Rain Belt Research Articles

The Response of Cloud Precipitation Efficiency to Warming in a Rainfall Corridor Simulated by WRF

Due to model errors caused by local variations in cloud precipitation processes, there are still significant uncertainties in current predictions and simulations of short-duration heavy rainfall. To tackle this problem, the effects of warming on cloud-precipitation efficiency was analyzed utilizing a weather research and forecasting (WRF) model. The analysis focused on a rainstorm corridor event that took place in July 2020. Rainstorm events from 4–6 July formed a narrow rain belt with precipitation exceeded 300 mm in the middle and lower reaches of the Yangtze River. Temperature sensitivity tests revealed that warming intensified the potential temperature gradient between north and south, leading to stronger upward motion on the front. It also strengthened the southwest wind, which resulted in more pronounced precipitation peaks. Warming led to a stronger accumulation and release of convective instability energy. Convective available potential energy (CAPE) and convective inhibition (CIN) both increased correspondingly with the temperature. The precipitation efficiency increased sequentially with 2 °C warming to 27.4%, 31.2%, and 33.1%. Warming can affect the cloud precipitation efficiency by both promoting and suppressing convective activity, which may be one of the reasons for the enhancement of extreme precipitation under global warming. The diagnostic relationship between upward moisture flux and lower atmospheric stability during precipitation evolution was also revealed.

Mid-holocene changes in the global ITCZ: meridional structure and land–sea rainfall differences

Changes in the global and annual Intertropical Convergence Zone (ITCZ) during the mid-Holocene are quantified in this study, using simulations from the Paleoclimate Modelling Intercomparison Project Phase 4. We find an ensemble mean northward migration of ITCZ position by 0.2∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ $$\\end{document}, 0.3∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ $$\\end{document}, and 0.8∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ $$\\end{document} using three different metrics, which is consistent with proxy evidence of a slight (within one degree) northward shift during the mid-Holocene. The width of the ITCZ exhibits no changes during this period, while the strength has a minor weakening by 0.9% and 0.6% based on precipitation and streamfunction metrics, respectively. Moreover, there is an ensemble mean increase in northern-to-southern hemisphere precipitation (4.6%) and ω\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega $$\\end{document} ratio indices (12%) during the mid-Holocene, suggesting a more uneven and right-skewed meridional structure of the ITCZ with a greater asymmetry. Additionally, the moisture budget analysis indicates the eddy flux term and dynamic term primarily enhance the inter-hemispheric asymmetry of precipitation and poleward migration of both the northern and the southern rain belts within the ITCZ. Further investigation reveals that the northward migration of annual rainfall within the ITCZ predominantly occurs over terrestrial regions, which therefore dominate the change towards more asymmetric structure of the zonally averaged ITCZ. Moisture budgets for land and ocean separately indicate that the land-sea difference in the annual rainfall changes is primarily due to different changes in evaporation.

Kilometer-Scale Precipitation Forecasting Utilizing Convolutional Neural Networks: A Case Study of Jiangsu’s Coastal Regions

High-resolution precipitation forecasts play a pivotal role in formulating comprehensive disaster prevention and mitigation plans. As spatial resolution enhances, striking a balance between computation, storage, and simulation accuracy becomes imperative to ensure optimal cost-effectiveness. Convolutional neural networks (CNNs), a cornerstone of deep learning, are examined in this study for their downscaling capabilities in precipitation simulation. During a precipitation event on 23 June 2022, in Jiangsu Province, China, distinct rain belts emerged in both southern and northern Jiangsu, precisely captured by a numerical model (the Weather Research and Forecasting, WRF) with a 3 km spatial resolution. Specifically, precipitation was prevalent in northern Jiangsu from 00:00 to 11:00 Beijing Time (BJT), transitioning to southern Jiangsu from 12:00 to 23:00 BJT on the same day. Upon dynamic downscaling, the model reproduced precipitation in these periods with an average error of 12.35 mm at 3 km and 12.48 mm at 1 km spatial resolutions. Employing CNN technology for statistical downscaling to a 1 km spatial resolution, samples from the initial period were utilized for training, while those from the subsequent period served for validation. Following dynamic downscaling, CNNs with four, five, six, and seven layers exhibited average errors of 8.86 mm, 8.93 mm, 9.71 mm, and 9.70 mm, respectively, accompanied by correlation coefficients of 0.550, 0.570, 0.574, and 0.578, respectively. This analysis indicates that for this precipitation event, a shallower CNN depth yields a lower average error and correlation coefficient, whereas a deeper architecture enhances the correlation coefficient. By employing deep network architectures, CNNs are capable of capturing nonlinear patterns and subtle local features from complex meteorological data, thereby providing more accurate predictions during the downscaling process. Leveraging faster computation and reduced storage requirements, machine learning has demonstrated immense potential in high-resolution forecasting research. There is significant scope for advancing technologies that integrate numerical models with machine learning to achieve higher-resolution numerical forecasts.

Outburst floods and their impact on Chinese Neolithic cultures during the 4.2 ka BP event: Evidence from Dayeze Lake in the lower reaches of the Yellow River

Abrupt climate fluctuations between 4.2 and 3.5 ka BP, and in particular the 4.2 ka BP event, exerted a profound impact on the global ancient civilizations. However, hydroclimatic conditions within the Asian Summer Monsoon (ASM) regions during this event remain uncertain. Here we report a multi-proxy analysis of a sediment core obtained from Dayeze Lake in the lower reaches of the Yellow River in monsoonal China, to elucidate the hydroclimatic variabilities over the past 4.2 ka. Core intervals (4.2–3.5, 1.1–0.6 cal ka BP) containing high levels of sand fraction, low-frequency magnetic susceptibility and zirconium, and low levels of organic matter and calcium oxide, reflect outburst floods from the Yellow River. This is supported by the widespread fluvial deposits and slackwater deposits preserved in archaeological sites and loess-paleosol profiles from the middle and lower reaches of the Yellow River. In contrast, various climate records, such as lake level, pollen, and tree ring data, from the marginal regions of the ASM reflect widespread droughts during the same time period. This finding highlights the significant spatial heterogeneity of hydroclimate within ASM regions associated with the 4.2 ka BP event, which may be related to migrations of the monsoonal rain belt and the West Pacific subtropical high, as well as frequent El Niño–Southern Oscillation events. Referring to archaeological data, we conclude that the decline and collapse of Chinese Neolithic cultures were related to a pattern of droughts in the marginal regions of the ASM and floods in the middle and lower reaches of the Yellow River.

Detecting Hailstorms in China from FY-4A Satellite with an Ensemble Machine Learning Model

Hail poses a significant meteorological hazard in China, leading to substantial economic and agricultural damage. To enhance the detection of hail and mitigate these impacts, this study presents an ensemble machine learning model (BPNN+Dtree) that combines a backpropagation neural network (BPNN) and a decision tree (Dtree). Using FY-4A satellite and ERA5 reanalysis data, the model is trained on geostationary satellite infrared data and environmental parameters, offering comprehensive, all-day, and large-area hail monitoring over China. The ReliefF method is employed to select 13 key features from 29 physical quantities, emphasizing cloud-top and thermodynamic properties over dynamic ones as input features for the model to enhance its hail differentiation capability. The BPNN+Dtree ensemble model harnesses the strengths of both algorithms, improving the probability of detection (POD) to 0.69 while maintaining a reasonable false alarm ratio (FAR) on the test set. Moreover, the model’s spatial distribution of hail probability more closely matches the observational data, outperforming the individual BPNN and Dtree models. Furthermore, it demonstrates improved regional applicability over overshooting top (OT)-based methods in the China region. The identified high-frequency hail areas correspond to the north-south movement of the monsoon rain belt and are consistent with the northeast-southwest belt distribution observed using microwave-based methods.

Joint Impacts of the North African and the Western Pacific Subtropical Highs on Summer Precipitation over the Tibetan Plateau

Abstract Focusing on summer precipitation over the Tibetan Plateau (TP), this study mainly investigates the joint impacts of the North African subtropical high (NASH) and the western Pacific subtropical high (WPSH) by examining circulation and moisture anomalies. Results show that there are several boundary combination types of the two subtropical highs. The anomalous vertical motion with sufficient moisture transport under different boundary types plays a dominant role in TP precipitation anomaly. When the WPSH strengthens westward approaching the TP, it can transport water vapor northward from the northwest Pacific and north Indian Oceans to the south edge of the TP and induce ascending motion over the southeastern TP, contributing to more precipitation there. When the NASH enhances and extends eastward, it can transport water vapor eastward from the North Atlantic Ocean to the southwest eastern TP and give rise to ascending motion there, inducing positive precipitation anomaly over the southwest eastern TP. When the two subtropical highs simultaneously intensify and extend to the TP, water vapor can be transported to the TP widely from the North Atlantic Ocean, the north Indian Ocean, and the northwest Pacific Ocean with the strengthening of the westerly, resulting in the location of the ascending motion and rain belt shifting obviously northward. Further analyses indicate that the prewinter El Niño–Southern Oscillation (ENSO) and summer North Atlantic air–sea interaction are two indispensable possible modulation factors for the joint impact of the two subtropical highs on TP precipitation. Significance Statement Under the thermal and topographic effects of the Tibetan Plateau (TP), the subtropical high belt breaks over the TP, forming the western Pacific subtropical high (WPSH) on its east and the North African subtropical high (NASH) on its west. As a permanent anticyclonic circulation over the northwest Pacific, the formation, impact, and prediction of WPSH have been fully revealed. However, few studies have been focused on the NASH. In this study, we examine the joint impacts of the two subtropical highs on TP summer precipitation based on various reanalysis datasets and phase 6 of Coupled Model Intercomparison Project (CMIP6) historical simulations. The results show distinct precipitation features with several boundary combination types of the two subtropical highs. Besides, controlling water vapor transport and vertical motion is an important way for the two subtropical highs to affect TP precipitation in summer. Further study shows that the effect of the two subtropical highs on TP summer precipitation is generally modulated by the prewinter El Niño–Southern Oscillation (ENSO) and summer North Atlantic air–sea interaction. The results from CMIP6 support the conclusions drawn from reanalysis. These findings could help deepen our understanding of the joint influencing factors on TP summer precipitation.

Interdecadal variations and possible causes of rain belt’s advancing velocity in Eastern China based on evolutionary circulation pattern

Interdecadal variations and possible causes of rain belt’s advancing velocity in Eastern China based on evolutionary circulation pattern

Divergent future change in South Atlantic Ocean Dipole impacts on regional rainfall in CMIP6 models

The South Atlantic Ocean Dipole (SAOD) exerts strong influence on climate variability in parts of Africa and South America. Here we assess the ability of an ensemble of 35 state-of-the-art coupled global climate models to simulate the SAOD impacts on regional rainfall for the historical period (1950–2014), and their future projections (2015–2079). For both periods we consider the peak phase of the dipole in austral winter. Observational analysis reveals four regions with spatially coherent SAOD impacts on rainfall; Northern Amazon, Guinea Coast, Central Africa, and Southeast Brazil. The observed rainfall response to the SAOD over Northern Amazon (0.31 mm d−1), Guinea Coast (0.38 mm d−1), and Southeast Brazil (0.12 mm d−1) are significantly underestimated by the modeled ensemble-mean response of 0.10 ± 0.15 mm d−1, 0.05 ± 0.15 mm d−1, −0.01 ± 0.04 mm d−1, respectively. A too southerly rain belt in the ensemble, associated with warmer-than-observed Atlantic cold tongue, leads to better performance of models over Central Africa (46% simulate observations-consistent SAOD-rainfall correlations) and poor performance over the Guinea Coast (only 5.7% simulate observations-consistent SAOD-rainfall correlations). We also find divergent responses among the projections of ensemble members precluding a categorical statement on the future strength of the SAOD-rainfall relationship in a high-emissions scenario. Our results highlight key uncertainties that must be addressed to enhance the value of SAOD-rainfall projections for the affected African and South American countries.

Factors influencing the variation of the Sepik-Ramu River system's sediment plume off the north coast of New Guinea

The Sepik-Ramu River system (SRRs) is a principal contributor of terrestrial materials to the pelagic waters of the tropical Western Pacific, boasting the highest sediment discharge in New Guinea. However, this system's sediment outflow and dispersal patterns are not well-documented. This study seeks to address this gap by analyzing the estuarine sediment plumes, which are the key indicators of the marine dispersion of terrestrial materials. Utilizing Moderate Resolution Imaging Spectroradiometer (MODIS) images from 2010 to 2020 and applying the Novoa17 algorithm, we examined the distribution and temporal evolution of the sediment plume of the SRRs estuary. The sediment plume was categorized into two distinct zones: core and diffuse, based on suspended sediment concentration (SSC) levels. Our findings reveal significant seasonal variations of these sediment plumes in the nearshore. The plume area expands during the wet season and contracts during the dry season, respectively, with core and diffuse plumes sharing similar change characteristics. The diffuse plume primarily extends northeast in the wet season and subsequently shifts northwest in the dry season, and the core plume consistently points to the northeast. The study further explores the driving factors and mechanisms behind these patterns, identifying river discharge as the primary influence on the core plume and sea surface winds and coastal currents as determinants of the diffuse plume's behavior. Interannual variations in the plume characteristics were found to be influenced by the El Niño-Southern Oscillation (ENSO), which indirectly affects plume dynamics through its impact on regional precipitation. During El Niño events, characterized by drier conditions and reduced discharge, the plume SSC and area typically decrease. During La Niña events, the plume's SSC and area typically increase, except for the 2011 super La Niña's negative anomaly, caused by the rain belt's excessive westward shift.

Clouds and plant ecophysiology: missing links for understanding climate change impacts

Observations and models indicate that human activity is altering cloud patterns on a global scale. Clouds impact incident visible and infrared radiation during both day and night, driving daily and seasonal variability in plant temperatures—a fundamental driver of all physiological processes. To understand the impacts of changing cloud patterns on essential plant-based processes such as carbon sequestration and food production, changes in local cloud regimes must be linked, via ecophysiology, with affected plant systems. This review provides a comprehensive treatment of cloud effects (apart from precipitation) on fundamental ecophysiological processes that serve as the basis of plant growth and reproduction. The radiative effects of major cloud types (cumulus, stratus, cirrus) are differentiated, as well as their relative impacts on plant microclimate and physiology. Cloud regimes of major climate zones (tropical, subtropical, temperate, polar) are superimposed over recent changes in cloud cover and primary productivity. The most robust trends in changing global cloud patterns include: (i) the tropical rain belt (comprised mostly of deep convective clouds) is narrowing, shifting latitudinally, and strengthening, corresponding with shorter but more intense rainy seasons, increased clouds and precipitation in some parts of the tropics, and decreases in others; (ii) tropical cyclones are increasing in intensity and migrating poleward; (iii) subtropical dry zones are expanding, resulting in fewer clouds and drier conditions at these latitudes; (iv) summer mid-latitude storm tracks are weakening and migrating poleward, and clouds in temperate regions are decreasing; and (v) clouds over the Arctic are increasing. A reduction in coastal fog and low clouds (including those associated with montane cloud forests) have also been observed, although these trends can be partially attributed to local patterns of deforestation, urbanization, and/or reductions in aerosols associated with clean air initiatives. We conclude by highlighting gaps in the cloud-ecophysiology literature in order to encourage future research in this under-studied area.

Mesoscale and Microphysical Characteristics of a Double Rain Belt Event in South China on May 10–13, 2022

Mesoscale and Microphysical Characteristics of a Double Rain Belt Event in South China on May 10–13, 2022

Analysis and comparison of water vapor transport features and circulation anomalies during the super-strong Meiyu period of 2020 and 1998*

2020 and 1998 are the strongest Meiyu years in recent decades. The characteristics of the super-strong Meiyu precipitation and water vapor sources in 2020 and 1998 were compared, and the atmospheric circulation anomalies and the forcing factor SST were examined. (1) In 2020, the Meiyu duration, accumulated precipitation, and number of rainstorm days were greater than in 1998, and the highest since 1961. The Meiyu period in 2020 experienced 11 rainstorm processes. In 1998, a typical “second Meiyu” phenomenon occurred, and the area of heavy rainfall in 1998 was located further southward than that in 2020 (2) The contribution of the Bay of Bengal-South China Sea (BOB-SCS) to the total supply of water vapor in 2020 and 1998 was 43.0% and 42.0%, respectively, i.e., much higher than that of the climatological mean (25.5%). In 2020, the sources that provide most water vapor were the BOB, SCS, and central Pacific Ocean, while in 1998 were the Arabian Sea, BOB, and the western Pacific Ocean. (3) During the Meiyu period in 2020 and 1998, the position of atmospheric circulation pattern “two ridges and one trough” are different. Analysis of the vertical structure revealed that the specific humidity intensity above the area of heavy rainfall in 1998 was weaker than that in 2020, and the low-level convergence zone was further south and not as strong as in 2020. The positions of the western Pacific subtropical high (WPSH) and the western North Pacific anticyclone (WNPAC) in 1998 were both further south than those in 2020, which resulted in the more southerly locations of the southwesterly jet stream and rain belt. It should be pointed out that, the important contributions of the SST anomalies in the equatorial central eastern Pacific and the tropical Indian Ocean to the anomalous WNPAC in 1998 and 2020, respectively.

Hydroclimatic changes in eastern China during the Holocene based on pollen data and climate modeling

The Asian monsoon system represents one of the world's most dynamic interactions of the cryosphere-continent-ocean-atmosphere system. Understanding and responding to changes in monsoonal precipitation is a major component of environmental management in this region, given its profound influence on socioeconomic activity in monsoonal Asia. In particular, characterizing the spatiotemporal variability of the East Asian summer monsoon (EASM) is critical for comprehensively understanding its dynamics and future impacts. Although substantial progress has been made in reconstructing past changes in the EASM, the spatial pattern of EASM intensity in China on the orbital-scale remains controversial. This is mainly because of uncertainties in the climatic interpretation of EASM-related proxies. Here, we present a quantitative seasonal precipitation reconstruction for monsoonal China during the Holocene, using the Modern Analog Technique (MAT) based on pollen data. The results show that during the Holocene both the annual and summer precipitation in monsoonal China increased gradually and reached a peak during the early mid-Holocene, with respective values that were ∼ 170 mm and 60 mm higher than today, followed by a decrease in the late Holocene. On the regional scale, the temporal pattern of monsoon rainfall was discrepant: a decrease from the early through late Holocene in northern China, and an increase from the early through late Holocene in southern China.To investigate the possible forcing mechanisms of these phenomena, we used the full TraCE-21 k simulation and single-forcing transient simulations to analyze spatial and temporal rainfall patterns. The results suggest that the north-south pattern is the product of orbital forcing. Intensified summer insolation during the early Holocene enhanced the land-sea thermal contrast, which strengthened the EASM along with the northward extension of the west Pacific subtropical high. Both factors caused the increased withdrawal of oceanic water vapor and the northward advance of the EASM rain belt, delivering more rainfall to northern China and less rainfall to southern China, and vice versa. Overall, our results indicate that insolation variations were the dominant factor determining the spatial pattern of EASM precipitation during the Holocene. Our findings are relevant to the calibration of palaeoclimate models and they contribute to an improved understanding of the Asian monsoon sub-systems.

Neural network-based climate index: Advancing rainfall prediction in EI Niño contexts

Accurate short-term climate predictions, specifically the prediction of dominant rain belts during flood seasons, represent a significant challenge, particularly in the absence of notable external forcing signal anomalies in the previous winter. To address this challenge, we propose a novel climate index based on an Auto-Encoder (AE) Neural Network that exhibits superior performance in indicating several significant precipitation events in the Yangtze and Huaihe River Basins under varying El Niño conditions. Notably, the novel climate index rectifies the discrepancy between the 2019/2020 Niño index and the 2020 summer precipitation. In order to understand the information source of AE, the causality between AE and other indices was further analyzed by Granger Causality. The results show that AE index mainly contains the information of subtropical high index and ocean index, which is consistent with previous studies.

The method of calculating sprinklers for wide-reach sprinklers

The quality of irrigation with wide-coverage sprinkler equipment largely depends on the design of sprinklers and their location on the rain belt. The purpose of the presented article is to improve the methodology for calculating sprinklers and to develop recommendations on the applicability of sprinklers in various conditions. The article presents a method for determining the nozzle diameter based on ensuring uniformity of irrigation, characteristics of the water flow coming off the deflector, and the radius of capture by rain. The trajectories of movement in the opposite direction of the wind for droplets with different sizes are given. The optimal angle is indicated depending on the wind speed. The maximum radius corresponds to the angle of departure of the water flow to the horizon within 28..32 °. The distance between the sprinklers along the water supply pipeline of wide-reach sprinklers should be at least 2/3 of the radius of rain capture, without taking into account the effects of wind.

Joint Impacts of Intraseasonal Oscillation and Diurnal Cycle on East Asian Summer Monsoon Rainfall

Abstract Intraseasonal and diurnal variations are two basic periodic oscillations in global/regional climate and weather. To investigate their joint impacts over East Asia, this paper categorizes the boreal summer intraseasonal oscillations (ISOs) in 1998–2019 into two groups with different diurnal cycles. It is shown that the active ISOs with large diurnal cycles feature a northwestward-moving anomalous anticyclone with strong southerlies at the western flank. These ISOs have in-phase patterns of geopotential height anomaly between low and midlatitudes over East Asia, associated with the simultaneous expansions of the western Pacific subtropical high (WPSH) and South Asian high (SAH). They couple with the anomalous ABL heating by daytime solar radiation over East Asia, which acts to enhance monsoon southerlies at midnight. The nocturnally strengthened southerlies facilitate dynamic lifting, moisture transport, and convective instability for producing midnight to morning rainfall at their northern terminus, thereby yielding a remarkable northward propagation of the monsoon rain belt. In contrast, the other ISOs with small diurnal cycles are related to a westward-moving anomalous anticyclone, while the WPSH and SAH have relatively small expansions and the westerly trough is active at middle latitudes. They lead to the dipole patterns of geopotential height anomaly and weak ABL heating over East Asia. The daily-mean southerlies and moisture conditions as well as their nocturnal enhancements are relatively weak, and thus, the northward shift of the monsoon rain belt is less pronounced. These results highlight that the large-scale conditions of ISOs can be distinguished by their different couplings with regional-scale diurnal forcings, which help the understanding and prediction of multiscale rainfall activities.

An age-depth model for Lake Bosumtwi (Ghana) to reconstruct one million years of West African climate and environmental change

Situated within a 1.07 million-year-old meteorite crater, Lake Bosumtwi in Ghana stands as a pivotal location for comprehending climatic, ecological and environmental fluctuations within the sub-Saharan region of West Africa. The region's susceptibility to seasonal environmental shifts and climate oscillations is heightened by the annual movements of the tropical rain belt driven by atmospheric circulation. Yet, there is no satisfying age-depth model available for the entire sedimentary sequence strongly limiting our understanding of changes in this circulation pattern and associated (broad-scale) environmental responses during the last million years in the local to regional context of Lake Bosumtwi. To overcome this, we statistically examine the cyclicity in total natural gamma ray (NGR) data on a core from the lake's centre and create a cyclostratigraphic age-depth model. The calculated maximum age of 946 ka agrees well with the meteorite impact age (∼10 % offset). In order to refine this purely statistical approach, we also perform a correlative age-depth model using 33 tie points accounting for the complexity of climatic and environmental imprints to the NGR record that may exceed direct insolation related effects. Special attention is paid to the core's robustly dated (14C, OSL, U/Th) uppermost part covering the last 200 ka. Here, high NGR and co-varying K counts coincide with warm periods (except of the water-saturated and unconsolidated Holocene part) and the inverse for glacials and stadials. Based on this, we define tie points for correlating our NGR data to the age-depth model of a NE Atlantic SST record. Comparing our results to the correlation target, other global climate records and Sahara dust flux data reveals striking similarities and supports a proxy understanding with increased in wash of K-enriched terrigenous material from the crater rims in warm and moist periods (high NGR) and K-depleted dust input in stadials possibly contributing to low NGR values in addition to reduced input of K-enriched sediments from the crater rims. Our correlative age model results in precession amplitudes matching eccentricity well, providing further support especially because an over-tuning is unlikely with the used 33 tie points. Overall we provide crucial chronological context to numerous datasets along with environmental constrains that can be used to study the potential habitat availability of early anatomically modern humans in West Africa.

The centennial-resolution loess δDwax record indicates summer precipitation variations in the marginal region of the East Asian monsoon during the last deglaciation

Precipitation isotopic composition variations that are directly recorded in geological samples play an important role in understanding past hydroclimatic changes. In arid regions, the hydrogen isotopes of leaf wax (δDwax) in loess sections can provide records of summer precipitation isotopes. However, previous studies have primarily focused on the orbital scale, and there was still a lack of clear understanding of variations in precipitation isotopes on shorter timescales and their implications for climate change. In this study, we report centennial-resolution loess δDwax records from the central Chinese Loess Plateau (CLP) from the last deglaciation to the early Holocene. We compared the loess optically stimulated luminescence chronology and U-Th ages conveyed by linking stalagmite δ18O and loess δDwax to validate the δDwax method as a potential tool for assessing loess chronology on the suborbital scale. Our findings also indicated that regional precipitation isotopes experienced a depletion of approximately 24‰ for δD and around 3.2‰ for δ18O during the last deglaciation. The overall precipitation isotope amplitude in the central CLP was similar to that of typical East Asian monsoon regions and lower than that of the Indian monsoon and westerly regions. However, the precipitation isotope oscillations on the millennial scale in the central CLP were significantly weaker than those in eastern to central China. The finding affirmed that although the summer precipitation in the CLP was primarily influenced by the East Asian monsoon system at the orbital scale, the northern boundary of the summer rain belt remained a distance away from the interior of the CLP during the last deglaciation. As a result, the short-term oscillations of atmospheric circulation were not strongly reflected in the precipitation isotopes of the central CLP. This result highlighted spatial and temporal differences in precipitation isotope variability between the dominant and marginal regions of the East Asian monsoon system.

A sequence of abrupt climatic fluctuations in the north-eastern Caribbean related to the 8.2 ka event

A speleothem collected from Palco Cave (Puerto Rico) spans the 8.2 ka event, a time interval associated with fluctuations of Atlantic Ocean circulation and possible drying in the Caribbean region. While stalagmite δ18O, δ13C, and Mg/Ca data do not show a sustained change in mean state over the 8.2 ka event, the proxies provide robust evidence for three abrupt fluctuations toward drier conditions in rapid succession, each lasting less than two decades, occurring at 8.20, 8.14, and 8.02 ka BP. A cave monitoring program at Palco Cave supports the interpretation of the speleothem proxy records. Because changes in the position of the Intertropical Convergence Zone (ITCZ) are directly coupled to sea-surface temperature variations in the North Atlantic, we hypothesize that cold events in the North Atlantic temporarily limited the northward migration of the ITCZ and tropical rain belt in boreal summer during these abrupt drying periods. The speleothem record suggests that the 8.2 ka event was associated with rapid rainfall fluctuations in the northern Caribbean followed by a comparably warm and wet phase after the 8.2 ka event. This enhanced variability during the transitional period of the deglaciation appears to be linked to a fast coupling between interacting oceanic and atmospheric processes. This involves, in particular, the Atlantic Meridional Overturning Circulation in modulating interhemispheric heat transport.

Spatiotemporal Intertropical Convergence Zone dynamics during the last 3 millennia in northeastern Brazil and related impacts in modern human history

Abstract. Changes in tropical precipitation over the past millennia have usually been associated with latitudinal displacements of the Intertropical Convergence Zone (ITCZ). Recent studies provide new evidence that contraction and expansion of the tropical rain belt may also have contributed to ITCZ variability on centennial timescales. Over tropical South America few records point to a similar interpretation, which prevents a clear diagnosis of ITCZ changes in the region. In order to improve our understanding of equatorial rain belt variability, our study presents a reconstruction of precipitation for the last 3200 years from the northeastern Brazil (NEB) region, an area solely influenced by ITCZ precipitation. We analyze oxygen isotopes in speleothems that serve as a faithful proxy for the past location of the southern margin of the ITCZ. Our results, in comparison with other ITCZ proxies, indicate that the range of seasonal migration, contraction, and expansion of the ITCZ was not symmetrical around the Equator on secular and multidecadal timescales. A new NEB ITCZ pattern emerges based on the comparison between two distinct proxies that characterize the ITCZ behavior during the last 2500 years, with an ITCZ zonal pattern between NEB and the eastern Amazon. In NEB, the period related to the Medieval Climate Anomaly (MCA – 950 to 1250 CE) was characterized by an abrupt transition from wet to dry conditions. These drier conditions persisted until the onset of the period corresponding to the Little Ice Age (LIA) in 1560 CE, representing the longest dry period over the last 3200 years in NEB. The ITCZ was apparently forced by teleconnections between Atlantic and Pacific that controlled the position, intensity, and extent of the Walker cell over South America, changing the zonal ITCZ characteristics, while sea surface temperature changes in both the Pacific and Atlantic stretched or weakened the ITCZ-related rainfall meridionally over NEB. Wetter conditions started around 1500 CE in NEB. During the last 500 years, our speleothems document the occurrence of some of the strongest drought events over the last centuries, which drastically affected population and environment of NEB during the Portuguese colonial period. The historical droughts were able to affect the karst system and led to significant impacts over the entire NEB region.