakly coupled data assimilation scheme

AbstractThe East Asian summer monsoon (EASM) has undergone significant decadal variations since the late 1970s, which greatly affects regional economic and societal activities. However, most available EASM predictions are limited to seasonal to interannual scales, with indistinctive improvements. This study significantly improves decadal prediction skills of the 10‐year‐averaged EASM index (EASMI) and related decadal variations of the East China summer precipitation anomalies (ECSPAs) in the 10‐member decadal prediction experiments started once a year from 1960 to 2005 using a coupled climate model. These improvements are mainly attributed to the use of more realistic and well‐balanced initial conditions (ICs) from a weakly coupled data assimilation system that incorporates the monthly mean atmospheric reanalysis data into the model using the dimension‐reduced projection four‐dimensional variational data assimilation approach, a kind of four‐dimensional ensemble‐variational hybrid method. The atmospheric initialization ameliorates the ICs of Pacific Decadal Oscillation (PDO) through the air‐sea coupling, and thus leads to better PDO hindcasts and forecasts (under the representative concentration pathway 4.5). The improved PDO hindcasts (forecasts) result in more accurate hindcasts (forecasts) of land‐sea thermal contrast, and thus have significant impacts on the EASMI. The improved decadal predictions of the EASMI then contribute to the ameliorated prediction on decadal variations of the spatial distribution of ECSPAs. This study highlights the importance of ICs for a coupled model in reasonably presenting decadal variabilities of the EASMI.

Annual and seasonal precipitation trends and their attributions in the Qinling Mountains, a climate transitional zone in China

In this study, annual and seasonal precipitation trends and their connection with large-scale climate indices in the Qinling Mountains (QMs) were investigated using the innovative trend analysis (ITA), based on observed monthly precipitation data between 1959 and 2016 from 32 meteorological stations. The results indicated a declining trend in annual precipitation in the QMs. Seasonally, a decreasing trend was also observed in spring and autumn, while increasing trends were observed in summer and winter. Spring and autumn precipitations significantly contributed to this observed decline in annual precipitation. More importantly, both low and high values indicated a declining trend, which would have a significant influence on ecology and livelihood in the QMs. Additionally, the results of wavelet coherence showed that annual precipitation is strongly associated with the East Asian Summer Monsoon Index (EASMI), Southern Oscillation Index (SOI), South Asian Summer Monsoon Index (SASMI), South China Sea Summer Monsoon Index (SCSMI), and Southwest Australian Circulation Index (SWACI). However, its relationship with the North Atlantic Oscillation (NAO) and West African Summer Monsoon Index (WASMI) was insignificant, and seasonally, EASMI had negative effects on the precipitation in each season. It was also observed that spring and autumn precipitations were more sensitive to SOI than SWACI, while SASMI had a strong positive relationship with winter precipitation, and SCSMI was more negatively related to autumn and winter precipitation. This study will provide scientific basis for precipitation forecast, prevention, and mitigation of flood in the future.

Spatiotemporal variations of extreme precipitation and its potential driving factors in China’s North-South Transition Zone during 1960–2017

Based on the daily data collected from 69 meteorological stations in the Qinling-Daba Mountains (Qinba mountains) and its surrounding areas during 1960–2017. We analyzed The spatiotemporal variations of extreme precipitation events in the Qinba mountains and the relationship between the changes of extreme precipitation indices and potential factors (including geographical factors and atmospheric circulation patterns). The Mann-Kendall method and linear trend analysis were used to test the variations of extreme precipitation indices. Besides, the Pearson correlation analysis method was used to analyze the correlation between precipitation extremes and potential controlling factors (including geographic and atmospheric factors). The results showed that (1) consecutive dry days (CDD), simple daily intensity index (SDII), highest 1-day precipitation (RX1day) and very heavy rain days (R20mm), very wet days (R95P) and extremely wet days (R95P) and extremely wet days (R99P) showed an increasing trend, all other extreme precipitation indices showed decreasing trend and the change trends in all extreme indices were non-significant in annual and seasonal scales over Qinba mountains; (2) extreme precipitation increased in the eastern part of Qinba mountains while decreased in the western region; (3) there is a significant correlation between altitude, longitude, latitude and extreme precipitation; (4) the large-scale atmospheric circulation patterns also a significant impact on the spatiotemporal variations of extreme precipitation in the transition areas; the change of extreme precipitation indices is closely related to the El Niño–Southern Oscillation (ENSO) at interannual scales; (5) East Asian Summer Monsoon Index (EASMI) and the South China Sea Summer Monsoon Index (SCSSMI) show significant correlation with the extreme precipitations in summer while Arctic Oscillation (AO) show significant correlation wih the extreme indices in winter in Qinba mountains. Results of this study may help to deeper understand and predict the extreme precipitation events in Qinba mountains.

Contribution of the Northeast Cold Vortex Index and Multiscale Synergistic Indices to Extreme Precipitation Over Northeast China

AbstractThe northeast cold vortex (NECV) is one of the major synoptic systems affecting Northeast China. The activity of NECV is an important reason for severe convective storms. However, research on extreme precipitation over Northeast China and their associations with the northeast cold vortex index (NECVI) is limited. Based on nonstationary generalized extreme value models, we analyze and quantify the contribution of the NECVI and the multiscale synergistic indices. Then, we verify the necessity of the NECVI by the likelihood ratio test and the blank control experiment, and further verify the impact of the NECVI on the extreme precipitation over Northeast China in combination with the climate index atmospheric circulation analysis. Results suggest that the models established with East Asian summer monsoon index, Southern Oscillation Index, and NINO3.4 index as covariates the most common. The NECVI and the synergies also make significant contribution and have passed the likelihood ratio test at 80% confidence. Especially in late summer, accounting for 18.69% of the 10 selected best models and 29.41% of the nine selected best nonstationary models. Based on the blank experiments, the models with the NECVI have a maximum reduction of 4.72% than those without the NECVI in the Akaike information criterion values in late summer. In early summer and late summer, the center of the high values of the water vapor anomaly is mainly located in southwestern in the strong NECVI years. These findings help to understand the genetic mechanism of extreme precipitation over Northeast China and provide reference for risk management.

Prediction Skill for East Asian Summer Monsoon Indices in a KMA Global Seasonal Forecasting System (GloSea5)

Prediction Skill for East Asian Summer Monsoon Indices in a KMA Global Seasonal Forecasting System (GloSea5)

The modulation of westerlies‐monsoon interaction on climate over the monsoon boundary zone in East Asia

AbstractMonsoon boundary zone (MBZ) is a transitional zone between the arid Central Asia (ACA) and humid Asia monsoon area, located in North China‐Mongolia. During boreal summer, both the mid‐latitude westerlies and East Asian Summer monsoon (EASM) play essential roles in the precipitation variations in the MBZ, via causing anomalous cold air mass from the west and warm/humid air from the south to the MBZ. In this study, we defined a summer westerly index (SWI) over the key westerly domain (35°‐42.5°N, 80°‐100°E) and an EASM index (EASMI) over the key EASM domain (25°‐35°N, 107.5°‐125°E) to investigate westerlies‐monsoon interaction and their effect on MBZ climate. The results show that westerlies and EASM have a synergistic effect on the precipitation in the MBZ and this synergistic effect could be amplified by the westerlies‐monsoon interaction. The westerlies and EASM interaction could induce a local cyclonic anomaly in the MBZ, this cyclonic anomaly further intensifies the westerlies and monsoon flow through a dynamical amplification, favours the precipitation in the MBZ. The MBZ precipitation also contributes to maintain the cyclonic anomaly via the latent heating release. The interannual variability of westerlies is largely modulated by the mid‐latitude Silk Road pattern (SRP) and the meridional displacement of the Asian westerly jet (AWJ), and the EASM variability is mainly modulated by El Niño‐Southern Oscillation (ENSO), the combined effects from these mid‐latitude circulation systems and tropical SST contribute to the climate variability in MBZ.