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1.
Projections of daily mean temperature variability in the future: cross-validation tests with ENSEMBLES regional climate simulations 总被引：1，自引：0，他引：1
Because of model biases, projections of future climate need to combine model simulations of recent and future climate with information on observed climate. Here, 10 methods for projecting the distribution of daily mean temperatures are compared, using six regional climate change simulations for Europe. Cross validation between the models is used to assess the potential performance of the methods in projecting future climate. Delta change and bias correction type methods show similar cross-validation performance, with methods based on the quantile mapping approach doing best in both groups due to their apparent ability to reduce the errors in the projected time mean temperature change. However, as no single method performs best under all circumstances, the optimal approach might be to use several well-behaving methods in parallel. When applying the various methods to real-world temperature projection for the late 21st century, the largest intermethod differences are found in the tails of the temperature distribution. Although the intermethod variation of the projections is generally smaller than their intermodel variation, it is not negligible. Therefore, it should be preferably included in uncertainty analysis of temperature projections, particularly in applications where the extremes of the distribution are important. 相似文献
2.
Climate projections from multi-model ensembles are commonly represented by the multi-model mean (MMM) climate change. As an alternative, various subjectively formulated schemes for performance-based weighting of models have been proposed. Here, a more objective framework for model weighting is developed. A key ingredient of this scheme is a calibration step quantifying the relationship between intermodel similarity in observable climate and intermodel similarity in simulated climate change. Models that simulate the observable climate better are only given higher weight where and when such an intermodel relationship is found, and the difference in weight between better and worse performing models increases with the strength of this relationship. The method is applied to projections of temperature change from the Third Coupled Model Intercomparison Project. First, cross-validation is used to estimate the potential of the method to improve the accuracy of climate change estimates and to search for suitable predictor variables. The decrease in cross-validation error allowed by the weighting is relatively modest but not negligible, and it could potentially be increased if better predictor variables were found. Second, observations are used to weight the models, to study the differences between the weighted mean and MMM estimates of twenty-first century temperature change and the sensitivity of these differences to the predictor variables and observational data sets used. 相似文献
3.
There are a number of sources of uncertainty in regional climate change scenarios. When statistical downscaling is used to obtain regional climate change scenarios, the uncertainty may originate from the uncertainties in the global climate models used, the skill of the statistical model, and the forcing scenarios applied to the global climate model. The uncertainty associated with global climate models can be evaluated by examining the differences in the predictors and in the downscaled climate change scenarios based on a set of different global climate models. When standardized global climate model simulations such as the second phase of the Coupled Model Intercomparison Project （CMIP2） are used, the difference in the downscaled variables mainly reflects differences in the climate models and the natural variability in the simulated climates. It is proposed that the spread of the estimates can be taken as a measure of the uncertainty associated with global climate models. The proposed method is applied to the estimation of global-climate-model-related uncertainty in regional precipitation change scenarios in Sweden. Results from statistical downscaling based on 17 global climate models show that there is an overall increase in annual precipitation all over Sweden although a considerable spread of the changes in the precipitation exists. The general increase can be attributed to the increased large-scale precipitation and the enhanced westerly wind. The estimated uncertainty is nearly independent of region. However, there is a seasonal dependence. The estimates for winter show the highest level of confidence, while the estimates for summer show the least. 相似文献
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5.
This article discusses the particularity of young people’s politics as it unfolds in the practice of everyday life. By exploring
a conflict concerning the use of a public park in the City of Oulu, Finland, we discuss how young people may participate in
struggles over urban space trough politics that is not based on voice but voicelessness. This political engagement can be
understood as a form of nonparticipatory politics that is easily left unnoticed—politics that shirks civic involvement, customary
participatory practices and articulated resistance. We deem it important to acknowledge such action as political for two reasons.
First, voiceless politics is a weapon of the weak: It is used when other political agencies are not feasible e. Viewing non-participation
as apolitical will only further marginalize those who practice politics in such ways. Second, it is important to find ways
of acknowledging nonparticipatory action because, while not commonly understood as politics, it is not easily bypassed in
political struggles either. By distinguishing political aspects from young people’s urban behaviors, instead of hearing their
presence as mere noise, provides tools for bringing their politics to the public agenda and thus developing more democratic
urban spaces. 相似文献
6.
Evaluation of delta change and bias correction methods for future daily precipitation: intermodel cross-validation using ENSEMBLES simulations 总被引：1，自引：0，他引：1
Due to inherent limitations in climate models, their output is biased in relation to observed climate and as such does not provide reliable climate projections. In this study, nine methods used to account for biases in daily precipitation are tested. First, cross-validation tests were made using a set of ENSEMBLES regional model simulations to gain insights in the potential performance of the methods in the future climate. The results show that quantile mapping type methods, being able to modify the shape of the precipitation distribution, often outperform other types of methods. Yet, as the performance depends on time of the year, location and part of the distribution considered, it is not possible to distinguish one universally best performing method. In addition, the improvement relative to the projections that would have been obtained assuming unchanged climate is relatively modest, particularly in the early twentyfirst century conditions. Further tests with different method combinations show that the projections could be potentially improved by using several well performing methods in parallel. In the second part of the study, contributions of method and model differences to the overall variation of precipitation projections are assessed. It is shown that although intermodel differences play an important role, uncertainties related to intermethod differences are substantial, particularly in the tails of the distribution. This suggests that method uncertainty should be taken into account when constructing daily precipitation projections, possibly by using several methods in parallel. 相似文献
7.
Stefan Fronzek Timothy R. Carter Jouni Räisänen Leena Ruokolainen Miska Luoto 《Climatic change》2010,99(3-4):515-534
A comparison of two approaches for determining probabilistic climate change impacts is presented. In the first approach, ensemble climate projections are applied directly as inputs to an impact model and the risk of impact is computed from the resulting ensemble of outcomes. As this can involve large numbers of projections, the approach may prove to be impractical when applied to complex impact models with demanding input requirements. The second approach is to construct an impact response surface based on a sensitivity analysis of the impact model with respect to changes in key climatic variables, and then to superimpose probabilistic projections of future climate onto the response surface to assess the risk of impact. To illustrate this comparison, an impact model describing the spatial distribution of palsas in Fennoscandia was applied to estimate the risk of palsa disappearance. Palsas are northern mire complexes with permanently frozen peat hummocks, located at the outer limit of the permafrost zone and susceptible to rapid decline due to regional warming. Probabilities of climate changes were derived from an ensemble of coupled atmosphere–ocean general circulation model (AOGCM) projections using a re-sampling method. Results indicated that the response surface approach, though introducing additional uncertainty, gave risk estimates of area decline for palsa suitability that were comparable to those obtained using multiple simulations with the original palsa model. It was estimated as very likely (>90% probability) that a decline of area suitable for palsas to less than half of the baseline distribution will occur by the 2030s and likely (>66%) that all suitable areas will disappear by the end of the twenty-first century under scenarios of medium (A1B) and moderately high (A2) emissions. For a low emissions (B1) scenario, it was more likely than not (>50%) that conditions over a small fraction of the current palsa distribution would remain suitable until the end of the twenty-first century. 相似文献
8.
Jouni Räisänen 《Climate Dynamics》2005,24(2-3):309-323
The impact of increasing atmospheric CO2 on high and low extremes of monthly-to-annual precipitation is studied using 20 model experiments participating in the second phase of the coupled model intercomparison project (CMIP2). In marked contrast with previous research on daily precipitation extremes, the simulated changes in extremes on these longer time scales are well correlated with the changes in the long-term mean precipitation: wet extremes become more severe especially where the mean precipitation increases, and dry extremes where the mean precipitation decreases. Changes in relative variability play a smaller but discernible role. In an ensemble-mean sense, the variability increases slightly in most areas, so that the contrast between the high and low precipitation extremes grows larger with increasing CO2. The changes in the frequency of extremes (fraction of cases with precipitation above a high or below a low predefined threshold) are much larger than the changes in their magnitude. Most of the ensemble-averaged changes in the frequency of extremes can be reconstructed by using the changes in time mean precipitation alone, provided that the variation in time mean precipitation change between different models is taken into account. The nonlinear relationship between the mean precipitation and the frequency of extremes complicates the interpretation of the frequency changes, especially when averaging frequencies over different models. 相似文献
9.
A case study of airborne and satellite remote sensing of a spring bloom event in the Gulf of Finland
Sampsa Koponen Jenni Attila Jouni Pulliainen Kari Kallio Timo Pyhälahti Antti Lindfors Kai Rasmus Martti Hallikainen 《Continental Shelf Research》2007
The concentrations of chlorophyll-a (chl-a), total suspended solids (TSS) and the absorption coefficient of colored dissolved organic matter (aCDOM(400)) are estimated in Case II waters using medium resolution imaging spectrometer (MERIS) satellite (full resolution [FR] level 1b, 300 m resolution) and AISA airborne spectrometer data acquired during a spring bloom in the Gulf of Finland, Baltic Sea on April 27, 2004. The accuracy of the estimation is analyzed using empirical band-ratio algorithms together with in situ observations that include water samples analyzed in a laboratory (variation ranges: 22–130 μg/l, 2.9–20 mg/l, and 1.29–2.61 m−1 for chl-a, TSS and aCDOM(400), respectively). Additional in situ estimates (transects) on these characteristics are available through absorption and scattering coefficients measured with an ac-9 absorption and attenuation meter installed in a flow-through system. The retrieval accuracy (R2) of all three water quality characteristics with MERIS data is close to or above 0.9, while the RMSE is 7.8 μg/l (22%), 0.74 mg/l (16%) and 0.08 m−1 (5%), for chl-a, TSS and aCDOM(400), respectively. The validity of the chl-a algorithm is tested using nine additional data points. The BIAS-error for these points is 5.2 μg/l and the RMSE is 10.6 μg/l. The effects of changes in the atmospheric characteristics on band-ratio algorithms in cases where no concurrent in situ reference data are available are analyzed using the MODerate spectral resolution atmospheric TRANSmittance algorithm and computer model (MODTRAN). The additional error due to these changes is estimated to be below 20% for the applied ratio algorithms. The water quality data available in the level 2 MERIS-product distributed by the European Space Agency did not include valid results for the date investigated here. 相似文献
10.
Jouni I. Peltoniemi Jukka Piironen Jyri Nrnen Juha Suomalainen Risto Kuittinen Lauri Markelin Eija Honkavaara 《ISPRS Journal of Photogrammetry and Remote Sensing》2007,62(6):434-446
The Sjökulla test site is used for testing and calibrating aerial images. The permanent test field is made of four types of gravel (dark gabbro, grey granite, red granite, white limestone) in two sizes (diameters 8–16 mm and 4–8 mm) set in various patterns. The bidirectional reflection properties of the targets together with their temporal changes must be known in order to carry out radiometric and spectral evaluation and calibration.The bidirectional reflectance distribution functions (BRF) of the gravel have been measured several times in the test fields using portable field goniospectrometers belonging Finnish Geodetic Institute (FGI), and once using the European Goniometic Facility (EGO) of the Joint Research Centre (JRC) at Ispra, Italy. Detailed BRFs have been obtained, showing features typical to particulate media, e.g. a small bowl shape, strong backscattering, and smooth wavelength dependence. Temporal range measurements over several years show that the black gabbro and red granite are fairly stable, while the grey granite has changed somewhat over the years and the white limestone has experienced dramatic darkening effects, requiring action to be taken.The measured BRF data have increased the usability of the test field considerably. The results are also useful in the development and validation of scattering models for particulate media. The site has proved to be a good test bench for goniospectrometric instruments, too. 相似文献