Rainfall trends in the African Sahel: Characteristics, processes, and causes

Wiley Interdisciplinary Reviews Climate Change, Год журнала: 2019, Номер 10(4)

Опубликована: Июнь 4, 2019

Abstract Sahel rainfall is dynamically linked to the global Hadley cell and regional monsoon circulation. It therefore susceptible forcings from remote oceans land alike. Warming of enhances stability tropical atmosphere weakens deep ascent in Sahara nearby changes structure position shallow circulation allows more intense convective systems that determine seasonal rain accumulation. These processes can explain observed interannual multidecadal variability. Sea surface temperature anomalies were dominant forcing drought 1970s 1980s. In most recent decades, amounts have partially recovered, but rainy season characteristics changed: intermittent wetting concentrated late away west coast. Similar subseasonal subregional differences trends characterize simulated response increased greenhouse gases, suggesting an anthropogenic influence. While uncertainty future projections remains, confidence them encouraged by recognition mean depends on large‐scale drivers atmospheric circulations are well resolved current climate models. Nevertheless, observational modeling efforts needed provide refined changes, expanding beyond total accumulation metrics intraseasonal risk extreme events, coordination between scientists stakeholders generate relevant information useful even under uncertainty. This article categorized under: Paleoclimates Current Trends > Modern Climate Change

Язык: Английский

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Prediction and projection of heatwaves

Nature Reviews Earth & Environment, Год журнала: 2022, Номер 4(1), С. 36 - 50

Опубликована: Дек. 13, 2022

Язык: Английский

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Nonstationary weather and water extremes: a review of methods for their detection, attribution, and management

Hydrology and earth system sciences, Год журнала: 2021, Номер 25(7), С. 3897 - 3935

Опубликована: Июль 7, 2021

Abstract. Hydroclimatic extremes such as intense rainfall, floods, droughts, heatwaves, and wind or storms have devastating effects each year. One of the key challenges for society is understanding how these are evolving likely to unfold beyond their historical distributions under influence multiple drivers changes in climate, land cover, other human factors. Methods analysing hydroclimatic advanced considerably recent decades. Here we provide a review drivers, metrics, methods detection, attribution, management, projection nonstationary extremes. We discuss issues uncertainty associated with approaches (e.g. arising from insufficient record length, spurious nonstationarities, incomplete representation sources modelling frameworks), examine empirical simulation-based frameworks analysis extremes, identify gaps future research.

Язык: Английский

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Climate change in the Baltic Sea region: a summary

Earth System Dynamics, Год журнала: 2022, Номер 13(1), С. 457 - 593

Опубликована: Март 15, 2022

Abstract. Based on the Baltic Earth Assessment Reports of this thematic issue in System Dynamics and recent peer-reviewed literature, current knowledge effects global warming past future changes climate Sea region is summarised assessed. The study an update Second Climate Change (BACC II) published 2015 focuses atmosphere, land, cryosphere, ocean, sediments, terrestrial marine biosphere. summaries gained palaeo-, historical, regional research, we find that main conclusions from earlier assessments still remain valid. However, new long-term, homogenous observational records, for example, Scandinavian glacier inventories, sea-level-driven saltwater inflows, so-called Major Inflows, phytoplankton species distribution, scenario simulations with improved models, glaciers, lake ice, food web, have become available. In many cases, uncertainties can now be better estimated than before because more models were included ensembles, especially Sea. With help coupled feedbacks between several components system been studied, multiple driver studies performed, e.g. projections web include fisheries, eutrophication, change. New datasets led to a revised understanding some variables such as salinity. Furthermore, it has evident natural variability, particular ocean multidecadal timescales, greater previously estimated, challenging our ability detect observed projected climate. context, first palaeoclimate regionalised are instructive. Hence, increased. addition well-known influence North Atlantic Oscillation, was found also other low-frequency modes internal Multidecadal Variability, profound region. Challenges identified, systematic discrepancy cloudiness trends difficulty confidently attributing large ecosystems Finally, compare results coastal sea assessments, Region (NOSCCA), change differ those Sea, since oceanography very different seas While dynamics dominated by tides, characterised brackish water, perennial vertical stratification southern subbasins, seasonal ice cover northern subbasins.

Язык: Английский

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Event‐Based Storylines to Address Climate Risk

Earth s Future, Год журнала: 2020, Номер 9(2)

Опубликована: Дек. 15, 2020

Abstract The climate science community is challenged to adopt an actionable risk perspective, which difficult align with the traditional focus on model‐based probabilistic change projections. Event‐based storylines can provide a way out of this conundrum by putting emphasis plausibility rather than probability. This links directly common practices in disaster management using “stress‐testing” for emergency preparedness based events that are conditional specific and plausible assumptions. allow explanations, without full attribution every causal factor, crucial when some aspects latter complex highly uncertain.

Язык: Английский

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Attributing Extreme Events to Climate Change: A New Frontier in a Warming World

One Earth, Год журнала: 2020, Номер 2(6), С. 522 - 527

Опубликована: Июнь 1, 2020

The emerging field of extreme-event attribution (EEA) seeks to answer the question: "Has climate change influenced frequency, likelihood, and/or severity individual extreme events?" Methodological advances over past 15 years have transformed what was once an unanswerable hypothetical into a tractable scientific question—and for certain types events, influence anthropogenic has emerged beyond reasonable doubt. Several challenges remain, particularly those stemming from structural limitations in process-based models and temporal geographic historical observations. However, growing use large climate-model ensembles that capture natural variability, fine-scale simulations better represent underlying physical processes, lengthening observational record could obviate some these concerns near future. EEA efforts important implications risk perception, public policy, infrastructure design, legal liability, adaptation warming world. There is now extremely high level confidence human activities are only plausible explanation observed ∼1.2°C rise global mean temperature, fingerprint likewise been found numerous other changes climate. although useful metric overall change, it remains statistical construct: no place actually experiences its local mean. Moreover, aspects greatest effects on society ecosystems—such as heatwaves, downpours, hurricanes, droughts, wildfires—are inherently far Therefore, understand, mitigate, adapt harm health well-being humans ecosystems, imperative understand how (and why) climate-related extremes changing This branch science, often referred (EEA), evolved rapidly recent years. evolution faced number challenges. In particular, models, well observations, lead substantial quantification validation. methodological advances, coupled with longer records improved opened door systematically addressing question whether likelihood events. news media ask: "Did cause this specific weather event?" very literal sense, such rigidly posed will always be "no." All events dynamically Earth system ultimately product complex, interrelated processes acting across wide range spatiotemporal scales. thus rarely (if ever) traceable singular any event, variability play role. Indeed, recently decade ago, common response scientists "no single event can attributed change." Weather climate, course, not same. describes variations short day-to-day timescales, whereas integrates much time horizons. A key step forward development acknowledgment exist continuum. Because aggregate properties weather—in words, envelope conditions at particular point time—it encompasses "typical" but also rare, high-magnitude extremes. From perspective, understanding multi-decadal reasonably framed exercise quantifying shifts probability distribution conditions. As result, increasingly recognized strict binary causality ill posed. probabilistic descriptor largely stochastic stands reason investigations upon should terms. Additionally, considerable body evidence suggests human-caused low-probability, high-consequence "tails" considerably different might inferred extrapolating studies instead begun ask more nuanced seemingly subtle shift perspective transforms essentially about absolute one both scientifically practically actionable—and directly addressed existing numerical modeling tools. expanded decade, research groups pioneered novel approaches. Virtually all approaches share epistemology: using combination real-world simulations, rigorous techniques separate actual counterfactual "climate without influence." It critical general framing because results strongly dependent assumptions analysis employed. sections follow, we first outline basic steps shared most (Figure 1) then deeply explore historically employed contexts. 1.Define event. What scale variable(s) best characterize event? Given heatwave, instance, appropriate metrics include daily maximum temperatures city, weekly average region, combined heat humidity metrics, or drivers strength atmospheric high-pressure system.2.Estimate "counterfactual" Quantifying requires magnitude influence. One approach quantify forcing. Alternative removing long-term trend series, relationships between variable data period little influence.3.Compare Are there statistically distinguishable differences climates? used, including fractional difference magnitude, ratio (often called "risk ratio"), portion total contributed by (i.e., "fraction attributable risk"). addition, uncertainty priority model- observation-focused Key sources ability accurately simulate variable, "forced response" simulated "irreducible uncertainty" forced internal variability.4.Make formal statement. Most bar attribution: typical null hypothesis did rejecting "beyond doubt" standard. If sufficient versus rejected, affirmative statement made level. multiple uncertainty, statements components "there 95% increased least factor 2.86"). New frameworks suggested simplify final 1D). Initial decisions regarding define entire process described Figure 1. addition scales, deeper philosophical choice which down chain complex methodology extended. These shape conclusion. Consider study focused coastal inundation produced hurricane making landfall location. possible would consider full sample hurricanes affected region flooding exceeding threshold. "absolute" considers accounting initial preconditioned fact occurred location time) contribution contributing (e.g., sea level, precipitation intensity, storm strength). complicate aspect For example, methods isolate conditions, difficult differentiate contributions sea-level (which increase background water levels), increasing water-vapor content contributes intensity given storm), ocean decreasing vertical wind shear (both act intensify hurricanes). Another approach, conditional "storyline" takes (such large-scale event) asks had detectable effect modulating outcome Often, involve perturbing subset relevant variables characterizing state atmosphere increment commensurate change. 5 days before model simulation prescribing surface removed. help significant weakness cannot diagnose constituent An alternative "ingredient-based" 2). Here, investigators ascertain essential known contribute assess aims combine strengths (1) enhances influencing they co-occur; (2) makes set event; (3) potentially enables poorly sparsely sampled datasets. Fundamentally, two typically assessed studies: defined rate exceedance fixed threshold baseline—for 99.99th quantile during 1920–1980. Conversely, associated probability, "design floods" based 100-year recurrence interval. definitions sides same analytical coin sometimes highly consequential broader communication practical decision making. regional centuries Superstorm Sandy's York City 22% (from ∼2.3 ∼2.8 m probability). According (Lin et al., 2016Lin N. Kopp R.E. Horton B.P. Donnelly J.P. Hurricane flood frequency year 1800 2100.Proc. Natl. Acad. Sci. U S A. 2016; 113: 12071-12075Crossref PubMed Scopus (116) Google Scholar), tripled ∼1,200- ∼400-year return severity). colloquial terms, ∼20% sound modest, tripling sounds indeed—perhaps leading divergence perception study's outcome. Yet, equally valid—and consistent—metrics role probability-based metric, civil engineering context. ranging drainage culverts dams designed accommodate thresholds amount interval), increases original design imply capacity exceeded. magnitude-based hand, heightened relevance policy context—instances know fraction losses distinction "collective attribution." Individual collective type?" 3). focus, vegetation flammability vicinity Paradise, California, November 2018 (the California's deadliest destructive wildfire modern history) likely severe warming. Collective attribution, focus western United States (and, hence, record-setting "consistent with" expected change). Recently, offer "rapid targeted toward real-time make even place. Emerging apply signal forecasts enable evaluations rapid predicated precomputed via event-attribution methodologies samples observations evaluate type extreme. Similar used globe forcing already 3) verify out-of-sample prediction-verification frameworks. Although science advanced dramatically since benchmark 2003 European heatwave (Stott 2004Stott P.A. Stone D.A. Allen M.R. Human 2003.Nature. 2004; 432: 610-614Crossref (1144) several remain. prominent relate uncertainties surrounding creation Researchers climate-modeling counterfactual, consensus suitable representation absence challenge exacerbated that, many cases, estimate current sufficiently simply too temporally geographically limited robust quantification. option parametric curve fitting value theory approximate interval demonstrated sensitive assumed functional form yield estimates present-day vary orders magnitude. Large ensembles, larger sizes, avoid need distribution. Yet still subject major caveat present-generation reliably responsible points fit purpose context EEA. trade-off fine resolution necessary resolving phenomena produce long integrations needed fully climate-system distinguish able ∼103-km-scale systems coarse behavior ∼102-km-scale tropical cyclones face greater simulating localized occur spatial scales smaller than grid cell. why varies heatwaves moderate cyclones; 4). Together, raise distinct possibility finding reflecting either capabilities. consideration emerges: does "absence evidence" truly "evidence absence"? Clarifying interpretations negative result communicating makers public. Recent developments interdisciplinary highlight potential near-term advancement Perhaps growth field, researchers developing, testing, applying variety disrupting around Efforts compare—and independently verify—different emerge. Further codification open access tools accelerate capacity. develop clear consistent language characteristics ingredients being attributed, along uncertainties, Growth supercomputing resources enabled continued improvement resolution, ensemble size, integration length, allowing realism routinely conducted strong motions—such thunderstorms, cyclones—can explicitly represented. "non-hydrostatic" generally their scope, early indications offers promise improving phenomena. Similarly, generation multiple, single-model identical boundary forcings physics perturbed conditions) promising allows intercomparison refinement predictive skill variations. accurate within offering partial solution inadequacies record. "single-forcing" various greenhouse gases, aerosols, land uses respective roles competing influences. rising profile applications legal, public-policy, climate-adaptation arenas continue increase. oil companies entities liability warming, assigning culpability subsequent penalties becomes demonstrably caused loss damage. Likewise, factored investment decisions, funding requirements federal disaster declarations. Civil considerations incorporating new information order maintain adequate safety margins resilience Ultimately, just improve risks: quantitatively address urgent, societally questions well-being. individuals sense contemporary disasters, helping contextualize relative reference aiding preparedness activities. plays shaping risks, action levels pose unacceptable risks systems. D.L.S. supported joint collaboration Institute Environment Sustainability University Los Angeles, Center Climate Extremes National Atmospheric Research, Nature Conservancy California. N.S.D. acknowledges support Stanford University. D.S. Washington State D.T. Santa Barbara.

Язык: Английский

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Compound droughts and hot extremes: Characteristics, drivers, changes, and impacts

Earth-Science Reviews, Год журнала: 2022, Номер 235, С. 104241 - 104241

Опубликована: Ноя. 8, 2022

Язык: Английский

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Heat Waves: Physical Understanding and Scientific Challenges

Reviews of Geophysics, Год журнала: 2023, Номер 61(2)

Опубликована: Апрель 26, 2023

Abstract Heat waves (HWs) can cause large socioeconomic and environmental impacts. The observed increases in their frequency, intensity duration are projected to continue with global warming. This review synthesizes the state of knowledge scientific challenges. It discusses different aspects related definition, triggering mechanisms, changes future projections HWs, as well emerging research lines on subseasonal forecasts specific types HWs. We also identify gaps that limit progress delineate priorities for research. Overall, physical drivers HWs not understood, partly due difficulties quantification interactions responses climate change. Influential factors convey processes at spatio‐temporal scales, from warming large‐scale atmospheric circulation regional local affected area upwind regions. Although some thermodynamic have been identified, there is a lack understanding dynamical aspects, forcings feedbacks, changes. hampers attribution trends individual events, reduces ability provide accurate projections. Sustained observational networks, models diverse complexity, narrative‐based methodological approaches artificial intelligence offer new opportunities toward process‐based interdisciplinary

Язык: Английский

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Understanding human influence on climate change in China

National Science Review, Год журнала: 2021, Номер 9(3)

Опубликована: Июнь 23, 2021

China's climate has been warming since the 1950s, with surface air temperature increasing at a rate higher than global average. Changes in have exerted substantial impacts on water resources, agriculture, ecosystems and human health. Attributing past changes to causes provides scientific foundation for national international policies. Here, we review recent progress attributing observed over decades China. Anthropogenic forcings, dominated by greenhouse gas emissions, are main drivers increases mean extreme temperatures. Evidence of effect anthropogenic forcings precipitation is emerging. Human influence increased probability heat events, likely changed occurrence probabilities some heavy events. The way specific attribution question posed conditions under which addressed present persistent challenges appropriately communicating results non-specialists.

Язык: Английский

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Towards advancing scientific knowledge of climate change impacts on short-duration rainfall extremes

Philosophical Transactions of the Royal Society A Mathematical Physical and Engineering Sciences, Год журнала: 2021, Номер 379(2195), С. 20190542 - 20190542

Опубликована: Март 1, 2021

A large number of recent studies have aimed at understanding short-duration rainfall extremes, due to their impacts on flash floods, landslides and debris flows potential for these worsen with global warming. This has been led in a concerted international effort by the INTENSE Crosscutting Project GEWEX (Global Energy Water Exchanges) Hydroclimatology Panel. Here, we summarize main findings so far suggest future directions research, including: benefits convection-permitting climate modelling; towards mechanisms change; usefulness temperature-scaling relations; detecting attributing extreme need coordination collaboration. Evidence suggests that intensity long-duration (1 day+) heavy precipitation increases warming close Clausius–Clapeyron (CC) rate (6–7% K −1 ), although large-scale circulation changes affect this response regionally. However, rare events can scale higher rates, localized (hourly sub-hourly) intensities respond more strongly (e.g. 2 × CC instead CC). Day-to-day scaling supports scaling, proposed related local-scale dynamics convective storms, but its relevance change is not clear. Uncertainty extremes remains influenced many factors, including circulation, storm andstratification. Despite this, research increased confidence both detectability various aspects intense rainfall. To make further progress, datasets, model experiments evaluations will be required, consistent standardized comparison methods metrics, recommendations are made frameworks. article part discussion meeting issue ‘Intensification implications flood risks’.

Язык: Английский

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