New directions in tropical phenology.

Earth's most speciose biomes are in the tropics, yet tropical plant phenology remains poorly understood. Tropical phenological data are comparatively scarce and viewed through the lens of a 'temperate phenological paradigm' expecting phenological traits to respond to strong, predictably annual shifts in climate (e.g.

Growing impact of wildfire on western US water supply.

Streamflow often increases after fire, but the persistence of this effect and its importance to present and future regional water resources are unclear. This paper addresses these knowledge gaps for the western United States (WUS), where annual forest fire area increased by more than 1,100% during 1984 to 2020. Among 72 forested basins across the WUS that burned between 1984 and 2019, the multibasin mean streamflow was significantly elevated by 0.

Disentangling the Regional Climate Impacts of Competing Vegetation Responses to Elevated Atmospheric CO.

Biophysical vegetation responses to elevated atmospheric carbon dioxide (CO) affect regional hydroclimate through two competing mechanisms. Higher CO increases leaf area (LAI), thereby increasing transpiration and water losses. Simultaneously, elevated CO reduces stomatal conductance and transpiration, thereby increasing rootzone soil moisture.

Seven centuries of reconstructed Brahmaputra River discharge demonstrate underestimated high discharge and flood hazard frequency.

The lower Brahmaputra River in Bangladesh and Northeast India often floods during the monsoon season, with catastrophic consequences for people throughout the region. While most climate models predict an intensified monsoon and increase in flood risk with warming, robust baseline estimates of natural climate variability in the basin are limited by the short observational record. Here we use a new seven-century (1309-2004 C.

Climate change reshapes the drivers of false spring risk across European trees.

Temperate forests are shaped by late spring freezes after budburst - false springs - which may shift with climate change. Research to date has generated conflicting results, potentially because few studies focus on the multiple underlying drivers of false spring risk. Here, we assessed the effects of mean spring temperature, distance from the coast, elevation and the North Atlantic Oscillation (NAO) using PEP725 leafout data for six tree species across 11 648 sites in Europe, to determine which were the strongest predictors of false spring risk and how these predictors shifted with climate change.

Coupled Modes of North Atlantic Ocean-Atmosphere Variability and the Onset of the Little Ice Age.

Hydroclimate extremes in North America, Europe, and the Mediterranean are linked to ocean and atmospheric circulation anomalies in the Atlantic, but the limited length of the instrumental record prevents complete identification and characterization of these patterns of covariability especially at decadal to centennial timescales. Here we analyze the coupled patterns of drought variability on either side of the North Atlantic Ocean basin using independent climate field reconstructions spanning the last millennium in order to detect and attribute epochs of coherent basin-wide moisture anomalies to ocean and atmosphere processes. A leading mode of broad-scale moisture variability is characterized by distinct patterns of North Atlantic atmosphere circulation and sea surface temperatures.

Large contribution from anthropogenic warming to an emerging North American megadrought.

Severe and persistent 21st-century drought in southwestern North America (SWNA) motivates comparisons to medieval megadroughts and questions about the role of anthropogenic climate change. We use hydrological modeling and new 1200-year tree-ring reconstructions of summer soil moisture to demonstrate that the 2000-2018 SWNA drought was the second driest 19-year period since 800 CE, exceeded only by a late-1500s megadrought. The megadrought-like trajectory of 2000-2018 soil moisture was driven by natural variability superimposed on drying due to anthropogenic warming.

Diversity buffers winegrowing regions from climate change losses.

Agrobiodiversity-the variation within agricultural plants, animals, and practices-is often suggested as a way to mitigate the negative impacts of climate change on crops [S. A. Wood , 30, 531-539 (2015)].

Land-atmosphere feedbacks exacerbate concurrent soil drought and atmospheric aridity.

Compound extremes such as cooccurring soil drought (low soil moisture) and atmospheric aridity (high vapor pressure deficit) can be disastrous for natural and societal systems. Soil drought and atmospheric aridity are 2 main physiological stressors driving widespread vegetation mortality and reduced terrestrial carbon uptake. Here, we empirically demonstrate that strong negative coupling between soil moisture and vapor pressure deficit occurs globally, indicating high probability of cooccurring soil drought and atmospheric aridity.

Oceanic and radiative forcing of medieval megadroughts in the American Southwest.

Multidecadal "megadroughts" were a notable feature of the climate of the American Southwest over the Common era, yet we still lack a comprehensive theory for what caused these megadroughts and why they curiously only occurred before about 1600 CE. Here, we use the Paleo Hydrodynamics Data Assimilation product, in conjunction with radiative forcing estimates, to demonstrate that megadroughts in the American Southwest were driven by unusually frequent and cold central tropical Pacific sea surface temperature (SST) excursions in conjunction with anomalously warm Atlantic SSTs and a locally positive radiative forcing. This assessment of past megadroughts provides the first comprehensive theory for the causes of megadroughts and their clustering particularly during the Medieval era.

Climate variation, reproductive frequency and acorn yield in English Oaks.

Aims -: Annually variable, but synchronous production of large seed crops ('masting') is a widespread phenomenon in temperate trees. Mounting concerns about the impacts of anthropogenic climate change (ACC) on plant reproduction, gives urgency to our need to understand better the role of climate on tree reproduction, and in particular, mast events. Unlike our understanding of reproductive phenology however, there is little consensus regarding how climate affects plant reproductive effort, or indeed the actual environmental triggers that underpin masting behaviour.

Twentieth-century hydroclimate changes consistent with human influence.

Although anthropogenic climate change is expected to have caused large shifts in temperature and rainfall, the detection of human influence on global drought has been complicated by large internal variability and the brevity of observational records. Here we address these challenges using reconstructions of the Palmer drought severity index obtained with data from tree rings that span the past millennium. We show that three distinct periods are identifiable in climate models, observations and reconstructions during the twentieth century.

Rethinking false spring risk.

Temperate plants are at risk of being exposed to late spring freezes. These freeze events-often called false springs-are one of the strongest factors determining temperate plants species range limits and can impose high ecological and economic damage. As climate change may alter the prevalence and severity of false springs, our ability to forecast such events has become more critical, and it has led to a growing body of research.

20,000 years of societal vulnerability and adaptation to climate change in southwest Asia.

The Fertile Crescent, its hilly flanks and surrounding drylands has been a critical region for studying how climate has influenced societal change, and this review focuses on the region over the last 20,000 years. The complex social, economic, and environmental landscapes in the region today are not new phenomena and understanding their interactions requires a nuanced, multidisciplinary understanding of the past. This review builds on a history of collaboration between the social and natural palaeoscience disciplines.

Distinct Influences of Land Cover and Land Management on Seasonal Climate.

Anthropogenic land use and land cover change is primarily represented in climate model simulations through prescribed transitions from natural vegetation to cropland or pasture. However, recent studies have demonstrated that land management practices, especially irrigation, have distinct climate impacts. Here we disentangle the seasonal climate impacts of land cover change and irrigation across areas of high agricultural intensity using climate simulations with three different land surface scenarios: (1) natural vegetation cover/no irrigation, (2) year 2000 crop cover/no irrigation, and (3) year 2000 crop cover and irrigation rates.

Six centuries of Upper Indus Basin streamflow variability and its climatic drivers.

Our understanding of the full range of natural variability in streamflow, including how modern flow compares to the past, is poorly understood for the Upper Indus Basin (UIB) because of short instrumental gauge records. To help address this challenge, we use Hierarchical Bayesian Regression (HBR) with partial pooling to develop six centuries long (1394-2008 C.E.

The Sensitivity of Land-Atmosphere Coupling to Modern Agriculture in the Northern Midlatitudes.

Modern agricultural land cover and management are important as regional climate forcings. Previous work has shown that land cover change can significantly impact key climate variables, including turbulent fluxes, precipitation, and surface temperature. However, fewer studies have investigated how intensive crop management can impact background climate conditions, such as the strength of land-atmosphere coupling and evaporative regime.

Exacerbation of the 2013-2016 Pan-Caribbean Drought by Anthropogenic Warming.

The Caribbean islands are expected to see more frequent and severe droughts from reduced precipitation and increased evaporative demand due to anthropogenic climate change. Between 2013 and 2016, the Caribbean experienced a widespread drought due in part to El Niño in 2015-2016, but it is unknown whether its severity was exacerbated by anthropogenic warming. This work examines the role of recent warming on this drought, using a recently developed high-resolution self-calibrating Palmer Drought Severity Index data set.

Competing influences of anthropogenic warming, ENSO, and plant physiology on future terrestrial aridity.

The 2011-2016 Californian drought illustrates that drought-prone areas do not always experience relief once a favorable phase of El Niño-Southern Oscillation (ENSO) returns. In the 21 century, such an expectation is unrealistic in regions where global warming induces an increase in terrestrial aridity larger than the aridity changes driven by ENSO variability. This premise is also flawed in areas where precipitation supply cannot offset the global warming-induced increased evaporative demand.

A reconstruction of global hydroclimate and dynamical variables over the Common Era.

Hydroclimate extremes critically affect human and natural systems, but there remain many unanswered questions about their causes and how to interpret their dynamics in the past and in climate change projections. These uncertainties are due, in part, to the lack of long-term, spatially resolved hydroclimate reconstructions and information on the underlying physical drivers for many regions. Here we present the first global reconstructions of hydroclimate and associated climate dynamical variables over the past two thousand years.

The 2016 southeastern US drought: an extreme departure from centennial wetting and cooling.

The fall 2016 drought in the southeastern United States (SE US) appeared exceptional based on its widespread impacts, but the current monitoring framework that only extends from 1979-present does not readily facilitate evaluation of soil-moisture anomalies in a centennial context. A new method to extend monthly gridded soil-moisture estimates back to 1895 is developed, indicating that since 1895, October-November 2016 soil moisture (0-200 cm) in the SE US was likely the second lowest on record, behind 1954. This severe drought developed rapidly and was brought on by low September-November precipitation and record-high September-November daily maximum temperatures (Tmax).

Critical impact of vegetation physiology on the continental hydrologic cycle in response to increasing CO.

Predicting how increasing atmospheric CO will affect the hydrologic cycle is of utmost importance for a range of applications ranging from ecological services to human life and activities. A typical perspective is that hydrologic change is driven by precipitation and radiation changes due to climate change, and that the land surface will adjust. Using Earth system models with decoupled surface (vegetation physiology) and atmospheric (radiative) CO responses, we here show that the CO physiological response has a dominant role in evapotranspiration and evaporative fraction changes and has a major effect on long-term runoff compared with radiative or precipitation changes due to increased atmospheric CO This major effect is true for most hydrological stress variables over the largest fraction of the globe, except for soil moisture, which exhibits a more nonlinear response.

Investigating the causes of increased 20-century fall precipitation over the southeastern United States.

Much of the eastern United States (US) experienced increased precipitation over the 20 century. Characterizing these trends and their causes is critical for assessing future hydroclimate risks. Here, US precipitation trends are analyzed during 1895-2016, revealing that fall precipitation in the southeastern region north of the Gulf of Mexico (SE-Gulf) increased by nearly 40%, primarily increasing after the mid-1900s.