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  • 551.6  (38)
  • English  (38)
  • 2020-2022  (38)
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  • English  (38)
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  • 1
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    “Surface,” “satellite” or “simulation”: Mapping intra-urban microclimate variability in a desert city (2021)
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    Publication Date: 2021-11-01
    Description: Mapping spatial and temporal variability of urban microclimate is pivotal for an accurate estimation of the ever-increasing exposure of urbanized humanity to global warming. This particularly concerns cities in arid/semi-arid regions which cover two fifths of the global land area and are home to more than one third of the world's population. Focusing on the desert city of Be'er Sheva Israel, we investigate the spatial and temporal patterns of urban–rural and intra-urban temperature variability by means of satellite observation, vehicular traverse measurement, and computer simulation. Our study reveals a well-developed nocturnal canopy layer urban heat island in Be'er Sheva, particularly in the winter, but a weak diurnal cool island in the mid-morning. Near surface air temperature exhibits weak urban–rural and intra-urban differences during the daytime (〈1°C), despite pronounced urban surface cool islands observed in satellite images. This phenomenon, also recorded in some other desert cities, is explained by the rapid increase in surface skin temperature of exposed desert soils (in the absence of vegetation or moisture) after sunrise, while urban surfaces are heated more slowly. The study highlights differences among the three methods used for describing urban temperature variability, each of which may have different applications in fields such as urban planning, climate change mitigation, and epidemiological research.
    Keywords: 551.6 ; Israel ; desert city ; urban microclimate ; mapping methods
    Language: English
    Type: map
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  • 2
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    Potential for Early Forecast of Moroccan Wheat Yields Based on Climatic Drivers (2021)
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    Publication Date: 2021-10-27
    Description: Wheat production plays an important role in Morocco. Current wheat forecast systems use weather and vegetation data during the crop growing phase, thus limiting the earliest possible release date to early spring. However, Morocco's wheat production is mostly rainfed and thus strongly tied to fluctuations in rainfall, which in turn depend on slowly evolving climate dynamics. This offers a source of predictability at longer time scales. Using physically guided causal discovery algorithms, we extract climate precursors for wheat yield variability from gridded fields of geopotential height and sea surface temperatures which show potential for accurate yield forecasts already in December, with around 50% explained variance in an out-of-sample cross validation. The detected interactions are physically meaningful and consistent with documented ocean-atmosphere feedbacks. Reliable yield forecasts at such long lead times could provide farmers and policy makers with necessary information for early action and strategic adaptation measurements to support food security.
    Keywords: 551.6 ; causal discovery algorithms ; teleconnections ; seasonal forecast ; machine learning ; wheat forecast ; climate precursors
    Language: English
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  • 3
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    Estimating near-surface air temperature across Israel using a machine learning based hybrid approach (2021)
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    Publication Date: 2021-10-27
    Description: Rising global temperatures over the last decades have increased heat exposure among populations worldwide. An accurate estimate of the resulting impacts on human health demands temporally explicit and spatially resolved monitoring of near-surface air temperature (Ta). Neither ground-based nor satellite-borne observations can achieve this individually, but the combination of the two provides synergistic opportunities. In this study, we propose a two-stage machine learning-based hybrid model to estimate 1 × 1 km2 gridded intra-daily Ta from surface skin temperature (Ts) across the complex terrain of Israel during 2004–2016. We first applied a random forest (RF) regression model to impute missing Ts from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua and Terra satellites, integrating Ts from the geostationary Spinning Enhanced Visible and InfraRed Imager (SEVIRI) satellite and synoptic variables from European Centre for Medium-Range Weather Forecasts' (ECMWF) ERA5 reanalysis data sets. The imputed Ts are in turn fed into the Stage 2 RF-based model to estimate Ta at the satellite overpass hours of each day. We evaluated the model's performance applying out-of-sample fivefold cross validation. Both stages of the hybrid model perform very well with out-of-sample fivefold cross validated R2 of 0.99 and 0.96, MAE of 0.42°C and 1.12°C, and RMSE of 0.65°C and 1.58°C (Stage 1: imputation of Ts, and Stage 2: estimation of Ta from Ts, respectively). The newly proposed model provides excellent computationally efficient estimation of near-surface air temperature at high resolution in both space and time, which helps further minimize exposure misclassification in epidemiological studies.
    Keywords: 551.6 ; air temperature ; health 〈 6. application/context ; health exposure ; MODIS ; random forest ; remote sensing 〈 1. tools and methods ; statistical methods 〈 1. tools and methods ; surface skin temperature
    Language: English
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  • 4
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    Broad Consistency Between Observed and Simulated Trends in Sea Surface Temperature Patterns (2021)
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    Publication Date: 2021-10-27
    Description: Using seven single-model ensembles and the two multimodel ensembles CMIP5 and CMIP6, we show that observed and simulated trends in sea surface temperature (SST) patterns are globally consistent when accounting for internal variability. Some individual ensemble members simulate trends in large-scale SST patterns that closely resemble the observed ones. Observed regional trends that lie at the outer edge of the models' internal variability range allow two nonexclusive interpretations: (a) Observed trends are unusual realizations of the Earth's possible behavior and/or (b) the models are systematically biased but large internal variability leads to some good matches with the observations. The existing range of multidecadal SST trends is influenced more strongly by large internal variability than by differences in the model formulation or the observational data sets.
    Keywords: 551.6 ; sea surface temperature patterns ; internal variability ; global climate models ; large ensembles ; model evaluation
    Language: English
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  • 5
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    Interannual to millennial-scale variability of River Ammer floods and its relationship with solar forcing (2021)
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    Publication Date: 2021-10-26
    Description: The relationship between River Ammer flood frequency variability, extreme summer climate over Europe, and solar forcing is investigated. First, we used observational data to evaluate extreme weather and climate anomaly patterns associated with flood and solar forcing as well as the possible dynamical mechanisms behind them. Then, the annual resolution flood layer record from the Lake Ammer sediments is analysed to evaluate millennial-scale variability of floods and possible related extreme climate patterns back to 5,500 years BP. A composite analysis reveals that observed River Ammer flood frequency variability at interannual to multidecadal time scales is connected to large-scale extreme precipitation and temperature patterns. From a synoptic-scale perspective, the extreme precipitation pattern associated with floods is related to an increase in the frequency of high upper-level potential vorticity (PV) events over western Europe and a decrease over eastern Europe and western Russia. Increased (decreased) frequency of upper-level high PV events is related to more (less) surface extreme precipitation occurrence. Furthermore, we show that increased frequency of upper-level high PV events over western Europe is associated with enhanced blocking activity over eastern Europe. Therefore, the out of phase interannual to millennial-scale variations of River Ammer flood frequency and solar irradiance, as presented in previous studies, can be explained by a solar modulation of eastern European-western Russia summer blocking and associated upstream upper-level wave breaking activity. In addition, we identify two distinct quasi-periodic signals in both frequency of Lake Ammer flood layer and solar irradiance records with periods of ~900 years and ~2,300 years. We argue that similar cycles should dominate millennial-scale variations of blocking activity in eastern Europe-western Russia as well as extreme precipitation and flood frequency variability over central and western Europe during the last ~5,500 years.
    Keywords: 551.6 ; floods ; extreme precipitation ; potential vorticity ; solar forcing
    Language: English
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  • 6
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    Opportunistic Constant Target Matching—A New Method for Satellite Intercalibration (2021)
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    Publication Date: 2021-10-26
    Description: Opportunistic constant target matching is a new method for satellite intercalibration. It solves a long-standing issue with the traditional simultaneous nadir overpass (SNO) method, namely, that it typically provides only data points with cold brightness temperatures for humidity sounding instruments on sun-synchronous satellites. In the new method, a geostationary infrared sensor (SEVIRI) is used to select constant target matches for two different microwave sensors (MHS on NOAA 18 and Metop A). We discuss the main assumptions and limitations of the method and explore its statistical properties with a simple Monte Carlo simulation. The method was tested in a simple case study with real observations for this combination of satellites for MHS Channel 3 at 183 ± 1 GHz, the upper tropospheric humidity channel. For the studied 3-month test period, real observations are found to behave consistently with the simulations, increasing our confidence that the method can be a valuable tool for intercalibration efforts. For the selected case study, the new method confirms that the bias between NOAA 18 and Metop A MHS Channel 3 is very small, with absolute value below 0.05 K.
    Keywords: 551.6 ; satellite ; calibration ; collocation ; microwave ; infrared
    Language: English
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  • 7
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    Arctic Ocean Surface Energy Flux and the Cold Halocline in Future Climate Projections (2021)
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    Publication Date: 2021-10-25
    Description: Ocean heat transport is often thought to play a secondary role for Arctic surface warming in part because warm water which flows northward is prevented from reaching the surface by a cold and stable halocline layer. However, recent observations in various regions indicate that occasionally, warm water is found directly below the surface mixed layer. Here we investigate Arctic Ocean surface energy fluxes and the cold halocline layer in climate model simulations from the Coupled Model Intercomparison Project Phase 5. An ensemble of 15 models shows decreased sea ice formation and increased ocean energy release during fall, winter, and spring for a high-emission future scenario. Along the main pathways for warm water advection, this increased energy release is not locally balanced by increased Arctic Ocean energy uptake in summer. Because during Arctic winter, the ocean mixed layer is mainly heated from below, we analyze changes of the cold halocline layer in the monthly mean Coupled Model Intercomparison Project Phase 5 data. Fresh water acts to stabilize the upper ocean as expected based on previous studies. We find that in spite of this stabilizing effect, periods in which warm water is found directly or almost directly below the mixed layer and which occur mainly in winter and spring become more frequent in high-emission future scenario simulations, especially along the main pathways for warm water advection. This could reduce sea ice formation and surface albedo.
    Keywords: 551.46 ; 551.6 ; Arctic ; climate change ; cold halocline ; climate modeling
    Language: English
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  • 8
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    Poleward Shift of Northern Subtropics in Winter: Time of Emergence of Zonal Versus Regional Signals (2021)
    Details
    Publication Date: 2021-10-25
    Description: The Northern Hemisphere mid-latitudes will be exposed to hydroclimatic risk in next coming decades because the subtropical expansion. However, it is not clear when the anthropogenic signal will emerge from the internal climate variability. For this purpose, we investigate the time of emergence (ToE) of the hemispheric and regional shift of northern subtropical margins in the Max Planck Institute Grand Ensemble. For several indicators, the ToE of the poleward shift of Northern subtropical margin will not occur by the end of the 21st century, neither at regional nor at hemispheric scale. The exceptions are the Mediterranean/Middle East and, to a lesser degree, Western Pacific, where the ToE would occur earlier. According to our results, given the fundamental role played by internal variability, trends of Northern Hemisphere subtropical poleward shift that have been identified over last decades in reanalyses cannot be considered as robust signals of anthropogenic climate change.
    Keywords: 551.6 ; Northern Hemisphere subtropics ; poleward shift ; MPI-ESM Grand Ensemble ; forced response ; natural variability ; time of emergence
    Language: English
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  • 9
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    Stronger Global Warming on Nonrainy Days in Observations From China (2021)
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    Publication Date: 2021-10-25
    Description: Nonrainy days have rather different hydrologic and radiative conditions than rainy days, but few investigations considered how these different conditions contribute to the observed global warming. Here, we show that global warming is considerably stronger on nonrainy days using observations from China. We find that trends in mean temperature on nonrainy days are about 0.1 ° C/10 yr higher than on rainy days, and that about 80% of the total temperature increase is contributed by nonrainy days. The main reason is likely to be a stronger sensitivity of downwelling longwave radiation to greenhouse forcing on nonrainy days due to fewer clouds and water vapor compared with rainy days, which is not a hydrological effect but mainly a radiative effect. Our findings are consistent with the stronger mean temperature trends in drier regions and imply that the different temperature sensitivities on nonrainy and rainy days may have profound effects on natural and social systems.
    Keywords: 551.6 ; global warming ; rainy day ; temperature trend
    Language: English
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  • 10
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    Climate change impacts on agriculture's southern frontier – Perspectives for farming in North Patagonia (2021)
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    Publication Date: 2021-10-15
    Description: Winter chill is expected to decrease in many of the suitable growing regions for deciduous trees. Argentinean North Patagonia hosts extensive fruit tree cultivation, which provides an important contribution to both local and global food security. Using historic records from 11 weather stations from North Patagonia, we evaluate the possible impacts of climate change on fruit tree cultivation. We assess winter chill and seasonal heat availability, and the risk of spring frost events based on outputs from 15 Global Climate Models (GCMs) for two Representative Concentration Pathway (RCP) scenarios and two future time periods (represented by central years 2050 and 2085). Metrics were estimated for 47 years of records from the weather stations, as well as typical conditions for 10 past scenarios and 60 future GCM and RCP projections. Scenarios consisted of 100 plausible annual temperature records produced by a weather generator. Results suggest that fruit tree dormancy in Argentinean North Patagonia will not be strongly affected by climate change. Compared to the past, winter chill may only decrease by 9% in the RCP4.5 scenario by 2050 in the northeastern and eastern subregion, while in the central-south and west the reduction seems unlikely to exceed 6% by the same RCP scenario and year. Our models project stable high growing season heat in the northeastern and eastern regions, and major increases in the south by 2085 in both RCP scenarios. Projections of spring frost events varied between 0 and about 25 hours below 0°C depending on the site. Increasing heat availability may create opportunities for fruit and nut growers to introduce new species and cultivars to the region. Our results provide a basis for planning such introductions and for enabling growers to exploit new opportunities for producing temperate orchard crops beyond their traditional ranges.
    Keywords: 551.6 ; chill models ; chill requirement ; heat requirement ; Prunus sp. ; spring frost risk ; temperate trees ; warm winters
    Language: English
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