Regional Climate Dynamics Research Articles

Hydrochemical characteristics and paleoclimate changes recorded from Sugan Lake on the northern boundary of Tibetan Plateau since mid-Holocene

The Qaidam Basin, located in the northern Tibetan Plateau, is one of the three largest interior basins in China. It is surrounded by Kunlun, Altun and Qilian mountains with arid climate, sparsely vegetated landscape and a fragile ecological environment. Investigations on Holocene climate variations in this northern part of the Tibetan Plateau are essential for a better understanding of regional climate dynamics. A mid-Holocene sediment record from Sugan Lake in the Qaidam Basin was investigated using the grain size, mineral, total organic matter content (TOC), C:N ratio (C/N) and element analyses. A depth-age model since ∼ 7750 cal a BP had been made based on 8 AMS 14C data after taking out 2200 years carbon reservoir effect. SO42--type water and sparse terrestrial vegetation with considerable evaporation caused by high temperature during the Holocene Megathermal Maximum were recorded from ca. 7750 to 5800 cal a BP. From 5800 cal a BP, hydrochemical characteristics shifted dramatically to the Cl-type, while aeolian activities intensified concurrently. A higher lake level with low evaporation/precipitation ratio as the result of cool and wet conditions were inferred between 5800 and 3580 cal a BP when the EASM weakened and westerly jet intensified. Colder and drier conditions were recorded probably due to the strengthening of the mid-latitude westerly circulation after 3580 cal a BP. However, the EASM probably prevailed shortly at 3580 ∼ 3000 cal a BP and 1800 ∼ 810 cal a BP, respectively. Cold/dry, cold/wet and cold/dry Little Ice Age fluctuation climate conditions and aeolian activities with risen lake level and diluted water were inferred from 580 to 280 cal a BP.

Study on the Dynamic Change of Regional Water Level and Climate Based on Forecast Equation

Abstract Because there are too many factors affecting the change of hydrometeorological elements in the long term, it is necessary to use a single linear relationship to construct the forecast equation, which will omit too many forecast factors. Therefore, it is necessary to use a variety of nonlinear function types of correlation coefficient calculation and comparison, clear optimization of forecast factors to build the corresponding forecast equation. In this paper, we study spatial change of water in the understanding of trend test principle, analysis method and dynamic time series model, on the basis of based on regional water level change to build the corresponding forecast equation, the design and implementation of the regional water level change and climate dynamics forecasting system software, the empirical analysis found that the regional water level has a close relationship between dynamic change and climate change.

Patterns and Mechanisms of Northeast Pacific Temperature Response to Pliocene Boundary Conditions

AbstractOcean‐atmosphere dynamics in the north Pacific play an important role in the global climate system and influence hydroclimate in western North America. However, changes to this region's mean climate under increased atmospheric greenhouse gas concentrations are not well understood. Here we present new alkenone‐based records of sea surface temperature (SST) from the northeast Pacific from the mid‐Piacenzian warm period (approximately 3.3–3.0 Ma), an interval considered to be an analog for near‐future climate under middle‐of‐the‐road anthropogenic emissions. We compare these and other alkenone‐based SST records from the north Pacific to fully‐coupled climate model simulations to examine the impact of mid‐Pliocene CO2 and other boundary conditions on regional climate dynamics and to explore factors governing model disagreement about regional temperature patterns. Model performance varies regionally, with Community Earth System Model 1.2 (CESM 1.2) and CESM2 performing best in regions with greater warming like the California Margin, though these models underestimate the warming evidenced in our new proxy record and others from the region. Single forcing simulations reveal a strong influence for prescribed land surface changes and higher CO2 levels on coastal warming patterns along the California Margin in CESM2. Furthermore, differences in shortwave and longwave radiation and circulation between the models, likely related to changes in the atmospheric component of the model, may play a key role in the ability of models to capture regionally‐varying patterns of Pliocene warmth. Regional patterns of temperature change inferred from geochemical records could therefore help to understand the impacts of different model parameterization schemes on regional climate patterns.

High-frequency vegetation and climatic changes during the Lateglacial inferred from the Lapsou pollen record (Cantal, southern Massif Central, France)

The Lateglacial period is marked by strong changes in environment and climate in Europe, associated to the different steps of the deglaciation. This paper aims to reconstruct the vegetation and climate changes from the deglaciation to the early Holocene (15.2–10.8 ka cal BP) in Western Europe. Pollen investigations are performed at a centennial resolution on a sedimentary core from the Lapsou peat bog (Cantal, France). The chronology is well constrained from three radiocarbon dates and a double tephra layer. The pollen record and quantitative climate reconstructions evidence strong changes associated with the Lateglacial period, in agreement with the regional vegetation and climate dynamics. At the onset of Lateglacial Interstadial (14.5–14.1 ka cal BP), a Juniperus - Betula succession is attributed to the Bølling. Associated climate reconstructions indicate a winter warming of 10 °C and precipitations above 1000 mm. A development of Pinus forests is then evidenced for the Allerød, for which rather constant warm conditions and lower precipitations (drop of 200 mm) are reconstructed. A two-phase pattern characterizes the Younger Dryas (12.6–11.5 ka cal BP): after a first phase with rather constant vegetation and climate conditions compared to the Allerød, a more steppic vegetation developed from 12.2 ka cal BP, indicating a marked cooling and a pronounced aridity (precipitations around 400 mm). Finally, the reconstruction of a cool deciduous forest dominated by Betula and temperate climate conditions defines the early Holocene. A comparison with chironomid-inferred reconstructions of July temperature from the close La Roustière site allows to support pollen-inferred climate quantifications, also showing the interest of applying multi-proxy approach in palaeo-environmental studies.

MODELING OF SEA SURFACE TEMPERATURE BASED ON PARTIAL LEAST SQUARE - STRUCTURAL EQUATION

Variability of Sea Surface Temperature (SST) is one of the climatic features that influence global and regional climate dynamics. Missing data (gaps) in the SST dataset are worth investigating since they may statistically alter the value of the SST change. The partial least square-structural equation modeling (PLS-SEM) approach is used in this work to estimate the causality relationships between exogenous and endogenous latent variables. The findings of this study, which are significant indicators that have a loading factor value > 0.7 are as follows: i) sea surface temperature (oC) as a measure of the latent variable changes in SST, ii) wind speed (m/s) and relative humidity (%) as a measure of the latent variable of weather, and iii) air temperature (oC), long-wave solar radiation (w/m2) as a measure of climate latent variables. The size of the Rsquare value is influenced by the number of gaps. The results of the boostrapping show that the latent variables of weather and climate have a significant effect on changes in SST which are indicated by the value of tstatistics > ttabel. The structural model obtained Changes in SST (η) = -0.330 weather + 0.793 climate + ζ. The model shows that the weather has a negative coefficient, which means that the better the weather conditions, the lower the SST changes. Climate has a positive coefficient, which means that the better the climate, the SST changes will also increase. Rising sea surface temperatures caused by an increase in climate can lead to global warming, impacting El-Nino and La-Nina events.

Climate, cryosphere and carbon cycle controls on Southeast Atlantic orbital-scale carbonate deposition since the Oligocene (30–0 Ma)

Abstract. The evolution of the Cenozoic cryosphere from unipolar to bipolar over the past 30 million years (Myr) is broadly known. Highly resolved records of carbonate (CaCO3) content provide insight into the evolution of regional and global climate, cryosphere, and carbon cycle dynamics. Here, we generate the first Southeast Atlantic CaCO3 content record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca / Fe) data collected at Ocean Drilling Program Site 1264 (Walvis Ridge, SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (∼ 316 m; 30 Myr). This constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this location. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to major developments in climate, the cryosphere and the carbon cycle: (1) strong ∼ 110 kyr eccentricity pacing prevails during Oligocene–Miocene global warmth (∼ 30–13 Ma), (2) increased eccentricity-modulated precession pacing appears after the middle Miocene Climate Transition (mMCT) (∼ 14–8 Ma), and (3) pervasive obliquity pacing appears in the late Miocene (∼ 7.7–3.3 Ma) following greater importance of high-latitude processes, such as increased glacial activity and high-latitude cooling. The lowest CaCO3 content (92 %–94 %) occurs between 18.5 and 14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climatic Optimum (∼ 17–14.5 Ma) by 1.5 Myr. The emergence of precession pacing of CaCO3 deposition at Site 1264 after ∼ 14 Ma could signal a reorganisation of surface and/or deep-water circulation in this region following Antarctic reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 between 14 and 13 Ma is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or recurrent influxes of cooler, less corrosive deep waters. The highest carbonate content (%CaCO3) and MARs indicate that the late Miocene–early Pliocene Biogenic Bloom (LMBB) occurs between ∼ 7.8 and 3.3 Ma at Site 1264; broadly contemporaneous with the LMBB in the equatorial Pacific Ocean. At Site 1264, the onset of the LMBB roughly coincides with appearance of strong obliquity pacing of %CaCO3, reflecting increased high-latitude forcing. The global expression of the LMBB may reflect increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes, due to enhanced glacial activity and increased meridional temperature gradients. Regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation in the late Miocene.

Lateglacial–Holocene environments and human occupation in the Upper Lena region of Eastern Siberia derived from sedimentary and zooarchaeological data from Lake Ochaul

In the current study, different geochemical and biological proxies, including pollen, non-pollen palynomorphs, ostracods and molluscs, from an AMS radiocarbon-dated sediment core from Lake Ochaul (54°14′N, 106°28′E; 641 m a.s.l.) are presented and discussed. Ochaul is a fresh-water lake and an archaeological site situated ca. 100 km northwest of Lake Baikal in the upper reaches of the Lena River. The 260-cm-long sedimentary record presented here spans the Lateglacial–Holocene interval, between ca. 13,500 cal yr BP and the present. The reconstructions of the postglacial vegetation and lake system development are discussed along with the regional climate dynamics and the hemispheric-scale environmental changes. During the Allerød interstadial the region around Lake Ochaul was dominated by sparse taiga forests. Cooling during the Younger Dryas led to a more open tundra landscape where trees formed patchy forest stands in climatically favourable environments. This facilitated a rapid spread of forests at the onset of the Early Holocene during which the study region was probably characterized by seasonally dry climate controlled by the interplay of higher insolation, lower global sea levels and remaining ice sheets in the North Atlantic region. After thermal and moisture optimum conditions and a maximum spread of forests during the Middle Holocene, continuous cooling and a trend to more open forests landscapes marked the Late Holocene. These long-term trends were interrupted by several relatively short episodes of change in the vegetation and algal records, which coincide with short-term (centennial-scale) Northern Hemisphere cooling/drying phases. This shows that the regional vegetation reacted sensitively to these climate oscillations. Six AMS radiocarbon dates of bone material of large herbivorous animals from the Ochaul archaeological site located at the northern shore of the lake provide important information about prehistoric hunter-gatherers and indicate that activities at the site took place at ca. 27,780–27,160 cal yr BP (95% probability range) as well as during the Mesolithic (ca. 8850–8450 cal yr BP), Early, Middle and Late Neolithic (between ca. 6840 and 5490 cal yr BP) and the Iron Age (ca. 2120–1930 cal yr BP). Our results demonstrate that despite major environmental transformations following the Last Glacial Maximum, Lake Ochaul and the Malaya Anga River valley remained attractive for large herbivores and for prehistoric hunter-gatherers, even during the Middle Neolithic cultural “hiatus” (ca. 6660–6060 cal yr BP) in Cis-Baikal, as documented by the published archaeological records.

Late Holocene climate variation on the northern Tibetan Plateau inferred from Lake Ayakum

Understanding late Holocene climate variation on the northern Tibetan Plateau is essential for understanding regional climate dynamics, especially the potential response to mid-latitude westerlies. A continuous lacustrine sediment record covering the past 1500 years was recovered from Lake Ayakum on the northern margin of the Tibetan Plateau, in which a typical cold-phase mineral (mirabilite) was detected. Assisted by the simulation results in the Pitzer model, the preservation of mirabilite in the sediment core as well as its relative proportion was interpreted in terms of past temperature variations, in which a high mirabilite content corresponded to a relatively cold environment. Grain size analysis and subsequent end-member modeling results revealed potential correlations with regional moisture conditions, that more coarse materials were transported by increased river discharge under relatively wet conditions. The results showed that cold and humid conditions dominated the Dark Age Cold Period and Little Ice Age, while warm and dry conditions dominated the Medieval Warm Period. Following the increase in regional temperature, more coarse materials were deposited during the last 200 years owing to probable increased fluvial transport supplied by glacier meltwater. The overall temperature and moisture variations were broadly consistent with records from western China and central Asia, indicating that the northern Tibetan Plateau was predominately influenced by the mid-latitude westerlies during the late Holocene. In addition, the temperature change showed a close correlation with solar irradiance, pointing to a potential response to solar activity. On the other hand, the moisture change responded sensitively to the North Atlantic Oscillation and the migration of mid-latitude westerlies.

Late-Holocene palaeoenvironmental reconstruction from a lake in the Amazon Rainforest-Tropical Savanna (Cerrado) boundary in Brazil using a multi-proxy approach

As an ecotone, the region between the Amazon Rainforest and Tropical Savanna (Cerrado) biomes is, by definition, more susceptible to climate change. Therefore, understanding palaeoenvironmental dynamics is essential to address the future responses of such transition areas to climatic fluctuations. In this context, we present a new sediment record for the Late-Holocene retrieved from Barro-Preto, currently an oxbow lake located in an ecotone at the southern Brazilian Amazon border. Our multi-proxy data include carbon and nitrogen isotopes, as well as bulk TOC, chlorophyll derivatives, grain-size and microcharcoal analyses, all anchored on a radiocarbon-dated chronology. The sedimentary process recorded at the Barro-Preto Lake responded to both local and regional climate dynamics. It was influenced by river excursions associated to local responses to precipitation changes by the activation of the palaeochannel connecting the main-stem river and the Barro-Preto lake. This activation was evidenced by the presence of different colour lithology laminations accompanied by coarser sediments and also by climate conditions known to influence the Amazon region. Depositional processes linked to lake dynamics and different oxbow lake cycle stages were also important to explain the changes verified in the Barro-Preto record, endorsing the use of this lake formation for palaeoclimatic reconstructions. The record indicated a rising humidity trend, reflected by a progressive increase in lacustrine productivity, in accordance to other studies carried out in the Amazon region concerning the Late-Holocene, associated with a more southward displacement of the Intertropical Convergence Zone. Despite this rising humidity trend, dry episodic events during the Late-Holocene were evidenced by charcoal data, also coherent with regional Amazon studies, albeit exhibiting increased intensity, suggesting that the transitional nature of the environment might have influenced susceptibility to fires.

Vegetation Dynamics, Environmental Changes, and Anthropogenic Impacts on the Coastal Hyrcanian Forests in Northern Iran

Gu, F.; Ramezani, E.; Alizadeh, K., and Behling, H., 2021. Vegetation dynamics, environmental changes, and anthropogenic impacts on the coastal Hyrcanian forests in northern Iran. Journal of Coastal Research, 37(3), 611–619. Coconut Creek (Florida), ISSN 0749-0208.The Hyrcanian forest has been recognized as a hotspot of biodiversity and an important refugium of broad-leaved trees that survived from Quaternary ice ages. However, nowadays this coastal ecosystem has been endangered due to increased anthropogenic impacts. Multiproxy analysis, including pollen, spores, nonpollen palynomorphs, macrocharcoal, and X-ray fluorescence analysis have been applied on a sediment core from the northwestern coastal region of Iran, Zarbijar wetland to reconstruct past vegetation, regional climate dynamics, fire events, and human impacts on the coastal region of Hyrcanian forest. This study provides evidence that the anthropogenic impacts have greatly influenced the ecosystems of the coastal plain of the southern Caspian Sea during the last 600 years and demonstrate that human activities became intensified in the last 100 years. It is suggested that due to the human activities by construction, the geochemical composition of the wetland deposits was markedly artificially changed. The study also indicates that the dynamics of the Hyrcanian lowland forests and local fire frequency were mainly codominated by human impact and local climate conditions. Increased anthropogenic activities such as agriculture, construction, and human-induced fires played an important role in the decline of the Hyrcanian forest. Therefore, this study also suggests that more effort is urgently needed to protect this unique global heritage, and that not only the local government but also the international forest conservation agencies should introduce certain effective corresponding policies to prevent deforestation, control the expansion of land use by agricultural, and construction.

Summer thermal comfort in Russian big cities (1966-2015)

The main goal of the study is the assessment of modern bioclimatic conditions (1966-2015) for determining the level of comfort in large Russian cities based on the observations at the meteorological stations, including Physiological Equivalent Temperature (PET) for the main extent of thermal comfort. According to the distribution of thermal stress events (calculated for meteorological fix hours, 8 times per day) the authors created the comfort diagram for each city during daytime heat wave period and evaluated their comfort conditions. In the current research we are operating with WMO climatic data for eleven biggest cities of the Russian Federation: from the European part (Moscow, Saint-Petersburg, Ekaterinburg, Voronezh, Volgograd, Kazan, Nizhny Novgorod, Perm, Ufa) and from Siberia (Omsk and Krasnoyarsk). The most interesting result of the comparison of the long-period (50 years) urban trends (PET-index and Air Temperature) in different parts of Russia is its extraordinary cross-shaped form in Moscow (in other cities the trends lines are practically parallel to each other). It means that at the level of the average annual values, only in Moscow the PET index (and, hence, potentially the thermal stress) grows faster than the regional climate warms. In other cities this tendency is much weaker (N.Novgorod) or not significant. This interesting tendency is caused by both Moscow related urban planning dynamics in post-USSR period and by regional climate dynamics.

Phenology of myxomycetes in Turrialba, Costa Rica

Long-term monitoring and phenological patterns of microbial communities are rare in the scientific literature. Myxomycetes have life cycle characteristics that allow both to be documented. The present study summarizes the integrated floristic and bioclimatic components of a 30-month assessment of myxomycete sporocarps in a premontane tropical forest in Turrialba, Costa Rica. Based on monthly visits and a standard sampling effort of 120 minutes per visit, myxomycetes were recorded on leaves, twigs, and logs on the ground by two to three people in 20-minute periods associated with six different collecting sites within a 34-hectare successional forest patch. Biological data were analyzed using three recorded climatic variables obtained <em>in situ</em> during the complete period of study. Also, the Oceanic Niño Index (ONI), provided by NOAA, an estimate of El Niño-Southern Oscillation (ENSO), was evaluated in the analyses. Overall, 54 species and 2245 records of myxomycetes were recorded, with an average of 14.5 species (range between 6-24) and 78.4 records (range between 20-110) detected each month. In general, neither the number of records nor the number of species were associated with individual climate variables, but multiple regression analyses showed that a combination of the accumulated precipitation of the four days before sampling and the average relative humidity can explain most of the fruiting dynamics (R2 = 0.56). When the ONI index was included in the analyses, the explained variability increased (R2 = 0.64), and when a categorization of months based on the same index was used, analyses showed that both the number of records and species evenness were affected by ENSO. At the species level, <em>Hemitrichia calyculata</em> was the only species observed during every month, closely followed by <em>Arcyria cinerea</em>, <em>A. denudata</em>, and <em>Physarum compressum</em>, recorded on most visits. Sporadic fruiting in some species such as <em>Tubifera microsperma</em>, <em>P. tenerum</em>, <em>P. bogoriense</em>, <em>P. melleum</em>, and <em>Metatrichia vesparia</em> could have been associated with local climate oscillations influenced by ENSO patterns. Phenological patterns were observed at the species level, indicating that in the Neotropics, under favorable conditions, myxomycete sporocarps are practically always present, but species assemblages vary temporally. These variations are primarily driven by local climate, but regional climate dynamics also affect fruiting patterns. Presumably, the remaining ecological effect on fruiting patterns in the Neotropics can be attributed to certain finer factors such as ecosystem structure, substrate quality/ availability, and biotic interactions. As such, phenomena such as climate change can have an important effect on the production of sporocarps by tropical myxomycetes, with subsequent effects of their ecological dynamics.

Comportamento e distribuição das chuvas na Região de São Carlos/SP a partir de dados de Estações Climatológicas no per�odo de 1993-2014

As alterações climáticas, em diferentes escalas espaciais e temporais, alicerçam diversas pesquisas em climatologia a fim de compreender a dinâmica climatológica, bem como os atributos climáticos em tal processo. As chuvas, nesse sentido, representam a complexidade no entendimento da dinâmica atmosférica, uma vez que essas apresentam sua gênese apoiadas em diferentes processos atmosféricos. O presente estudo compreende o comportamento das chuvas na região de São Carlos a partir de dados diários de chuvas nas estações climatológicas na região de São Carlos/SP na série histórica de 1993 a 2014. Foram determinados os cálculos dos �ndices propostos por Zhang e Yang (2004) de RX 1 dia (máximo acumulado em um único dia), SDII (�ndice simples de intensidade), DCU (dias consecutivos úmidos), DCS (dias consecutivos secos) e PRCPTOT (precipitação total nos dias úmidos), pelo software R com script RClimdex. Os dados calculados apresentaram grande flutuação ao longo da série histórica 1993-2014 para todos os �ndices adotados, o que configura a presença de anos abaixo e acima da média para cada �ndice, bem como aponta para o dinamismo climático regional com os valores diários das chuvas junto ao planejamento regional.
 Palavras-chave: �?ndices, Climatologia Estat�stica, Chuvas, RClimdex.

Climate and vegetation dynamics of the Northern Apennines (Italy) during the Late Pleistocene and Holocene

This study reconstructs the regional vegetation and climate dynamics between the upper Late Pleistocene and Holocene around Pian del Lago, a coastal mountain marshland located at 831 m asl in western Liguria (NW-Italy), based on the pollen analysis of a 13 m-long sediment core. The record provided a unique opportunity to study a poorly documented period in northern Italy and across many parts of southwestern Europe. We propose an event stratigraphy based upon the identification of seven interstadials (NAI-7 to NAI-1) spanning the upper Late Pleistocene. The correlation with other terrestrial records in Italy, and with Mediterranean marine sequences and the Greenland ice cores, permitted a coherent reconstruction of main environmental changes from >∼43,000 cal. BP. Significantly, the pollen record indicates the persistence of a mesophilous mountain vegetation cover, mainly composed of Quercus (deciduous and evergreen), Abies, Fagus and Alnus over the whole time period recorded. At the Last Glacial Maximum (LGM) and during the Late Würm Lateglacial, despite the presence of steppic vegetation composed of Artemisia, woodlands dominated by Pinus, with Abies, Picea, Fagus, Alnus and Betula are present. This forest composition provides an important insight into the history of Picea in southern Europe and Late Pleistocene refugia for mesophilous species. During the Early Holocene, Pinus is first replaced by Abies and then by deciduous Quercus and mixed temperate species as the dominant forest component. Both arboreal and herbaceous anthropogenic pollen indicators only make their appearance during the Late Holocene, attesting to the increasing importance of human activities.

High-resolution record of Holocene climate change dynamics from southern Africa's temperate-tropical boundary, Baviaanskloof, South Africa

South Africa's southern Cape is a highly dynamic climatic region that is influenced by changes in both temperate and tropical atmospheric and oceanic circulation dynamics. Recent research initiatives suggest that the major elements of the regional climate system have acted both independently and in combination to establish a mosaic of distinct climate regions and potentially steep climate response gradients across the southern Cape. To consider this further, we present new high resolution δ13C and δ15N data from a rock hyrax (Procavia capensis) midden from Baviaanskloof, in the Cape Fold Mountains of South Africa's Eastern Cape Province. Spanning the last 7200 years, these data provide detailed information regarding environmental changes in the mid- and late Holocene, allowing us to assess the spatio-temporal nature of climate change anomalies across the wider region. Throughout the full duration of the record, a negative correlation between humidity and palaeotemperature reconstructions from nearby Cango Cave is observed. In conjunction with correlations with Southern Ocean sea-surface temperatures and sea-ice presence, we infer a dominant influence of the southern westerlies in determining multi-millennial scale hydroclimate variability. At shorter, multi-centennial to millennial timescales, the Baviaanskloof data indicate a clearer expression of tropical influences, highlighting a delicate balance between the mechanisms driving regional climate dynamics across timescales, and the sensitivity of the region to changes in global boundary conditions.

Multi‐century drought variability in the southern Min Mountains

AbstractInformation on moisture variability is important for climate adaptation and planning, which is urgently needed for the Jiuzhaigou County after it was hit by a magnitude 7.0 earthquake in August 2017, resulting in potential interactions between the earth surface processes and the hydroclimate. To study the regional hydroclimatic history beyond instrumental records, the first tree‐ring hydroclimate reconstruction, based on Pinus tabuliformis, was conducted in the southern Min Mountains, which is situated close to the areas affected by the Jiuzhaigou earthquake. The reconstruction, spanning from 1684 to 2017, explained 59% of the variance for May–August standardized precipitation evapotranspiration index at a 12‐month scale during 1962–2017. The recent drought, which occurred from 1992 to 2017 was the longest in duration, largest in magnitude, and had the second highest intensity. The most severe single year drought occurred in 1824, which was lower than the long‐term mean by 4σ and affected several regions in and around the Northeast Qinghai‐Tibet Plateau. The drought reconstruction was consistent with other moisture reconstructions, but dissimilar were also exist during some periods. There was a significant correlation between drought reconstruction and sea surface temperature over many oceans. However, the correlations were unstable over time. This study suggests the importance of developing a density tree‐ring network to identify the spatial and temporal drought variability, as well as long‐term record for understanding regional climate dynamics.

Synchronous Growth Releases in Peatland Pine Chronologies as an Indicator for Regional Climate Dynamics—A Multi-Site Study Including Estonia, Belarus and Sweden

Fourteen tree-ring chronologies developed from 788 peatland Scots pines sampled at sites in Estonia, Belarus and Sweden were compared for common growth trends and possible links to regional climate dynamics. Several synchronous growth release events were detected, especially during the 1910s, 1930s, and around 1970 and 1990, indicating that hydrological shifts and associated tree growth responses have been governed by similar forcing mechanisms, at least during the 20th century. In general, the best agreements were observed between the tree populations from Estonia and Belarus, but synchronous growth changes could also be detected between the Swedish and Estonian material. Trends detected in single tree-ring chronologies may be linked to local peatland management or land-use changes, whereas common variations detected at multiple sites are more likely linked to hydrological changes in the peatlands associated with regional climate dynamics. Understanding the links between climate and processes that involve peatland hydrology and vegetation responses is important since peatland ecosystems are key players in the global carbon cycle.

Impact of ENSO 2016–17 on regional climate and malaria vector dynamics in Tanzania

Large scale modes of climate variability, including the El Niño Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), have been shown to significantly impact mosquito-borne diseases in the Tropics, including malaria. However, the mechanistic cascade from ENSO and the IOD, to induced changes in regional climate and ultimately mosquito abundance and behaviour is poorly understood. Mosquito population dynamics, behaviour and their potential to transmit disease are all sensitive to micro-climatic conditions. The warm phase of ENSO (El Niño) tends to be associated with increased precipitation and outbreaks of various vector-borne diseases, while the cold phase (La Niña) can cause drought during the short rains over East Africa. The sensitivity of Anopheles mosquito population dynamics and host-seeking behaviour to ENSO and to the resulting micro-climatic conditions, were investigated in the Kilombero Valley in Tanzania. From June 2016 to September 2017, changes in the timing and intensity of the rainy seasons and temperature due to the ENSO 2016–17 were observed. Mosquitoes were collected using Centres for Disease Control and Prevention (CDC) light traps indoors and mosquito electrocuting traps in- and outdoors. Changes in abundance and biting behaviour of Anopheles arabiensis and Anopheles funestus were correlated with climate and micro-climate. The impacts of El Niño on climate and mosquito abundance were not clear. However, the study area experienced a drought due to La Niña during which both vector species declined significantly. An. arabiensis densities stayed more stable at higher temperatures and were found in higher numbers outdoors with respect to An. funestus. For both species, indoor temperature and season determined their host-seeking location, with higher temperatures and the wet season driving them outside. The study confirmed the influence of ENSO and micro-climate on malaria vector abundance and host-seeking behaviour, generating hypotheses for predicting the impact of future ENSO on malaria risk and vector control. Our observation of higher outdoor biting during warmer conditions indicates that indoor vector control strategies may become proportionally less effective during this time.

Enhanced Himalayan Glacial Melting During YD and H1 Recorded in the Northern Bay of Bengal

AbstractOcean‐land thermal feedback mechanisms in the Indian Summer Monsoon (ISM) domain are an important but not well understood component of regional climate dynamics. Here we present a δ18O record analyzed in the mixed‐layer dwelling planktonic foraminifer Globigerinoides ruber (sensu stricto) from the northernmost Bay of Bengal (BoB). The δ18O time series provides a spatially integrated measure of monsoonal precipitation and Himalayan meltwater runoff into the northern BoB and reveals two brief episodes of anomalously low δ18O values between 16.3±0.4 and 16±0.5 and 12.6±0.4 and 12.3±0.4 thousand years before present. The timing of these events is centered at Heinrich event 1 and the Younger Dryas, well‐known phases of weak northern hemisphere monsoon systems. Numerical climate model experiments, simulating Heinrich event‐like conditions, suggest a surface warming over the monsoon‐dominated Himalaya and foreland in response to ISM weakening. Corroborating the simulation results, our analysis of published moraine exposure ages in the monsoon‐dominated Himalaya indicates enhanced glacier retreats that, considering age model uncertainties, coincide and overlap with the episodes of anomalously low δ18O values in the northernmost BoB. Our climate proxy and simulation results provide insights into past regional climate dynamics, suggesting reduced cloud cover, increased solar radiation, and air warming of the Himalaya and foreland areas and, as a result, glacier mass losses in response to weakened ISM.

Disentangling the influence of local and remote anthropogenic aerosols on South Asian monsoon daily rainfall characteristics

Wet and dry periods within the South Asian summer monsoon season can have acute societal impacts. Recent studies have identified changes in daily rainfall characteristics of the monsoon, but the underlying causes are poorly understood. In particular, although the dominant role of anthropogenic aerosols in shaping historical changes in seasonal-mean monsoon rainfall has been documented, their influence on daily-scale rainfall remains unconstrained. Using an ensemble of single-forcing climate simulations, we find that anthropogenic aerosols have a stronger influence on late-twentieth century changes in the frequency of wet events, dry events and rainless days, compared with other climate forcings. We also investigate the role of aerosol-cloud interactions (“indirect effects”) in the total aerosol response, and the contribution of aerosols emitted from South Asia versus from remote sources. Based on additional simulations with the GFDL-CM3 climate model, we find that the simulated aerosol response over South Asia is largely associated with aerosol-indirect effects. In addition, local aerosols suppress wet-event frequency and enhance dry-event frequency over eastern-central India, where increases in aerosol loading are the largest. Remote aerosols cause a north–south dipole pattern of change in mean rainfall over India and fewer rainless days over western India. However, the overall spatial response of South Asian rainfall characteristics to total aerosol forcing is substantially influenced by the combined non-linear climate response to local and remote aerosols. Together, our results suggest that understanding the influence of different aerosol emissions trajectories on the regional climate dynamics is critical for effective climate-risk management in this populated, vulnerable region.