Changes In Aridity Research Articles

Utilizing Recent Climate Data in Eastern Texas to Calculate Trends in Measures of Aridity and Estimate Changes in Watering Demand for Landscape Preservation

AbstractEastern Texas houses a transition zone from semiarid conditions in the far west to some of the wettest areas of the continental United States not influenced by mountainous terrain. The region, vulnerable to drought and flooding rains, is projected to experience higher water demand with its growing population. In the coming decades, municipal consumption, including water for landscape preservation, will supplant irrigation as the largest usage category. The amount of supplemental water required to maintain plantings is dependent on evapotranspirative demand and precipitation patterns. Reference evapotranspiration can be calculated using four daily climate parameters in the FAO-56 Penman–Monteith equation. This was combined with soil moisture capacity and daily accumulated precipitation to determine historical evapotranspiration rates at 14 observation stations across the eastern region of Texas from 1973 through 2017 and allowed for the creation of a recursive algorithm that introduced supplemental water for vegetation preservation as conditions crossed thresholds of dryness. Time series data analysis showed an increasing degree of aridity, as higher temperatures have decreased relative humidity and dry periods have become more prolonged and severe under stable average annual precipitation totals. Without additional increases in rainfall, the region is expected to continue its drying trend, leading to moisture-stressed plant life and higher water demands to maintain landscapes in a well-watered state.

Palaeoenvironment and palaeoclimate during the late Carboniferous–early Permian in northern China from carbon and nitrogen isotopes of coals

Coupling carbon and nitrogen isotopes and petrography of coals and related intra-seam carbonaceous mudstone partings from basins in northern China provides insight into regional palaeoenvironments and palaeoclimate during the late Carboniferous–early Permian. The carbon isotopic composition (δ13Ccoal, VPDB) of coal samples from the Taiyuan and Shanxi formations of Qinshui and North China-Bohaiwan basins ranges from −25.3‰ to −22.7‰, with an average of −23.7‰. The average δ13Ccoal value is −23.6‰ in the late Carboniferous, −23.4‰ in the early Permian and −23.5‰ in the mid–early Permian. By contrast, equivalent early Permian coals in the southern North China-Bohaiwan Basin to the east were found to be significantly more negative at −25.2‰, likely as a function of regional aridity changes. Related δ15N in coal seams ranges from +2.3‰ to +4.7‰, with an average of +3.7‰. Within the thick, economically important #15coal seam of the Qinshui Basin, δ15Ncoal is significantly more negative than δ15N in mudstone partings (avg. +7.1‰), implying that the coals underwent a stronger degree of microbial degradation during peat formation. δ15N of mudstone partings varies stratigraphically, with significantly more positive δ15N (+8.1‰, +8.3‰) for the lower partings and lower δ15N (+4.8‰) for the upper parting. This may reflect varying degrees of microbial activity, but could reflect higher thermal maturity in the upper part of the seam as indicated in the coal rank profile.δ13Ccoal in this region was used to calculate the carbon isotopic composition of atmospheric CO2(δ13Ca). Calculated δ13Ca ranges from −6.0‰ to −3.4‰, with an average of −4.5‰, which is more positive than the δ13Ca of modern atmospheric CO2(−8.5‰, Graven et al., 2017). Two δ13Ca excursions are noted: a positive one (magnitude 3.7‰) in the late Carboniferous and a tentative negative excursion (magnitude 6.0‰) in the mid–early Permian. The positive shift coincided with a sea-level transgression in the Qinshui Basin. The rise in sea level may have led to the burial of more terrestrial plant debris that decreased photosynthesis and enriched atmospheric CO2in 13C. More data are needed to understand mid-early Permian variation in δ13C, as this could reflect a regional aridity or humidity effect rather than a global signal.

Changes in soil C:N:P stoichiometry along an aridity gradient in drylands of northern China

Changes in soil carbon (C): nitrogen (N): phosphorus (P) stoichiometric ratios have significant influences on biogeochemical cycles and ecosystem functions. Soil C, N, and P dynamics are closely related to climatic aridity and soil texture, two factors that are not easily separated at large spatial scale due to their geographic co-variation. While it is well understood that soil C, N, and P cycling are decoupled and soil C:N:P ratios change across climatic gradients, we know little about the role of soil texture in mediating such stoichiometric variation. Here, we examined the regional variation of soil C:N:P ratios with changes in aridity and soil texture based on observations from 57 sites along a 3000-km aridity transect in drylands of northern China. Across the aridity gradient, C:N ratios of bulk soil first decreased and then increased with increasing aridity with a threshold at the aridity value of 0.8 (aridity defined here as 1-precipitation/evapotranspiration), whereas C:P and N:P ratios of bulk soil significantly decreased with increasing aridity. Across the transect, C:N ratios in bulk soils were positively related to sand contents and negatively related to silt and clay contents, while C:P and N:P ratios in bulk soils were negatively related to sand contents and positively related to silt and clay contents. Aridity, soil pH, and silt contents could best predict the variations in bulk soil C:N and N:P ratios, while aridity, soil pH, and clay contents were the most significant variables driving the bulk soil C:P ratio. Aridity could play a more important role than soil texture in driving variations of soil C:N:P ratios, where the predicted increases in aridity in drylands could cause imbalances in the biogeochemical cycles of C, N and P. Our results further highlight the role of soil texture in driving stoichiometric flexibility of soil C:N:P ratios across the aridity gradient, in that element-specific correlations with soil texture played an important role in regulating the decoupled soil C:N:P stoichiometry in response to increasing aridity.

The aridity Index under global warming

Aridity is a complex concept that ideally requires a comprehensive assessment of hydroclimatological and hydroecological variables to fully understand anticipated changes. A widely used (offline) impact model to assess projected changes in aridity is the aridity index (AI) (defined as the ratio of potential evaporation to precipitation), summarizing the aridity concept into a single number. Based on the AI, it was shown that aridity will generally increase under conditions of increased CO2 and associated global warming. However, assessing the same climate model output directly suggests a more nuanced response of aridity to global warming, raising the question if the AI provides a good representation of the complex nature of anticipated aridity changes. By systematically comparing projections of the AI against projections for various hydroclimatological and ecohydrological variables, we show that the AI generally provides a rather poor proxy for projected aridity conditions. Direct climate model output is shown to contradict signals of increasing aridity obtained from the AI in at least half of the global land area with robust change. We further show that part of this discrepancy can be related to the parameterization of potential evaporation. Especially the most commonly used potential evaporation model likely leads to an overestimation of future aridity due to incorrect assumptions under increasing atmospheric CO2. Our results show that AI-based approaches do not correctly communicate changes projected by the fully coupled climate models. The solution is to directly analyse the model outputs rather than use a separate offline impact model. We thus urge for a direct and joint assessment of climate model output when assessing future aridity changes rather than using simple index-based impact models that use climate model output as input and are potentially subject to significant biases.

Glacial Indonesian Throughflow weakening across the Mid-Pleistocene Climatic Transition

The Indonesian Throughflow (ITF) controls the oceanic flux of heat and salt between the Pacific and Indian Oceans and therewith plays an important role in modulating the meridional overturning circulation and low latitude hydrological cycle. Here, we report new sea surface temperature and aridity records from the west coast of Australia (IODP Site U1460), which allow us to assess the sensitivity of the eastern Indian Ocean to the major reorganization of Earth’s climate that occurred during the Mid-Pleistocene Transition. Our records indicate glacial coolings at 1.55 and 0.65 million years ago that are best explained by a weakening of the ITF as a consequence of global sea level and tectonic changes. These coincide with the development of pronounced gradients in the carbon isotope composition of the different ocean basins and with substantial changes in regional aridity, suggesting that the restrictions of the ITF influenced both the evolution of global ocean circulation and the development of the modern hydrological cycle in Western Australia.

Temporal–spatial variations in aeolian flux on the Chinese Loess Plateau during the last 150 ka

AbstractAeolian dust deposits from continent and ocean have been extensively investigated to reflect past changes in source aridity and atmospheric circulations. Aeolian flux (AF) as a quantitative dust proxy has been widely used in both palaeoenvironmental reconstruction and numerical simulation. However, available AF data on the Chinese Loess Plateau (CLP) is too limited to assess the temporal–spatial variations at glacial–interglacial timescales, and therefore cannot be used as robust input parameters in palaeoclimate models. Here we investigate eight loess profiles along two N–S-aligned transects on the CLP to quantitatively estimate the AF variations over the last glacial–interglacial cycle. We first establish a refined chronological framework based on optically stimulated luminescence chronology and pedostratigraphic correlation. AF was then estimated by multiplying the sedimentation rate and bulk density. The results show that the AF increases from 2–18 g cm−2 ka−1 in the southeastern CLP to 14–105 g cm−2 ka−1 in the northwestern CLP. At glacial–interglacial scales, the AF varies from 2–20 g cm−2 ka−1 during the last interglacial to 8–105 g cm−2 ka−1 in the last glaciation. Due to more spatial coverage and better age constraints, our AF data can be used to refine other AF datasets and to improve the proxy–model comparison.

Spatiotemporal changes in aridity and the shift of drylands in Iran

Abstract The spatial and temporal changes in annual and seasonal aridity, the shift of land from one arid class to another and the effect of this shift on different landuses in Iran during 1951–2016 have been assessed in this study. The monthly rainfall data of global precipitation climatology center (GPCC), and the monthly mean temperature and potential evapotranspiration (PET) data of climate research unit (CRU) having a spatial resolution of 0.5° were used for this purpose. The novelty of the study is the assessment of the significance in the shift of arid land between 1951–1980 and 1987–2016. Besides, the association of rainfall and temperature with aridity in different arid zones were assessed to understand the driving factors of the shift of arid lands. The results revealed an increase in annual and seasonal aridity in Iran, which caused expansion of arid land. The most remarkable changes include conversion of 4.84% semi-arid land to arid land due to an increase in annual aridity, shift of 4.84% arid land to hyper-arid during summer and 6.45% semi-arid land to arid during winter. However, only the expansion of semi-arid land to dry-subhumid land was found statistically significant. Analysis of results revealed different contributions of rainfall and temperature in the expansion of different classes of arid lands. The decrease in rainfall was the cause of the increasing aridity in the arid and semi-arid region, while the increasing temperature was found to play a major role in increasing aridity in the humid region. The overlapping of landuse map on aridity shift map revealed that the rangelands and farmlands in the north and the northwest were more affected by the expansion of aridity which might have severe consequences on agricultural production and food security of the country.

Nonlinear responses of soil nematode community composition to increasing aridity

AbstractAimIncreasing aridity under global change is predicted to have a profound impact on the structure and functioning of terrestrial ecosystems, yet we have a poor understanding of how belowground communities respond. In order to understand the longer term responses of different trophic levels in the soil food web to increasing aridity, we investigated the abundance, richness and community similarity of the soil nematode community along a 3,200 km aridity gradient.LocationA transect across semi‐arid and arid grasslands in Northern China, where the aridity ranges from .43 to .97.Time periodJuly and August 2012.Major taxa studiedSoil‐borne Nematoda.MethodsWe used generalized additive (mixed) models to analyse the abundance, richness and community similarity patterns of soil nematodes. We used structural equation modelling (SEM) to disentangle the direct and indirect environmental drivers (aridity, soil and plant variables) of the nematode community.ResultsThe abundance, richness and similarity of nematode communities declined nonlinearly with increasing aridity. The most pronounced decline in nematode richness and community similarity occurred in arid conditions (aridity > .80). However, the shape of the response to aridity differed among nematode feeding groups. In arid conditions, the abundance and richness of bacterial feeders were less sensitive to changes in aridity than for fungal feeders. The SEM analysis revealed that nematode community responses to aridity were not mediated via changes in plant and soil variables, but instead were affected directly by aridity.Main conclusionsOur results showed that in mesic grasslands, increasing aridity primarily caused a decline in nematode abundance, whereas increasing aridity in xeric grasslands led to a loss of nematode diversity. The nonlinear responses of nematodes to aridity could also result in nonlinear shifts in ecosystem functioning, because soil nematodes operate at various trophic levels in the soil food web, thereby influencing the performance of plants, soil biodiversity and biogeochemical cycling.

Wind variability over the northern Indian Ocean during the past 4 million years – Insights from coarse aeolian dust (IODP exp. 359, site U1467, Maldives)

The lithogenic fraction of carbonate drift sediments from IODP Exp. 359 Site U1467 (Maldives) provides a unique record of atmospheric dust transport over the northern Indian Ocean during the past 4 Myr. Grain-size data provide proxies for dust flux (controlled by source area aridity) as well as wind transport capacity (wind speed). Entrainment and long-range transport of dust in the medium to coarse silt size range is linked to the strength of the Arabian Shamal winds and the occurrence of convective storms which prolong dust transport. Dust flux and the size of dust particles increased between 4.0 and 3.3 Ma, corresponding to the closure of the Indonesian seaway and the intensification of the South Asian Monsoon. There is no clear trend in dust flux between 3.3 and 1.6 Ma, whereas wind transport capacity decreased. Between 1.6 Ma and the Recent, dust flux increased and shows higher variability, especially during the last 500 kyr. Transport capacity increased between 1.2 and 0.5 Ma and slightly decreased since then. Frequency analysis shows that dust transport varies on orbital timescales, with eccentricity control being the most prominent (400 kyr throughout the record, 100 kyr between 2.0 and 1.3 Ma, and since 1.0 Ma). Higher frequency cycles (obliquity and precession) are more pronounced in wind transport capacity than in the amount of dust. This indicates that the amount of coarse dust in sediments from the Maldives as a far-field site is more prone to changes in transport mechanisms than to changes in dust source-area aridity.

Rock magnetic signature of a Miocene playa cycle in Central Asia and environmental implications

The increased aridification of Central Asia during the Miocene coincides in time with lake formations and the evolution of playa environments in the region. However, Miocene continental climate dynamics and the forcing of aridification are still not well constrained. Neogene lacustrine mudflat deposits in the Ili Basin in southeast Kazakhstan provide a well-exposed paleoclimate archive. Here, we present a detailed rock magnetic study of a middle Miocene playa cycle deposited in a closed basin. We use high-resolution rock magnetic parameters, lithological studies and geochemistry to reconstruct the playa environment and the depositional conditions. The rock magnetic mineralogy of the playa cycle is controlled by hematite and two fine-grained magnetite phases. Increased magnetic concentrations occur during dry mudflat conditions, with a lower groundwater table and increased aridity. The underlying processes controlling the observed variation in magnetic concentrations are a complex interplay of diagenetic processes during and after deposition. The data support an authigenic origin of both magnetite phases, one formed before and the other after sediment consolidation. Early diagenetic formation of fine-grained magnetite by microbial activity is followed by post-depositional formation of a secondary fine-grained magnetite phase. The rock magnetic results such as magnetic concentration-dependent parameters, ARM/SIRM and s-ratio indicate a sensitive record of (ground) water availability and aridity changes in the Ili Basin. We suggest that they can serve as an effective proxy for detailed paleo-environment reconstruction of playa evolution, not only in the middle Miocene Ili Basin but also in comparable floodplain/playa lake settings.

Forestry Aridity Index in Vojvodina, North Serbia

Abstract In investigating aridity in Vojvodina (a region in the northern part of Serbia), the Forestry Aridity Index (FAI) was used. This index was chosen due to being one of the most suitable indices for the analysis of the interaction of climate and vegetative processes, especially in forestry. The spatial distribution of the FAI for annual and decennial periods, as well as its annual trend, is analysed. Satisfactory compatibility between the low (forest) and high (steppe) FAI values with the forest and steppe vegetation on the Vojvodina terrains was obtained. The calculated values of the FAI showed that there was no particular annual trend. These results correspond to the earlier calculated values of the De Martonne aridity index and the Pinna combinative index. Therefore, it can be concluded that there were no recent changes in aridity during the observed period. Results of the correlation indicate weak linearity between the FAI, and the North Atlantic Oscillation and El-Niño South Oscillation.

Aridity change and its correlation with greening over drylands

A drying trend and an expansion of drylands through history, as well as an expectation to continue under the future climate, have been inferred by recent studies. However, this seems to conflict with observed greenness over drylands. In this study, the changes in aridity over drylands from 1982 to 2011 were examined using the aridity index (ratio of precipitation and potential evapotranspiration), precipitation minus actual evapotranspiration, and soil moisture derived from a combination of observation and modelling. In addition, corresponding changes in vegetative greenness and their relationships with aridity changes were explored. The results show that above three indicators all point to a little change in aridity of drylands over the past three decades, and their trends in spatial patterns agree well each other. Simultaneously, significant greening (p < 0.05) occurred in more than 36% of vegetated drylands, in contrast to the 7% with significant browning (p < 0.05). Drylands as a whole, vegetative greenness demonstrated a significant positive relationship (p < 0.05) with precipitation change. At the biome scale, significant relationships (p < 0.05) were observed for vegetative greenness and precipitation for all other vegetation types except forests, suggesting that the increasing precipitation was one of the main drivers of greening over drylands. In addition, the largest increase of greening was observed for croplands, implying a strong impact from agricultural activities particularly irrigation practices. Results from this study provide clues for understanding the greening of drylands and are also crucial for the understanding of environmental changes in the context of climate change.

Spatiotemporal changes in aridity of Pakistan during 1901–2016

Abstract. The changing characteristics of aridity over a larger spatiotemporal scale have gained interest in recent years due to climate change. The long-term (1901–2016) changes in spatiotemporal patterns of annual and seasonal aridity during two major crop growing seasons of Pakistan, Kharif and Rabi, are evaluated in this study using gridded precipitation and potential evapotranspiration (PET) data. The UNESCO aridity index was used to estimate aridity at each grid point for all the years between 1901 and 2016. The temporal changes in aridity and its associations with precipitation and PET are evaluated by implementing a moving window of 50 years of data with an 11-year interval. The modified Mann–Kendall (MMK) trend test is applied to estimate unidirectional change by eliminating the effect of natural variability of climate, and Pettitt's test is used to detect year of change in aridity. The results revealed that the climate over 60 % of Pakistan (mainly in southern parts) is arid. The spatial patterns of aridity trends show a strong influence of the changes in precipitation on the aridity trend. The increasing trend in aridity (drier) is noticed in the southwest, where precipitation is low during Kharif, while there is a decreasing trend (wetter) in the Rabi season in the region which receives high precipitation due to western disturbances. The annual and Kharif aridity is found to decrease (wetter) at a rate of 0.0001 to 0.0002 per year in the northeast, while Kharif and Rabi aridity are found to increase (drier) at some locations in the south at a rate of −0.0019 to −0.0001 per year. The spatial patterns of aridity changes show a shift from arid to the semi-arid (wetter) climate in annual and Kharif over a large area while showing a shift from arid to hyper-arid (drier) region during Rabi in a small area. Most of the significant changes in precipitation and aridity are observed in the years between 1971 and 1980. Overall, aridity is found to increase (drier) in 0.52 %, 4.44 % and 0.52 % of the area and decrease (wetter) in 11.75 %, 7.57 % and 9.66 % of the area for annual, Rabi and Kharif seasons respectively during 1967–2016 relative to 1901–1950.

Oxygen isotope analyses of ungulate tooth enamel confirm low seasonality of rainfall contributed to the African Humid Period in Somalia

During the African Humid Period (AHP), between ~14 and 5 ka, north and eastern Africa were much wetter and greener than they are today. Although the AHP has long been attributed to an increase in rainfall driven by orbital forcing, many details regarding the timing, pacing, and contributing moisture sources remain to be determined, especially for eastern Africa. Recent research suggests that both Atlantic and Indian Ocean moisture contributed to the AHP in eastern Africa. Large mammalian faunas from two Late Pleistocene/Holocene rockshelter sites in southern Somalia, Gogoshiis Qabe and Guli Waabayo, provide an unusual opportunity to investigate the AHP in an area of eastern Africa that is orographically isolated from Atlantic Ocean moisture. To track changes in aridity at these sites, we used the oxygen isotope aridity index, which exploits the difference in tooth enamel oxygen isotope (δ18O) values between evaporation insensitive obligate drinkers and evaporation sensitive non-obligate drinkers to calculate a water deficit value. Water deficit values calculated from dik-dik (Madoqua spp.; non-obligate drinkers) and warthog (Phacochoerus spp.; obligate drinkers) tooth enamel δ18O values at Gogoshiis Qabe and Guli Waabayo are in agreement and progressively increase toward the present. Additionally, two of three direct dated serially-sampled warthog teeth (ID 4032 and 4033) from Guli Waabayo demonstrate low seasonality of rainfall during much of the AHP (range in δ18O ≤ 1.8‰). One tooth (ID 4035) with high amplitude variability in δ18O values (3.1‰) dates to 8470 ± 66 cal yr B.P., a period identified as a lowstand in several lake level records. Our results suggest that regions isolated from Atlantic Ocean moisture likely experienced a less-pronounced AHP than those receiving moisture from multiple sources but indicate less seasonal variability than present. Our findings also support the presence of climate variability within the AHP.

Mid-Holocene drylands: A multi-model analysis using Paleoclimate Modelling Intercomparison Project Phase III (PMIP3) simulations

This study examines changes in aridity levels during the mid-Holocene (approximately 6000 cal. yr ago) using multi-model simulations from the Paleoclimate Modelling Intercomparison Project Phase III. Overall, there is little difference in the total area of drylands from the preindustrial period; global drylands are 8% wetter than during the preindustrial period as measured by an aridity index; and 16% of preindustrial drylands convert to a wetter climate subtype, double the sum of zones that are replaced by a drier category. Considerable variations are present among regions with major contractions of each dryland subtype from northern Africa to South Asia and the main expansions of arid, semiarid, and dry subhumid climates in southern hemisphere continents. The difference in precipitation is the leading factor of the aforementioned changes. The second factor is the altered potential evapotranspiration as mainly induced by relative humidity, which contributes to additional aridity changes in a same direction as precipitation does. The collective effects of precipitation and relative humidity account for more than 80% of the dryland variations. In comparison, the simulated aridity change is in reasonable agreement with reconstructions, while there are model–data discrepancies for Australia and uncertainties across proxies for southern Africa.

Dry/wet pattern changes in global dryland areas over the past six decades

Abstract As reported in previous studies, global warming has caused a clear uptick in dryland areas since the 1950s. Meanwhile, the accelerated expansion of drylands has become particularly evident over the past 40 years, with dry/wet patterns showing significant differences prior to and after 1980. This paper uses the Precipitation/Potential evaporation (P/PET) index to analyze changes occurring in the dry/wet structure of various spatial and temporal scales during 1948–2008. The results show the emergence of complex aridity changes on a regional scale. While aridity generally decreased in the drylands of Asia during 1948–2008, the change in aridity was opposite in the drylands of the American and African continents between 1948 and 1979 and 1980–2008. Specifically, drylands in the American continent showed a wetting tendency during 1948–1979 and a drying tendency during 1980–2008, whereas drylands in the African continent underwent significant drying during 1948–1979 followed by subtle wetting in 1980–2008. Even though rapid warming since the 1980s has become an increasingly important cause of the recent global drying trend, especially in East and Central Asia, the changes in aridity in the American and African drylands is attributable to natural variabilities in precipitation associated with multi-decadal surface sea temperature changes, along with large-scale circulation patterns.

Aridity in the Iberian Peninsula (1960–2017): distribution, tendencies, and changes

Aridity is a climatic characteristic that has a significant impact on many aspects of life, mainly in agriculture but also in other economic sectors, and temperature and precipitation are the variables by which the effects of aridity can be measured. It is necessary to know its distribution and trend in different climate change scenarios. The Iberian Peninsula presents a strong contrasting climate, comprising both humid and very dry regions. Forty-five climatic time series were used to perform a spatial and temporal analysis and to identify possible points of trend change in annual aridity for the period from 1960 to 2017. Two indices were considered: the De Martonne Index (IDM) and the Food and Agriculture Organisation (FAO) Index (IF). By means of ordinary kriging, maps of spatial, temporal, and trend distributions were made. The trends of the aridity indices, annual temperature, and annual precipitation were analysed by applying the techniques of the modified Mann-Kendall test and Sen’s estimator; furthermore, to identify gaps of years in the series, the Buishand range test was used. The results showed a significant average annual temperature increase at all stations. Although annual precipitation decreased across the board, this decrease was not significant. Semi-arid was the dominant class, although the study area showed great variability, i.e. from extremely humid areas to arid zones. Forty-one out of the 45 series presented increasing aridity during the study period, although the trend was significant in only 16 of the series. From the Buishand range test for both aridity indices, the results revealed a noteworthy changing point for IDM and for IF. Although the changing point was variable, it was concentrated around the late 1970s and early 1980s, and from that period, the aridity tendency was dependent on the analysed series.

Past climate changes over South Korea during MIS3 and MIS1 and their links to regional and global climate changes

To test past climate change in central Korea in terms of latitudinal differences over the Korean Peninsula, we reconstructed relative abundances between C3 and C4 plants in Hanam area based on sedimentary total organic carbon isotope values (δ13CTOC) of a 2.8 m long trench in an archeological site and compared these data with climate changes at different latitudes of Korea. During marine isotope stage 3 (MIS3) corresponding to past 60,000–25,000 years, the millennial-timescale fluctuations of the δ13CTOC values in Hanam were more similar to those in Hongcheon located in the inner mountain area of central Korea than those in Cheollipo area in west coast of Korea. Periods with significantly decreased δ13CTOC values representing decreased C4 plants under wetter climates in these two inland areas are comparable with millennial-timescale Dansgaard–Oeschger (D-O) warming events recorded in Greenland ice cores, suggesting strong climatic teleconnection between East Asia and subpolar areas during the last glacial period. During MIS1 (Holocene), the changes in vegetation and climate in Hanam have been influenced by the long-term summer monsoon changes. Regarding past latitudinal change in aridity or humidity over Korea, during the middle Holocene, δ13CTOC values in areas of central South Korea gradually decreased, suggesting moving to a more humid climate. This is contrary to the increasing δ13CTOC values in southern South Korea indicating more dry climates. Furthermore, it is likely that there were two severe dry climates at different times at different latitudes (1000 cal BP in Hanam in northern South Korea and 2500 cal BP in Geoje in southern South Korea), suggesting possible different climate changes at millennial timescales over Korea.

Paleoenvironmental reconstruction of the semi-arid Chaco region of Argentina based on multiproxy lake records over the last six hundred years

In this paper, we analyze the paleoclimatic and paleoenvironmental evolution of Laguna Yema in semi-arid Chaco region of Argentina over the past six hundred years. High resolution multiproxy studies of lake sediments utilize analyses of lithology, mineralogy, geochemistry, palynology, and are constrained by radiocarbon and gamma spectrometry dating. Laguna Yema sediments were mainly composed of well stratified fine sediments (silts and clays), with variable proportions of quartz, clays (illite) and feldspar (microcline and albite). Twelve light and heavy geochemical elements were registered. Most elements (Al, Si, K, Ti, Fe, Rb, Ba, and Br) are associated with illite and albite. Different material transport processes related to the changes in aridity and humidity of the basin were identified using the main mineralogical origins of geochemical elements. Palynological records indicate cycles of contraction and expansion of the lake, with an increase in concentration of Alternanthera aquatica during wet periods (expansion of lake), and an increase in Ambrosia, Poaceae and fern spores during dry periods (contraction of lake). These changes are linked to fluctuations in moisture conditions in the Subandean Mountains and semi-arid Chaco regions, in response to interactions between the South American Monsoon System (SAMS) and the South American Low Level Jet (SALLJ), which send warm and humid air to northern Argentina. In a regional context, the Laguna Yema records are in accordance with the analyses of the temporal and spatial pattern of moisture distribution for the last six centuries.

Preparedness or repeated short-term relief aid? Building drought resilience through early warning in southern Africa

Southern Africa is highly vulnerable to drought because of its dependence on climate-sensitive sectors of agriculture, hydroenergy and fisheries. Recurring droughts continue to impact rural livelihoods and degrade the environment. Drought severity in southern Africa is exacerbated by poor levels of preparedness and low adaptive capacity. Whilst weather extremes and hazards are inevitable, the preparedness to manage such hazards determines their impact and whether they become disasters. Southern Africa is often caught unprepared by drought as existing early warning systems lack the drought forecastingcomponent, which often results in reactionary interventions as opposed to well-planned and proactive response mechanisms. This study assesses the spatio-temporal changes of rainfall and aridity in southern Africa through an analysis of long-term precipitation and evaporation trends from 1960 to 2007. Stakeholder consultation was conducted in Madagascar, Malawi, Zambia and Zimbabwe during the peak of the 2015/16 drought, focusing on overall drought impacts, current water resource availability, existing early warning systems, adaptation mechanisms and institutional capacity to mitigate and managedroughts as part of overall disaster risk reduction strategies. Average rainfall has decreased by 26% in the region between 1960 and 2007, and aridity has increased by 11% between 1980 and 2007. The absence of drought forecasting and lack of institutional capacity to mitigate drought impede regional drought risk reduction initiatives. Existing multi-hazard early warning systems in the region focus on flooding and drought monitoring and assessment. Drought forecasting is often not given due consideration, yet it is a key component of early warning and resilience building. We propose a regional drought early warning framework, emphasising the importance of both monitoring and forecasting as being integral to a drought early warning system and building resilience to drought.