Interdecadal Variability Research Articles

Spatiotemporal effects of urban ecological land transitions to thermal environment change in mega-urban agglomeration

Urban ecological land transitions (UELTs) have far-reaching effects on the thermal environment, but their dynamic effects in urban agglomerations remain poorly understood. This study defines the UELTs concept and quantifies its spatiotemporal effects and driving mechanisms on land surface temperature interdecadal variations (LSTIVs) in the Guangdong–Hong Kong–Macao Greater Bay Area using remote sensing, fuzzy overlay, shape-weighted landscape evolution index, and Geodetector methods. The results showed that UELTs shifted from degradation, increasing pressure, and decreasing vegetation proportion in the central city to scattered restoration, pressure relief, and increasing vegetation proportion in 2010–2020. LSTIVs simultaneously transitioned from rapid growth and contiguous expansion to reduction and dispersion. Moreover, the contribution of UELTs to LSTIVs increased by 19.49% from 2000 to 2020, and gradually shifted from being driven by dominant transition (isolating and adjacent degradation) (mean q = 0.58) to recessive transition (increased population and construction land pressure) (mean q = 0.62), where q is the determinant power. Interactions between edge-expansion and infilling restoration with the blue–green ratio (BGR; i.e., ratio of waterbodies to vegetation), habitat quality, and population layout had significant effects on LSTIVs. In addition, the relative magnitude of the effect of UEL restoration–degradation and BGR on LSTIVs was not fixed, but rather related to their interaction effect and the urban agglomeration development stage. Therefore, in addition to promoting an increase in UEL, optimizing the landscape structure of UEL (e.g., increasing aggregation and connectivity, adjusting BGR) and UEL distribution with other human factors are also crucial to reduce the urban thermal environment.

The predictability study of the two flavors of ENSO in the CESM model from 1881 to 2017

In this study, we evaluated the predictability of the two flavors of the El Niño Southern Oscillation (ENSO) based on a long-term retrospective prediction from 1881 to 2017 with the Community Earth System Model. Specifically, the Central-Pacific (CP) ENSO has a more obvious Spring Predictability Barrier and lower deterministic prediction skill than the Eastern-Pacific (EP) ENSO. The potential predictability declines with lead time for both the two flavors of ENSO, and the EP ENSO has a higher upper limit of the prediction skill as compared with the CP ENSO. The predictability of the two flavors of ENSO shows distinct interdecadal variation for both actual skill and potential predictability; however, their trends in the predictability are not synchronized. The signal component controls the seasonal and interdecadal variations of predictability for the two flavors of ENSO, and has larger contribution to the CP ENSO than the EP ENSO. There is significant scope for improvement in predicting the two flavors of ENSO, especially for the CP ENSO.

Worsening drought of Nile basin under shift in atmospheric circulation, stronger ENSO and Indian Ocean dipole

Until now, driving mechanisms behind recurring droughts and hydroclimate variations that controls the Nile River Basin (NRB) remains poorly understood. Our results show significant hydroclimatic changes that contributed to recent increasing aridity of NRB since the 1970s. Besides climate warming, the influence of stronger ENSO and Indian Ocean dipole (IOD) in NRB has increased after 1980s, which have significantly contributed to NRB’s drought severity at inter-annual to inter-decadal timescales. Our results demonstrate that warming, El Niño and IOD have played a crucial role on NRB’s inter-decadal hydroclimate variability, but IOD has played a more important role in modulating NRB’s hydroclimate at higher timescales than El Niño. Results also indicate that the impacts of positive phases of ENSO and IOD events are larger than the negative phases in the NRB hydroclimate. Further, the southward (westward) shift in stream functions and meridional (zonal) winds caused an enhancement in the blocking pattern, with strong anticyclonic waves of dry air that keeps moving into NRB, has resulted in drier NRB, given stream function, geopotential height and U-wind anomalies associated with El Niño shows that changes in regional atmospheric circulations during more persistent and stronger El Niño has resulted in drier NRB. After 1970s, El Niño, IOD, and drought indices shows significant anti-phase relationships, which again demonstrates that more frequent and severe El Niño and IOD in recent years has led to more severe droughts in NRB. Our results also demonstrate that IOD and and the western pole of the Indian Ocean Dipole (WIO) are better predictors of the Nile flow than El Niño, where its flow has decreased by 13.7 (upstream) and by 114.1 m3/s/decade (downstream) after 1964. In summary, under the combined impact of warming and stronger IOD and El Niño, future droughts of the NRB will worsen.

A tripole winter precipitation change pattern around the Tibetan Plateau in the late 1990s

Classical monsoon dynamics considers the winter/spring snow amount on the Tibetan Plateau (TP) as a major factor driving the East Asian summer monsoon (EASM) for its direct influence on the land–sea thermal contrast. Actually, the TP snow increased and decreased after the late 1970s and 1990s, respectively, accompanying the two major interdecadal changes in the EASM. Although studies have explored the possible mechanisms of the EASM interdecadal variations, and change in TP snow is considered as one of the major drivers, few studies have illustrated the underlying mechanisms of the interdecadal changes in the winter TP snow. This study reveals a tripole pattern of change, with decreased winter precipitation over the TP and an increase to its north and south after the late 1990s. Further analyses through numerical experiments demonstrate that the tropical Pacific SST changes in the late 1990s can robustly affect the winter TP precipitation through regulating the Walker and regional Hadley circulation. The cooling over the tropical central-eastern Pacific can enhance the Walker circulation cell over the Pacific and induce ascending motion anomalies over the Indo-Pacific region. These anomalies further drive descending motion anomalies over the TP and ascending motion anomalies to the north through regulating the regional Hadley circulation. Therefore, the positive–negative–positive winter precipitation anomalies around the TP are formed. This study improves the previously poor understanding of TP climate variation at interdecadal timescales.摘要在20世纪70年代和90年代末, 伴随着东亚夏季风的两次主要年代际变化, 高原积雪分别显著增加和减少. 尽管很多学者研究了东亚夏季风年代际变化的可能机制, 高原积雪变化也被认为是主要因素之一, 但是关于高原冬季积雪本身发生年代际变化的潜在机制尚鲜有研究. 本文揭示了20世纪90年代末高原及周边冬季降水的三极子变化特征: 高原主体上空主要为降水减少, 其南北两侧区域降水增加. 数值试验结果表明, 热带太平洋海温变化可以通过调节沃克环流和局地哈德莱环流, 对上述三极子降水变化型态产生显著影响.

Synergistic impacts of westerlies and monsoon on interdecadal variations of late spring precipitation over the southeastern extension of the Tibetan Plateau

AbstractBased on multiple long‐term observational and reanalysis datasets, this study investigated the characteristics and physical mechanisms of the interdecadal variations in late spring (i.e., May) precipitation (LSP) over the southeastern extension of the Tibetan Plateau (SETP) since 1900. It was revealed that by and large, LSP over the SETP experienced interdecadal decrease during the period preceding 1927, 1962–1988, and 2004 onwards, but saw an increase during the periods of 1928–1961 and 1989–2003. The atmospheric circulations responsible for interdecadal variations in LSP over the SETP were also analysed. These analyses identified significant synergistic impacts of decreased mid‐latitude upstream westerlies and increased low‐latitude monsoonal southerlies over the Central North Bay of Bengal (CNBOB) on interdecadal variations in precipitation, suggesting striking interactions between extratropical eastward cold air and tropical northward warm/humid air. Further observational and modelling evidence suggested that Atlantic Multidecadal Oscillation (AMO) was likely to be a salient oceanic driver for the interdecadal synergy between upstream westerlies and CNBOB monsoonal southerlies. The elevated sea surface temperature anomalies associated with the warm phase of the AMO could spark favourable local atmospheric anomalies, forcing an upper‐tropospheric, planetary‐scale teleconnection emanating from the east of the North Atlantic sector, which may serve as an effective bridge linking the remote AMO signal and the synergy between westerlies and monsoonal southerlies around the SETP on interdecadal timescales. Our findings provided new insights into the understanding of the synergistic roles of westerlies and monsoons in the modulation of interdecadal LSP over the SETP, prior to the peak Asian summer monsoon season.

Interdecadal Variation of the Antarctic Circumpolar Wave Based on the 20CRV3 Dataset

As a large-scale ocean–atmosphere coupling system in the Southern Hemisphere, the Antarctic Circumpolar Wave (ACW) greatly impacts the global climate. However, the interdecadal variation of the ACW has rarely been studied due to the lack of long-term data. In this research, the latest 20th Century Reanalysis Version 3 dataset is used to analyze the interdecadal variations of sea level pressure (SLP) and sea surface temperature (SST) signals in the ACW during 1836–2015. The results indicate that the ACW has not always been present in the recent 180 years, and it has remarkable interdecadal variations. Specifically, the ACW was hard to distinguish before the 1870s. The SLP anomalies propagated eastwards over the South Pacific and South Atlantic during part of the 1880s–1940s. The SST anomalies also have an eastward propagation in the 1880s–1960s. The most active period of the SLP signal is in the 1950s–1990s, while that of the SST signal is in the 1980s–1990s. The ACW has not been significant since the 21st century. The interdecadal variation of the SLP may be related to the variations of the long-term Southern Annular Mode and Pacific-South American pattern, while the interdecadal variation of the SST is more associated with the ENSO.

БАЙЕСОВЫ ОЦЕНКИ ИЗМЕНЕНИЯ СТОКА АМУРА И СЕЛЕНГИ В XXI ВЕКЕ ПО РЕЗУЛЬТАТАМ АНСАМБЛЕВЫХ МОДЕЛЬНЫХ РАСЧЕТОВ CMIP6

The analysis is carried out for changes in runoff of the Amur and Selenga rivers in the 21st century according to the CMIP6 (Coupled Model Intercomparison Project, Phase 6) climate model ensemble simulations using the Bayesian approach versus stream gage data on annual runoff and GPCP-2.3 dataset on annual precipitation over catchments on different timescales. For both catchments, significant intermodel differences are associated with the projections of multiyear mean runoff and interannual variability. The intermodel distribution of Bayesian weights indicates a high role of uncertainty related to initial conditions for model simulations. There is a positive trend in total runoff in the Amur River basin in the 21st century under all analyzed anthropogenic forcing scenarios. For total runoff of the Selenga River, there are no trends in the 21st century for all analyzed scenarios. No significant trends for the Amur and Selenga surface runoff were revealed for all algorithms for considering Bayesian weights and all anthropogenic forcing scenarios. At the same time, significant interdecadal variations in the interannual variability of runoff were found.

Climatology of developing and nondeveloping disturbances for tropical cyclone genesis over the western North Pacific

Tropical disturbances play an important role in the formation of tropical cyclones (TCs), but their climate characteristics are still poorly understood. The present study investigated the characteristics of tropical disturbances over the western North Pacific (WNP) for the period 1965–2020 using the reanalysis datasets. An algorithm based on the threshold of synoptic-scale vorticity and convection was developed to identify and track tropical disturbances. Approximately 116 tropical disturbances were detected primitively in the WNP from June to November each year, and about 13.1% of them subsequently developed into TCs. These developing disturbances contributed to the formation of 80.9% TCs in the WNP. Compared with nondeveloping disturbances, the position of developing disturbances is more eastward and southward, whereas the majority of their lifetimes and propagation speeds are similar. The annual numbers of developing disturbances exhibit significant interannual (interdecadal) variability. The percentage of TCs associated with disturbances also experiences a significant inverse interdecadal relationship with the number of TC genesis in the WNP, indicating that the formation probability of TCs is inconsistent with the transition probability from disturbances to TCs. In addition, the long-term trends of developing and nondeveloping disturbances suggest that global warming might be responsible for more tropical disturbances in the WNP instead of higher transition probability from disturbances to TCs.

Impact of synoptic climate system interaction on surface ozone in China during 1950–2014

The effects of meteorological conditions controlled by specific synoptic patterns on regional surface ozone episodes have been widely discussed. However, the impacts of synoptic climate systems and their interaction on long-term variation of ozone are less known. In this study, we use the daily meteorological data and hourly surface ozone concentrations in the summer of 1950–2014 from CMIP6 to investigate the relationship between ozone variations and synoptic climate types (SCTs). Eight SCTs are identified by an objective circulation classification method of an R package called synoptReg. Our results show that the mainland of China is controlled by the low-pressure system for SCT1–5, while dominated by Siberian high for SCT6–8. During SCT1–5 days, the interactions of Asian continental low, Western Pacific Subtropical High (WPSH), warm ridge at 700 hPa, high-level shallow Asian trough, westerly belt, and topography lead to high surface temperature, low relative humidity, and poor diffusion over Northern China with frequent ozone exceedance days. However, the low-level ozone concentrations over Northern China are shown under SCT6–8, affected by the weakened Asian continental low, enhanced Siberian high, stronger WPSH, and denser westerly belt. While over Southern China, ozone concentrations are higher for SCT6–8 than SCT1–5, due to the significantly reduced cloud and precipitation affected by the delivery of cold dry air mass from high latitudes to the South. The interdecadal variabilities of ozone during all SCTs may be controlled by the large-scale climate system of the East Asian monsoon.

Characteristics of rapidly intensifying tropical cyclones in the South China Sea, 1980–2016

The differences in the characteristics of the rapid intensification (RI) during the TCs that form in the SCS (referred as local TCs) and that enter the SCS from the western North Pacific (WNP; referred as entering TCs) have not been well studied, which could contribute the inaccuracy of current TC intensity forecast in the SCS. In this study, we used TC observations, reanalysis data and model experiments to analyze the RI occurrences during local TCs and entering TCs in 1980–2016. We found that the significant interannual and interdecadal variations in RI occurrences during local eastward-moving TCs were related to the strong intraseasonal oscillation (ISO) over the SCS and the WNP under La Niña conditions. RI during local westward-moving TCs showed insignificant variations as a result of the complex interactions among the monsoon trough, ISO and the large-scale circulation. RI during entering TCs showed strong interdecadal variations, with increased RI after 1997, even though the total number of entering TCs has decreased since 1997, which is a result of a higher number of entering TCs in the northwestern quadrant of the WNP, a stronger ISO and weak vertical windshear over the SCS and east of the Philippines under negative phase of Pacific Decadal Oscillation. The different variations and related mechanisms of RI indicates that distinct forecasting factors should be considered for intensity prediction during local eastward- and westward-moving TCs and entering TCs.

The decadal shift in TC-induced precipitation over China

This study examines changes in tropical cyclone (TC) rainfall and the associated contributing factors over China during 1960–2018. The dominant mode of TC rainfall decreases from south to north, with a maximum in Guangdong Province. The associated time series of principal components reveals clear interdecadal variation, and three change points can be identified based on Lepage analysis: the late 1970s, early 1990s, and early 2000s. Before the 2000s, TC rainfall patterns are dominated by different processes in different subregions of South China. The maximum TC-induced rainfall in South China is attributed mainly to the TC rainfall frequency effect and TC genesis effect. TC-induced rainfall in East China is modulated primarily by TC rainfall intensity and TC track. After the 2000s, TCs north of the Yangtze River increase, especially in Shandong Province. Further examination of TC passage frequency reveals that increasing TC rainfall in the north of southeastern China is contributed largely by a northwestward shift in TC tracks.

Future changes in precipitation over the upper Yangtze River basin based on bias correction spatial downscaling of models from CMIP6

Global climate change will change the temporal and spatial distribution of precipitation, as well as the intensity and frequency of extreme precipitation. The Yangtze River basin is one of the world’s largest basins, and understanding the future precipitation changes should be vital to flood control, water resources supply, and hydropower electricity generation in this basin. In this study, projected future characteristics of precipitation are analyzed in the upper Yangtze river basin (UYRB). To this end, based on the observed data from national meteorological stations, the bias correction spatial downscaling (BCSD) of five models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) is carried out. Then, based on the results of multi model ensemble (MME), we find that, relative to the historical period (1988–2014), the mean annual precipitation in the whole UYRB during 2015–2064 increases by 4.23%, 1.11%, 1.24% under SSP1-2.6, SSP2-4.5, SSP5-8.5, respectively, and it increases more in the long term (2040-2064) than that in the near term (2015–2039). Under SSP1–2.6, the precipitation will increase more significantly, which means lower emission of aerosols and greenhouse gases may increase the risk of flood disaster in the future over the UYRB. Interdecadal precipitation variability is more intense than interannual precipitation variability. Future precipitation changes in four seasons are spatially heterogeneous under three scenarios. Three extreme precipitation indices, including R95p, Rx1day and R10 mm, generally increase in the UYRB. R95p and Rx1day increase more in the WR and YBYCR basins with relatively high mean annual precipitation than that in other three sub-basins. R10 mm changes slightly in all sub-basins. The results reveal that the lower region of the UYRB may face greater risk of extreme precipitation. This study provides a timely updated finding about future changes in precipitation in the UYRB based on more accurate climate projections and ground-based observation.

Hydrologic balance and inundation dynamics of Southeast Asia's largest inland lake altered by hydropower dams in the Mekong River basin

Inland lakes have been increasingly impacted by climate change and human activities, leading to unprecedented environmental consequences. Among many rapidly changing lakes is the Tonlé Sap Lake (TSL) in Cambodia—Southeast Asia's largest inland lake—which is under growing threats from altered flows and inundation dynamics due to compounding effects of climate change and dam construction in the Mekong River basin (MRB). While previous studies have examined the potential causes of recent changes in open water areas, a mechanistic quantification of the lake's shifting hydrologic balance and inundation dynamics due to natural climate variability and dam operations is lacking. Here, using a hydrological-hydrodynamic modeling system that includes the major dams in the MRB, we show that while climate variability has been a key driver of inter-decadal variabilities in the lake's water balance, the operation of Mekong dams has exerted a growing influence—especially after 2010—on the Mekong flood pulse, Tonlé Sap River's flow reversal, and the TSL's inundation dynamics. The dam-induced dampening of the Mekong's peak discharge increased from 1–2% during 1979–2009 to ~7% in the 2010s, causing comparable alterations in the peak of inflow from the Mekong into TSL. More crucially, during the 2010s, the dams caused a reduction in annual inflow volume into TSL by 10–25% and shortened the annual inundation duration by up to 15 days in the lake's periphery. Further, seasonally inundated areas decreased (increased) most substantially by ~245 km2 or ~3% (~270 km2 or ~6%) in August (April) during the 2010s. These results demonstrate that Mekong dams have already caused substantial alterations in the hydrologic balance and inundation dynamics of the TSL. Our findings offer critical insights relevant for improved transboundary water management and decision making in light of growing concerns about the adverse impacts of large dams in the MRB.

Decomposition of Trend and Interdecadal Variation of Evaporation over the Tropical Indian Ocean in ERA5

Based on ERA5 from 1980 to 2018, we compare and analyze the trend and interdecadal variation of evaporation anomalies over the tropical Indian Ocean by the evaporation decomposition method. This method mainly decomposes the evaporation anomalies into the Newtonian cooling, stability, relative humidity, wind speed, and transfer coefficient terms. The annual mean evaporation anomalies show an increasing trend (0.083 mm/d/decade). The Newtonian cooling term (0.026 mm/d/decade), the relative humidity term (0.032 mm/d/decade), and the wind speed term (0.026 mm/d/decade) play a major role in the increasing trend. The interdecadal variation of evaporation anomalies shows decreases in the 1980s and after the early 2000s, and an increase in the 1990s. The decreased evaporation anomalies in the 1980s are affected by the transfer coefficient term, which is associated with the North Atlantic Oscillation (NAO). The increased evaporation anomalies in the 1990s and the decreased evaporation anomalies since the early 2000s are largely controlled by the wind speed term, which are dominated by the Atlantic Multidecadal Oscillation (AMO). The Pacific Decadal Oscillation (PDO) may have important impacts on the interdecadal increase of evaporation anomalies by affecting the wind speed in the 1990s.

Tree-ring cellulose oxygen isotopes indicate atmospheric aridity in the western Kunlun Mountains

As an important indicator of atmospheric aridity, the vapor pressure deficit (VPD) is being paid increasing attention in global change researches during recent decades. However, available proxy data with the capability to represent VPD is still scarce in the globe. Herein we demonstrated a “hidden” frequency-dependent indication of tree-ring cellulose oxygen isotope (δ18OTRC) to atmospheric aridity in the western Kunlun Mountains, Central Asia. In applying correlation and partial correlation analysis, frequency-dependent climatic drivers triggering the δ18OTRC values were detected. For the raw data with inter-decadal variability, δ18OTRC variations mainly indicated May–August precipitation (Local: r = –0.59, p < 0.001; Moisture source: r = –0.53, p < 0.001), evapotranspiration (ET) (Local: r = –0.57, p < 0.001; Moisture source: r = –0.51, p < 0.001). After a 5-year high-pass filter, the δ18OTRC series revealed highly significant correlation with May–August VPD (Local: r = 0.82, p < 0.001; Moisture source: r = 0.80, p < 0.001). The partial correlation further confirmed the strong linkages with high-frequency VPD when the impact of any additional eco-climatological variable (precipitation, temperature, ET, soil moisture 0–40 cm) was excluded. In contrast, if the effect of May–August VPD was excluded, relationships between δ18OTRC and other variables turned insignificant. Collectively, it was concluded that δ18OTRC from the western Kunlun Mountains may indicate VPD at timescales < 5 years. Our results suggest that frequency-dependent climatic significances should be considered when interpreting multi-process determined δ18OTRC as a climate-proxy.

Interdecadal Variation of the Number of Days with Drought in China Based on the Standardized Precipitation Evapotranspiration Index (SPEI)

Abstract Based on the standardized precipitation evapotranspiration index (SPEI), a significant increase after the mid-1990s is detected in the annual number of days with drought in the zonal belt from southern Xinjiang to southern Northeast China and North China. This change features the predominant mode of the annual number of days with drought in China. Meanwhile, two significant breakpoints in 1981 and 2001 indicate a continuous increase of days with drought in the meridional belt from eastern Northwest China to eastern Southwest China. The increase in days with drought is closely related to the significant warming in the zonal belt but is attributed to both the increase of temperature and the decrease of precipitation in the meridional belt. The typical circulation patterns responsible for the increase of days with drought comprise a wave train stretching from North Atlantic to East Asia, the generally anomalous high pressure over China, the northerly anomalies prevailing over northern and central China, and the suppressed convection in most of the zonal and meridional belt. Both the AMO and the PDO after the 1980s have a close relationship with the interdecadal variation of the number of days with drought. On one hand, either a positive AMO phase or negative PDO phase motivates the typical circulation patterns favorable for the occurrence of drought. On the other hand, both the AMO and PDO affect the warming in the zonal and meridional belt, and the PDO is also closely connected with the precipitation in the meridional belt.

Long-Term Variability on Suspended Particulate Matter Loads From the Tributaries of the World’s Largest Choked Lagoon

Continental freshwater contributions are the main long-term control on the variability of suspended particulate matter (SPM) concentrations in choked lagoons. The current work aims to assess the seasonal to interdecadal variability in SPM concentrations from Patos Lagoon tributaries, as a case study towards the understanding of tributaries contributions to coastal lagoons. Thus, an interdecadal dataset (1984–2020) was collected in the region of the tributaries of Patos Lagoon (southern Brazil), integrating Landsat series (653 scenes) and in situ measurements. SPM concentrations were estimated from the scenes using a semi-analytical multiwavelength algorithm, applied in the regions of the lower course of the tributaries. Results identified SPM concentrations variability in seasonal scales, enhanced by El Niño Southern Oscillation (ENSO) in interannual time scales, also influencing in interdecadal trends. The seasonal SPM concentration variability reached 50 g.m–3 to each tributary. Higher SPM concentration values occurred from winter to spring, enhanced during El Niño periods and frequently reaching annual means higher than 100 g.m–3. Periods from summer to autumn, however, presented lower SPM concentrations, especially during La Niña periods, when the mean annual SPM concentration remained mostly below 50 g.m–3. Seasonal and interannual (ENSO) forcings combined developed configurations of high input periods (HIP) and low input periods (LIP). During the LIP, the river plumes are limited to their tributary zone of influence and the whole lagoon has reduced SPM concentrations. During the HIP, the river plumes spread over the lagoon sub-environments, and the SPM concentrations of all tributaries reach the estuarine zone and the ocean. Thus, the mentioned natural phenomena influence the river plumes spreading, the SPM concentrations in the lagoon, and the export to the Atlantic Ocean in time scales varying from seasonal to interdecadal.

Possible Relationships between the Interdecadal Anomalies of Heavy Rainfall under Northeastern China Cold Vortexes and the Sea Surface Temperature (SST)

As an important component of the East Asian monsoon system, the northeast cold vortex (NECV) exerts a significant impact on weather and climate, especially in Northeast China. This study investigated the interdecadal spatiotemporal variability of heavy rainfall under the cold vortex of Northeast China (NECVHR) and its relationship with sea surface temperature (SST) during 1961–2019 over Northeast China. To investigate the dominant factors affecting variability in the heavy rainfall between May and September, an empirical orthogonal function (EOF) analysis was performed. To detect the trends and changes, a Mann-Kendall (MK) test was used. The sliding t-test was used to identify the change points and the significance. Pearson correlation analysis was used to analyze the relationship between SST and NECVHR, and the t-test was used to verify the significance. The results showed that the total amount of cold vortex heavy rainfall during May–September ranged from 153 to 12,509 mm for 1961–2019. An abrupt interdecadal change was seen after 2014 in Northeast China. The EOF analyses revealed that the first, second, and third EOFs explain 76%, 12.1%, and 5.5% of the total variance, respectively. The EOF followed the heavy rainfall pattern, with increases in the south (southeast) and decreases in the north (northwest) over Northeast China. Heavy rainfall over Northeast China positively correlated with the Atlantic multidecadal oscillation (AMO) index. The heavier rainfall under cold vortex (MCVHR) years revealed that the equipotential height was obviously located over the Sea of Japan, west of Northeast China and the Qinghai Tibet plateau. The cyclonic circulation over the East China Sea and north (northeasterly) wind prevails over Northeast China during less heavy rainfall under cold vortex (LCVHR) years. A high anticyclonic circulation over the Qinghai Tibet plateau resulted in stronger cold advection over Northeast China. The anticyclonic circulations over the East China Sea and the Sea of Japan (east), and the western (southwesterly) winds prevail over Northeast China, with a relatively shallow cold trough over the Qinghai Tibet plateau. The findings in this paper provided a better understanding of the interdecadal variability of NECVHR over Northeast China. The findings can be helpful for several stakeholders regarding agricultural production, water resource management, and natural habitat conversation in Northeast China.

Dominant Modes of Tibetan Plateau Summer Surface Sensible Heating and Associated Atmospheric Circulation Anomalies

Based on empirical orthogonal function (EOF) analysis, the dominant modes of variations in summer surface sensible heating (SH) over the Tibetan Plateau (TP), as well as the associated atmospheric circulation anomalies, were investigated in this study. The results show that the first dominant mode of summer SH presents a feature of decadal reduction over the whole TP on an interdecadal time scale, and the second dominant mode is characterized by a zonally asymmetric pattern with positive (negative) SH anomalies in the western (eastern) TP on an interannual time scale. The variations of summer SH are dominated by anomalies in downwelling surface shortwave radiation (DSWR), which are associated with atmospheric circulation changes. The first dominant mode of variation in SH is connected to the interdecadal variation of the Silk Road Pattern (SRP). Further analysis reveals that the interdecadal phase shift of the SRP induces anticyclone circulation to the northeast of the TP, leading to enhanced water vapor supply and convergence over the TP. This can lead to an increase in the total cloud cover, and a reduction in DSWR, contributing to the decadal reduction in SH over the TP. The second dominant mode of variation in SH is related to a stationary teleconnection pattern over the Eurasian continent named the North Atlantic-East and North Asia pattern (NAENA). Corresponding to the positive phase of the NAENA, there is a cyclone anomaly to the west TP, leading to anomalous water vapor convergence (divergence) over the eastern (western) TP. This can result in enhanced (decreased) cloud cover, reduced (increased) DSWR, and therefore, an anomalous decrease (enhancement) in SH over the east (west) of the TP. Furthermore, the southwesterly wind anomaly, which is accompanied by the anomalous cyclone to the west TP, leads to positive SH in the western TP.

Interdecadal variation in sediment yield from a forested mountain basin: The role of hydroclimatic variability, anthropogenic disturbances, and geomorphic connectivity

Variation in sediment yield may reflect a signal of disturbances in the upstream landscape, modified by sediment routing. This study, conducted in a forested drainage basin in the inland Pacific Northwest, USA, sought to generate a better insight into the interdecadal variability of sediment yield in mountain landscapes in response to environmental change during the last century. To this end, we examined: (1) sediment yield fluctuations; and (2) their association with streamflow and land use changes; as well as (3) streamflow links to climate variability modes; and (4) the influence of sediment delivery from hillslope sources to streams (lateral connectivity) and its downstream routing through the stream network (longitudinal connectivity) on land use signal at the basin's outlet. Sediment yield between 1910 and 2017, estimated based on reconstructed fluvial delta growth, displayed an order of magnitude variability, which indicates a substantial geomorphic sensitivity. The interpretation of temporal patterns and an exploratory statistical analysis pointed to land use-related sediment supply changes as the primary driver of these fluctuations, dominating system behavior before changes in environmental regulations and practices in the mid-1970s. Hydroclimatically controlled streamflow variability appeared to be more prominent in the subsequent period. Our connectivity analysis suggested that a considerable portion of coarse sediment mobilized by harvest and road construction may still reside within the channel network. In light of previous research in this landscape system, we speculate that, despite limited anthropogenic pressures in the recent decades, its characteristics and behavior continue to be conditioned by land use legacies. Overall, this study contributes to the growing understanding of profound anthropogenic transformation of the earth surface. Specifically, it demonstrates that historical resource extraction may have left a lasting imprint even in relatively remote mountain landscapes. Given the ongoing rapid environmental change, such understanding is crucial for watershed management, conservation, and restoration.