Dry Events Research Articles

Limited role of climate change in extreme low rainfall associated with southern Madagascar food insecurity, 2019–21

Southern Madagascar recently experienced a severe food security crisis, made significantly worse by well below average rainfall from July 2019 to June 2021. This exceptional drought has affected a region with high pre-existing levels of vulnerability to food insecurity (subsistence agriculture and pastoralism in the region is rain-fed only), while impacts have been compounded further by COVID-19 restrictions and pest infestations. The rainy seasons of both 2019/20 and 2020/21 saw just 60% of normal rainfall across the Grand South region and was estimated as a 1-in-135 year dry event, only surpassed in severity by the devastating drought of 1990–92. Based on a combination of observations and climate modelling, the likelihood of experiencing such poor rains in the region was not significantly increased due to human-caused climate change: while the observations and models combine to indicate a small shift toward more droughts like the 2019–2021 event as a consequence of climate change, these trends remain overwhelmed by natural variability. This result is consistent with previous research, with the Intergovernmental Panel on Climate Change (IPCC)’s Sixth Assessment Report concluding that any perceptible changes in drought will only emerge in this region if global mean temperatures exceed 2 °C above pre-industrial levels.

Evolution of the NMME Rainfall Seasonal Forecasting over Central Africa

The North American Multi-Model Ensemble (NMME) has grown into a fully developed scientific database for seasonal and sub-seasonal climate forecasts, progressing prediction from global to regional scales. The NMME has continuously developed, with new models replacing old ones; it is hypothesized that this development will generate more accurate forecasts over time. However, to date, this hypothesis has not been verified in Central Africa (CA). This study investigates the hypothesis that the skill of NMME models will increase as the forecasting system advances, focusing on rainfall in CA. The study is conducted for the four configuration (phases) of NMME models, from the oldest to the most recent. The analyses are performed with Short Lead (SL) time and Long Lead (LL) time hindcasts very coherent with the perspectives of the CA. The results show from configuration 1 (phase 1) to configurations 4 (phase 4), the NMME models reasonably replicate the spatial structures in the seasonal rainfall climatology of the observations with a remarkable bias at LL. The mean absolute error and root mean square difference reveal small but incremental improvements in the prediction skills of NMME models from phase 1 to phase 4. The Pearson coefficient (r) increased in SL by about 1%, i.e., from 0.94 to 0.95 during June–August (JJA) season and about 4% during the September–November (SON), i.e., from [Formula: see text] in phase 1 to [Formula: see text] in phase 4, about 3% from phase 1 to phase 4 during the March–May (MAM). The categorical scores show that the Probability of Detection (POD) and False Alarm (FAR) increased very slightly from phase 1 to phase 4, but is it noted that the different combinations of the NMME forecasting system present difficulties in predicting rainy and dry events. It should be added that by introducing newer models into a multi-model ensemble as they are developed, and by eliminating older models, small skill gains are observed in the NMME forecasting system in CA.

Compound impacts from droughts and structural vulnerability on human mobility.

Extreme dry events already disrupt populations' ability to migrate. In a warming climate, compound drought events could amplify vulnerability and drive forced migration. Here, we contribute the first multi-method research design on societal impacts from compound drought events. We show how mobility patterns are shaped by the intersection of drought and social vulnerability factors in three drought-prone countries- Madagascar, Nepal, and Mexico. We find that internal migration in agricultural communities in Mexico increased by 14 to 24 basis points from 1991 to 2018 and will prospectively increase by 2 to 15 basis points in Nepal in case of a compound drought event in 2025. We show that consecutive drought events exacerbate structural vulnerabilities, limiting migrants' adaptation options, including long-range migration. We conclude that the additional social pre-conditions, e.g., social isolation and lack of accurate information, ultimately limit migration as an adaptation option for households vulnerable to compound drought events.

Grain-Size End-Members of Anguli-Nuur Lake Core Sediments: Evidence for Moisture Variability in Northern China since the Last Deglaciation

The common methods used for grain-size analysis have their own deficiencies and limitations in terms of explaining the genesis of grain-size components. In this study, the end-member modeling analysis method is applied to multi-mode grain-size distributions of core sediment from Anguli-nuur lake to help to understand the sediment provenance, transport processes and sedimentary environment. Four optimal end-members are unmixed, and three transport-deposition processes are revealed, including the runoff, wave and aeolian processes. The humidity index synthesized by the runoff and aeolian end-members in the core sediment is used to reconstruct the humidity variability in the East Asian monsoonal domain since the last deglaciation. Our record shows that the patterns of humidity variability are coincidentally linked with the monsoonal precipitation index from the same core and stalagmite record in southern China. The Holocene optimum is identified in early and middle Holocene. In addition, a series of millennial- and multi-centennial-scale dry events documented in our record are well correlated with the ice-rafted debris events in the North Atlantic. The results reveal that the grain-size record from Anguli-nuur lake is sensitive in response to moisture variability in northern China.

Hydrological Drought Responding to Meteorological Drought in Prek Thnot River Basin

Drought is an inevitable consequence of climate variability and is pervasive across many regions all over the globe. This study aims to explore the relationship of drought and to evaluate the adaptivity and sensitivity in the Prek Thnot River Basin, Cambodia. The drought indicators were used between the occurrence of droughts based on Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) to assess the impact in 8 stations in its base months (June, August, and November) for each time scale (1-month, 3-month, and 9-month). The results indicated that 1998 and 2005 were the most critical years. Furthermore, the dry event could be seen in each basin mostly in June and August as a state in drought frequency as in all stations. The outcomes indicated that most stations experienced drought conditions. The small amount of rainfall occurs over these stations during the year indicated, and they had a high frequency of drought. The drought conditions during the period could have many impacts on population living livelihood, especially on sanitation, economy while the most damaging negative impact is on crop production in the regions, given Cambodians’ dependence on agricultural resources.

Органическое земледелие в лесостепи западной Сибири: оценка повторяемости атмосферных засух на основе SPI

This paper presents the findings of a study to assess the recurrence of moisture/drought conditions on the territory of the forest-steppe zone of Western Siberia for the period from 1971 to 2021. The degree of moistening was investigated on the basis of the Standardized Precipitation Index (SPI). Calculations were made for 4 areas (Altai Territory, Kemerovo, Novosibirsk and Omsk regions) with meteorological stations located on the territory of the forest-steppe zone of Western Siberia. In the studied areas, it was found that the drought conditions of different categories were manifested with a certain periodicity. SPI categories "moderately dry", "severely dry" and "extremely dry" for the studied period in May-July in Altai Territory account for 15,68% of years, in Novosibirsk Region for 13,72%, in Kemerovo Region for 19,6% and in Omsk Region for 13,72% of years. Local manifestation of extreme droughts for the time interval under study in the forest-steppe zone of Western Siberia was observed 7 times. Frequency of occurrence of deficiency of atmospheric precipitation during a part of vegetative period from May till July in territories of subjects in forest-steppe zone of Western Siberia is on the average 15,68%. The years with atmospheric precipitation shortage during the 51-year period in May accounted for 6 to 10 years, and 6 to 8 years in June. For Altai Territory, Novosibirsk and Kemerovo regions in the dynamics revealed trends in improving wetting conditions, characteristic both for most of the growing season of May-July, and separately for May and June. For territory of the Omsk region the trend indicating decrease in quantity of atmospheric precipitation in June is established. Frequency of occurrence of the dry events connected with deficiency of atmospheric precipitation remains high enough (once in 7-8 years). The results of studies on the degree of moisture/drought of the territory, carried out by SPI calculations, can be used for risk analysis and assessment of the effectiveness of crop production, as well as for the development and adaptation of farming systems, including organic agriculture to changing climatic conditions, where the role of natural factors in the crop production process becomes much more prominent. Keywords: ATMOSPHERIC DROUGHT, STANDARDIZED PRECIPITATION INDEX, SPI, FOREST-SEPHERE ZONE, WESTERN SIBERIA

Characterizing the Turning Points in Ecosystem Functioning and Their Linkages to Drought and Human Activities over the Arid and Semi-Arid Regions of Northern China

Identifying the changes in dryland functioning and the drivers of those changes are critical for global ecosystem conservation and sustainability. The arid and semi-arid regions of northern China (ASARNC) are located in a key area of the generally temperate desert of the Eurasian continent, where the ecological conditions have experienced noticeable changes in recent decades. However, it is unclear whether the ecosystem functioning (EF) in this region changed abruptly and how that change was affected by natural and anthropogenic factors. Here, we estimated monthly rain use efficiency (RUE) from MODIS NDVI time series data and investigated the timing and types of turning points (TPs) in EF by the Breaks For Additive Season and Trend (BFAST) family algorithms during 2000–2019. The linkages between the TPs, drought, the frequency of land cover change, and socioeconomic development were examined. The results show that 63.2% of the pixels in the ASARNC region underwent sudden EF changes, of which 26.64% were induced by drought events, while 55.67% were firmly associated with the wetting climate. Wet and dry events were not detected in 17.69% of the TPs, which might have been caused by human activities. TP types and occurrences correlate differently with land cover change frequency, population density, and GDP. The improved EF TP type was correlated with the continuous humid climate and a reduced population density, while the deteriorated EF type coincided with persistent drought and increasing population density. Our research furthers the understanding of how and why TPs of EF occur and provides fundamental data for the conservation, management, and better decision-making concerning dryland ecosystems in China.

Morphology of ctenostome bryozoans: 6. Amphibiobeania epiphylla.

Ctenostome bryozoans are unmineralized and mostly marine. Their lack of calcified skeletal features requires other characters to be considered for systematic and phylogenetic considerations. As a continuation of an ongoing series of studies, we herein investigate the morphology of Amphibiobeania epiphylla, a unique bryozoan inhabiting mangrove leaves that are highly exposed to tidal cycles and regular dry events according to the tidal cycle. Besides this interesting mode of life, the species was originally interpreted to be a weakly mineralized cheilostome bryozoan, whereas molecular data place it among ctenostome bryozoans. To elucidate the systematic and phylogenetic position of the genus and also find morphological adaptations to an extreme habitat, we investigated the morphology of A. epiphylla in detail. Zooids show a lophophore with eight tentacles and a simple gut with a prominent caecum, lophophoral anusand most notably a distinct gizzard in the cardiac region. Gizzard teeth are multiple, simple homogeneous cuticular structures. The cuticle of the zooid is rather uniform and shows no respective thickenings into opercular flaps or folds. Likewise, apertural muscles are represented by a single pair of muscles. There are no specific closing muscles in the apertural area like the operculum occlusors of cheilostomes. Most prominent within zooids is a spongiose tissue filling most of the body cavity. Although not properly understood, this tissue may aid in keeping animals moist and hydrated during prolonged dry times. In summary, all morphological characters support a ctenostome rather than a cheilostome affinity, possibly with Vesicularioidea or Victorelloidea. In addition, we provide new molecular data that clearly supports such a closer relationship.

Evolution and Trends of Meteorological Drought and Wet Events over the Republic of Djibouti from 1961 to 2021

Drought is a meteorological and hydrological phenomenon affecting the environment, agriculture, and socioeconomic conditions, especially in arid and semi-arid regions. A better understanding of drought characteristics over short and long timescales is therefore crucial for drought mitigation and long-term strategies. For the first time, this study evaluates the occurrence, duration, and intensity of drought over the Republic of Djibouti by using a long-term (1961–2021) rainfall time series at Djibouti Airport, completed by the CHIRPS precipitation product and local records from 35 weather stations. The drought is examined based on the Standardized Precipitation–Evapotranspiration Index (SPEI) and the Standardized Precipitation Index (SPI) at 3-, 6-, 9-, 12-, and 24-month timescales, so as to document short-, medium-, and long-duration events. The SPEI and SPI showed a significant drying tendency for the indices computed over 12 and 24 months at Djibouti Airport. The eastern coastal region of the Republic of Djibouti was the most affected by the increased drought incidence in recent decades, with more than 80% of the extremely and severely dry events occurring within the period 2007–2017. In contrast, the western regions recorded a positive trend in their SPIs during the period 1981–2021, due to the dominance of the June–September (JJAS) rains, which tend to increase. However, in the last few decades, the whole country experienced the droughts of 2006/2007 and 2010/2011, which were the longest and most intense on record. Large-scale climate variability in the Indo-Pacific region partially affects drought in Djibouti. The SPI and SPEI are significantly positively correlated with the Indian Ocean Dipole during October–December (OND), while for JJAS the SPI and SPEI are negatively correlated with Nino3.4. The wet event in 2019 (OND) causing devastating floods in Djibouti city was linked with a positive IOD anomaly. This study provides essential information on the characteristics of drought in the Republic of Djibouti for decision-makers to better plan appropriate strategies for early warning systems to adapt and mitigate recurrent droughts that put the country’s agro-pastoral populations in a precarious situation.

Effects of meteorological droughts on water resources in Northern Morocco: Case study of the Martil watershed

Recent droughts in the Northern Morocco have highlighted the increasing vulnerability of water resources to this natural hazard, with reduced potential for drinking water supply in the city of Tetouan and its coastal area. Therefore, the main objectives of this work are: the identification of dry events that affected the Martil watershed on the one hand, and the study of the effects of meteorological droughts on water resources on the other hand. For this purpose, a meteorological-hydrological modelling framework was adopted, using standardized precipitation index (SPI) values and the volume of surface water resources recorded at the Torreta station. The results obtained show that the last decade of the 20th century and the beginning of the 21st century have seen the heaviest and most critical droughts in the study area, namely the drought of 1994-95, 1998-99, 2004-05, 2006-07, 2011-12 and 2013-14. Also, water resources have been reduced by 62% to 82% during critical dry years compared to the long-term average for the period 1970-71/2014-15. Finally, this study showed that the rainfall variability is the determining factor in the fluctuations of surface water resources at the Martil watershed because it explains 84% of their total variance.

Impacts of landscape-scale forest loss and a dry event on the demographic structure of the endangered palm Euterpe edulis Mart. in the Atlantic Forest

Forest loss is one of the most serious threats to biodiversity in the tropics and mainly occurs due to the conversion of native forests by the expansion of human activities. In addition, regional climate change is likely to adversely affect the remaining biota. These disturbances may have direct or indirect consequences on the demographic structure of plant species in human-modified landscapes. To test this hypothesis, and thus look for management practices aimed at enhancing the population viability, we used the palm species Euterpe edulis Mart. (Arecaceae) to assess the demographic structure of five ontogenetic stages prior (2014) and after (2017) a prolonged drought event (2015) that occurred in the northeastern Atlantic Forest of Brazil. We also investigated the influence of landscape forest cover on the ontogenetic demographic structure, given that forest remnants were embedded within landscapes ranging from 6 to 97% of forest amount. We revealed that forest cover was a key predictor explaining the abundance patterns of E. edulis, with all ontogenetic stages (except seedlings, immature, and adults) exhibiting lower abundance in forest remnants surrounded by lower amount of native forests. Conversely, the regional drought event unaffected the demographic structure of this palm species, which may suggest that populations of E. edulis were able to cope with an isolated, though severe, drought event. The impacts of forest loss on E. edulis demographic structure, particularly on juveniles, raises a concern about the future persistence of E. edulis populations, since the early stages represent the adult generation in the near future. Management measures, including species reintroduction, forest restoration, environmental education programmes and the enforcement of environmental laws must be encouraged to safeguard E. edulis populations in the Atlantic Forest.

Evaluating carbon and water fluxes and stocks in Brazil under changing climate and refined regional scenarios for changes in land use

Climate change and land-use change can alter the role of natural vegetation as a sink or source of atmospheric carbon. In this work, we evaluate the response of water and carbon fluxes and stocks in Brazilian biomes as a proxy for ecosystem services of regional climate regulation under two contrasting future scenarios: a sustainable development scenario, where some deforested areas are restored by vegetation regrowth combined with a low representative concentration pathway, and a pessimistic scenario, where there is still high deforestation rates and strong climate change. We used refined regional scenarios for land-use change in Brazil, together with climate projections of the HADGEM2-ES model for RCPs 2.6 and 8.5 to drive a land surface model and assess possible future impacts in surface fluxes. Our results show that drying climate and shifts of natural vegetation into anthropogenic land use might shift part of upperstory biomass into understory biomass, which can be more vulnerable to dry events. The simulations also show that climate change appears to drive most of the water balance changes compared to land-use change, especially over the Amazon.

Characterization of dominant factors on evapotranspiration with seasonal soil water changes in two adjacent forests in the semiarid Loess Plateau

Evapotranspiration is an essential process of ecosystem water consumption and is controlled by meteorological factors and soil water conditions. In this study, evapotranspiration based on soil water budget was investigated with respect to major influencing factors during the growing seasons of 2012–2015 for two adjacent forest communities in the semiarid Loess Plateau region: a natural secondary forest dominated by oak (Quercus liaotungensis) and a plantation of exotic black locust (Robinia pseudoacacia). Based on the combination of precipitation, soil water storage, and evapotranspiration dynamics, four distinct periods were differentiated to explore the evapotranspiration response to the main meteorological factors. The correlation matrixes showed that, in most investigated days, evapotranspiration was limited by soil water storage, while an increase in soil water storage shifted dominance from water-related to energy-related factors. The stepwise regression of ≥5-day dry events in each period had a better fitness when paired with the relationship between the summations of evapotranspiration and dominant factors (R2 > 0.7, p < 0.01 for all) than the stepwise results for daily averages. A receiver operating characteristic (ROC) curve was applied to validate the division and determine thresholds. All divisions were thoroughly validated, and the soil water storage thresholds of the black locust (120.2 mm and 150.7 mm) were higher than those of the oak (105.8 mm and 137.9 mm). Our results suggest that the oak had an adaptive water consumption strategy, while the black locust had a higher sensitivity to soil water insufficiency. The method for determining the threshold of soil water storage to separate the dominant factors of evapotranspiration was validated. The approach may be applied to other semiarid forest communities with distinct evapotranspiration response patterns.

Deciphering paleohydrology from the petrography and microstratigraphy of stalagmites (MIS 5 – Holocene, Moulis Cave, Ariège, S. France)

A stalagmite from Moulis Cave in the northern Pyrenean piedmont in SW France provides a discontinuous record between the last interglacial and the Holocene. The integrated study of petrography, microstratigraphy and internal architecture of the stalagmite documents paleohydrological history of the drip site during speleothem growth, including infiltration conditions and calcite saturation state of the water feeding the stalagmite. Following diagenetic screening which demonstrates the excellent state of preservation of the speleothem, a set of petrographical, mineralogical and geochemical analytical techniques was used to characterize: 1. the successive growth units and their bounding surfaces, including facies and nature of processes occurring at the level of each discontinuity, and 2. the morphological changes of the stalagmite apex and stacking pattern.Observations reveal that each bounding surface results from a particular group of events, the nature and effects of which are petrographically clearly identifiable. During the interstadials 5b-5a of the last interglacial, the stalagmite developed at a relatively moderate growth rate and under stable drip rate conditions, except at the onset of the 5b cooling. The highest growth rates are recorded during the Bølling-Allerød to Younger Dryas, and the Early-Middle Holocene. During the Younger Dryas, a cold and humid climate is suggested on the northern piedmont of the Pyrenean range while temperate and humid conditions prevailed during the Early Holocene. The Middle Holocene was still humid North of the Pyrenees, except during the cold and dry event at ∼6.2 kyrs. Finally, during the last growth phase of the stalagmite, the growth rate slowed down drastically in relation to increasing frequency of high infiltration events, possible floodings and a decreasing saturation of the drip water relatively to calcite.

Recent droughts in the United States are among the fastest-developing of the last seven decades

Drought has traditionally been characterized as a slow process that requires seasons or even years to fully develop. Recent fast-evolving drying events, however, have challenged our forecasting and response capabilities. A fundamental question emerges: are droughts setting in more quickly? We address this question by evaluating drought intensification rates for the contiguous United States and find that median drought onset rates did not change significantly in 1951–2021. Conversely, development of fast onset droughts (i.e., the 95th percentile of the drought intensification rates per drought region in a given month of the time series) has been speeding up in recent years across most of the country. As a result, intensification rates of the quickest-onset droughts in 2011–2021 are among the fastest of the last seven decades.

Green Sahara tipping points in transient climate model simulations of the Holocene

The ‘Greening’ and subsequent desertification of the Sahara during the early to mid-Holocene is a dramatic example of natural climate change. We analyse a suite of simulations with a newly palaeo-conditioned configuration of the HadCM3 coupled model that is able to capture an abrupt desertification of North Africa during this time. We find that this model crosses a threshold of moisture availability for vegetation at around 6000 years before present. The resultant rapid reduction in vegetation cover acts to reduce precipitation through moisture recycling and surface albedo feedbacks. Precursor drying events which are not directly forced also indicate that the model is close to a critical moisture level. Similar precursor-like events appear in a Holocene record from the East of the continent, hinting that the natural system may resemble some of the properties of this model simulation. The overall response is not fundamentally altered by the inclusion of solar irradiance variations or volcanic eruptions. The simulated timing of the abrupt transition is mostly controlled by orbital forcing and local positive feedbacks, but it is also modulated to some extent by the state of the atmosphere and ocean. Comparisons with proxy records across North Africa show good agreement with the model simulations, although the simulations remain overly dry in the East. Overall, a threshold response may present a useful model of the real transition, but more high-resolution palaeoclimate records would help to discriminate among the predictions of climate models.

Climatic legacy effects on the drought response of the Amazon rainforest.

Extreme precipitation and drought events are predicted to become more intense and more frequent over the Amazon rainforest. Because changes in forest dynamics could prompt strong feedback loops to the global climate, it is of crucial importance to gain insight into the response of tropical forests to these recurring extreme climatic events. Here, we evaluated the Amazon forest stability (resistance and resilience) to drought in the context of past dry and wet climatic events using MODIS EVI satellite imagery and cumulative water deficit anomalies. We observed large spatial differences in the occurrence of extreme climatic events from 1980 to 2019, with an increase in drought frequency in the central and northern Amazon and drought intensity in the southern Amazon basin. An increasing trend in the occurrence of wet events was found in the western, southern, and eastern Amazon. Furthermore, we found significant legacy effects of previous climatic events on the forest drought response. An extreme drought closely preceding another drought decreased forest resilience, whereas the occurrence of a recent drier-than-usual event also decreased the forest resistance to later droughts. Both wetter-than-usual and extreme wet events preceding an extreme drought increased the resistance of the forest, and with similar effects sizes as dry events, indicating that wet and dry events have similarly sized legacy effects on the drought response of tropical forests. Our results indicate that the predicted increase in drought frequency and intensity can have negative consequences for the functioning of the Amazon forest. However, more frequent wet periods in combination with these droughts could counteract their negative impact. Finally, we also found that more stable forests according to the alternative stable states theory are also more resistant and resilient to individual droughts, showing a positive relationship between the equilibrium and non-equilibrium stability dynamics.

Summer dry events on synoptic and intraseasonal timescales in the Southeast Region of Brazil

The occurrence of dry events in the Southeast Region of Brazil (SEB) during summer (rainfall season) has been in evidence in the last years, mainly due to previous extreme events in the 2013/14 and 2014/15 seasons. Drought analyses are usually carried out with monthly data. Here our methodology addresses the issue with daily data to generate a thorough analysis. Dry events were evaluated in different homogeneous precipitation sub-regions within the SEB, over 37 December-February (DJF) seasons and with two different timescales of duration: synoptic (5-9 days) and intraseasonal (≥10 days). Two main distinct dynamic patterns were found for dry events in southern and central-northern parts of SEB, respectively, but no significant differences were identified in the different timescales of occurrence. Southern events were characterized by a stationary ridge acting over the whole of southern South America, making the approximation of the transient system to southern SEB difficult. At the same time, this pattern showed a northern-shifted South Atlantic Convergence Zone (SACZ) configuration. In the central-northern events, a high pressure centered between Brazil’s South and Southeast regions was associated with the dryness conditions. An anomalous southward shift of meteorological systems characteristic of the South American summer was also verified for these events. Over the South Atlantic, an opposite SST anomaly configuration was identified between southern and central-northern events.

Holocene climate events and associated land use changes in the eastern coast of India: Inferences from the Chilika Lagoon

The Holocene arid events and related societal responses are important scientific inquiries due to concerns about their reoccurrences in the future. In the Indian subcontinent, significant number of studies have focussed on understanding the Holocene aridification events at 8.2 and 4.2 ka. Despite these studies, high resolution palaeoclimatic records from the eastern India during Holocene, particularly around the above-mentioned aridification events are lacking. In this study, we present high resolution Holocene palaeoclimate records reconstructed based on geochemical and isotopic data from the Chilika Lagoon located in the east coast of India. A 130 cm long sediment core, retrieved from the southern end of the lagoon, revealed a continuous sedimentation history between 8.49 and 0.99 ka. The variations in organic carbon isotopic compositions, total organic carbon contents, along with major and trace element abundances suggested a strong effect of 8.2 dry event and a shift in chemical weathering at around 4.2 ka in the eastern coast of India. Additionally, a strong warm climate anomaly was observed at 1.2 ka. Interestingly, higher sedimentation rates were observed post 4.2 ka, which potentially indicated a significant change in settlement dynamics and human interventions. It appears that the eastern coast of India experienced human migration and surge in agricultural practices similar to that in northwest India after the 4.2 ka climatic event. It is likely that people relocated themselves, which eventually increased the pastoral activities in newly occupied lands. Consequently, enhanced land use and land cover changes accelerated soil erosion in the region leading to higher sedimentation rate in the lagoon.

Reconstruction of the holocene climate and environmental changes of Niayes peat bog in northern coast of Senegal (NW Africa) based on stable isotopes and charcoals analysis

A core from a peat bog in the “Niayes” region, northwest of Senegal, provides a valuable insight into the evolution of the landscape and fire regime related to the West African Monsoon rainfall and to human impact over the Holocene. The high-resolution multiproxy approach based on stable carbon isotopic composition (δ13C), Rock-Eval® thermal analysis, and charcoal analysis, provides an understanding of vegetation composition (C3/C4) and fire regime in the continental watershed. The analysis of our data indicates a more woody landscape and a higher water table level, related to increased monsoonal rainfall during the African Humid period (AHP) between 9.5 and 5.5 cal kyr BP. High insolation and orbital changes account for a northward migration of the African Rain Belt and a reinforced West Africa monsoon. The amount of forest fires was low and most likely of natural occurrence, as human density was very low. A short dry event interrupts the AHP and gives rise to a weakly grassy landscape at around 8.2 cal kyr BP. This drought of centennial scale (400 years) occurring between 8.4 and 8 cal kyr BP is concomitant with the general cooling observed in the Northern Hemisphere. After a period of transition, the millennial-scale Late Holocene dry period begins at 4.8 cal kyr BP. The low water table level, resulting from a decrease in precipitation, coincides with the appearance of a grassy savanna landscape. Insolation decrease and reduced vegetation were likely driven by a southward migration of the African Rain Belt and a weakening of the monsoon. During the late Holocene the “Niayes” zone evolved into a phase of environmental stress often interrupted by Little Humid Periods (LHP) of centennial scale (500 and 600 years) respectively between 4.4 and 3.9 and between 1.1 and 0.5 cal kyr BP. After 0.5 cal kyr BP the decrease in precipitation and the increase in savanna fires, probaly of anthropogenic origin, favor the landscape opening.