Table of contents

Tropical dry forests are distinct from wet and moist tropical forests by the presence of a strong dry season. This collection of papers explores the unique biodiversity, plant functional traits, coupling between carbon and water cycles, and threats to these important ecosystems. These studies have relevance for conservation and management of tropical dry forests.

Most economic theorists assume that energy efficiency—the biggest global provider of energy services—is a limited and dwindling resource whose price- and policy-driven adoption will inevitably deplete its potential and raise its cost. Influenced by that theoretical construct, most traditional analysts and deployers of energy efficiency see and exploit only a modest fraction of the worthwhile efficiency resource, saving less and paying more than they should. Yet empirically, modern energy efficiency is, and shows every sign of durably remaining, an expanding-quantity, declining-cost resource. Its adoption is constrained by major but correctable market failures and increasingly motivated by positive externalities. Most importantly, in both newbuild and retrofit applications, its quantity is severalfold larger and its cost lower than most in the energy and climate communities realize. The efficiency resource far exceeds the sum of savings by individual technologies because artfully choosing, combining, sequencing, and timing fewer and simpler technologies can save more energy at lower cost than deploying more and fancier but dis-integrated and randomly timed technologies. Such 'integrative design' is not yet widely known or applied, and can seem difficult because it is simple, but is well proven, rapidly evolving, and gradually spreading. Yet the same economic models that could not predict the renewable energy revolution also ignore integrative design and hence cannot recognize most of the efficiency resource or reserves. This analytic gap makes climate-change mitigation look harder and costlier than it really is, diverting attention and investment to inferior options. With energy efficiency as its cornerstone and needing its pace redoubled, climate protection depends critically on seeing and deploying the entire efficiency resource. This requires focusing less on individual technologies than on whole systems (buildings, factories, vehicles, and the larger systems embedding them), and replacing theoretical assumptions about efficiency's diminishing returns with practitioners' empirical evidence of expanding returns.

In view of the economic, social and ecological importance of Canada's forest ecosystems, there is a growing interest in studying the response of these ecosystems to climate change. Accurate knowledge regarding growth trajectories is needed for both policy makers and forest managers to ensure sustainability of the forest resource. However, results of previous analyses regarding the sign and magnitude of trends have often diverged. The main objective of this paper was to analyse the current state of scientific knowledge on growth and productivity trends in Canada's forests and provide some explanatory elements for contrasting observations. The three methods that are commonly used for assessments of tree growth and forest productivity (i.e. forest inventory data, tree-ring records, and satellite observations) have different underlying physiological assumptions and operate on different spatiotemporal scales, which complicates direct comparisons of trend values between studies. Within our systematic review of 44 peer-reviewed studies, half identified increasing trends for tree growth or forest productivity, while the other half showed negative trends. Biases and uncertainties associated with the three methods may explain some of the observed discrepancies. Given the complexity of interactions and feedbacks between ecosystem processes at different scales, researchers should consider the different approaches as complementary, rather than contradictory. Here, we propose the integration of these different approaches into a single framework that capitalizes on their respective advantages while limiting associated biases. Harmonization of sampling protocols and improvement of data processing and analyses would allow for more consistent trend estimations, thereby providing greater insight into climate-change related trends in forest growth and productivity. Similarly, a more open data-sharing culture should speed-up progress in this field of research.

Permafrost soils in the high northern latitudes contain a substantial amount of carbon which is not decomposed due to frozen conditions. Climate change will lead to a thawing of at least part of the permafrost, implying that the stored carbon will become accessible to decomposition and be released to the atmosphere. We use a land surface model to quantify the amount of carbon released up until 2300 and determine the net carbon balance of the northern hemisphere permafrost region under climate warming following the RCP scenarios 2.6, 4.5, and 8.5. Here we show for the first time that the net carbon balance of the permafrost region is not just strongly dependent on the overall warming, but also on the CO₂ concentration pathway. As a result moderate warming scenarios may counterintuitively lead to lower net carbon emissions from the permafrost region than low warming scenarios.

The response of plant diversity to increased snowfall, i.e., precipitation that falls in a solid state rather than a liquid state, is unclear. We investigated the potential effects of 12 year snowfall augmentation on species richness using coordinated distributed experiments, including ten sites across a rainfall gradient of 211–354 mm and spanning 440 km in length in the temperate steppe. Snowfall augmentation decreased species richness rather than enhancing it. Abiotic factor driven by soil pH was the dominant determinant affecting the variation in species richness under changing precipitation regimes, overriding biotic factor. The strongest reduction in species richness induced by snowfall augmentation occurred in the low-rainfall sites. Our study provides insights into the relationship between precipitation and biodiversity in arid and semiarid regions.

Targets agreed to in Paris in 2015 aim to limit global warming to 'well below 2 °C and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels'. Despite the far-reaching consequences of this multi-lateral climate change mitigation strategy, the implications for global river flows remain unclear. Here we estimate the impacts of 1.5 °C versus 2.0 °C mitigation scenarios on peak flows by using daily river flow data from a multi-model ensemble which follows the HAPPI Protocol (that is specifically designed to simulate these temperature targets). We find agreement between models with regard to changing risk of river flow extremes. Moreover, we find that the response at 2.0 °C is not a uniform extension of the response at 1.5°, suggesting a non-linear global response of peak flows to the two mitigation levels. Yet committing to the 2.0 °C warming target, rather than 1.5 °C, is projected to lead to an increase in the frequency of occurrence of extreme flows in several large catchments. In the most affected areas, predominantly in South Asia, while region-specific features such as aerosol loads may determine precipitation patterns, we estimate that under our 1.5 °C scenario the historical 1-in-100 year flow occurs with a frequency of 1-in-25 years. At 2.0 °C, similar increases are observed in several global regions. These shifts are also accompanied by changes in the duration of rainy seasons which influence the occurrence of high flows.

This study investigates the robustness of the long-term changes in the wintertime surface Arctic Oscillation (AO) in the ERA20C reanalysis. A statistically significant trend in the AO is found in ERA20C over the period 1900–2010. These long-term changes in the AO are not found in two other observational datasets. The long-term change in the AO in ERA20C is associated with statistically significant negative trend (approximately −6 hPa per century) in mean-sea level pressure (MSLP) over the Northern Hemisphere polar regions. This is not seen in the HADSLP2 observational dataset, suggesting that the trends in the ERA20C AO index may be spurious. The spurious long-term changes in MSLP and the AO index in ERA20C result in a strengthening of the meridional MSLP gradient in ERA20C. The strengthening of the meridional MSLP gradient is consistent with increases in wintertime storminess in Northern Europe and the NH high latitudes.

In an increasingly globalized world, invasive species cause major human, financial, and environmental costs. A cosmopolitan pest of great concern is the cassava mealybug Phenacoccus manihoti (Hemiptera: Pseudococcidae), which invaded Asia in 2008. Following its arrival, P. manihoti inflicted measurable yield losses and a 27% drop in aggregate cassava production in Thailand. As Thailand is a vital exporter of cassava-derived commodities to China and supplies 36% of the world's internationally-traded starch, yield shocks triggered price surges and structural changes in global starch trade. In 2009 a biological control agent was introduced in Asia-the host-specific parasitoid, Anagyrus lopezi (Hymenoptera: Encyrtidae). This parasitoid had previously controlled the cassava mealybug in Africa, and its introduction in Asia restored yield levels at a continent-wide scale. Trade network and price time-series analyses reveal how both mealybug-induced production loss and subsequent parasitoid-mediated yield recovery coincided with price fluctuations in futures and spot markets, with important cascading effects on globe-spanning trade networks of (cassava) starch and commodity substitutes. While our analyses may not imply causality, especially given the concurrent 2007–2011 food crises, our results do illuminate the important interconnections among subcomponents of the global commodity system. Our work underlines how ecologically-based tactics support resilience and safeguard primary productivity in (tropical) agro-ecosystems, which in turn help stabilize commodity markets in a similar way as pesticide-centered approaches. Yet, more importantly, (judiciously-implemented) biological control can deliver ample 'hidden' environmental and human-health benefits that are not captured by the prices of globally-traded commodities.

This paper explores regional response strategies to potential water scarcity. Using a model of integrated human-earth system dynamics (GCAM), we test a wide range of alternate water demand scenarios to explore regional response strategies. We create a typology that categorizes countries and basins according to their responses in electricity and agriculture to potential water scarcity. Three different categories are found. First, little response is observed for many basins because water demands do not increase enough to create scarcity. Second, the primary response is adjustments in the electricity sector (e.g. most basins in Western Europe, the United States and China) with a transition to water-saving cooling systems but marginal impact on total power generation or the fuel mix. Third, where there is a lack of sufficient responding capacity in the electricity sector (e.g. Pakistan, Middle East and several basins in India), additional response occurs through reduced irrigation water withdrawals, either by switching from domestic production to imports or from irrigated agriculture to rain-fed production. The primary response mechanism to demand-based water scarcity for individual basins is quite robust across the range of water demand scenarios tested. The results and typology in this paper will be valuable for future research exploring global water scarcity due to both demand and supply drivers.

Wind is a key component of the urban climate due to its relevance for ventilation of air pollution and urban heat, wind nuisance, as well as for urban wind energy engineering. These winds are governed by the dynamics of the atmosphere closest to the surface, the atmospheric boundary layer (ABL). Making use of a conceptual bulk model of the ABL, we find that for certain atmospheric conditions the boundary-layer mean wind speed in a city can surprisingly be higher than its rural counterpart, despite the higher roughness of cities. This urban wind island effect (UWI) prevails in the afternoon, and appears to be caused by a combination of differences in ABL growth, surface roughness and the ageostrophic wind, between city and countryside. Enhanced turbulence in the urban area deepens the ABL, and effectively mixes momentum into the ABL from aloft. Furthermore, the oscillation of the wind around the geostrophic equilibrium, caused by the rotation of the Earth, can create episodes where the urban boundary-layer mean wind speed is higher than the rural wind. By altering the surface properties within the bulk model, the sensitivity of the UWI to urban morphology is studied for the 10 urban local climate zones (LCZs). These LCZs classify neighbourhoods in terms of building height, vegetation cover etc, and represent urban morphology regardless of culture or location. The ideal circumstances for the UWI to occur are a deeper initial urban boundary-layer than in the countryside, low-rise buildings (up to 12 m) and a moderate geostrophic wind (∼5 m s⁻¹). The UWI phenomenon challenges the commonly held perception that urban wind is usually reduced due to drag processes. Understanding the UWI can become vital to accurately model urban air pollution, quantify urban wind energy potential or create accurate background conditions for urban computational fluid dynamics models.

Buildings and the atmosphere are intrinsically connected via cooling and heating systems. Global climate is projected to grow warmer, with an increasing fraction of the population living in urban centers. This introduces the challenge for new approaches to project future energy demand changes in cities. In New York City (NYC), the focus of our study, while air conditioning only accounts for 9% of all building energy end use, it is the main driver of annual peak electric demand. Here, we present end of century building cooling electric demand projections for NYC using a high resolution (1 km) configuration of the Weather Research and Forecasting model coupled to a building energy model and forced by bias-corrected CESM1 global simulations. High resolution urban canopy parameters such as building height and plant area fraction derived from a public tax-lot level dataset are used as input to the urban physics parameterization. Cooling demand increases in RCP4.5 ranged between 1% and 20% across all days, with largest increases on days below 50th percentile demand. Results show that end of century building cooling demand on days below the 50th percentile may be up to 80% higher than the 2006–2010 period in the RCP8.5 scenario. The largest percent increases per unit area were found over less densely populated boroughs of Brooklyn, Queens, and Staten Island. Maximum summer cooling demand for the entire city is projected to increase between 5% and 27% for RCP4.5 and RCP8.5, respectively. Overall, analysis shows a close to 8% increase in cooling demand per 1 °C increase in temperature.

West African countries' energy and climate policies show a pronounced focus on decarbonising power supply through renewable electricity (RE) generation. In particular, most West African states explicitly focus on hybrid mixes of variable renewable power sources—solar, wind and hydropower—in their targets for the electricity sector. Hydropower, the main current RE resource in West Africa, is strongly sensitive to monsoon rainfall variability, which has led to power crises in the past. Therefore, solar and wind power could play a stronger role in the future as countries move to power systems with high shares of RE. Considering the policy focus on diversified RE portfolios, there is a strong need to provide climate services for assessing how these resources could function together in a power mix. In this study, climate data from the state-of-the-art ERA5 reanalysis is used to assess the synergies of solar photovoltaic (PV) and wind power potential in West Africa at hourly resolution. A new metric, the stability coefficient C_stab, is developed to quantify the synergies of solar PV and wind power for achieving a balanced power output and limiting storage needs. Using this metric, it is demonstrated that there is potential for exploiting hybrid solar/wind power in a larger area of West Africa, covering more important centers of population and closer to existing grid structures, than would be suggested by average maps of solar and wind resource availability or capacity factor for the region. The results of this study highlight why multi-scale temporal synergies of power mixes should be considered in RE system planning from the start.

This study, for the first time, investigates the historical changes of the water use in China's electric power sector on a regional level and quantifies the impacts of four factors that have influenced the remarkable changes: population, power production per capita, power plants' type and their cooling technology choice. From 2000 to 2015, water withdrawal and consumption in China's electric power sector, excluding hydropower, have increased from 40.75 and 1.25 billion m³, respectively, to 124.06 and 4.86 billion m³. As population growth in China has stabilized, population no longer provides an upward pressure on power production and the corresponding water use. On the contrary, power production per capita has played the most significant role contributing to 103.40 and 3.84 billion m³ of water withdrawal and consumption increases respectively, though the effect is now leveling off. The electric power sector's water use would have been much greater had it not been for changes in plant type and cooling water technology. Energy transformation to low-carbon sources has mitigated water withdrawals and consumption by 14.46 and 0.43 billion m³ respectively during the study period. This beneficial reduction in water use is a co-benefit of a series of policies primarily aimed to reduce carbon emissions and other air pollutants. Changing cooling technologies has offset 14.07 and 0.10 billion m³ of water withdrawal and consumption increases nationally, but the effects varied by region.

Green infrastructure, such as green roofs, is increasingly being used to reduce 'heat stresses' associated with urban heat island effects. This article discusses strategies to identify vulnerable neighborhoods in the City of Chicago, where green roofs could achieve multiple goals to mitigate urban heat-related challenges. Numerical simulations were performed using the urbanized version of the Advanced Research Weather Research and Forecasting model to predict rooftop temperatures, a representative variable for exposure in this study. The model was dynamically coupled with a physically-based green rooftop algorithm as a part of the urban parameterization within the model. Our approach integrates information from multiple sources: social vulnerability indices (a function of exposure, sensitivity, and adaptive capacity), high-resolution temperature simulations over the urban area, and observed electricity (air conditioning) consumption data. The social vulnerability indicators were used to develop a quantitative heat vulnerability index for Chicago. We found that an analysis of multiple drivers is needed to identify neighborhoods that will likely benefit from mitigation strategies like green roofs. Our case study identified a large number of census tracts in south and west Chicago, along with isolated tracts throughout the city that would strongly benefit from green roof implementation. The tools and methodology from this study can be easily adopted for other urban regions and would be informative for stakeholders and managers, in general, in making adaptation strategies for extreme heat management.

Egypt produces half of the 20 million tons of wheat that it consumes with irrigation and imports the other half. Egypt is also the world's largest importer of wheat. The population of Egypt is currently growing at 2.2% annually, and projections indicate that the demand for wheat will triple by the end of the century. Combining multi-crop and -climate models for different climate change scenarios with recent trends in technology, we estimated that future wheat yield will decline mostly from climate change, despite some yield improvements from new technologies. The growth stimulus from elevated atmospheric CO₂ will be overtaken by the negative impact of rising temperatures on crop growth and yield. An ongoing program to double the irrigated land area by 2035 in parallel with crop intensification could increase wheat production and make Egypt self-sufficient in the near future, but would be insufficient after 2040s, even with modest population growth. Additionally, the demand for irrigation will increase from 6 to 20 billion m³ for the expanded wheat production, but even more water is needed to account for irrigation efficiency and salt leaching (to a total of up to 29 billion m³). Supplying water for future irrigation and producing sufficient grain will remain challenges for Egypt.

Offshore wind power deployment has been concentrated in Europe, and remains limited in other areas of the world. Among the many challenges to deployment is the need to understand the value that offshore wind provides within electricity markets. This article develops a rigorous method to assess the economic value of offshore wind along the eastern coastline of the United States, seeking improved understanding of how the value of offshore wind varies both geographically and over time, and what has driven that variation. The article uses historical (2007–2016) weather data at thousands of potential offshore wind sites, combined with historical wholesale electricity market outcomes and renewable energy certificate (REC) prices at hundreds of possible transmission interconnection points. We find that the average historical market value of offshore wind from 2007 to 2016—considering energy, capacity, and RECs—varies significantly by project location, from $40/MWh to more than $110/MWh, and is highest for sites off of New York, Connecticut, Rhode Island, and Massachusetts. As energy and REC prices have fallen in recent years, so too has the market value of offshore wind. The historical value of offshore wind is found to exceed that of onshore wind, due to offshore wind sites being located more favorably in terms of constrained pricing points, and also due to a more-favorable temporal profile of electricity production. Cost reductions that approximate those witnessed recently in Europe may be needed for offshore wind to offer a credible economic value proposition on a widespread basis in the United States.

As global temperatures rise, drought-induced human relocation is expected to increase. Using original national survey data from Kenya, we investigate whether people who report relocating due to drought are more likely to be victims of violence than people who do not move. We also examine whether this migrant sample supports the use of violence at higher levels than the general population, conditional on their experiences. We measure the duration of relocation (temporary versus permanent) as well as the characteristics of the arrival area, including co-ethnic demographics. Controlling for many individual-level and contextual variables, we find that those who have relocated are consistently more likely to be victims of violence than those who have not. We also find that those who relocated temporarily support the use of violence at higher levels than the general population if and only if they are themselves victims of violence. Vulnerable migrant populations may be subject to violence as observational aggregate studies suggest, but they are not likely to be the sources of violence unless victimized first.

Amazonian rainfall plays a critical role in the global climate system and the hydrological cycle. It is thus important to quantify changes in the Amazonian rainfall and clarify its mechanism. Previous studies indicate that the interannual variability of Amazonian precipitation could be largely attributed to variabilities in the South American monsoon system and the El Niño Southern Oscillation. However, the trend of the wet season tropical Amazonian precipitation during recent decades is not very well investigated. In this study, by combining both satellite and in situ observations, it is revealed that tropical Amazonian precipitation has significantly increased by ∼180 to 600 mm (in different datasets) in the wet season during the satellite era from 1979 to 2015. We then use a state-of-the-art atmospheric model to simulate the impact of the tropical sea surface temperatures (SSTs) on the precipitation changes. Results show that the multidecadal warming of the tropical Atlantic has contributed more than half of this precipitation change over the past three decades, while the east Pacific cooling plays a secondary role. We finally combine the simulation results and the reanalysis data to investigate the mechanisms of this process, i.e. the SST variability dramatically increases the convergence of the moisture transport over the Amazon region. The precipitation changes over the Amazon region largely impact on the local hydrological cycle and the ecosystem, and have important impacts on the global climate system by mediating the teleconnection between the Pacific and the Atlantic oceans. Our results show that the long-term change in the wet season Amazonian precipitation is important and deserves further investigation and discussion.

Understanding how ecosystem vulnerability in response to climate change is generated and distributed is an important topic; however, quantitative assessments of the vulnerability process remain relatively rare. The Intergovernmental Panel on Climate Change (IPCC) regards ecosystem vulnerability as sensitivity or susceptibility to harm, lacking the capacity to cope and adapt. Through analysis of the concept of vulnerability, we propose a response-based quantitative method to assess ecosystem vulnerability, integrating the concepts of sensitivity and adaptability. This method was applied to assess ecosystem vulnerability in China from 1981 to 2050. The results indicated that vulnerability would develop in nearly 30% of the terrestrial ecosystems of China. Vulnerability would be severe in the grassland and desert ecosystems, distributed mainly in the Tianshan Mountain and the Inner Mongolia Plateau. As the effects of sensitivity and adaptability to temperature and precipitation differ, obvious regional differences exist between the ecosystem vulnerability zones in China. For example, the effects of climate warming would be severe in the northwest of the Loess Plateau, with the vulnerability caused mainly by high sensitivity to warming. However, the vulnerability in the southeastern part would be caused mainly by low adaptability to increasing precipitation. Compared with previous research, our method emphasizes the critical role of adaptability, which enhances the scientificity and reasonableness of assessing ecosystem vulnerability, and enriches the methodology adopted under the IPCC framework. However, as we did not consider fully the autonomous adaptation mechanism in ecosystem vulnerability, this aspect should be combined with other factors in future study.

Direct and indirect human impacts may be causing widespread vegetation changes African tropical dry forests (TDFs). This study provides the first field-based large-scale assessment of vegetation changes for the miombo region, using nation-wide re-measured permanent plots for the Republic of Zambia. Using path analysis, a technique used to describe and quantify causal relationships, we investigated the drivers of change for the 2006–2014 period, under different land-use and productivity trajectories. We assessed the change in vegetation metrics representing stand structure and tree diversity, identified causal factors for species richness, basal area, and productivity and compared the biomass change of different species. We assessed carbon emissions and absorptions from forestlands and used error propagation and sensitivity analysis to quantify uncertainty. Our results suggest that Zambia's TDFs are resilient in the face of human activities, with significant biomass gains observed in the re-measured plots over the country. However, the proximity to roads, fragmentation by other land uses, and to a lesser extent fire occurrence were found to negatively affect productivity. We found that biomass gains were concentrated in several dominant species, mostly belonging to a single subfamily of non-nodulating legumes (Fabaceae, subfamily Caesalpinioideae) characteristic of the region. Our results indicate that Zambia's TDFs have been acting as an overall carbon sink, despite large carbon emissions from land-cover change. Decline in biomass for certain dominant species signal a risk of over-exploitation. We also identified important differences in plant diversity and functional traits between miombo woodlands and other types of African savanna vegetation, signaling differences in ecological processes at play. These results illustrate the ecological complexity and diversity of Africa's vegetation, and caution against overgeneralizations of ecological processes in the context of global change and carbon management. Future research should focus on understanding the observed species-specific biomass gain and identifying its potential drivers.

In 2015, California established a mandate that requires on-road greenhouse gas (GHG) emissions to be reduced by 40% below 1990 levels by 2030. We explore the feasibility of meeting this goal by large-scale commercialization of drop-in biofuels. Drop-in biofuels, although not clearly defined, are a class of fuels that can be produced from biomass and blended with either crude oil or finished fuels without requiring equipment retrofits. This article focuses on thermochemical routes at or near commercialization. We provide a bottom-up, spatially explicit cost analysis to evaluate whether California can meet its 2030 GHG reduction target with drop-in fuels alone. A takeaway from our analysis is that drop-in fuels, if their performance is consistent with small-scale and simulated results, can be viable low-carbon substitutes for gasoline and diesel. We find that California can meet, and even exceed, its 2030 GHG emissions target for on-road vehicles with drop-in biofuels alone, but this requires use of biomass resources located outside the state. Meeting the 40% reduction target in a cost-effective manner requires pyrolysis of herbaceous agricultural residues (96% of total fuel output) and the conversion of woody residues via methanol-to-gasoline (4%). This scale of production would require 58 million metric tons of biomass feedstock, or 20% of total available biomass residues in the United States. For comparison, California is responsible for 11% of transportation-related petroleum consumption in the US. The approximately 5 billion gallons (19 billion liters) per year of drop-in fuel would displace 30% of gasoline and 60% of diesel demand in California. If electricity offset credits are eliminated, the target can be met with a similar scale of production, but methanol-to-gasoline becomes the dominant route (>99%), biomass requirements increase by 33%, and average production costs increase by 20%. Following this policy pathway would increase national biofuel production by 30% relative to 2015 production levels.

Many studies on drought consider precipitation and potential evapotranspiration (PET) impacts. However, catchment water retention is a factor affecting the interception of precipitation and slowing down runoff which also plays a critical role in determining the risks of hydrological drought. The Budyko framework links retention to the partitioning of precipitation into runoff or evapotranspiration. Applied worldwide, we demonstrate that retention changes are the dominant contribution to measured runoff changes in 21 of 33 major catchments. Similarly, assessing climate simulations for the historical period suggests that models substantially underestimate observed runoff changes due to unrepresented water management processes. Climate models show that water retention (without direct water management) generally decreases by the end of the 21st century, except in dry central Asia and northwestern China. Such decreases raise runoff, mainly driven by precipitation intensity increases (RCP4.5 scenario) and additionally by CO₂-induced stomata closure (RCP8.5). This mitigates runoff deficits (generally from raised PET under warming) by increasing global mean runoff from −2.77 mm yr⁻¹ to +3.81 mm yr⁻¹ (RCP4.5), and −6.98 mm yr⁻¹ to +5.11 mm yr⁻¹ (RCP8.5).

Observations show a significant positive correlation between the Atlantic Multidecadal Oscillation (AMO) and the Indian Summer Monsoon (ISM) over the past 100 years. Whether this connection is intrinsic to the climate system or caused by external forcing remains unclear in view of the substantial existence of anthropogenic greenhouse gases and aerosols in observations. Two state-of-the-art climate models (GFDL-CM3 and HadGEM2-ES), the historical simulations (1850–2005) of which show positive correlations between the AMO and ISM, similar to observation, are used to address this question. A significant positive AMO-ISM correlation exists in the control simulations with fixed preindustrial forcing with HadGEM2-ES, but not with GFDL-CM3. An in-depth analysis illustrates that the positive correlation in the HadGEM2-ES control run is more reasonable, since it simulates a similar teleconnection of the AMO with the North Pacific to that in both observations and previous studies. In comparison, the GFDL-CM3 control run fails to simulate the teleconnection of the AMO with the North Pacific. The positive AMO-ISM correlation in the historical simulation in GFDL-CM3 may be attributable to the role of the external forcing, since it is so strong that the AMO signals are excited additionally in the North Pacific. This study suggests that the AMO-ISM connection is intrinsic to the climate system, and highlights the crucial role played by the North Pacific in bridging such a connection.

The characteristics of tropical cyclones (TCs) and their response to climate change is an issue of broad concern. Based on the Power Dissipation Index (PDI) proposed by Emanuel in 2005, the destructiveness of TCs in the typhoon season (July–October) during the period 1979–2016 over the western North Pacific is investigated. Results show that a regime shift in the destructive potential of TCs took place around 1998. The destructive potential of TCs has a considerable increasing trend from 1998 to 2016 (the P2 period), mainly contributed by the average intensity of TCs (51.20% of PDI change). We find that the PDI of TCs is mainly regulated by the El Niño/Southern Oscillation cycle in whole study period, whereas the Pacific Decadal Oscillation pattern shows significant enhancement in P2, which acts as a more important constraint on the typhoon season PDI over the western North Pacific.

Health risk assessments for extreme heat and the design of corresponding interventions can be enhanced with more information regarding causal drivers of year-to-year variability in adverse outcomes. Summer 2016 was a record-setting year in terms of summer heat and its impacts on health in Maricopa County, Arizona, USA. The month of June was the warmest observed in the county and the six-month warm season spanning May through October was the fourth warmest. In the same year, a record number of heat-associated deaths was reported by the heat surveillance program run by the county health department. We analyzed the time series of heat-associated deaths to quantify the extent to which the unprecedented death count in 2016 was driven by anomalous weather. We first estimated the historical association between temperature and heat-associated deaths for the time period 2006–2015 using a time series regression model. Subsequently, we used the model to generate predictions of daily heat-associated deaths in 2016 based on the observed weather. We found no evidence that the unusually high number of heat-associated deaths observed in Maricopa County in 2016 was related to observed meteorological conditions. Regardless of the exposure variable or model parameterization chosen, the prediction for 2016 fell near or below the historical average number of heat-associated deaths. If the conventional methods for estimating the temperature–mortality association are reasonably approximating a causal relationship, factors other than the weather were mostly responsible for the surge in deaths in 2016. These findings highlight the importance of non-meteorological factors as drivers of temporal variability in the health burden associated with heat, which have generally not been included in quantitative retrospective or prospective studies. Further, they highlight a shortcoming in preparedness and response efforts for heat in the study setting that should be diagnosed and addressed as soon as possible.

Extreme climate events such as droughts and heat waves exert strong impacts on ecosystems and human well-being. Estimations of the risks of climate extremes typically focus on one variable in isolation. In this study, we present a method to examine the likelihood of concurrent extreme temperature and precipitation modes at the interannual scale, including compound cool/dry and cool/wet events during the cold season as well as compound hot/dry and hot/wet events during the warm season. A comparison of changes in the likelihood of such joint climate extremes was then conducted between the first (1961–1987) and second (1988–2014) halves of the full observed records. Our findings indicate a decrease in the occurrence probability for most concurrent modes over much of China, despite positive shifts found over southwestern and northeastern parts of China for the compound hot/dry events in the warm season. We further examined changes in likelihood related to these four compound climate extremes between the historical observed period (1961–2014) and the future period (2021–2080) based on climate model simulations with the RCP8.5 scenario. Our results show widespread increases in the occurrence probability for wintertime cool/dry and summertime hot/dry and hot/wet events over most parts of China but with different magnitudes, while much of China may experience declining likelihood of the wintertime cool/wet extremes in the future.

The South Pacific convergence zone (SPCZ) is a key component in the weather and climate system. By analogy to the intertropical convergence zone, the SPCZ is also part of the 'engine' for the tropical convection. There have been many studies about the tropical impacts on the SPCZ. Here, we show that the SPCZ, especially the precipitation in this region, is subject to the influence of South Pacific quadrapole (SPQ) in the subtropics via the mechanism of wind-evaporation-sea surface temperature feedback (SST). The anomalous winds (at 850 hPa) induced by the SST anomaly gradient produce low-level convergence and activate upward motion over the SPCZ region, ultimately leading to deep convection and enhanced precipitation there. As a result, the variability in the SPQ leads the changes in the SPCZ by about 5 months. Such extratropical impacts on the SPCZ are independent of the El Niño/Southern Oscillation, which has been demonstrated to have significant impacts on the SPCZ in existing studies. The process study unveils a new connection between the subtropics in the Southern Hemisphere and the tropics, which can potentially enhance predictive understanding of the SPCZ with obvious implications for the weather and climate system.

The forests of Kalimantan are under severe pressure from extensive land use activities dominated by logging, palm oil plantations, and peatland fires. To implement the forest moratorium for mitigating greenhouse gas emissions, Indonesia's government requires information on the carbon stored in forests, including intact, degraded, secondary, and peat swamp forests. We developed a hybrid approach of producing a wall-to-wall map of the aboveground biomass (AGB) of intact and degraded forests of Kalimantan at 1 ha grid cells by combining field inventory plots, airborne lidar samples, and satellite radar and optical imagery. More than 110 000 ha of lidar data were acquired to systematically capture variations of forest structure and more than 104 field plots to develop lidar-biomass models. The lidar measurements were converted into biomass using models developed for 66 439 ha of drylands and 44 250 ha of wetland forests. By combining the AGB map with the national land cover map, we found that 22.3 Mha (10⁶ ha) of forest remain on drylands ranging in biomass from 357.2 ± 12.3 Mgha⁻¹ in relatively intact forests to 134.2 ± 6.1 Mgha⁻¹ in severely degraded forests. The remaining peat swamp forests are heterogeneous in coverage and degradation level, extending over 3.62 Mha and having an average AGB of 211.8 ± 12.7 Mgha⁻¹. Emission factors calculated from aboveground biomass only suggest that the carbon storage potential of more than 15 Mha of degraded and secondary dryland forests will be about 1.1 PgC.

Globally, combinations of drought and warming are driving widespread tree mortality and crown dieback. Yet thresholds triggering either tree mortality or crown dieback remain uncertain, particularly with respect to two issues: (i) the degree to which heat waves, as an acute stress, can trigger mortality, and (ii) the degree to which chronic historical drought can have legacy effects on these processes. Using forest study sites in southwestern Australia that experienced dieback associated with a short-term drought with a heatwave (heatwave-compounded drought) in 2011 and span a gradient in long-term precipitation (LTP) change, we examined the potential for chronic historical drought to amplify tree mortality or crown dieback during a heatwave-compounded drought event for the dominant overstory species Eucalyptus marginata and Corymbia calophylla. We show pronounced legacy effects associated with chronically reduced LTP (1951–1980 versus 1981–2010) at the tree level in both study species. When comparing areas experiencing 7.0% and 11.5% decline in LTP, the probability of tree mortality increased from low (<0.10) to high (>0.55) in both species, and probability of crown dieback increased from high (0.74) to nearly complete (0.96) in E. marginata. Results from beta regression analysis at the stand-level confirmed tree-level results, illustrating a significant inverse relationship between LTP reduction and either tree mortality (F = 10.39, P = 0.0073) or dieback (F = 54.72, P < 0.0001). Our findings quantify chronic climate legacy effects during a well-documented tree mortality and crown dieback event that is specifically associated with an heatwave-compounded drought. Our results highlight how insights into both acute heatwave-compounded drought effects and chronic drought legacies need to be integrated into assessments of how drought and warming together trigger broad-scale tree mortality and crown dieback events.

With projections of increasing drought in the future, understanding how the natural carbon cycle responds to drought events is needed to predict the fate of the land carbon sink and future atmospheric CO₂ concentrations and climate. We quantified the impacts of the 2011 and 2012 droughts on terrestrial ecosystem carbon uptake anomalies over the contiguous US (CONUS) relative to non-drought years during 2010–2015 using satellite observations and the carbon monitoring system—flux inversion modeling framework. Soil moisture and temperature anomalies are good predictors of gross primary production anomalies (R² > 0.6) in summer but less so for net biosphere production (NBP) anomalies, reflecting different respiration responses. We showed that regional responses combine in complicated ways to produce the observed CONUS responses. Because of the compensating effect of the carbon flux anomalies between northern and southern CONUS in 2011 and between spring and summer in 2012, the annual NBP decreased by 0.10 ± 0.16 GtC in 2011, and increased by 0.10 ± 0.16 GtC in 2012 over CONUS, consistent with previous reported results. Over the 2011 and 2012 drought-impacted regions, the reductions in NBP were ∼40% of the regional annual fossil fuel emissions, underscoring the importance of quantifying natural carbon flux variability as part of an overall observing strategy. The NBP reductions over the 2011 and 2012 CONUS drought-impacted region were opposite to the global atmospheric CO₂ growth rate anomaly, implying that global atmospheric CO₂ growth rate is an offsetting effect between enhanced uptake and emission, and enhancing the understanding of regional carbon-cycle climate relationship is necessary to improve the projections of future climate.

In Tanzania, the majority of the rural population still relies on fuelwood as their major source of cooking energy. The adaptation measures of small-scale farmers in response to increasing fuelwood scarcity play a key role in altering the course of nutrition insecurity, environmental degradation, and economic instability. This study delivers a classification of coping strategies that does not exist in the literature. Furthermore, it analyses the adaptation measures applied by small-scale farmers in the semi-arid region of Dodoma district in response to fuelwood scarcity. A comparison between two case study sites provides information on the choice of adaptation measures by households. Overall, 28 coping strategies from 24 studies are identified, then differentiated into preventive and acute measures that are arranged into eight clusters. The classification is then used as a codebook to identify applied coping strategies at two case study sites. In total, 23 adaptation measures, including two strategies not cited in the literature, were identified through 39 household interviews. This suggests that the majority of coping strategies applied are independently from regional and social conditions. The majority of the strategies applied at the case study sites and described in the literature are acute measures that do not tackle the underlying problem triggering forest degradation. It is observed that the adaptation measures across the case study sites are widely congruent, thus showing that acute strategies are not replaced by preventive strategies but rather co-exist.

Ecological restoration has increased in prominence since the last century as an active way to reverse ecosystem deterioration derived from human interventions. The goal of this study was to assess the impact of restoration approaches on ecological and economic conditions of typical regions in the Qinghai-Tibetan Plateau. Data were collected using structured questionnaires delivered to 195 herders living in areas with average elevation above 3773 m. Land use maps, MODIS images, and government statistics were also used for the study. It was found that local herders have adopted five major approaches, i.e. enclosure, grazing prohibition, enclosure + deratization, enclosure + deratization + grass seeding, and enclosure + deratization + crop-forage cultivation + warm sheds, to ensure success of the restoration programs initiated by the government. The results show that vegetation coverage, especially for high and very high coverage grasslands, increased across the study sites and across approaches used, with a high grassland recovery rate observed in the areas where either grazing is prohibited or grassland management was dominated by integration approaches. Furthermore, households who employed integrated approaches tended to have more animals to rear, higher capability of resisting risks, and higher income than those who did not. These findings imply that balanced ecological and economic development is possible when appropriate management approaches are adopted. However, evaluation and monitoring of grassland conditions are needed to readjust restoration policy and associated approaches in a timely manner.

Globally, forest die-off from global-change-type drought events (hotter droughts) are of increasing concern, with effects reported from every forested continent. While implications of global-change-type drought events have been explored for above-ground vegetation, below-ground organisms have received less attention, despite their essential contributions to plant growth, survival, and ecosystem function. We investigated rhizosphere fungal communities in soils beneath trees affected by a global-change-type drought in a Mediterranean climate-type ecosystem in southwestern Australia, quantifying how fungal richness, composition and functional groups varied along a drought impact gradient. Following a forest die-off three years previously, we collected soils beneath dead and alive trees within forest exhibiting high, minimal and relatively unaffected levels of forest die-off. Rhizosphere fungal DNA was extracted from soils, amplified and subjected to high throughput sequencing. Fungal community composition varied significantly (P < 0.001) along the drought impact gradient with less richness in drought affected stands. There was some evidence of community differentiation between dead versus alive trees (P = 0.09), and no difference in rarefied richness and diversity. When considered by functional group, die-off-impacted plots had more arbuscular mycorrhizal fungi (AM) and saprotrophs, and fewer ectomycorrhizal fungi (ECM), compared with living trees from the unaffected plots. Further, within die-off plots, dead versus alive tree rhizosphere samples contained more AM, saprotrophs and pathogens, and fewer ECM. Disruptions to rhizosphere fungal communities, such as altered functional groups, can have implications for ecosystem persistence and function, particularly in regions projected to experience increased global-change-type drought events.

Spanning a vast territory of approximately 13 million km², Asian Russia was home to 38 million people in 2016. In an effort to synthesize data and knowledge regarding urbanization and sustainable development in Asian Russia in the context of socioeconomic transformation following the breakup of the Soviet Union in 1990, we quantified the spatiotemporal changes of urban dynamics using satellite imagery and explored the interrelationships between urbanization and sustainability. We then developed a sustainability index, complemented with structural equation modeling, for a comprehensive analysis of their dynamics. We chose six case cities, i.e., Yekaterinburg, Novosibirsk, Krasnoyarsk, Omsk, Irkutsk, and Khabarovsk, as representatives of large cities to investigate whether large cities are in sync with the region in terms of population dynamics, urbanization, and sustainability. Our major findings include the following. First, Asian Russia experienced enhanced economic growth despite the declining population. Furthermore, our case cities showed a general positive trend for population dynamics and urbanization as all except Irkutsk experienced population increases and all expanded their urban built-up areas, ranging from 13% to 16% from 1990 to 2014. Second, Asian Russia and its three federal districts have improved their sustainability and levels of economic development, environmental conditions, and social development. Although both regional sustainability and economic development experienced a serious dip in the 1990s, environmental conditions and social development continuously improved from 1990 to 2014, with social development particularly improving after 1995. Third, in terms of the relationships between urbanization and sustainability, economic development appeared as an important driver of urbanization, social development, and environmental degradation in Asian Russia, with economic development having a stronger influence on urbanization than on social development or environmental degradation.

This study focuses on the assessment of forest cover and disturbance changes in the heavily polluted Ore Mountains (Czechia, Central Europe) during the second half of the 20th century and onward. It analyzes the driving forces of forest changes with reference to environmental, societal and political development in the region. Anthropogenic air pollution, prevalently SO₂ from adjacent coal-burning industry, caused extensive forest decline, especially between the 1970s and 1980s. The most affected tree species was the main economical timber species, Norway spruce, which proved to be remarkably pollution-sensitive. We used Landsat time series, and a combination of an integrated forest Z-score and Disturbance Index (DI), to analyze the forest cover change and disturbance development during 1985–2016. In 1994, the forest cover reached its minimum there. The breakdown of communism in the 1990s implied fulfilling EU pollution standards via air protection regulations, investment in power plant desulphurization, and forest management measures, which were the main drivers of the forest recovery. The forest recovery continued till about 2005; however, fluctuations in forest cover and DI have continued during the last decade. Apparently, forests weakened by old loads are prone to new stress factors. Landsat time series represent a powerful data source to monitor the impact of these drivers on forests on a regional scale. Originally, the severely damaged eastern part with heavier acidic load and large forest decline recovered faster after remarkable lowering of air pollution loads compared to the western part, with lower loads and less damaged forests. However, the interactions of persisting driving forces (soil acidification, adverse meteorological events, climate change factors, air pollution, tree species composition and physiological state, pest outbreaks) still threaten the forests there, which remain moderately damaged in both parts of the Ore Mountains. This may lead to unpredictable forest development independently of societal and political driving forces.