Changes In Aridity Research Articles

Multifaceted characteristics of dryland aridity changes in a warming world

Drylands are an essential component of the Earth System and are among the most vulnerable to climate change. In this Review, we synthesize observational and modelling evidence to demonstrate emerging differences in dryland aridity dependent on the specific metric considered. Although warming heightens vapour pressure deficit and, thus, atmospheric demand for water in both the observations and the projections, these changes do not wholly propagate to exacerbate soil moisture and runoff deficits. Moreover, counter-intuitively, many arid ecosystems have exhibited significant greening and enhanced vegetation productivity since the 1980s. Such divergence between atmospheric and ecohydrological aridity changes can primarily be related to moisture limitations by dry soils and plant physiological regulations of evapotranspiration under elevated CO2. The latter process ameliorates water stress on plant growth and decelerates warming-enhanced water losses from soils, while simultaneously warming and drying the near-surface air. We place these climate-induced aridity changes in the context of exacerbated water scarcity driven by rapidly increasing anthropogenic needs for freshwater to support population growth and economic development. Under future warming, dryland ecosystems might respond non-linearly, caused by, for example, complex ecosystem–hydrology–human interactions and increased mortality risks from drought and heat stress, which is a foremost priority for future research.

Effects of plant intraspecific variation on the prediction of C3/C4 vegetation ratio from carbon isotope composition of topsoil organic matter across grasslands

AbstractAimsUnderstanding the patterns and drivers of carbon isotope discrimination (13Δ) in C3 and C4 functional groups is critical for predicting C3/C4 vegetation ratio from the isotopic composition of soil organic matter. In this study, we aimed to evaluate how intraspecific variation will modify functional group-level 13Δ values and the associated prediction of C3/C4 vegetation ratio.MethodsWe investigated 13Δ of 726 individual plants (96 species; C3 and C4 functional groups) and topsoil organic matter in 26 grassland communities along an aridity gradient in northern China. The fraction of C4 contribution was calculated with mixing models that considered: (i) both intra- and interspecific effects on the 13Δ values of C3 and C4 functional groups; (ii) only interspecific effects; or (iii) none of these effects.Important FindingsWe found divergent responses of plant 13Δ at the intraspecific level to the changes of aridity across the gradient. The 13Δ of both C3 and C4 functional groups was negatively correlated with an aridity index, with higher sensitivity for C3 than for C4 functional groups. Intraspecific 13Δ variation played a key role in driving the total 13Δ variations of C3 plants. Overlooking such intraspecific effect in mixing models led to a greatly increased fraction of C4 contribution to soil organic carbon. A correction for the effects of intraspecific variation is therefore essential for correctly inferring C3/C4 vegetation ratio in the past. Our findings provide basic information for the reconstruction of past vegetation change from bulk materials in arid and semiarid biomes.

Interdecadal aridity variations in Central Asia during 1950–2016 regulated by oceanic conditions under the background of global warming

As a typical inland arid and semiarid region, Central Asia (CA) is vulnerable to the forced global warming (FGW) due to anthropogenic activity. Aiming at the interdecadal variation of the FGW-forced aridity pattern (FAP) in CA, we try to extract the associated oceanic and atmospheric modes by analyzing observations, reanalysis data and multi-model simulations during 1950–2016. The FAP in CA features a tripolar pattern with wetting–drying-wetting responses arranging from southeast to northwest and shows strong interdecadal-to-interannual amplitude variations. It is found that the sea surface temperature (SST) in the tropical South Atlantic (TSA) well correlates with the amplitude variation of FAP on interdecadal time scale, possibly through modulating the interannual SST modes characterized by the North Atlantic horseshoe-like dipole (NAHD) and the El Nino and South Oscillation (ENSO). Corresponding to the enhancing FAP from the middle 1970s to early 2000s, the TSA-modulated NAHD and ENSO, together with the Pacific Decadal Oscillation-modulated Indian Ocean Dipole-like mode, show connections with an Eurasian middle-latitude wave train coupled with the North Arctic Oscillation and equatorial low, which favors the moisture transport to strengthen the tripolar FAP by forming a local circulation dipole with positive/negative anomaly over the northwest/southeast CA. But after the early 2000s, the increasing FAP amplitude is decelerated due to the interdecadal decline of TSA accompanied by the weakened/reversed relationship between FAP and the NAHD/ENSO. Because of the corresponding breakdown of the wave train, the favorable local circulation is unavailable to support the sustained enhancement of FAP. Therefore, the multiscale coupling between the above oceanic and atmospheric modes is significantly related to the characteristic of stage of the forced aridity change in CA under the background of global warming.

Distinct vegetation response to drying and wetting trends across an aridity threshold

Aridity regulates the terrestrial ecosystem productivity in water-limited regions. The aridity index (AI) is often defined as the ratio of annual precipitation to annual potential evapotranspiration. However, how the drying and wetting influence the vegetation response and its characteristic along aridity gradient remains unclear. Here, we examined trends of the AI and normalized difference vegetation index (NDVI) in the drylands of East Asia from 1982 to 2015, which denoted the drying and wetting trends and vegetation response, respectively. The results show that the variability in land area and AI from 1982–2015 was lower in the whole dryland than its subtypes including hyper-arid, arid, semi-arid, and dry sub-humid regions. Drying and wetting trends were observed in each AI interval along a spatial aridity gradient. Wetting trends are prevalent owing to their area and magnitude were twice those of drying trends. Spatial variation of aridity shaped the pattern of trends in vegetation response to drying and wetting trends; drier regions had smaller and narrower ranges of variation in NDVI trends relative to wetter regions. A shift in AI trends and NDVI trends along the spatial aridity gradient occurred at 0.4 of AI. Distinct patterns of vegetation response to aridity change were observed across the aridity threshold, and the transition region was identified in the studied drylands. The results suggest that changes in the subtypes might be masked by the entire drylands and then leading to failure in recognizing the transformation of the subtypes. This implies that terrestrial carbon storage variability prediction should consider the spatial aridity changes to avoid the uncertainties due to the divergent vegetation response to AI trends at different aridity levels.

Spatial Patterns and Drivers of Nonperennial Flow Regimes in the Contiguous United States

AbstractOver half of global rivers and streams lack perennial flow, and understanding the distribution and drivers of their flow regimes is critical for understanding their hydrologic, biogeochemical, and ecological functions. We analyzed nonperennial flow regimes using 540 U.S. Geological Survey watersheds across the contiguous United States from 1979 to 2018. Multivariate analyses revealed regional differences in no‐flow fraction, date of first no flow, and duration of the dry‐down period, with further divergence between natural and human‐altered watersheds. Aridity was a primary driver of no‐flow metrics at the continental scale, while unique combinations of climatic, physiographic and anthropogenic drivers emerged at regional scales. Dry‐down duration showed stronger associations with nonclimate drivers compared to no‐flow fraction and timing. Although the sparse distribution of nonperennial gages limits our understanding of such streams, the watersheds examined here suggest the important role of aridity and land cover change in modulating future stream drying.

Future changes in aridity in the Upper Indus Basin during the twenty-first century

The Upper Indus Basin (UIB) supplies water resources for the downstream areas of the Indus Basin, and the associated climate changes have attracted considerable attention. Here, we project the aridity changes in the UIB during the 21st century relative to 1995-2014 based on 12 Coupled Model Intercomparison Project Phase 6 (CMIP6) models under the 3 Shared Socioeconomic Pathway (SSP) scenarios. The aridity index (AI), defined as the ratio of annual precipitation to potential evapotranspiration (PET), is applied to quantify the dry conditions. According to the median of the preferred models, the annual mean temperature is projected to increase continually in the UIB across the 21st century under SSP2-45 and SSP5-85, and it increases before the 2050s and then stabilizes afterwards under SSP1-26. Generally, PET will increase and AI will decrease (a drying trend) in the UIB during the 21st century. The regionally averaged AI over the UIB linearly decreases as global warming intensifies at a slope of 0.1 °C-1 under both SSP2-45 and SSP5-85. Remarkable increases in aridity occur in the northern and northwest parts of the UIB. Seasonally, the largest decrease in AI is seen in December-January-February, and the smallest occurs in June-�July-August. Furthermore, PET plays a key role in AI changes, excluding the southeast part of UIB, and the percent contribution of PET to AI changes tends to increase over time in the 21st century. Overall, AI and PET changes are primarily determined by thermodynamic factors in the UIB.

ON THE POSSIBLE ROLE OF MIGRATION PROCESS IN SHAPING THE AZOV-DNIEPER CULTURE

The emergence of new techniques and technologies has always been one of the main issue of discussion in archaeology. Especially in the case of innovations introduced from outside rather than development of the local tradition. Was it the result of migrations or was it just the transmission of «fashion trends»? Were environmental changes the cause of their spread, and if so, which exactly were? In 2019, the author continued excavations the single-layer site Chapayevka in the Azov Sea region. The results of excavations confirmed the emergence of a completely different population in the region in the early 6th Mill. BC, which is radically different from the local Late Mesolithic and Early Neolithic societies. Previously, this group has never been considered separately. In the literature, it is customary to refer them to the earliest period of the AzovDnieper culture. Nevertheless, the uniqueness of the materials allowed us to assume the presence of migration movements at the beginning of the 6th Mill BC. It was realy newcomer population who left the Chapaevka type sites and later, as a result of mixing (or maybe giffusion) with the local residents, the Azov-Dnieper culture in its classical form was formed. According to radiocarbon dating, in the Northern Pontic Region comb-ornamented pottery appeared in quantities at the beginning of the 6th mill. BC. Around the same time, impresso ware appeared in the European continent (Thessaly, Adriatic, Southeast Balkans etc.). The most likely cause event triggered the spread of early farmers, by different routes out of West Asia and the Near East was climate changes of aridity of 8200 cal BP. Perhaps the population could also move eastward to the Northern Pontic Region (water and/or landway). We will try to prove the fact of the migration proces but not only spread of the fashion trend in to Ukrainian steppe region in the very beginning of the 6th millennium BC. on example of Chapaevka type sites. After reviewing the numerous literature about ancient migrations and based on our regional specifics, we created a fairly simple scheme that combines various criteria. As a result, we have four thematic blocks of our evidence base. The main idea of the article is considering the causes and possible penetration paths of newcomers in to the region. Comparison of the materials identifies the weather it was a real migration of an identical population but not only borrowing of "fashion trend". This research will allow to revise the set of contemporary outdated explanations 6 of the Neolithisation of the Northern Pontic region. The results will enable to explain the migration routes and the ways of spreading Neolithic innovations.

Divergent forcing of water use efficiency from aridity in two meadows of the Mongolian Plateau

The future climate change predicts higher drought risks in deteriorating the functions and services of dryland ecosystems. Interpreting the sensitivity of ecosystem water use efficiency (WUE) to aridity could provide important environmental implications to water conservation and carbon budgets of drylands. The effects of temporal aridity changes on WUE in semi-arid ecosystems, particularly in meadow steppes, have been poorly investigated. In this study, we used eddy-covariance data from two representative temperate meadows on Mongolian Plateau, Changling (2007-2015, China) and Bayan (2014-2018, Mongolia), to understand the inter- and intra-annual changes of WUE by evaporative fraction (EF), as well as the climatic and biotic controls on gross ecosystem production (GEP), evapotranspiration (ET) and partitioned evaporation (T) and transpiration (E). Results showed that the response of annual WUE to EF was positive in Changling meadow with dry atmosphere but insignificant in Bayan with cold climate; the contrasting WUEs were driven by divergent GEP and ET responses to EF in two meadows. Monthly T/ET increased linearly with EF in both meadows, but logarithmically with leaf area index (LAI). Bayan and Changling meadows had a similar instantaneous WUE (WUEp, GEP/T) that were insensitive to EF change. We also found that the frequency of growing season precipitation affected WUE at both sites. We conclude that contrasting GEP responses to EF determined the meadow WUE variations. The magnitude and changes in transpiration and evaporation provide further insights on the biophysical regulations (i.e., LAI) of ecosystem water use and WUEp. This study indicated that differences in ecosystem water yield, soil water status and sensitivities of GEP and ET partitioning jointly contributed to the divergent WUE at the two meadow steppes in this semi-arid region.

Drought and the collapse of the Tiwanaku Civilization: New evidence from Lake Orurillo, Peru

Tiwanaku was a regionally significant, state level polity in the south-central Andes from ca. 500–1000 CE. The development of complex society in the region was greatly facilitated through intensified agricultural systems that relied on monsoonal precipitation. At the end of the first millennium CE, the Tiwanaku political regime collapsed, and their raised field systems were mostly abandoned within 200 years or less. It has been suggested that a prolonged period of aridity contributed to the collapse, but questions have remained about its chronology and severity. In this study, we investigated the relationship between δ2Hwax and δ18Ocalcite values, aridity and societal change. A period of nondeposition or erosion occurred between 915 and 1025 CE indicating a low lake stand exposing the core site. This extended and pronounced drought ending 1025 CE was recorded in the isotopic proxies extracted from lake sediments that show this period of aridity persisted into the 13th century. The broad agreement between our record and other regional paleoenvironmental archives of Holocene climate variability is consistent with Northern Hemisphere oceanic and atmospheric circulation patterns as a mechanism for driving centennial scale climate change in the Andes and supports the correspondence between prolonged drought and the collapse of Tiwanaku.

The 3.6-Ma aridity and westerlies history over midlatitude Asia linked with global climatic cooling

Midlatitude Asia (MLA), strongly influenced by westerlies-controlled climate, is a key source of global atmospheric dust, and plays a significant role in Earth's climate system . However, it remains unclear how the westerlies, MLA aridity, and dust flux from this region evolved over time. Here, we report a unique high-resolution eolian dust record covering the past 3.6 Ma, retrieved from the thickest loess borehole sequence (671 m) recovered to date, at the southern margin of the Taklimakan desert in the MLA interior. The results show that eolian dust accumulation, which is closely related to aridity and the westerlies, indicates existence of a dry climate, desert area, and stable land surface, promoting continuous loess deposition since at least ∼3.6 Ma. This region experienced long-term stepwise drying at ∼2.7, 1.1, and 0.5 Ma, coeval with a dominant periodicity shift from 41-ka cyclicity to 100-ka cyclicity between 1.1 Ma and 0.5 Ma. These features match well with global ice volume variability both in the time and frequency domains (including the Mid-Pleistocene Transition), highlighting global cooling-forced aridity and westerlies climate changes on these timescales. Numerical modeling demonstrates that global cooling can dry MLA and intensify the westerlies, which facilitates dust emission and transport, providing an interpretive framework. Increased dust may have promoted positive feedbacks (e.g., decreasing atmospheric CO2 concentrations and modulating radiation budgets), contributing to further cooling. Unraveling the long-term evolution of MLA aridity and westerlies climate is an indispensable component of the unfolding mystery of global climate change.

A monitoring of the spatial and temporal evolutions of aridity in northern Algeria

In order to enhance the understanding of the potential impact of climate change on water availability in the North of Algeria, the spatial and temporal evolutions of the De Martonne aridity index and the Pinna combinative index during the 1980–2018 period were investigated in the present study. The temporal trends in the aridity index time series were examined using the Mann–Kendall and Sen’s slope estimator tests, while the spatial interpolation of the aridity indices and their trends were conducted in a geographic information system environment using the Inverse Distance Weighting technique. The most important outcomes of this study are that the De Martonne aridity index is more appropriate for climate classification in the North of Algeria and that there were no statistically significant aridity changes in most regions during the studied period even though two regional behaviors with respect to aridity index trends were identified in the study area.

Global aridity changes due to differences in surface energy and water balance between 1.5 °C and 2 °C warming

Increased aridity and drought risks are significant global concerns. However, there are few comprehensive studies on the related risks with regard to the differences between relatively weak levels of warming, including the recent targets of the United Nations Framework Convention on Climate Change (UNFCCC) of 1.5 °C or 2 °C. The present study investigates the impacts of 1.5 °C and 2 °C warming on aridification and their non-linearity based on the relationship between available water and energy at the Earth’s terrestrial surface. Large multi-model ensembles with a 4000-model-year in total are sourced from the Half a degree Additional warming, Prognosis, and Projected Impacts (HAPPI) project. Results demonstrate that 2 °C warming results in more frequent dry states in the Amazon Basin, western Europe, and southern Africa, and a limited warming to 1.5 °C will mitigate aridification and increase the frequency of extreme dry-year in these regions. In the Mediterranean region, a significant acceleration of aridification is found from the 1.5 °C to 2 °C warming projections, which indicates a need to limit the warming by 1.5 °C. A substantial portion of Asia is projected to become increasingly humid under both 1.5 °C and 2 °C warming scenarios. In some geographic regions, such as Australia, a strong nonlinear shift of aridification is found as 2 °C warming results in shift to wetter state contrast to significant increases in aridity and dry-year frequency at the weaker level of warming. The results suggest that the responses of regional precipitation to global warming cause the aridity changes, but their nonlinear behaviors along with different warming levels should be assessed carefully, in particular, to incorporate the additional 0.5 °C warming.

Analysis of Trends in Aridity Changes for the Southern Ural Region over the Period 1960–2019 Using Various Methods

A statistical analysis of extreme episodes of aridity and humidity for the territory of the Southern Urals was performed. The calculations were based on the average daily air temperature and daily precipitation from 11 stations over the period 1960–2019. The spatial temporal characteristics of the summer droughts were studied on the basis of the station observations and calculated quantitative parameters. It has been established that the frequency of droughts in the Southern Ural region has increased over the past 19 years, the spread of the phenomenon reaches its peak in July.

Aridity trends in the Middle East and adjacent areas

Available water resources in the Middle East, as one of the most water-scarce regions of the world, have undergone extra pressure due to climatic change, population growth, and economic development during the past decades. The objective of this study is to detect the trends and quantify the changes in aridity with respect to precipitation and potential evapotranspiration in 20 countries of the Middle East and the adjacent area. A pixel-wise trend analysis was conducted on precipitation, potential evapotranspiration, and the aridity index for 71 years from 1948 to 2018. Results showed a statistically significant (|Z| > 1.96) increase up to 106% in aridity (a downward trend in the aridity index) from December to September in most parts of the region. Aridity in October and November had a downward tendency in most parts of the study area. At an annual time scale, 62.5% of the detected trends in aridity were found to be upward (up to 96% increase) due to the combined effects of the decrease in precipitation and the increase in potential evapotranspiration. Annual aridity was found to be downward in 37.5% of the detected trends (up to 61% decrease). The highest and the lowest trends in aridity were found in the north of Sudan (96%) and eastern Arabia (− 61%).

Assessing the Roles of Terrestrial Stilling and Solar Dimming in Land Surface Drying/Wetting across China

Decreases in wind speed (i.e., terrestrial stilling) and radiation (i.e., solar dimming) have been identified as important causes of aridity change both globally and regionally. To understand how their roles have varied across different natural and socioeconomic circumstances in China, this study presents a nationwide attribution analysis of land surface drying/wetting across the ten first-level river basins. The results suggest that consistent warming and reductions in relative humidity have significantly enhanced atmospheric evaporative demand and driven the land surface to become drier over the past six decades. However, the widespread terrestrial stilling and solar dimming have largely offset such trends by suppressing evaporation. While spatially varying changes in precipitation were the most influential driver of aridity change over half of the 713 used climate sites, decreasing wind speed and radiation were identified as the dominant cause of wetting at 15% and 13% of the sites, respectively. The impacts of terrestrial stilling and solar dimming were generally more prominent in the north (e.g., the Liao River, Songhuajiang, Hai River, and Huai River basins) and south (e.g., the Southeast, Pearl River, and Yangtze River basins) respectively, which could be associated with the weakening monsoon and intensified anthropogenic disturbances such as ecological restoration, urbanization, and air pollution. We conclude that more attention needs to be paid to the independent and combined climatological impacts of global- and regional-level human activities to develop proactive adaptation strategies of water and land management.

Mid‐Holocene environmental change and human occupation at Sai Island, Northern Sudan

AbstractHolocene environmental change in the northern and central Nile Valley was controlled primarily by shifts in the Intertropical Convergence Zone over time, leading to changes in aridity and water availability for early occupants of the region. Although local environmental changes may help to motivate societal changes such as those in settlement patterns or technological productions, evidence from pedogenic carbonates at Sai Island, in northern Sudan, indicate that the most significant environmental changes predated a key shift in local food production from foraging to pastoralism. Changes in local environmental conditions from a wetter and more diverse vegetative context to a more arid and C4‐dominant landscape occurred during the occupation of Khartoum Variant foragers, whereas later Abkan pastoralists arrived without any notable differences in the region compared to the environments inhabited by the most recent foragers. The lack of an external environmental driver for food production changes at Sai suggests that other, potentially cultural factors were more important in these economic decisions in the mid‐Holocene.

Human influence on joint changes in temperature, rainfall and continental aridity

Despite the pervasive impact of drought on human and natural systems, the large-scale mechanisms conducive to regional drying remain poorly understood. Here we use a multivariate approach1,2 to identify two distinct externally forced fingerprints from multiple ensembles of Earth system model simulations. The leading fingerprint, FM1(x), is characterized by global warming, intensified wet–dry patterns3 and progressive large-scale continental aridification, largely driven by multidecadal increases in greenhouse gas (GHG) emissions. The second fingerprint, FM2(x), captures a pronounced interhemispheric temperature contrast4,5, associated meridional shifts in the intertropical convergence zone6–9 and correlated anomalies in precipitation and aridity over California10, the Sahel11,12 and India. FM2(x) exhibits nonlinear temporal behaviour: the intertropical convergence zone moves southwards before 1975 in response to increases in hemispherically asymmetric sulfate aerosol emissions, and it shifts northwards after 1975 due to reduced sulfur dioxide emissions and the GHG-induced warming of Northern Hemisphere landmasses. Both fingerprints are statistically identifiable in observations of joint changes in temperature, rainfall and aridity during 1950–2014. We show that the reliable simulation of these changes requires combined forcing by GHGs, direct and indirect effects of aerosols, and large volcanic eruptions. Our results suggest that GHG-induced aridification may be modulated regionally by future reductions in sulfate aerosol emissions. Large-scale mechanisms causing regional drying are not well understood. Models and observational data reveal that human-caused changes in GHGs and aerosols led to detectable global and hemispheric signals in the joint behaviour of precipitation, temperature and aridity since the 1950s.

Interaction effects of the main drivers of global climate change on spatiotemporal dynamics of high altitude ecosystem behaviors: process-based modeling.

Soil organic carbon and nitrogen (SOC-N) dynamics are indicative of the human-induced disturbances of the terrestrial ecosystems the quantification of which provides insights into interactions among drivers, pressures, states, impacts, and responses in a changing environment. In this study, a process-based model was developed to simulate the eight monthly outputs of net primary productivity (NPP), SOC-N pools, soil C:N ratio, soil respiration, total N emission, and sediment C-N transport effluxes for cropland, grassland, and forest on a hectare basis. The interaction effect of the climate change drivers of aridity, CO2 fertilization, land-use and land-cover change, and best management practices was simulated on high altitude ecosystems from 2018 to 2070. The best management practices were developed into a spatiotemporally composite index based on SOC-N stock saturation, 4/1000 initiative, and RUCLE-C factor. Our model predictions differed from the remotely sensed data in the range of - 64% (underestimation) for the cropland NPP to 142% (overestimation) for the grassland SOC pool as well as from the global mean values in the range of - 97% for the sediment C and N effluxes to 60% for the total N emission from the grassland. The interaction exerted the greatest negative impact on the monthly sediment N efflux, total N emission, and soil respiration from forest by - 90.5, - 82.7, and - 80.3% and the greatest positive impact on the monthly sediment C effluxes from cropland, grassland, and forest by 139.3, 137.1, and 133.3%, respectively, relative to the currently prevailing conditions.

Effects of Climatic Warming and Wildfires on Recent Vegetation Changes in the Lake Baikal Basin

The vegetation changes in the area of the Russian part of the Lake Baikal water basin for the period 2010–2018 were investigated using MCD12C1 land cover. The decline in swamp systems area began in 2012 and continued until 2015, after which it partially recovered during the heavy rain season in 2018. During the period of 2010–2018, the area covered by forests did not exceed 20.3% of the Baikal basin of the total portion of the Baikal basin under study. Deforestation began in 2013 and continued until 2017. Over 2013–2018, the forest level decreased by 12.1% compared to the forest state in 2013. The analysis of summer rainfalls and aridity indexes was performed by using CRU TS and GPCC climatic datasets. It is shown that the interannual variations of precipitation and aridity changes are determined by the variability of the global circulation of moist air masses. The MCD64A1 (burned area) and MCD14ML (active fires) MODIS products were used for investigation of the influence of wildfires on vegetation changes. The spatial hotspot distributions and burned areas in general correspond to aridity zones, but they cannot explain the 20-fold increase in the number of wildfires. Most of the hotspot locations are away from settlements, roads, and loggings, in difficult-to-access mountainous areas, as well as in the low-inhabited areas of Siberia. We assume that the nature of such ignitions includes dry thunderstorms, pyrocumulus lightning, or remote impact.

Resolving combined influences of inflow and evaporation on western Greenland lake water isotopes to inform paleoclimate inferences

Stable isotopes of oxygen (δ18O) and hydrogen (δ2H) in precipitation are widely employed tracers of the global hydrologic cycle, and are frequently inferred from lake-water-derived proxies in sediments of high-latitude lakes. Lake-water isotope proxies archive precipitation δ18O and δ2H values, modulated by lake hydrological processes, which may be functionally classified into processes that affect source water isotope values (i.e. inflow δ18O and δ2H) and catchment-integrated evaporation. Respectively, these controls form the basis of interpretations of precipitation isotope and effective precipitation signals from lake-water isotope proxy records. Conventionally, a single control on lake water isotope variability is assumed for a given record. Yet sensitivity to these controls depends on regional hydroclimate and local hydrology, which may change through time. We quantified the relative impacts of variations in inflow δ18O and evaporative 18O enrichment on lake water δ18O in response to spatially variable aridity, using measurements of lake water δ2H and δ18O from 140 western Greenland lakes located between the Labrador Sea and western Greenland Ice Sheet margin. We calculated source water δ18O of lake waters (δI) using a recently developed Bayesian method and quantified evaporation-to-inflow ratios (E/I) using a modified Craig-Gordon model. δI varied by 11.1‰ across the study region, superimposed by evaporative 18O enrichment of up to 20.0‰ and E/I ranging from nearly no evaporative loss (E/I 1). Lakes can be broadly classified as predominantly sensitive to inflow or evaporation, corresponding to their location along the aridity gradient, and there are significant trends in both δI and E/I across the study area. Substantial local variability in δI and E/I suggests catchment hydrology determines the sensitivity of δI and E/I to changes in aridity, and implies that hydrological end-member lakes within a small region may provide complementary records of seasonal precipitation isotope values and ice-free-season evaporation. Deconvolving modern controls on lake water isotope values provides essential support for quantitative and seasonal paleoclimate inferences from paleolimnological isotope data, which will improve constraints on the long-term variability of the Arctic hydrologic cycle.