Historical evidence and climatic implications of a shift in the boreal forest tundra transition in central Canada

The line that marks the boundary between the boreal forest and the tundra regions is a relatively abrupt line in central Canada and appears to reflect a clearly defined climate boundary. Research suggests that relatively small changes in the climatic conditions should result in a movement of the treeline. Such a movement was apparently reported in 1772 by Samuel Hearne based upon the observations of generations of Indians who had lived in the area. A map of his voyages indicates a tree limit that was further west in the north/south section of western Canada and further south in the east/west section of central Canada. This location and subsequent movement appears to be logical in relation to the climatic conditions that occurred in the region as a result of the Little Ice Age and the warmer conditions thereafter.     

Possible impacts of climatic warming scenarios on water resources in the Saskatchewan River Sub-basin,Canada

Regional scale studies of the impacts of global warming scenarios provide a useful mechanism for identifying potential regional sensitivities, data gaps and research needs, and for raising awareness of the global warming issue at the regional level. Thus, a pilot study of water resources in the Saskatchewan River Sub-basin was undertaken in order to provide first-cut estimates of impacts in this region, and to identify future research needs. Thirty scenarios were constructed, using two hypothetical growth rates for irrigation, five scenarios based on outputs from General Circulation Models (GCMs), and ten hypothetical warming scenarios. During the course of this study, a number of methodological questions were raised, including the representativeness of data points, interpolation of observed and scenario data, and the quantification of uncertainty.Results indicated decreases in summer soil moisture and increases in irrigation demand, but no consensus on changes in runoff or annual net basin supply, primarily due to differences in the GCM-based scenario output at the Rocky Mountains, the major source region for runoff. There were a number of recommendations for follow-up research and monitoring.     

Climatic variation and trends in the boreal forest region of Western Canada

Long-term climatic trends were studied for the boreal forest region of western Canada. Mean monthly and annual temperature and precipitation data obtained between 1872 and 1981 were analyzed for the three subregions (forestgrassland, predominantly forest, and forest-tundra). Highly significant differences (P < 0.01) were detected in the mean monthly temperature among the subregions for each month, and similar differences were found for most of the months for precipitation. Long-term records showed statistically highly significant slightly increasing temperature and precipitation trends for the economically important predominantly forest subregion.     

Modeling land surface phenology in a mixed temperate forest using MODIS measurements of leaf area index and land surface temperature

The development of satellite-derived vegetation indices and metrics has enabled researchers to monitor land surface phenology (LSP). While the use of satellite data to monitor LSP is prevalent, there has been minimal effort to model LSP in temperate climates using satellite observations of the land surface. Satellite-derived LSP models are beneficial for studying past and future changes in phenology and related ecosystem processes (e.g., water, energy, and carbon fluxes). The purpose of this study was to model LSP during the spring in a mixed temperate forest using satellite-derived measurements of leaf area index (LAI) and land surface temperature (LST). As part of the model validation process, the use of LST as a proxy for air temperature to model LSP was also investigated. The results indicate that LST derived from the MODIS Terra sensor at 10:30?a.m. (local solar time) can be used to develop a LSP model that predicts the full profile of LAI from winter dormancy to maturity and the date when LAI reaches half of the annual maximum (LAI_50%) with relatively low error. In addition, the modeled LAI values closely tracked in situ observations of the phenological development of the dominant deciduous tree species located in the study area where the model was developed. A comparison of LST and daily maximum air temperature at two levels above the ground surface revealed distinct differences and nonlinearities in the relationship between these two variables. However, accumulated growing degree-days calculated from each of these variables were similar because the largest differences between LST and daily maximum air temperature occurred prior to the beginning of heat accumulation. Consequently, the model predictions of LAI_50% derived from the use of LST and daily maximum air temperature were similar. When the developed model was applied in two other mixed forests, the errors were larger due to substantial interannual variability in the relationship between LAI and heat accumulation and systematic differences in this relationship between sites. Although the model cannot be successfully applied in these other mixed forests, the ability of the model to capture a consistent relationship between satellite estimates of LAI and LST in the study area where it was developed demonstrates that satellite observations of the land surface can be used in certain locations to create LSP phenology models. When validated, the models can be used to examine past and future changes in phenology and related ecosystem processes.     

Impact of enhanced forest conditions on land surface characteristics over central India using LIS

Theoretical and Applied Climatology - Both runoff and rainfall do not happen at the same time and there is a certain lag in time. The length of lag time and lagged intensity are greatly affected by...     

Evaluating the impacts of land use and land cover changes on surface air temperature using the WRF-mosaic approach

如何量化土地利用/覆盖变化(LUCC)对区域气候的影响,是人类活动影响气候变化研究中的一个难点。本文利用卫星遥感反映过去三十年东亚区域土地利用变化数据,基于Mosaic近似考虑土地利用及其变化次网格尺度过程,量化了LUCC对地表辐射收支及气温的影响。过去三十年土地利用/覆盖变化对东亚区域总体呈降温效应(中国东部地区增温效应),LUCC导致的地表反照率变化影响地表辐射收支,中国和东亚区域的辐射强迫分别为-0.56 W m~(-2)和-0.50 W m~(-2)。     

土壤热异常影响地表能量平衡的个例分析和数值模拟

The statistical relationship between soil thermal anomaly and short-term climate change is presented based on a typical case study. Furthermore, possible physical mechanisms behind the relationship are revealed through using an off-line land surface model with a reasonable soil thermal forcing at the bottom of the soil layer.In the first experiment, the given heat flux is 5 W m-2 at the bottom of the soil layer (in depth of 6.3 m)for 3 months, while only a positive ground temperature anomaly of 0.06℃ can be found compared to the control run. The anomaly, however, could reach 0.65℃ if the soil thermal conductivity was one order of magnitude larger. It could be even as large as 0.81℃ assuming the heat flux at bottom is 10 W m-2. Meanwhile, an increase of about 10 W m-2 was detected both for heat flux in soil and sensible heat on land surface, which is not neglectable to the short-term climate change. The results show that considerable response in land surface energy budget could be expected when the soil thermal forcing reaches a certain spatial-tem poral scale. Therefore, land surface models should not ignore the upward heat flux from the bottom of the soil layer. Moreover, integration for a longer period of time and coupled land-atmosphere model are also necessary for the better understanding of this issue.     

Flow-distortion effects on scalar flux measurements in the surface layer: Implications for sensor design

Scalar fluxes measured through the eddy-correlation technique are prone to two types of errors caused by the sensor-induced flow distortion: those due to crosstalk from the horizontal flux, and those due to amplification or attenuation due to flow blocking. We show that the crosstalk error can be eliminated by designing the sensor array to be vertically symmetric about its horizontal midplane. In such an array, the flow-blocking effect causes the scalar flux to be overestimated, but this error can be made negligible by designing an array with minimal stagnation loss in streamwise speed at the flux-measurement point.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

GPCC's new land surface precipitation climatology based on quality-controlled in situ data and its role in quantifying the global water cycle

In 1989, the need for reliable gridded land surface precipitation data sets, in view of the large uncertainties in the assessment of the global energy and water cycle, has led to the establishment of the Global Precipitation Climatology Centre (GPCC) at Deutscher Wetterdienst on invitation of the WMO. The GPCC has calculated a precipitation climatology for the global land areas for the target period 1951–2000 by objective analysis of climatological normals of about 67,200 rain gauge stations from its data base. GPCC's new precipitation climatology is compared to several other station-based precipitation climatologies as well as to precipitation climatologies derived from the GPCP V2.2 data set and from ECMWF's model reanalyses ERA-40 and ERA-Interim. Finally, how GPCC's best estimate for terrestrial mean precipitation derived from the precipitation climatology of 786 mm per year (equivalent to a water transport of 117,000 km³) is fitting into the global water cycle context is discussed.     

Eddy correlation measurements of CO2, latent heat,and sensible heat fluxes over a crop surface

Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO₂ sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO₂ were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO₂ fluxes were near 1.0 mg m^–2 (ground area) s^–1.The eddy correlation technique was also employed in this study to measure nocturnal CO₂ fluxes caused by respiration from plants, soil, and roots. These CO₂ fluxes ranged from - 0.1 to - 0.25 mg m^–2s^–1.From the data collected over mature soybeans, a relationship between CO₂ flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m^–2 s^–1. The light compensation point was found to be about 160 Ei m^–2 s^–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.     

植被冠层截留对地表水分和能量平衡影响的数值模拟

利用NCAR_CLM4.0模式,通过有无植被冠层截留的试验对比分析,讨论了植被冠层截留对全球陆面水分和能量平衡产生的潜在影响.结果表明:就全球水分平衡而言,不考虑植被冠层截留时,全球平均土壤总含水量、表面径流和次表面径流增加,蒸散发减少.空间分布特征表明,低纬地区各水分平衡分量全年维持较高的差值分布,并随季节变化沿赤道南北振荡;北半球中高纬高值区有春季扩张、夏季极盛、秋冬季撤退的趋势.冠层截留消失后冠层蒸发的消失是蒸散发减弱的主要原因.对于能量平衡而言,不考虑冠层截留时,全球感热通量增加,冠层感热的增加明显大于地面感热的减少;潜热减少.此外,不同植被类型对不考虑冠层截留后产生的响应存在明显差异.     

The climatic impacts of land surface change and carbon management, and the implications for climate-change mitigation policy

Strategies to mitigate anthropogenic climate change recognize that carbon sequestration in the terrestrial biosphere can reduce the build-up of carbon dioxide in the Earth’s atmosphere. However, climate mitigation policies do not generally incorporate the effects of these changes in the land surface on the surface albedo, the fluxes of sensible and latent heat to the atmosphere, and the distribution of energy within the climate system. Changes in these components of the surface energy budget can affect the local, regional, and global climate. Given the goal of mitigating climate change, it is important to consider all of the effects of changes in terrestrial vegetation and to work toward a better understanding of the full climate system. Acknowledging the importance of land surface change as a component of climate change makes it more challenging to create a system of credits and debits wherein emission or sequestration of carbon in the biosphere is equated with emission of carbon from fossil fuels. Recognition of the complexity of human-caused changes in climate does not, however, weaken the importance of actions that would seek to minimize our disturbance of the Earth’s environmental system and that would reduce societal and ecological vulnerability to environmental change and variability.     

Diurnal and seasonal variations of wind farm impacts on land surface temperature over western Texas

This paper analyzes seasonal and diurnal variations of MODerate resolution Imaging Spectroradiometer (MODIS) land surface temperature (LST) data at ~1.1 km for the period of 2003–2011 over a region in West-Central Texas, where four of the world’s largest wind farms are located. Seasonal anomalies are created from MODIS Terra (~10:30 a.m. and 10:30 p.m. local solar time) and Aqua (~1:30 a.m. and 1:30 p.m. local solar time) LSTs, and their spatiotemporal variability is analyzed by comparing the LST changes between wind farm pixels (WFPs) and nearby non wind farm pixels (NNWFPs) using different methods under different quality controls. Our analyses show consistently that there is a warming effect of 0.31–0.70 °C at nighttime for the nine-year period during which data was collected over WFPs relative to NNWFPs, in all seasons for both Terra and Aqua measurements, while the changes at daytime are much noisier. The nighttime warming effect is much larger in summer than winter and at ~10:30 p.m. than ~1:30 a.m. and hence the largest warming effect is observed at ~10:30 p.m. in summer. The spatial pattern and magnitude of this warming effect couple very well with the geographic distribution of wind turbines and such coupling is stronger at nighttime than daytime and in summer than winter. Together, these results suggest that the warming effect observed in MODIS over wind farms are very likely attributable to the development of wind farms. This inference is consistent with the increasing number of operational wind turbines with time during the study period, the diurnal and seasonal variations in the frequency of wind speed and direction distribution, and the changes in near-surface atmospheric boundary layer (ABL) conditions due to wind farm operations. The nocturnal ABL is typically stable and much thinner than the daytime ABL and hence the turbine enhanced vertical mixing produces a stronger nighttime effect. The stronger wind speed and the higher frequency of the wind speed within the optimal power generation range in summer than winter and at nighttime than daytime likely drives wind turbines to generate more electricity and turbulence and consequently results in the strongest warming effect at nighttime in summer. Similarly, the stronger wind speed and the higher frequency of optimal wind speed at ~10:30 p.m. than that at ~1:30 a.m. might help explain, to some extent, why the nighttime LST warming effect is slightly larger at ~10:30 p.m. than ~1:30 a.m. The nighttime warming effect seen in spring and fall are smaller than that in summer and can be explained similarly.     

The marginal impacts of CO2, CH4 and SF6 emissions

Abstract

A new version of the PAGE model, PAGE2002, has been used to calculate the marginal impacts of CO₂, CH₄ and SF₆ emissions based on Scenario A2 of the IPCC. The mean marginal impact of CO₂ is found to be US$19 per tonne of carbon (or about US$5 per tonne of CO₂), for methane it is US$105 per tonne, and for SF₆ it is US$200,000 per tonne. For each gas, the range between the 5% and 95% points is about an order of magnitude. The climate change impacts of methane are a significant proportion of its market price, and for SF₆ the climate change impacts are much larger than the market price. The economics of schemes to reduce the leakage of SF₆ are transformed once the climate change impacts are properly counted.