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61.
This study presents the first 19th century cold season climate chronology for the Kingdom of Lesotho in southern Africa. The
chronology is constructed using a variety of documentary sources including letters, diaries, reports, monographs and newspaper
articles obtained from southern African and British archives. Information relating to cold season weather phenomena during
the austral autumn, winter and early spring months were recorded verbatim. Each of the cold seasons from 1833 to 1900 was
then classified as “very severe”, “severe” or “normal/mild”, with a confidence rating ranging from low (1) to high (3) awarded
against each annual classification. The accuracy of the document-derived chronology was verified against temperature data
for Maseru for the period 1893–1900. Excellent correspondence of the document-derived chronology with the Maseru instrumental
data and also with other global proxy temperature records for the 19th century is achieved. The results indicate 12 (18% of
the total) very severe, 16 (23%) severe and 40 (59%) normal/mild cold seasons between 1833 and 1900. The overall trend is
for more severe and snow-rich cold seasons during the early part of the study period (1833–1854) compared with the latter
half of the 19th century (with the exception of the 1880s). A reduction in the duration of the frost season by over 20 days
during the 19th century is also tentatively identified. Several severe to very severe cold seasons in Lesotho follow after
major tropical and SH volcanic eruptions; such years are usually characterized by early frosts, and frequent and heavy snowfalls.
The blocking of solar radiation and the enhanced northward displacement of polar fronts that are directly or indirectly associated
with volcanic events, may account for many of the most severe Lesotho winters during the 19th century. 相似文献
62.
This study uses a range of published and unpublished historical documentary sources to explore the nature of rainfall variability in the Kalahari Desert and adjacent hardveld regions of central southern Africa during the seventeen Pacific El Niño–Southern Oscillation (ENSO) episodes that occurred between 1840 and 1900. Documentary data are used in two ways. First, maps of relative annual rainfall levels are presented for each of the 12 single-year and five protracted ENSO episodes during the period, in order to identify the associated inter-annual rainfall variations. These suggest that the relationship between ENSO episodes and rainfall variability identified for the twentieth century, whereby warm events are frequently preceded by wetter conditions during the austral summer prior to the event year and succeeded by drought in the following summer, has broadly held for much of the last 160 years. This is despite the long-term fluctuations in precipitation and temperature which are known to have occurred over this period. Droughts are identified following at least thirteen of the 17 single-year and protracted ENSO episodes. Pre-ENSO wetter periods are less common, with only nine of the ENSO episodes preceded by above-normal rainfall. Second, the documentary data are analyzed in detail in order to reveal any evidence for high resolution intra-annual variations in the seasonal distribution of rainfall during ENSO events. Seasonal sequences of rainfall/drought appear to have closely followed contemporary patterns, with heavy rainfall commonly occurring late in the pre-ENSO year or early in the ENSO year(s), and drought at the start of the post-ENSO year. This relationship can be seen to hold most strongly for single-year ENSO warm events and for the first year of protracted events, but rainfall conditions were more variable during the later years of protracted events. 相似文献
63.
A synthesis of the geochemistry of silcretes and their host sediments in the Kalahari Desert and Cape coastal zone, using isocon comparisons, shows that silcretes in the two regions are very different. Kalahari Desert silcretes outcrop along drainage-lines and within pans, and formed by groundwater silicification of near-surface Kalahari Group sands. Silicification was approximately isovolumetric. Few elements were lost; silicon (Si) and potassium (K) were gained as microquartz precipitated in the sediment porosity and glauconite formed in the sub-oxic groundwater conditions. The low titanium (Ti) content reflects the composition of the host sands. Additional elements in the Kalahari Desert silcretes were supplied in river water and derived from weathering of silicates in basement rocks. Evaporation under an arid climate produced high-pH groundwater that mobilized and precipitated Si; this process is still occurring. In the Cape coastal zone, pedogenic silcretes cap hills and plateaus, overlying deeply weathered argillaceous bedrock. Silicification resulted from intensive weathering that destroyed the bedrock silicates, almost completely removing most elements and causing a substantial volume decrease. Some of the silica released formed a microcrystalline quartz matrix, and most Ti precipitated as anatase, so the Cape silcretes contain relatively high Ti levels. The intense weathering that formed the Cape silcretes could have occurred in the Eocene, during and after the Palaeocene-Eocene Thermal Maximum, when more acidic rainfall and high temperatures resulted in intensified silicate weathering worldwide. This could have been responsible for widespread formation of pedogenic silcretes elsewhere in Africa and around the globe. Trace element sourcing of silcrete artefacts to particular outcrops has most potential in the Cape, where differences between separate bedrock areas are reflected in the silcrete composition. In the Kalahari Desert, gains of some elements can override compositional differences of the parent material, and sourcing should be based on elements that show the least change during silicification. © 2020 John Wiley & Sons, Ltd. 相似文献
64.
Intra-seasonal oscillations (ISO) are observed in the zonal-mean of mesospheric wind and temperature measurements—and the numerical spectral model (NSM) generates such oscillations. Relatively large temperature ISO are evident also in stratospheric CPC (NCEP) data at high latitudes, where the NSM produces amplitudes around 3 K at 30 km. Analyzing the NCEP data for the years 1996–2006, we find in Fourier spectra signatures of oscillations with periods between 1.7 and 3 months. With statistical confidence levels exceeding 70%, the spectral features are induced by nonlinear interactions involving the annual and semi-annual variations. The synthesized data show for the 10-year average that the temperature ISO peak in winter, having amplitudes close to 4 K. The synthesized complete spectrum for periods around 2 months produces oscillations, varying from year to year, which can reach peak amplitudes of 15 and 5 K respectively at northern and southern polar latitudes. 相似文献
65.
Nested circulation models developed to date either exclude the flooding and drying process or prohibit flooding and drying
of nested boundaries; they are therefore ill-suited to the accurate modelling of inter-tidal areas. The authors have developed
a nested model with moving boundaries which permits flooding and drying of both the interior domain and the nested boundaries.
The model uses a novel approach to boundary formulation; ghost cells are incorporated adjacent to the nested boundary cells
so that the nested boundaries operate as internal boundaries. When combined with a tailored adaptive interpolation technique,
the approach facilitates a dynamic internal boundary. Details of model development are presented with particular emphasis
on the treatment of the nested boundary. Results are presented for Cork Harbour, a natural coastal system with an extensive
inter-tidal zone and a complex flow regime which provided a rigorous test of model performance. The nested model was found
to achieve the accuracy of a high resolution single grid model for a much lower computational cost. 相似文献
66.
Nash David J. Klein Jørgen Endfield Georgina H. Pribyl Kathleen Adamson George C. D. Grab Stefan W. 《Climatic change》2019,152(3-4):467-485
Climatic Change - Single- to multiple-year drought episodes posed significant challenges for agrarian communities across southern Africa during the nineteenth century and hence are widely recorded... 相似文献
67.
Since the UK introduced a Climate Change Act (CCA) in 2008, similar legislation has followed in a number of states, with each having a slightly different take. What unites these examples is that they all represent framework legislation that aims to facilitate climate change mitigation by creating continuous policy processes whereby mechanisms for the reduction of greenhouse gas (GHG) emissions are developed and implemented. This article is concerned with the extent to which they are living policy processes or rather symbolic gestures. We analyse seven European CCAs with regard to GHG emission reduction targets, planning/implementation mechanisms, and feedback/evaluations prescribed by the laws. These three features correspond with three aspects of climate policy integration (CPI): interpretations of CPI as a norm; CPI as a process of governing; CPI as a policy outcome. We show that CCAs address all three aspects of CPI and constitute living policy processes, although to varying extents. However, CCAs are also policy processes in that they are part of a political system, affected by political forces external to the legislation, positively and negatively.
Key policy insights
CCAs can provide a normative basis for policymaking on climate change at the national level, especially through quantitative emission reduction targets.
Whilst CCAs can bring some stability and predictability to policymaking on climate change (mainly because legislation is more difficult to amend or remove than policy strategies), they are still vulnerable to political developments.
Most CCAs lack either short/medium-term (Denmark, Finland, Ireland, Sweden) or long-term (Austria) targets. Given EU Member States’ aim to decarbonise in the next three decades and the Paris Agreement's global goal of pursuing efforts to limit warming to 1.5°C, states need to find ways to guide this process. One approach could be the inclusion of short-term, medium-term and long-term targets in their CCAs.
Since sanctioning mechanisms are lacking across all the CCAs analysed here, it is not clear what will happen if legally binding targets are not met. Just as it is difficult to imagine speed limits and speed cameras without accompanying penalties, it is hard to imagine how CCAs without sanctions can deliver decarbonization.
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