Large-scale Climate Teleconnections Research Articles

Recent Tianshan warming in relation to large-scale climate teleconnections

On the alpine areas such as Tianshan Mountains, snow and glaciers are widely distributed, which are sensitive to temperature changes. However, due to high altitude and scarcity of observed stations, the temperature changes and their causes in Tianshan are unclear. To address this issue, this study integrated Thiel-Sen trend test, Pearson correlation, and wavelet analysis methods to analyze the driving factors of temperature changes in Tianshan. We draw the following conclusions: (1) In the past 40 years, Tianshan warmed at a rate of 0.30 °C/decade. Seasonally, the temperature increased the most in spring and summer; spatially, the east Tianshan experienced the most warming. (2) Climate change has affected significant warming in the Tianshan. (3) The large-scale climate teleconnections found to be associated with warming in the Tianshan include North Pacific pattern, Atlantic Multidecadal Variability (AMV), North Atlantic Oscillation, and Western Hemisphere Warm Pool (WHWP). During the study period, the temperature changes lagged AMV and WHWP by 1.5 months, North Tropical Atlantic Index and Tropical Northern Atlantic Index by 3 months, and Arctic Oscillation by 4 months. This research contributes to understanding the response of dry mountains to global warming and atmospheric circulation changes.

Peak Spring Flood Discharge Magnitude and Timing in Natural Rivers across Northern Finland: Long-Term Variability, Trends, and Links to Climate Teleconnections

In northern regions, like Finland, peak river discharge is principally controlled by maximum snowmelt runoff during spring (March–May). Global warming and climate change extensively influence both the quantity and temporal characteristics of peak discharge in northern rivers by altering snowpack accumulation and melt processes. This study analyzed peak spring flood discharge (PSFD) magnitude (PSFDM) and timing (PSFDT) in four natural rivers (Simojoki, Kuivajoki, Kiiminkijoki, and Temmesjoki) across northern Finland, in terms of long-term (1967–2011) variability, trends, and links to large-scale climate teleconnections. The PSFDM significantly (p < 0.05) declined in the Simojoki, Kuivajoki, and Kiiminkijoki rivers over time. Both the Simojoki and Kuivajoki rivers also experienced significant decreasing trends of about −0.33 and −0.3 (days year−1), respectively, in the PSFDT during 1967–2011. In these two rivers, the less and earlier PSFDs were principally attributable to the warmer spring seasons positively correlated with the North Atlantic Oscillation (NAO) in recent decades. Moreover, daily precipitation time series corresponding to the PSFD events showed no considerable effects on PSFDM and PSFDT changes in all the natural rivers studied. This suggests that less and earlier historical PSFDs in natural rivers at higher latitudes in northern Finland were primarily induced by warmer springtime temperatures influencing snowpack dynamics.

Observed changes in extreme precipitation over the Tienshan Mountains and associated large-scale climate teleconnections

Under global warming, extreme hydrological events are experiencing increasingly violent fluctuations. Investigating changes in the intensity and frequency of extreme precipitation (EP) events is particularly critical for understanding the hydrological response to climate change. Based on high-precision and long-term daily grid precipitation data obtained from Asian Precipitation-Highly Resolved Observational Data Integration Towards Evaluation of Water Resources (APHRODITE), 25 EP indices were examined for the Tienshan Mountains region of Central Asia (TMCA). Here, the relationship between EP and associated large-scale climate teleconnections is revealed by using a series of approaches such as trend analysis and the geographical detector method (GMD), a statistical tool to measure and attribute spatial stratified heterogeneity. The results show an overall increase in EP during 1951–2014, as reflected in the 25 indices. Furthermore, the number of consecutive dry days (CDD) decreased from 87.02 to 69.35 while the number of consecutive wet days (CWD) increased from 3.89 to 4.61. Meanwhile, the increasing trend of total precipitation (PRCPTOT) was 18.43 mm/10a, and changes in EP frequency were shown to increase with event rareness. For R95p, the observed changes in frequency are 34.46%, but these jump to 96.58% for R99p. Moreover, the study also notes that changes in EP are elevation-dependent, with middle altitude areas (1500–3500 m) being most sensitive to change rates. As well, the study reveals that the occurrence of EP responds non-linearly to climatic teleconnections, and that the combined effect of two factors generally make much larger contributions to EP than the summation of individual factors. Further analyses indicate strong zonal circulation at 500 hPa, 1000 hPa potential height increases airflow from west to east. And the weakening of the East Asian Summer Monsoon accompanied by the westward extension of the western Pacific subtropical high and the increase in Mongolian anticyclone activity all bring sufficient exogenous water vapor from the North Atlantic and Indian Ocean to the TMCA.

A space–time Bayesian hierarchical modeling framework for projection of seasonal maximum streamflow

Abstract. Timely projections of seasonal streamflow extremes can be useful for the early implementation of annual flood risk adaptation strategies. However, predicting seasonal extremes is challenging, particularly under nonstationary conditions and if extremes are correlated in space. The goal of this study is to implement a space–time model for the projection of seasonal streamflow extremes that considers the nonstationarity (interannual variability) and spatiotemporal dependence of high flows. We develop a space–time model to project seasonal streamflow extremes for several lead times up to 2 months, using a Bayesian hierarchical modeling (BHM) framework. This model is based on the assumption that streamflow extremes (3 d maxima) at a set of gauge locations are realizations of a Gaussian elliptical copula and generalized extreme value (GEV) margins with nonstationary parameters. These parameters are modeled as a linear function of suitable covariates describing the previous season selected using the deviance information criterion (DIC). Finally, the copula is used to generate streamflow ensembles, which capture spatiotemporal variability and uncertainty. We apply this modeling framework to predict 3 d maximum streamflow in spring (May–June) at seven gauges in the Upper Colorado River basin (UCRB) with 0- to 2-month lead time. In this basin, almost all extremes that cause severe flooding occur in spring as a result of snowmelt and precipitation. Therefore, we use regional mean snow water equivalent and temperature from the preceding winter season as well as indices of large-scale climate teleconnections – El Niño–Southern Oscillation, Atlantic Multidecadal Oscillation, and Pacific Decadal Oscillation – as potential covariates for 3 d spring maximum streamflow. Our model evaluation, which is based on the comparison of different model versions and the energy skill score, indicates that the model can capture the space–time variability in extreme streamflow well and that model skill increases with decreasing lead time. We also find that the use of climate variables slightly enhances skill relative to using only snow information. Median projections and their uncertainties are consistent with observations, thanks to the representation of spatial dependencies through covariates in the margins and a Gaussian copula. This spatiotemporal modeling framework helps in the planning of seasonal adaptation and preparedness measures as predictions of extreme spring streamflows become available 2 months before actual flood occurrence.

Seasonality of primary productivity affects coastal species more than its magnitude

While the importance of extreme conditions is recognised, patterns in species' abundances are often interpreted through average environmental conditions within their distributional range. For marine species with pelagic larvae, temperature and phytoplankton concentration are key variables. Along the south coast of South Africa, conspicuous spatial patterns in recruitment rates and the abundances of different mussel species exist, with focal areas characterized by large populations. We studied 15 years of sea surface temperature (SST) and chlorophyll-a (chl-a) satellite data, using spectral analyses to partition their temporal variability over ecologically relevant time periods, including seasonal (101 to 365 days) and intra-seasonal cycles (20 to 100 days). Adult cover and mussel recruitment were measured at 10 sites along the south coast and regression models showed that about 70% of the variability in recruitment and adult cover was explained by seasonal variability in chl-a, while mean annual chl-a and SST only explained 30% of the recruitment, with no significant effect for adult cover. SST and chl-a at two upwelling centres showed less predictable seasonal cycles during the second half of the study period with a significant cooling trend during austral autumn, coinciding with one of the mussel reproductive peaks. This likely reflects recent changes in the Agulhas Current, the world's largest western boundary current, which affects coastal ecosystems by driving upwelling. Similar mechanisms probably operate in other marine systems with the potential to affect the distribution patterns of key ecosystem engineers. We propose that variability in the characteristic timescales of environmental fluctuations can explain the spatial patterns of abundance of foundational species by affecting larval recruitment. This is especially important in a context of global and pervasive climate change, as shifts in the periodicity of environmental fluctuations appear to reflect large scale climatic teleconnections driven by anthropogenic forcing.

Large-scale climate teleconnections with South Korean streamflow variability

ABSTRACTLeading patterns of observed seasonal extreme and mean streamflow on the Korean peninsula were estimated using an empirical orthogonal teleconnection (EOT) technique. In addition, statistical correlations on a seasonal basis were calculated using correlation and regression analyses between the leading streamflow patterns and various climate indices based on atmospheric–ocean circulation. The spatio-temporal patterns of the leading EOT modes for extreme and mean streamflow indicate an upstream mode for the Han River, with increasing trends in summer, and a downstream mode for the Nakdong River, with oscillations mainly on inter-decadal time scales in winter. The tropical ENSO (El Niño Southern Oscillation) forcing for both extreme and mean streamflow is coherently associated with summer to winter streamflow patterns. The western North Pacific monsoon has a negative correlation with winter streamflow variability, and tropical cyclone indices also exhibit significant positive correlation with autumn streamflow. Leading patterns of autumn and winter streamflow time series show predictability up to two seasons in advance from the Pacific sea-surface temperatures.

Variability of rainfall from tropical cyclones in the eastern USA and its association to the AMO and ENSO

Tropical cyclone (TC) rainfall along the eastern USA exhibits a high degree of variability with the potential to produce precipitation amounts in excess of 100 % of the annual mean at locations ranging from the immediate coastline to hundreds of kilometers inland. However, the spatiotemporal distribution of TC rainfall variability has not yet been fully characterized for this region, particularly with regard to large-scale climate teleconnections (e.g., El Nino-Southern Oscillation (ENSO) and Atlantic multidecadal oscillation (AMO)). The objectives of this study are to (1) assess temporal variability and trends in TC rainfall since 1960, and (2) characterize the spatial variability of TC rainfall during varying AMO and ENSO regimes. Kendall tau-b analysis highlighted the presence of statistically significant positive trends in TC rainfall at a number of locations. Principal components analysis revealed that AMO exhibited significant linkages to TC rainfall in northern New England as well as along the US Gulf Coast, while ENSO was most strongly linked to TC variability in Texas. Results illustrate the varied nature of TC rainfall across the eastern USA and the complex linkages to large-scale climate mechanisms at interannual and decadal time scales.

A century of hydrological variability and trends in the Fraser River Basin

This study examines the 1911–2010 variability and trends in annual streamflow at 139 sites across the Fraser River Basin (FRB) of British Columbia (BC), Canada. The Fraser River is the largest Canadian waterway flowing to the Pacific Ocean and is one of the world’s greatest salmon rivers. Our analyses reveal high runoff rates and low interannual variability in alpine and coastal rivers, and low runoff rates and high interannual variability in most streams in BC’s interior. The interannual variability in streamflow is also low in rivers such as the Adams, Chilko, Quesnel and Stuart where the principal salmon runs of the Fraser River occur. A trend analysis shows a spatially coherent signal with increasing interannual variability in streamflow across the FRB in recent decades, most notably in spring and summer. The upward trend in the coefficient of variation in annual runoff coincides with a period of near-normal annual runoff for the Fraser River at Hope. The interannual variability in streamflow is greater in regulated rather than natural systems; however, it is unclear whether it is predominantly flow regulation that leads to these observed differences. Environmental changes such as rising air temperatures, more frequent polarity changes in large-scale climate teleconnections such as El Niño-Southern Oscillation and Pacific Decadal Oscillation, and retreating glaciers may be contributing to the greater range in annual runoff fluctuations across the FRB. This has implications for ecological processes throughout the basin, for example affecting migrating and spawning salmon, a keystone species vital to First Nations communities as well as to commercial and recreational fisheries. To exemplify this linkage between variable flows and biological responses, the unusual FRB runoff anomalies observed in 2010 are discussed in the context of that year’s sockeye salmon run. As the climate continues to warm, greater variability in annual streamflow, and hence in hydrological extremes, may influence ecological processes and human usage throughout the FRB in the 21st century.

Pacific/North American teleconnection controls on precipitation isotope ratios across the contiguous United States

Large-scale climate teleconnections such as the Pacific/North American (PNA) pattern strongly influence atmospheric processes and continental climate. Here we show that precipitation δ 18O values in the contiguous United States are correlated with an index of the PNA pattern. The δ 18O/PNA relationship varies across the study region and exhibits two prominent modes, with positive correlation in the western USA and negative correlation in the east. This spatial pattern appears not to reflect variation in local climate variables, but rather primarily reflects differences in atmospheric circulation and moisture sources associated with PNA. Our results suggest that strong antiphase variation in paired paleo-water δ 18O proxy records from regions characterized by the two modes of δ 18O/PNA correlation, especially in the Midwest and southwestern USA, may provide a robust basis for reconstruction of past variation in the PNA pattern.

Regional Rainfall Forecasting using Large Scale Climate Teleconnections and Artificial Intelligence Techniques

Article Regional Rainfall Forecasting using Large Scale Climate Teleconnections and Artificial Intelligence Techniques was published on December 1, 2007 in the journal Journal of Intelligent Systems (volume 16, issue 4).

Last Glacial Maximum lacustrine and fluviatile Formations in the Tibesti and other Saharan mountains, and large-scale climatic teleconnections linked to the activity of the Subtropical Jet Stream

In the mountains of the central Sahara (lat ca. 20° to 22°N, long 16° to 19°E) and particularly in the Tibesti mountains, important lacustrine formations developed during the late Pleistocene, primarily during the Last Glacial Maximum (LGM). Two main phases, separated by a brief regression, intervened between ca. 20,000 and 15,500 BP, and between 15,000 and 12,500 BP. Pollen analyses were carried out on four samples of this formation. The high lacustrine levels were associated to both important precipitations and a reduced evaporation linked to lower temperatures. Similar lacustrine deposits were found in the Djebel Marra in the south of the Sahara. In the mountains of the central and eastern Sahara, during the same period and until the middle Holocene, the “Middle Terrace” Formation was deposited in the river valleys of the Tibesti, Hoggar, Air and the Red Sea Hills. Since the southern headwaters of the Nile were dry from ca. 20,000 to 12,500 BP, the fluviatile sediments deposited in the Nile valley in Nubia may have resulted almost entirely from the numerous wadis flowing from the Red Sea Hills. The rainfalls which fed these lacustrine and fluviatile formations were related to the Tropical Depressions which are formed in the southern part of the westerlies and are linked to the activity of the Subtropical Jet Stream (STJ), whose path remained over the central Sahara from 20,000 BP to the early Holocene. In the Rocky Mountains of the western US, the palaeolakes Lahontan and Bonneville were very large during the LGM and the main fluctuations exhibit similar chronology to that of the Saharan mountains. Broecker [Broecker, W.S., 1994. Massive iceberg discharges as triggers for global climate change. Nature 372, 421-424] estimates that these two large U.S. wet events between ca. 20,000–15,500 BP and ca. 15,000–12,500 BP may have been an indirect result of two large ice surges in the North Atlantic, related to Heinrich layers 1 and 2. We can assume, however, that the similar climatic variation of the Rocky Mountains and the central and eastern Saharan mountains was also a result of the activity of the STJ all along its path, which marks the boundary between the polar and tropical circulations. STJ activity can apparently produce long-distance climatic teleconnections. During the LGM similar teleconnections also existed in the Southern Hemisphere between South Africa and Australia. The Tropical Depressions result from the interaction of polar troughs and the influx of humid equatorial air forming transversal cloud bands. The large increase in the intensity of atmospheric circulation during the LGM was responsible for a large increase in Tropical Depressions in both hemispheres.