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  • 1
    Online Resource
    Online Resource
    India Meteorological Department ; 2008
    In:  MAUSAM Vol. 59, No. 3 ( 2008-07-01), p. 297-312
    In: MAUSAM, India Meteorological Department, Vol. 59, No. 3 ( 2008-07-01), p. 297-312
    Abstract: Rainfall variability in the low latitudes in general and over tropical and sub-tropical Africa in particular, is largely affected by land surface characteristics like, vegetation cover, albedo and soil moisture. Understanding the local and dynamical effects of land-cover changes is crucial to future climate prediction, given ongoing population growth and increasing agricultural needs in Africa. Here, a set of sensitivity studies with a synoptic-scale regional climate model is presented, prescribing idealized scenarios of reduced vegetation cover over Africa. Beside the vegetation ratio itself, the leaf area index, forest ratio, surface albedo and roughness length are changed as well, in order to obtain a consistent scenario of land surface degradation. In addition, a second set of experiments is realized with altered soil parameters as expected to be coming alongwith a reduction in vegetation cover.   Seasonal rainfall amount decreases substantially when the present-day vegetation continuously disappears. The strongest changes are found over the Congo Basin and subsaharan West Africa, where the summer monsoon precipitation diminishes by up to 2000 mm and 600 mm, respectively. The rainfall response to vegetation changes is non-linear and statistically significant over large parts of subsaharan Africa. Convective precipitation is more sensitive than large-scale precipitation.   The most prominent effect of land degradation is a decrease (increase) of latent (sensible) heat fluxes. As a consequence, the large-scale thermal gradients, as a key factor in the monsoonal flow over Africa, are modified leading to a southward shift of the intertropical convergence zone and enhanced moisture advection over the southernmost part of West Africa and the central Congo Basin. The mid-tropospheric jet and wave dynamics are barely affected by land-cover changes. Although the large-scale dynamical response is favourable to increasing rainfall amount, the moisture budget is predominantly governed by reduced evapotranspiration, overcompensating the positive dynamical effect and inducing a weakening of the regional-scale water recycling. The related changes in the soil properties may additionally contribute to a reduction in rainfall amount, albeit of lower amplitude.
    Type of Medium: Online Resource
    ISSN: 0252-9416
    URL: Issue
    Language: Unknown
    Publisher: India Meteorological Department
    Publication Date: 2008
    SSG: 16,13
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  • 2
    Online Resource
    Online Resource
    India Meteorological Department ; 2004
    In:  MAUSAM Vol. 55, No. 4 ( 2004-10-01), p. 561-582
    In: MAUSAM, India Meteorological Department, Vol. 55, No. 4 ( 2004-10-01), p. 561-582
    Abstract:  The leading mode of 20th century West African rainfall variability represents a well-documented drought tendency in the Sahel and the Guinea Coast region from the 1960s onward. The following three modes describe an out-of-phase relationship between the Sahel Zone (SHZ) and the Guinea Coast region (GCR) to the south, with positive rainfall anomalies in GCR being associated with even more severe drought conditions in SHZ between 1970 and 1998. This West African dipole in rainfall (WDR) has been of high relevance to migration processes in recent decades over the entire subsaharan region. WDR is equally revealed in long-term observational data and global climate model output. There is a clear scale-dependence of the anticorrelation, SHZ rainfall changes being decoupled from GCR ones in the low-frequency range. It is found that the high pass filtered interannual WDR fluctuations are closely tied to Atlantic sea surface temperatures (SSTs), particularly in the Gulf of Guinea. Soil moisture is not a dominant player in forcing the dipole anomalies. Sensitivity studies with a regional climate model support the physical link between tropical Atlantic SST and WDR. The simulated rainfall response to changing SST is non-linear and in the same order of magnitude as in the long-term observations. The SST impact accounts for up to 40% of total rainfall variability, particularly over the southernmost part of West Africa, and is statistically significant at the 1% level even with respect to the remarkable day-to-day variations. Prescribing late 21st century warmer tropical Atlantic SST as derived from global climate model experiments under increasing greenhouse gas (GHG) concentrations, leads to increasing rainfall amount in GCR (around+300mm) and a reduction in freshwater supply in SHZ (around -150mm) during the July-August main rainy season. Thus, the SHZ-GCR contrast in rainfall amount may rise in the future, inducing ongoing north-to-south migrations in whole subsaharan West Africa.
    Type of Medium: Online Resource
    ISSN: 0252-9416
    URL: Issue
    Language: Unknown
    Publisher: India Meteorological Department
    Publication Date: 2004
    SSG: 16,13
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  • 3
    Online Resource
    Online Resource
    Wiley ; 2004
    In:  International Journal of Climatology Vol. 24, No. 5 ( 2004-04), p. 643-662
    In: International Journal of Climatology, Wiley, Vol. 24, No. 5 ( 2004-04), p. 643-662
    Type of Medium: Online Resource
    ISSN: 0899-8418 , 1097-0088
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2004
    detail.hit.zdb_id: 1491204-1
    SSG: 14
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  • 4
    In: International Journal of Climatology, Wiley, Vol. 39, No. 8 ( 2019-06-30), p. 3639-3654
    Abstract: This study investigates the projected precipitation changes of the 21st century in the Mediterranean area with a model ensemble of all available CMIP3 and CMIP5 data based on four different scenarios. The large spread of simulated precipitation change signals underlines the need of an evaluation of the individual general circulation models in order to give higher weights to better and lower weights to worse performing models. The models' spread comprises part of the internal climate variability, but is also due to the differing skills of the circulation models. The uncertainty resulting from the latter is the aim of our weighting approach. Each weight is based on the skill to simulate key predictor variables in context of large and medium scale atmospheric circulation patterns within a statistical downscaling framework for the Mediterranean precipitation. Therefore, geopotential heights, sea level pressure, atmospheric layer thickness, horizontal wind components and humidity data at several atmospheric levels are considered. The novelty of this metric consists in avoiding the use of the precipitation data by itself for the weighting process, as state‐of‐the‐art models still have major deficits in simulating precipitation. The application of the weights on the downscaled precipitation changes leads to more reliable and precise change signals in some Mediterranean sub‐regions and seasons. The model weights differ between sub‐regions and seasons, however, a clear sequence from better to worse models for the representation of precipitation in the Mediterranean area becomes apparent.
    Type of Medium: Online Resource
    ISSN: 0899-8418 , 1097-0088
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 1491204-1
    SSG: 14
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  • 5
    Online Resource
    Online Resource
    Wiley ; 2023
    In:  International Journal of Climatology Vol. 43, No. 2 ( 2023-02), p. 772-786
    In: International Journal of Climatology, Wiley, Vol. 43, No. 2 ( 2023-02), p. 772-786
    Abstract: Wind energy is a key option in global dialogues about climate change mitigation. Here, we combined observations from surface wind stations, reanalysis datasets, and state‐of‐the‐art regional climate models from the Coordinated Regional Climate Downscaling Experiment (CORDEX Africa) to study the current and future wind energy potential in Zambia. We found that winds are dominated by southeasterlies and are rarely strong with an average speed of 2.8 m·s −1 . When we converted the observed surface wind speed to a turbine hub height of 100 m, we found a ~38% increase in mean wind speed for the period 1981–2000. Further, both simulated and observed wind speed data show statistically significant increments across much of the country. The only areas that divert from this upward trend of wind speeds are the low land terrains of the Eastern Province bordering Malawi. Examining projections of wind power density (WPD), we found that although wind speed is increasing, it is still generally too weak to support large‐scale wind power generation. We found a meagre projected annual average WPD of 46.6 W·m −2 . The highest WPDs of ~80 W·m −2 are projected in the northern and central parts of the country while the lowest are to be expected along the Luangwa valley in agreement with wind speed simulations. On average, Zambia is expected to experience minor WPD increments of 0.004 W·m −2 per year from 2031 to 2050. We conclude that small‐scale wind turbines that accommodate cut‐in wind speeds of 3.8 m·s −1 are the most suitable for power generation in Zambia. Further, given the limitations of small wind turbines, they are best suited for rural and suburban areas of the country where obstructions are few, thus making them ideal for complementing the government of the Republic of Zambia's rural electrification efforts.
    Type of Medium: Online Resource
    ISSN: 0899-8418 , 1097-0088
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 1491204-1
    SSG: 14
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  • 6
    Online Resource
    Online Resource
    American Meteorological Society ; 2009
    In:  Journal of Climate Vol. 22, No. 1 ( 2009-01-01), p. 114-132
    In: Journal of Climate, American Meteorological Society, Vol. 22, No. 1 ( 2009-01-01), p. 114-132
    Abstract: Human activity is supposed to affect the earth’s climate mainly via two processes: the emission of greenhouse gases and aerosols and the alteration of land cover. While the former process is well established in state-of-the-art climate model simulations, less attention has been paid to the latter. However, the low latitudes appear to be particularly sensitive to land use changes, especially in tropical Africa where frequent drought episodes were observed during recent decades. Here several ensembles of long-term transient climate change experiments are presented with a regional climate model to estimate the future pathway of African climate under fairly realistic forcing conditions. Therefore, the simulations are forced with increasing greenhouse gas concentrations as well as land use changes until 2050. Three different scenarios are prescribed in order to assess the range of options inferred from global political, social, and economical development. The authors find a prominent surface heating and a weakening of the hydrological cycle over most of tropical Africa, resulting in enhanced heat stress and extended dry spells. In contrast, the large-scale atmospheric circulation in upper levels is less affected, pointing to a primarily local effect of land degradation on near-surface climate. In the model study, it turns out that land use changes are primarily responsible for the simulated climate response. In general, simulated climate changes are not concealed by internal variability. Thus, the effect of land use changes has to be accounted for when developing more realistic scenarios for future African climate.
    Type of Medium: Online Resource
    ISSN: 1520-0442 , 0894-8755
    RVK:
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2009
    detail.hit.zdb_id: 246750-1
    detail.hit.zdb_id: 2021723-7
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  • 7
    Online Resource
    Online Resource
    American Geophysical Union (AGU) ; 2014
    In:  Journal of Geophysical Research: Biogeosciences Vol. 119, No. 3 ( 2014-03), p. 312-322
    In: Journal of Geophysical Research: Biogeosciences, American Geophysical Union (AGU), Vol. 119, No. 3 ( 2014-03), p. 312-322
    Abstract: CG flash rate is simulated to increase by up to 21% at the end of the century Global burned area was little affected by these changes However, there were considerable changes on the regional scale
    Type of Medium: Online Resource
    ISSN: 2169-8953 , 2169-8961
    URL: Issue
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2014
    detail.hit.zdb_id: 3094167-2
    detail.hit.zdb_id: 2220777-6
    SSG: 16,13
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  • 8
    Online Resource
    Online Resource
    MDPI AG ; 2021
    In:  Atmosphere Vol. 12, No. 10 ( 2021-10-02), p. 1287-
    In: Atmosphere, MDPI AG, Vol. 12, No. 10 ( 2021-10-02), p. 1287-
    Abstract: This study examines the relationship between variations of the Southern Annular Mode (SAM) and black carbon (BC) at 550 nm aerosol optical depth (AOD) in the Western Cape province (WC). Variations of the positive (negative) phase of the SAM are found to be related to regional circulation types (CTs) in southern Africa, associated with suppressed (enhanced) westerly wind over the WC through the southward (northward) migration of Southern Hemisphere mid-latitude cyclones. The CTs related to positive (negative) SAM anomalies induce stable (unstable) atmospheric conditions over the southwestern regions of the WC, especially during the austral winter and autumn seasons. Through the control of CTs, positive (negative) SAM phases tend to contribute to the build-up (dispersion and dilution) of BC in the study region because they imply dry (wet) conditions which favor the build-up (washing out) of pollutant particles in the atmosphere. Indeed, recent years with an above-average frequency of CTs related to positive (negative) SAM anomalies are associated with a high (low) BC AOD over southwesternmost Africa.
    Type of Medium: Online Resource
    ISSN: 2073-4433
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2605928-9
    SSG: 23
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  • 9
    In: Ecology and Evolution, Wiley, Vol. 13, No. 10 ( 2023-10)
    Abstract: Bioclimatic variables (BCVs) are the most widely used predictors within the field of species distribution modeling, but recent studies imply that BCVs alone are not sufficient to describe these limits. Unfortunately, the most popular database, WorldClim, offers only a limited selection of bioclimatological predictors; thus, other climatological datasets should be considered, and, for data consistency, the BCVs should also be derived from the respective datasets. Here, we investigate how well the BCVs are represented by different datasets for the extended Mediterranean area within the period 1970–2020, how different calculation schemes affect the representation of BCVs, and how deviations among the datasets differ regionally. We consider different calculation schemes for quarters/months, the annual mean temperature (BCV‐1), and the maximum temperature of the warmest month (BCV‐5). Additionally, we analyzed the effect of different temporal resolutions for BCV‐1 and BCV‐5. Differences resulting from different calculation schemes are presented for ERA5‐Land. Selected BCVs are analyzed to show differences between WorldClim, ERA5‐Land, E‐OBS, and CRU. Our results show that (a) differences between the two calculation schemes for BCV‐1 diminish as the temporal resolution decreases, while the differences for BCV‐5 increase; (b) with respect to the definition of the respective month/quarter, intra‐annual shifts induced by the calculation schemes can have substantially different effects on the BCVs; (c) all datasets represent the different BCVs similarly, but with partly large differences in some subregions; and (d) the largest differences occur when specific month/quarters are defined by precipitation. In summary, (a) since the definition of BCVs matches different calculation schemes, transparent communication of the BCVs calculation schemes is required; (b) the calculation, integration, or elimination of BCVs has to be examined carefully for each dataset, region, period, or species; and (c) the evaluated datasets provide, except in some areas, a consistent representation of BCVs within the extended Mediterranean region.
    Type of Medium: Online Resource
    ISSN: 2045-7758 , 2045-7758
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2023
    detail.hit.zdb_id: 2635675-2
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  • 10
    Online Resource
    Online Resource
    Elsevier BV ; 2013
    In:  Global and Planetary Change Vol. 110 ( 2013-11), p. 26-39
    In: Global and Planetary Change, Elsevier BV, Vol. 110 ( 2013-11), p. 26-39
    Type of Medium: Online Resource
    ISSN: 0921-8181
    RVK:
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2013
    detail.hit.zdb_id: 20361-0
    detail.hit.zdb_id: 2016967-X
    SSG: 13
    SSG: 14
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