Assessing potential impacts of climatic change on subalpine forests on the eastern Tibetan Plateau

Forest gap models have been used widely in the study of forest dynamics, including predicting long-term succession patterns and assessing the potential impacts of climate change on forest structure and composition. However, little effort is devoted to predict forest dynamics in the high elevation areas, although they have the sensitive response to global climate change. In the present study, based on a modified height-diameter function, we developed a new version (FAREAST-GFSM) of the forest patch model, FAREAST for simulating the changes of subalpine forests. The observed data from the Gongga Mt. Alpine Station were also used to test model precision. With the improved performance of FAREAST-GFSM, we explored the impact of three warming scenarios on subalpine forest on the eastern Tibetan plateau within a 100-year period. The study result indicates that the effects of climate change were evident on subalpine forests in the high elevation areas. The response of different species to the warming climate might eventually transform the subalpine Abies fabric forest into Betula utilis forest similar to that which is now widely distributed in the eastern Tibetan Plateau mountainous areas with the relatively lower elevation. Subalpine forests could move to higher and colder areas, which are currently tundra.     

Assessing impacts of climate change on forests: The state of biological modeling

Models that address the impacts of climate change on forests are reviewed at four levels of biological organization: global, regional or landscape, community, and tree. The models are compared for their ability to assess changes in fluxes of biogenic greenhouse gases, land use, patterns of forest type or species composition, forest resource productivity, forest health, biodiversity, and wildlife habitat. No one model can address all of these impacts, but landscape transition models and regional vegetation and land-use models have been used to consider more impacts than the other models. The development of landscape vegetation dynamics models of functional groups is suggested as a means to integrate the theory of both landscape ecology and individual tree responses to climate change. Risk assessment methodologies can be adapted to deal with the impacts of climate change at various spatial and temporal scales. Four areas of research needing additional effort are identified: (1) linking socioeconomic and ecologic models; (2) interfacing forest models at different scales; (3) obtaining data on susceptibility of trees and forest to changes in climate and disturbance regimes; and (4) relating information from different scales.The U.S. Government right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.Managed by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy under contract DE-AC05-84OR21400.     

A global assessment of the human pressure on the world's lakes

Millions of humans across the globe depend on lakes for numerous ecosystem services. Furthermore, humans use lakes as a food source and for a multitude of economic activities. Lakes are also essential to a plethora of taxa that rely on them for survival. Yet, despite the importance of lakes, we still lack an assessment of the extent lakes worldwide are being influenced by anthropogenic activities. In this study, I use the global database of lakes, the human footprint index from 1993 and 2009, and the more recent human modification index to measure the human pressure on the world's lakes. I found that one-third of the lakes are under considerable pressure. However, during the 16-year period examined, human pressure had increased in only 16% of the lakes, while it remained unchanged in 66%, and has even decreased in 18%. These patterns, though, were not uniform across the globe. Many lakes within tropical and subtropical regions, particularly in Africa—but also in South America and Asia—experienced sizeable increases in human pressure. Moreover, the percentage of lakes within Key Biodiversity Areas in which the human pressure had increased was three times larger the overall number. Although increases in human pressure were lower in lakes within protected areas—compared to lakes outside—there were numerous exceptions, particularly in the tropics. To protect biodiverse lakes in regions where human pressure is intensifying, it is important to improve the effectiveness of the protected areas and to address the socioeconomic factors driving the increases in human pressure.     

Estimating the world's potentially available cropland using a bottom-up approach

Previous estimates of the land area available for future cropland expansion relied on global-scale climate, soil and terrain data. They did not include a range of constraints and tradeoffs associated with land conversion. As a result, estimates of the global land reserve have been high. Here we adjust these estimates for the aforementioned constraints and tradeoffs. We define potentially available cropland as the moderately to highly productive land that could be used in the coming years for rainfed farming, with low to moderate capital investments, and that is not under intact mature forests, legally protected, or already intensively managed. This productive land is underutilized rather than unused as it has ecological or social functions. We also define potentially available cropland that accounts for trade-offs between gains in agricultural production and losses in ecosystem and social services from intensified agriculture, to include only the potentially available cropland that would entail low ecological and social costs with conversion to cropland. In contrast to previous studies, we adopt a “bottom-up” approach by analyzing detailed, fine scale observations with expert knowledge for six countries or regions that are often assumed to include most of potentially available cropland. We conclude first that there is substantially less potential additional cropland than is generally assumed once constraints and trade offs are taken into account, and secondly that converting land is always associated with significant social and ecological costs. Future expansion of agricultural production will encounter a complex landscape of competing demands and tradeoffs.     

面雨量计算方法及其在海河流域的应用

基于1961—2018年汉江流域57个国家气象站日降水观测资料,利用线性倾向估计、滑动平均等方法研究了汉江流域5个子流域极端面雨量时空分布特征,并对年最大极端面雨量（P_max）的重现期进行了拟合,结果表明：（1）汉江流域的年极端面雨量日数（D）与年极端5 d累积面雨量日数（D_5d）年均分布从上游向下游逐渐减少,年极端面雨量（R）与年极端5 d累积面雨量强度（I_5d）表现为两头多、中间少。（2）D和R年均分布在石泉以上、石泉安康和丹皇区间表现出一定的正相关,在安康丹江口和皇庄以下子流域表现出一定的反相关。（3）D、R、D_5d、I_5d等年代际分布特征较为相似,石泉以上、石泉安康、安康丹江口3个子流域呈双峰分布,皇庄以下子流域呈单峰分布,丹皇区间年代际特征不明显。（4）汉江各子流域D、R、D_5d、I_5d与年最大极端面雨量（P_max）等指数峰（谷）值出现的时间重叠性较高,表明同一子流域强降水发生频次较高（低）的年份,降水的持续性和极端性均相对较高（低）,但同一年所有子流域出现持续性极端降水事件的概率不大。（5）汉江流域P_max呈逐年增大趋势。重现期在50 a以前P_max增速较快,之后增速变缓。皇庄以下子流域不同重现期内P_max及其增幅最强。

     

2021年\

2021年,我国天气形势复杂,气候异常性显著,极端事件频发。本文简要回顾了我国主汛期和华西秋雨的异常性特征,并对河南和湖北4次高影响天气过程展开了初步分析。结果表明：(1)2021年4—10月全国平均降水较常年同期偏多7.8%,其中河南、河北和山西等部分地区偏多1倍以上。(2) 在外强迫因子“拉尼娜”异常海温的影响下,副热带高压外围水汽和北方冷空气异常活跃,导致华西秋雨降水量打破1961年以来历史记录。(3) 河南“21.7”特大暴雨发生在台风、低涡、切变线和辐合线共同作用的背景下,大量来自西北太平洋的水汽,在低空急流与边界层急流耦合、地形的动力阻挡抬升和热力抬升共同作用下,强降水雨带出现在山前。(4) 在有利的多尺度环流背景下,地形与低层风场辐合带的相互作用触发了对流,并使得降水维持在狭长山谷地形区域内,引发随州“8.12”极端强降水。(5)中γ尺度的强对流单体的合并加强导致了武汉两次对流大风事件,中层突然增强的水平风引发了下沉运动,下落后造成地面局地强冷池和地面极值大风。

     

Securing the climate benefits of stable forests

Stable forests – those not already significantly disturbed nor facing predictable near-future risks of anthropogenic disturbance – may play a large role in the climate solution, due to their carbon sequestration and storage capabilities. Their importance is recognized by the Paris Agreement, but stable forests have received comparatively little attention through existing forest protection mechanisms and finance. Instead, emphasis has been placed on targeting locations where deforestation and forest degradation are happening actively. Yet stopping deforestation and forest degradation does not guarantee durable success, especially outside the geographic scope of targeted efforts. As a result, today’s stable forests may be at risk without additional efforts to secure their long-term conservation.

We synthesize the gaps in existing policy efforts that could address the climate-related benefits derived from stable forests, noting several barriers to action, such as uncertainty around the level of climate services that stable forests provide and difficulties describing the real level of threat posed. We argue that resource and finance allocation for stable forests should be incorporated into countries’ and donors’ comprehensive portfolios aimed at tackling deforestation and forest degradation as well as resulting emissions. A holistic and forward-looking approach will be particularly important, given that success in tackling deforestation and forest degradation where it is currently happening will need to be sustained in the long term.

Key policy insights

• Climate policies, finance, and implementation have tended to focus on areas of recent forest loss and near-term threats of anthropogenic disturbance, resulting in an imbalance of effort that fails to adequately address stable forests.

• In some contexts, policy measuresintended to secure the climate-related benefits of stable forests have competed poorly against more urgent threats. Policymakers and finance mechanisms should view stable forests as a complementary element within a holistic, long-term approach to resource management.

• International mechanisms and national frameworks should be adjusted and resourced to promote the long-term sustainability and permanence of stable forests.

• Beyond additional resources, the climate benefits of stable forests may be best secured by pro-actively designing implementing policies that recognize the rights and interests of stakeholders who are affected by land management decisions.

     

中国区域逐日融合降水数据集与国际降水产品的对比评估

中国国家气象信息中心基于2400多个国家级台站观测日降水量和CMORPH卫星反演降水产品,采用概率密度匹配和最优插值相结合的两步数据融合方法,研制了中国区域1998年以来的0.25°×0.25°分辨率的逐日融合降水产品(CMPA_Daily)。通过该数据集与广泛应用于中国天气气候领域的两种国际上降水融合产品TRMM 3B42(Tropical Rainfall Measuring Mission, 3B42)和GPCP(Global Precipitation Climatology Project, 1 degree daily)的对比评估,考察CMPA_Daily产品的质量,评价其能否合理体现中国降水的天气气候特征。首先利用2008—2010年5—9月独立检验数据定量对比了CMPA_Daily、TRMM 3B42和GPCP 三种降水产品的误差,结果表明,在误差的时间变化和空间分布上,CMPA_Daily均具有最高的相关系数和最小的平均偏差及均方根误差,TRMM 3B42其次,GPCP的误差相对较大。CMPA_Daily只低估了大暴雨,TRMM 3B42低估了大雨以上量级的降水,而GPCP低估了除小雨以外的所有降水。CMPA_Daily产品因融入了更多的站点观测信息,不论在中国东部沿海,还是中西部地形复杂区,其精度均优于TRMM 3B42和GPCP产品,即使在站点稀疏的青藏高原地区,CMPA_Daily降水量也更加接近站点观测,呈现明显的高相关。CMPA_Daily与独立检验数据的高相关在地形起伏时效果也较稳定,TRMM和GPCP的相关系数则随着地形变化幅度陡变而非常明显地降低。进一步通过对比分析各降水产品1998—2012年的气候平均降水特征表明,3种资料对中国区域气候平均降水量、降水强度、频率分布以及年际变化的总体描述基本一致,因有效融入了更多的中国站点观测信息,不论降水空间分布还是降水量,CMPA_Daily与地面观测均最为接近,在中国的中东部大部分地区对降水的估计精度明显更高,而在站点分布较稀疏的青藏高原地区,CMPA_Daily的降水分布型与TRMM、GPCP卫星融合资料类似,较地面站点插值产品更能体现出合理的降水分布。对中国强降水事件监测对比表明,CMPA_Daily产品可以更加准确地描述降水的强度变化,细致刻画降水空间分布,在把握降水小尺度特征上具有明显的优势,体现出高分辨率、高精度降水产品的特点。     

Harvesting in boreal forests and the biofuel carbon debt

Owing to the extensive critique of food-crop-based biofuels, attention has turned toward second-generation wood-based biofuels. A question is therefore whether timber taken from the vast boreal forests on an increasing scale should serve as a source of wood-based biofuels and whether this will be effective climate policy. In a typical boreal forest, it takes 70–120 years before a stand of trees is mature. When this time lag and the dynamics of boreal forests more generally are taken into account, it follows that a high level of harvest means that the carbon stock in the forest stabilizes at a lower level. Therefore, wood harvesting is not a carbon-neutral activity. Through model simulations, it is estimated that an increased harvest of a boreal forest will create a biofuel carbon debt that takes 190–340 years to repay. The length of the payback time is sensitive to the type of fossil fuels that wood energy replaces     

Assessing integrated assessments

Integrated assessment of global environmental change is a relatively new field that is beginning to define itself and its forms of practice. As yet, the field has not grappled directly with issues of quality control and assessment of quality, and this work is a first attempt in that direction. We argue that if integrated assessment is to be successful in the long run, then building and maintaining credibility via quality control procedures is a necessary condition for realizing its potential. We highlight a number of pitfalls in the practice of integrated assessment, and discuss their causes. We buttress our concerns using examples from both within climate change integrated assessment, and from the history of other similar endeavors. We also provide a number of suggestions that we hope will serve to alleviate some of these pitfalls. For instance, tools, methods, and assumptions from disciplines form archetypes for components in integrated assessment models, and we need to apply greater scrutiny to these archetypes. Further, tools which may be reasonable to use in particular disciplinary, geographical, or temporal contexts may be unsuited to the broader contexts inherent in integrated assessment studies of global environmental change.     

Tropical forests and the greenhouse effect: A management response

The buildup of carbon dioxide in the global atmosphere represents one of the principal causes of the greenhouse effect that is overtaking the Earth's climatic systems and that threatens salient sectors of economic development in both the developed and developing worlds. A management response appears to offer substantial scope to counter the buildup of carbon dioxide, even though it has been little addressed in systematic fashion. It is a massive tree-planting programme in the humid tropics. Tree plantations absorb carbon dioxide from the atmosphere, and the humid tropics with year-round warmth and moisture are by far the best place for fast-growing tree plantations. Reforestation on a suitable scale in the humid tropics - accompanied of course by measures to halt deforestation - could eventually serve to sequester carbon in amounts significant for our efforts to counter the greenhouse effect.     

Simulating the effects of climate changes on Eastern Eurasia forests

The extensive forests of Eastern Eurasia cover an area of ca. 6 million km². The FAREAST model, a forest gap model that simulates the stand composition and dynamics of Eastern Eurasian forests under the current climate, was used to simulate the responses of the Eastern Eurasia Forests to the climate change. Two different scenarios of possible future climatic change were obtained from the IPCC (2001) report (CMIP2 and IS92a-GS) and were used as input to the FAREAST model to determine the compositional and structural sensitivity to climate changes for several locations and along montane elevation gradients. The simulation results suggest that, under the influence of the conditions in the two climate-change scenarios, the underlying forest dynamics should be quite different. Further, Eastern Eurasian forests maintain currents forest structure and biomass only within a small range of climate change. Broad-leaved deciduous trees of such genera as Fraxinus, Quercus and Tilia increase their ranges over Eastern Eurasia under the climate-change scenarios. Conifers, such as Larix and Picea, decrease sharply under climate change and the area of their distributions are reduced. The overall biomass of Pinus is not decreased over the region. While the Pinus distribution range shifts, the area associated with the range of the taxa is not changed.     

Ungulate herbivory modifies the effects of climate change on mountain forests

Recent temperature observations suggest a general warming trend that may be causing the range of tree species to shift to higher latitudes and altitudes. Since biotic interactions such as herbivory can change tree species composition, it is important to understand their contribution to vegetation changes triggered by climate change. To investigate the response of forests to climate change and herbivory by wild ungulates, we used the forest gap model ForClim v2.9.6 and simulated forest development in three climatically different valleys in the Swiss Alps. We used altitudinal transects on contrasting slopes covering a wide range of forest types from the cold (upper) to the dry (lower) treeline. This allowed us to investigate (1) altitudinal range shifts in response to climate change, (2) the consequences for tree species composition, and (3) the combined effect of climate change and ungulate herbivory. We found that ungulate herbivory changed species composition and that both basal area and stem numbers decreased with increasing herbivory intensity. Tree species responded differently to the change in climate, and their ranges did not change concurrently, thus causing a succession to new stand types. While climate change partially compensated for the reductions in basal area caused by ungulate herbivory, the combined effect of these two agents on the mix of the dominant species and forest type was non-compensatory, as browsing selectively excluded species from establishing or reaching dominance and altered competition patterns, particularly for light. We conclude that there is an urgent need for adaptive forest management strategies that address the joint effects of climate change and ungulate herbivory.     

Estimates of monoterpene and isoprene emissions from the forests in Switzerland

Emission rates of biogenic volatile organic compounds emitted by the forests were estimated for five geographical regions as well as for all Switzerland. Monoterpene and isoprene emissions rates were calculated for each main tree species separately using the relevant parameters such as temperature, light intensity and leaf biomass density. Biogenic emissions from the forests were found to be about 23% of the total annual VOC emissions (anthropogenic and biogenic) in Switzerland. The highest emissions are in July and lowest in January. Calculations showed that the coniferous trees are the main sources of the biogenic emissions. The major contribution comes from the Norway spruce (picea abies) forests due to their abundance and high leaf biomass density. Although broad-leaved forests cover 27% of all the forests in Switzerland, their contribution to the biogenic emissions is only 3%. Monoterpenes are the main species emitted, whereas only 3% is released as isoprene. The highest emission rates of biogenic VOC are estimated to be in the region of the Alps which has the largest forest coverage in Switzerland and the major part of these forests consists of Norway spruce. The total annual biogenic VOC emission rate of 87 ktonnes y^–1 coming from the forests is significantly higher than those from other studies where calculations were carried out by classifying the forests as deciduous and coniferous. The difference is attributed to the high leaf biomass densities of Norway spruce and fir (abies alba) trees which have a strong effect on the results when speciation of trees is taken into account. Besides the annual rate, emission rates were calculated for a specific period during July 4–6, 1991 when a photochemical smog episode was investigated in the Swiss field experiment POLLUMET. Emission rates estimated for that period agree well with those calculated for July using the average temperatures over the last 10 years.     

Assessing the value of price caps and floors

This article assesses the long-term economic and climatic effects of introducing price caps and price floors in hypothetical global climate change mitigation policy. Based on emission trends, abatement costs and equilibrium climate sensitivity from IPCC and IEA reports, this quantitative analysis confirms that price caps could significantly reduce economic uncertainty. This uncertainty stems primarily from unpredictable economic growth and energy prices, and ultimately unabated emission trends. In addition, the development of abatement technologies is uncertain. Furthermore, this analysis shows that rigid targets may entail greater economic risks with little or no comparative advantage for the climate. More ambitious emission objectives, combined with price caps and price floors, could still entail significantly lower expected costs while driving similar, or even slightly better, climatic outcomes in probabilistic terms.     

Psychrometric apparatus for Bowen-ratio determination over forests

The psychrometric apparatus design for Bowen ratio determination reported previously by Sargeant and Tanner was modified and a new apparatus built. Modification of the intake design improved the symmetry and rigidity of the sensor mounting. Wet- and dry-bulb differences were measured with an error less than 0.01 °C over a vertical distance of 1 m. Continuous measurements of the Bowen ratio over a 7.8-m Douglas fir forest were made for 6 weeks. An example of the energy balance for the forest for one day using this equipment is reported.     

Assessing geochemical carbon management

The challenge of reversing rising atmospheric CO₂ concentrations is growing with the continued expansion of CO₂-emitting energy infrastructure throughout the world and with the lack of coordinated, effective measures to manage and reduce emissions. Given this situation, it is prudent for society to explore all potential carbon management options, including those with seemingly low probability for success. Recent initiatives for advancing and enhancing carbon storage options have focused primarily on the physical trapping of CO₂ in underground geologic formations and on the biological uptake of CO₂; less attention has been given to approaches that rely primarily on geochemical reactions that enhance transformation of CO₂ gas into dissolved or solid phase carbon by liberating cations to neutralize carbonic acid. This paper provides a structured review of the technical status of these geochemical approaches, and also presents a simple framework for assessing the potential and limitations of various proposed geochemical approaches to assist prioritizing future research in this area. Despite major limitations, geochemical approaches have unique potential to contribute to CO₂ reductions in ways that neither physical nor biological carbon storage can by allowing for the direct removal of CO₂ from the atmosphere with minimal requirements for integrating with existing infrastructure. Recognizing the severity and urgency of the need for carbon management options, we argue for an increase in research activity related to geochemical approaches to carbon management.     

Assessing climate change impacts in the European north

Global climate change and its regional manifestation will result in significant impacts in the European North. However, in order to determine the consequences of such impacts, a holistic, integrated assessment is needed. This paper sets the stage for the remainder of this volume by describing an attempt to derive such an assessment for the Barents Sea Region through the EU-funded BALANCE project. The paper explains some of the major methodologies employed in the study. It also provides insight into major results obtained and attempts to answer a number of overarching questions. It will be shown that climate change does present a significant threat to environmental and societal integrity in the study region. However, it will also be shown that stakeholders regard other drivers of future changes (economical, political developments) at least as equally important for their personal lives.     

A global estimate of carbon stored in the world's mountain grasslands and shrublands,and the implications for climate policy

Carbon market and climate finance schemes (e.g. the CDM, REDD+ and the Green Climate Fund) are being investigated for their ability to achieve enhanced sustainability outcomes in terrestrial forests, lowland grasslands and marine ecosystems, all which store large amounts of carbon (C). To date however climate policy discourse has largely overlooked the conservation of existing C stored in mountain grasslands and shrublands. These ecosystems provide critical ecological goods and services to humanity yet are increasingly at risk from anthropogenic stressors including agricultural intensification, mining and climate change. The absence of a global estimate for these C stocks is likely to be one reason for their exclusion from climate change policy discussions, both on a political and scientific basis. This represents a missed opportunity in two respects: firstly, by conserving and restoring existing C stocks the impacts of climate change can be lessened; and secondly, carbon finance and climate finance might provide the necessary financial support to address the aforementioned stressors. In this paper we use spatial analysis and estimate there to be between 60.5 Pg C and 82.8 Pg of C contained within biomass and soils of the world's mountain grasslands and shrublands. To put this in perspective, globally tropical Savannas and grasslands, temperate forests and tropical peatlands are estimated to contain 326–330 Pg C, 159–292 Pg C and 88.6 Pg C respectively. Our review of existing empirical studies and of United Nations Framework Convention on Climate Change (UNFCCC) national greenhouse accounts suggests that this C is not reliably accounted for in international carbon budgets. Our estimate is the first to provide a global point of reference, useful in developing future research and in climate policy discussions. We conclude by briefly discussing how climate finance might be leveraged to support the sustainable management of these C stocks, and in so doing uphold the other important socioeconomic benefits provided to humanity.