Sunshine duration reconstruction in the southeastern Tibetan Plateau based on tree-ring width and its relationship to volcanic eruptions

Sunshine is as essential as temperature and precipitation for tree growth, but sunshine duration reconstructions based on tree rings have not yet been conducted in China. In this study, we presented a 497-year sunshine duration reconstruction for the southeastern Tibetan Plateau using a width chronology of Abies forrestii from the central Hengduan Mountains. The reconstruction accounted for 53.5% of the variance in the observed sunshine during the period of 1961-2013 based on a stable and reliable linear regression. This reconstructed sunshine duration contained six sunny periods (1630-1656, 1665-1697, 1731-1781, 1793-1836, 1862-1895 and 1910-1992) and seven cloudy periods (1522-1629, 1657-1664, 1698-1730, 1782-1792, 1837-1861, 1896-1909 and 1993-2008) at a low-frequency scale. There was an increasing trend from the 16th century to the late 18th and early 19th centuries and a decreasing trend from the mid-19th to the early 21st centuries. Sunshine displayed inverse patterns to the local Palmer drought severity index on a multidecadal scale, indicating that this region likely experienced droughts under more sunshine conditions. The decrease in sunshine particularly in recent decades was mainly due to increasing atmospheric anthropogenic aerosols. In terms of the interannual variations in sunshine, weak sunshine years matched well with years of major volcanic eruptions. The significant cycles of the 2- to 7-year, 20.0-year and 35.2-year durations as well as the 60.2-year and 78.7-year durations related to the El-Nino Southern Oscillation, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation suggested that the variation in sunshine duration in the southeastern Tibetan Plateau was possibly affected by large-scale ocean-atmosphere circulations. (C) 2018 Elsevier B.V. All rights reserved

Viruses mobilize plant immunity to deter nonvector insect herbivores.

A parasite-infected host may promote performance of associated insect vectors; but possible parasite effects on nonvector insects have been largely unexplored. Here, we show that Begomovirus, the largest genus of plant viruses and transmitted exclusively by whitefly, reprogram plant immunity to promote the fitness of the vector and suppress performance of nonvector insects (i.e., cotton bollworm and aphid). Infected plants accumulated begomoviral βC1 proteins in the phloem where they were bound to the plant transcription factor WRKY20. This viral hijacking of WRKY20 spatiotemporally redeployed plant chemical immunity within the leaf and had the asymmetrical benefiting effects on the begomoviruses and its whitefly vectors while negatively affecting two nonvector competitors. This type of interaction between a parasite and two types of herbivores, i.e., vectors and nonvectors, occurs widely in various natural and agricultural ecosystems; thus, our results have broad implications for the ecological significance of parasite-vector-host tripartite interactions

Anthropogenic Aerosols Cause Recent Pronounced Weakening of Asian Summer Monsoon Relative to Last Four Centuries

The Asian Summer Monsoon (ASM) affects ecosystems, biodiversity, and food security of billions of people. In recent decades, ASM strength (as represented by precipitation) has been decreasing, but instrumental measurements span only a short period of time. The initiation and the dynamics of the recent trend are unclear. Here for the first time, we use an ensemble of 10 tree ring-width chronologies from the west-central margin of ASM to reconstruct detail of ASM variability back to 1566 CE. The reconstruction captures weak/strong ASM events and also reflects major locust plagues. Notably, we found an unprecedented 80-year trend of decreasing ASM strength within the context of the 448-year reconstruction, which is contrary to what is expected from greenhouse warming. Our coupled climate model shows that increasing anthropogenic sulfate aerosol emissions over the Northern Hemisphere could be the dominant factor contributing to the ASM decrease. Plan Language Summary Monsoonal rainfall has a certain influence on agriculture and industry in the regions of Asian Summer Monsoon (ASM). An understanding of the spatial-temporal variability of the ASM and the associated dynamics is vital for terrestrial ecosystems, water resources, forests, and landscapes. We have developed a 448-year ASM reconstruction back to 1566 CE using 10 tree ring chronologies from the margin region of ASM. We find that historical severe droughts and locust plague disasters during weak ASM events. The recent decreasing ASM trend persisting for over 80 years is unprecedented over the past 448 years. Coupled climate models show that increasing anthropogenic aerosol emissions are the dominant underlying factor. Our aim is that the time series will find a wide range of utility for understanding past climate variability and for predicting future climate change.National Natural Science Foundation of China [41630531]; National Research Program for Key Issues in Air Pollution Control [DQGG0104]; Chinese Academy of Sciences [QYZDJ-SSW-DQC021, XDPB05, GJHZ1777]; Institute of Earth Environment, Chinese Academy of Sciences; State Key Laboratory of Loess and Quaternary Geology6 month embargo; first published: 09 April 2019This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Why Does Extreme Rainfall Occur in Central China during the Summer of 2020 after a Weak El Nino?

In summer 2020, extreme rainfall occurred throughout the Yangtze River basin, Huaihe River basin, and southern Yellow River basin, which are defined here as the central China (CC) region. However, only a weak central Pacific (CP) El Nino happened during winter 2019/20, so the correlations between the El Nino-Southern Oscillation (ENSO) indices and ENSO-induced circulation anomalies were insufficient to explain this extreme precipitation event. In this study, reanalysis data and numerical experiments are employed to identify and verify the primary ENSO-related factors that cause this extreme rainfall event. During summer 2020, unusually strong anomalous southwesterlies on the northwest side of an extremely strong Northwest Pacific anticyclone anomaly (NWPAC) contributed excess moisture and convective instability to the CC region, and thus, triggered extreme precipitation in this area. The tropical Indian Ocean (TIO) has warmed in recent decades, and consequently, intensified TIO basinwide warming appears after a weak El Nino, which excites an extremely strong NWPAC via the pathway of the Indo-western Pacific Ocean capacitor (IPOC) effect. Additionally, the ENSO event of 2019/20 should be treated as a fast-decaying CP El Nino rather than a general CP El Nino, so that the circulation and precipitation anomalies in summer 2020 can be better understood. Last, the increasing trend of tropospheric temperature and moisture content in the CC region after 2000 is also conducive to producing heavy precipitation

A July-August relative humidity record in North China since 1765 AD reconstructed from tree-ring cellulose delta O-18

Since the late 1970s, East Asian summer monsoon (EASM) has shown a significant weakening trend, and sustained drought has occurred across North China. Placing recent climate changes in the paleoclimatic context can better understand the EASM variations. Four delta O-18 sequences based on tree-ring cellulose of Chinese pine were developed from Mt. Beiwudang, North China, covering a period from 1700 to 2013. Based on a climatic response analysis, a transfer function was designed to reconstruct the relative humidity from July to August (RHJA hereafter). The RHJA spans from 1765 to 2013 and explains 49% (R-adj(2)= 48%) of the instrumental variance during the calibration period (1961-2013, r = - 0.70, p < 0.0001). The RHJA is mainly influenced by precipitation in the summer rainy season and reflect EASM variations. Spatial representation analysis indicates that RHJA represents the dry/wet variations across North China. At the interannual scale, RHJA records many extreme dry/wet events, among which the events in 1876-1878, 1900, and the 1920s are extensive droughts. Those events correspond well to ENSO events, plus further correlation and periodicity analysis indicate that RHJA contains ENSO signals. At the interdecadal scale, RHJA shows a decreasing trend and unprecedented low values from 1981 to 2013, suggesting that the weakening of EASM since the late 1970s is unprecedented in the past 249 years. Similarly, the significantly correlating region in the spatial correlation analysis, covering the Meiyu/Baiu/Changma rainfall belt and India, have also undergone a climatic shift since the late 1970s according to previous papers

How is the El Nino-Southern Oscillation signal recorded by tree-ring oxygen isotopes in southeastern China?

Previous studies universally found that tree-ring oxygen isotope (delta O-18(TR)) in southeastern China (SEC) significantly recorded the El Nino-Southern Oscillation (ENSO) signal. However, the correlation between the climate in SEC and ENSO is insignificant, so the local climatic response of SEC delta O-18(TR) fails to explain the significant positive correlations between these delta O-18(TR) records and ENSO. In this study, based on four delta O-18(TR) series from SEC, meteorological data, simulated precipitation oxygen isotope (delta O-18(P)) data, and a moisture uptake atlas deduced from Lagrangian backward trajectory experiments, a conceptual model was established to explain how the ENSO signal is recorded by SEC delta O-18(TR). During the El Nino decaying years, the Northwest Pacific (NWP) convective activity weakens; the convective weakening areas coincide with the main moisture sources for SEC, which enriches O-18 in moisture that is transported to SEC, resulting in positive anomalies of delta O-18(P) in SEC; finally, the ENSO-modulated delta O-18(P) signal is inherited by SEC delta O-18(TR). The opposite situations occur in the La Nina events. It was also indicated that the change in the moisture contribution percentage from different sources may not be a primary factor that connects SEC delta O-18(TR) with ENSO. These findings contribute to understanding climatic signals represented by delta O-18(TR) and delta O-18(P) in the East Asian monsoon region

An Asian Summer Monsoon-Related Relative Humidity Record from Tree-Ring delta O-18 in Gansu Province, North China

The monsoon fringe region in North China (NC) is also an ecologically fragile zone. Improving our comprehension of the paleoclimate variations and their driving mechanisms in this region has great significance for environmental protection and agricultural economic development. In order to provide more reliable data for future climate forecasting and reduce the effects of climatic disasters in NC, we established a 328-year stable oxygen isotope (delta O-18) chronology based on fourPinus tabulaeformisCarr. from Mt. Hasi, Gansu Province, and found that the tree-ring delta O-18 inherited the signals of summer (July-August) monsoonal precipitation delta O-18 (delta O-18(P)). Correlation function analysis indicated that the tree-ring delta O-18 series responded significantly to the observed local relative humidity from July to August (RHJA) withr= -0.65 (n= 55,p< 0.001). Based on the clear physiological mechanism, we reconstructed the RH(JA)variations from 1685 to 2012 using a transfer function. Our reconstruction was very stable and had strong spatial representativeness, it was significantly positively correlated with Asian summer monsoon (ASM) indices, indicating that our reconstruction reflected the variations of ASM to a large extent. The RH(JA)series successfully captured the weakening of the ASM since the 1930s. There was a close connection between the reconstructed sequence and the East Pacific sea surface temperature (SST). Further analyses revealed that El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) may play important roles in the summer monsoon precipitation in NC

Similarities and differences in driving factors of precipitation changes on the western Loess Plateau and the northeastern Tibetan Plateau at different timescales

Climate change constitutes the superposition of climatic variations at different timescales and is affected by driving factors at multiple scales. Therefore, clarifying the changes in and driving factors of the climate at different timescales is crucial for climate predictions. Here, using the ensemble empirical mode decomposition method, we obtained four components of the western Loess Plateau (WLP) precipitation at the interannual, interdecadal, multidecadal and centennial scales and the long-term change trend, which accounted for 40.4, 33.5, 11.5, 11.6 and 3.0%, respectively, of the total variance in the tree-ring-based precipitation reconstruction during 1566-2013 AD. El Nino-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Variability (AMV) mainly affected the interannual-decadal, multidecadal and centennial changes, respectively, before increasing anthropogenic aerosol emissions began influencing the WLP precipitation. Using the same method, we also obtained four components of the precipitation on the northeastern Tibetan Plateau (NETP) at different timescales and found that the interannual-decadal and multidecadal changes in the precipitation on the NETP exhibited good relationships with the changes in the WLP precipitation over the past four centuries and were also mainly affected by ENSO and the PDO, respectively. The correlation between the WLP and NETP precipitation at the centennial scale was mainly positive, and the precipitation relationship between these two regions was affected by solar radiation and the AMV to some extent. However, due to the effects of global warming on NETP precipitation and the effects of increasing anthropogenic aerosols on WLP precipitation, this correlation has become negative in recent decades, indicating that without the influences of human activities, the precipitation on the WLP would be positively related to the NETP precipitation

Tree-ring delta O-18 based PDSI reconstruction in the Mt. Tianmu region since 1618 AD and its connection to the East Asian summer monsoon

Previous studies on tree-ring stable oxygen isotopes (delta O-18) in the monsoon region of China have rarely involved in variations of the East Asian summer monsoon (EASM) and its rainbelt. In this study, a tree-ring delta O-18 chronology of Cryptomeria fortune at Mt. Tianmu, located south of the Yangtze River lower reaches, was developed and applied to reconstruct the local June-October Palmer Drought Severity Index (PDSI6-10) during the 1618-2013 AD period. The reconstruction explains 40.5% of the observational PDSI6-10 variances during 1951-2013, captures the actual variation features at both high and low frequencies, largely represents the PDSI6-10 in the middle and lower reach regions of the Yangtze River and further south, and the reconstruction is well-compared with other existing proxies. The reconstruction reveals that the durations of 1620 s-1660 s, 1680 s-1700 s, 1810 s-1830 s, 1850 s, 1900 s-1940 s, and 1960 s were drought periods, while wet durations were 1730 s-1770 s, 1790 s-1800 s, 1860 s-1870 s, 1950 s, and 1980 s-1990 s. Based on the meteorological re-analysis data and new EASM definitions, the reconstructed PDSI6-10 correlates with the meiyu rainbelt precipitation and EASM intensity during May-June, which is when Mt. Tianmu is affected by the EASM rainbelt. The Mt. Tianmu tree-ring delta O-18 chronology exhibits significantly positive correlations with El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). The relationship of the tree-ring delta O-18 chronology with the PDO could be due to EASM associations, while it is not clear to explain the mechanism of ENSO connecting to the tree-ring oxygen isotope

Tree-ring width-based precipitation reconstruction in Zhaogaoguan, China since 1805 AD

In order to further understand the past climate variation especially the history of drought and flood events in the East Asian summer monsoon (EASM) marginal area, precipitation from previous August to current July for the period of 1805-2014 AD was reconstructed from a ring-width chronology of Pinus tabulaeformis in Zhaogaoguan (ZGG), a site located in the EASM marginal area in northern China. The transfer function can explain 46.4% (adjusted to 45.4% for the loss of degrees of freedom) of the variance of the observed precipitation during the calibration period (1958-2014 AD). The reconstructed precipitation series revealed that the inter-annual variability was very prominent; 1843 and 1844 AD were the two wettest years, while 1931 and 1999 AD were the two driest years. We noticed that the droughts in 1900, 1906, 1931, 1955 and 1999 AD in the reconstruction series corresponded to the severe floods in the Yangtze River watershed in southern China during those same years. This phenomenon confirmed the typical climate pattern of northern droughts and southern floods in China. Moreover, the reconstructed precipitation series in ZGG showed synchronous variation patterns with the other tree-ring-based hydrological reconstructions in the marginal area of EASM on both inter-annual and inter-decadal scales, indicating the common precipitation variation characteristics of the EASM marginal area