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1.
L. S. Unganai 《Theoretical and Applied Climatology》1997,56(1-2):89-101
Summary The surface temperature variation over Zimbabwe, and, Harare and Bulawayo between 1933 and 1993, and, 1897 and 1993 respectively, is investigated. For the national average two significant warm phases are identified, with a net warming of +0.3 to +0.5°C since 1933. Warming occurs in maximum temperature, whereas the mean national temperature cools. The effect of the rainfall pattern on temperature is also investigated. If warming phases coincide with drought years and the warming is confined to the rainy months only, then reduced cloudiness could be an important factor in explaining some of the warming. The first warm phase occurs during the mid-1930s to late 1940 and the second major warm phase occurred from the early 1980s onwards. For Harare, with temperature records starting before 1900, a major warming phase occurred between about 1910 and late 1920. The effect of drought on the national temperature record is evident through a strong negative association between maximum temperature anomalies and rainfall anomalies. A number of possible causes of the observed changes are discussed. The effects of urbanisation and industrialisation on temperature trends over Harare and Bulawayo are quite conspicuous. The question that remains difficult to answer is whether the observed warming trend is a result of inherent climate variability, enhanced greenhouse effect or a combination of many factors.With 17 Figures 相似文献
2.
In a changing climate, changes in rainfall variability and, in particular, extreme rainfall events are likely to be highly significant for environmentally vulnerable regions such as southern Africa. It is generally accepted that sea-surface temperatures play an important role in modulating rainfall variability, thus the majority work to date has focused on these mechanisms. However past research suggests that land surface processes are also critical for rainfall variability. In particular, work has suggested that the atmosphere-land surface feedback has been important for past abrupt climate changes, such as those which occurred over the Sahara during the mid-Holocene or, more recently, the prolonged Sahelian drought. Therefore the primary aim of this work is to undertake idealised experiments using both a regional and global climate model, to test the sensitivity of rainfall variability to land surface changes over a location where such abrupt climate changes are projected to occur in the future, namely southern Africa. In one experiment, the desert conditions currently observed over southwestern Africa were extended to cover the entire subcontinent. This is based on past research which suggests a remobilisation of sand dune activity and spatial extent under various scenarios of future anthropogenic global warming. In the second experiment, savanna conditions were imposed over all of southern Africa, representing an increase in vegetation for most areas except the equatorial regions. The results suggest that a decrease in rainfall occurs in the desert run, up to 27% of total rainfall in the regional model (relative to the control), due to a reduction in available moisture, less evaporation, less vertical uplift and therefore higher near surface pressure. This result is consistent across both the regional and global model experiments. Conversely an increase in rainfall occurs in the savanna run, because of an increase in available moisture giving an increase in latent heat and therefore surface temperature, increasing vertical uplift and lowering near surface pressure. These experiments, however, are only preliminary, and form the first stage of a wider study into how the atmosphere-land surface feedback influences rainfall extremes over southern Africa in the past (when surface i.e. vegetation conditions were very different) and in the future under various scenarios of future climate change. Future work will examine how other climate models simulate the atmosphere-land surface feedback, using more realistic vegetation types based on past and future surface conditions. 相似文献
3.
Most deciduous fruit trees need sufficient accumulated chilling, or vernalisation, to break winter dormancy. Inadequate chilling due to enhanced greenhouse warming may result in prolonged dormancy, leading to reduced fruit quality and yield. The potential impact of warming on chill accumulation has been analysed using the Utah vernalisation model and temperature data from over 400 climate stations in southern Australia. Two experiments were performed: (i) a sensitivity study where temperatures were increased at all sites by either 1, 2 or 3 °C; (ii) a scenario study for the year 2030 where temperatures were increased according to spatially- and seasonally-varying warming scenarios derived from five global climate models under enhanced greenhouse conditions.The sensitivity study shows that warming causes greater reduction in chilling at sites with a higher present mean temperature and/or a wider diurnal temperature range. In the scenario study, two warming scenarios for the year 2030 were considered: a low (high) warming scenario which assumes a low (high) rate of increase of greenhouse gas emission, a low (high) global climate sensitivity to increased emissions, and a low (high) regional temperature response. The low warming scenario is less than 1 °C in southern Australia and is unlikely to affect the vernalisation of high-chill fruit, except for pome-fruit grown in south-west Western Australia. The high warming scenario exceeds 1.5 °C and would significantly increase the risk of prolonged dormancy for both stone-fruit and pome-fruit at many sites. 相似文献
4.
The various bases for making Australian and New Zealand scenarios of climate change at 2010 and 2050 AD are discussed. Atmospheric greenhouse gas increases will cause historically unprecedented warming by 2050 AD, but the likely regional rainfall changes are uncertain. By 2010 AD greenhouse gas climate change should be detectable with a warming relative to the present of 0.5–1.5 °C. At 2050 AD Australian and New Zealand temperatures will be 2–3 °C higher, the frost free season will be longer and the snowline higher. Rainfall changes will be very much determined by regional airflow and storm tracks, and the state of the Southern Oscillation. In order to obtain unproved and more detailed estimates of climate at 2010 and 2050 AD existing climate models need to be improved. For Australia and New Zealand models need to focus on the south west Pacific-Australia region. 相似文献
5.
Yonghui Yang Masataka Watanabe Zhiping Wang Yasuo Sakura Changyuan Tang 《Climatic change》2003,57(1-2):163-183
The WAVES model was used to simulate the effect of global warming on soil moisture on the semi-arid Taihang Mountain in China. Parameters of the WAVES model were first adjusted according to soil moisture data from a field global warming experiment. Then, the reliability of WAVES in predicting soil moisture changes induced by climatic change was confirmed by comparing the simulated and observed soil moisture values under different climatic conditions and plant growth rates of another field treatment. Next, 10 climate change scenarios incorporating increases in temperature and changes in precipitation were designed. When a simulation was conducted using the leaf area index (LAI) growth pattern from a field experiment under the present climatic conditions, the results suggested that the combination of temperature increase and precipitation decrease would greatly decrease soil water content throughout the entire simulation period. On the other hand, only when precipitation increased by 20% and temperatureincreased by 2 °C, the effect of precipitation increase on soil moisture was obviously positive. Although soil moisture conditions in the T2P1 (temperature increase by 2 °C and precipitation increase by 10%) and T4P2 (temperature increase by 4 °C and precipitation increase by 20%) scenarios were slightly better during the rainy season and notmuch changed before the rainy season, the positive effect of 10%precipitation increase on soil moisture was totally offset by moisture decrease caused bya 4 °C temperature increase in the T4P1 scenario. At the same time, the trends of soil-moisture change were highly coincident with predicted changes in productivity. Finally, the predicted LAI values from other studies were combined with the climatic change scenarios and used in the simulation. The results showed that changes in LAI alleviated, at least to some extent, the effects of temperature and precipitation changes on soil moisture. 相似文献
6.
Rainfall characteristics during the annual rainy season are explored for the Mzingwane catchment of south-western Zimbabwe, for both historic period (1886–1906) and more recent times (1950–2015), based on available daily and monthly precipitation series. Annual and seasonal rainfall trends are determined using the modified Mann-Kendall test, magnitude of trends test and Sen’s slope estimator. Rainfall variability is quantified using the coefficient of variation (CV), precipitation concentration index (PCI) and standard precipitation index (SPI). Results suggest that contemporary mean annual rainfall may not have changed from that measured during the historic period of 1886–1906. However, the number of rainy days (≥ 1 mm) has decreased by 34%, thus suggesting much more concentrated and increased rainfall intensity. A notable shift in both the onset and cessation dates of the rainy season is recorded, particularly during the twenty-first century, which has resulted in a significantly reduced (p < 0.05) length of the rainy season. The combination of a reduced number of rainy days (≥ 1 mm) and a shortened rainy season suggests that long intra-season dry spells have become more common through time and have considerable negative consequences for agriculture and wetland ecosystem in the region. In addition, high spatio-temporal rainfall variability and seasonal PCI values indicate strong seasonality in the rainy season. Based on the SPI results, the El Niño Southern Oscillation (ENSO) strongly influences rainfall variability. The results further suggest high uncertainty in rain season characteristics, which requires effective planning for water needs. 相似文献
7.
Summary Reports of changes in the seasonal and annual rainfall in Nigeria suggests that a more detailed analyses of the geographic
extent of these changes and of their impact on agriculture could be of value. Variation in the growing season (April to September)
rainfall from stations across Nigeria was analysed over the 30-yr period, 1960–90. Regression analyses were used to examine
long-term trends. Principal component and cluster analyses were used to group stations with similar trends in standardised
seasonal rainfall. Mean accumulated standardised seasonal rainfall were used to examine short- and medium-term trends for
each of the groups identified. Significant (P ≤ 0.05) decreases in rainy season rainfall were found at 8 stations mostly in the Guinea and arid/semi-arid savannas of northern
Nigeria, whereas no station showed significant increases. Examination of the monthly (April through September) rainfall showed
that only three – Kano, Sokoto and Potiskum in the arid/semi-arid savanna – of the twenty-three stations used in the analysis
had declining rainfall trends for each of the months April to September and subsequently declining seasonal rainfall trends.
However, 12 to 15 stations had consistently declining rainfall trends in atleast some but not all the growing season months.
However, a similar pattern was not the case in terms of increasing rainfall trends, where only one to three stations had consistently
increasing rainfall trends in some but not all of the months from April to September. Stations that showed increasing rainfall
trends were in the southern parts of Nigeria.
Six groups with similar patterns in standardised seasonal rainfall were identified by Principal Component and Cluster analyses.
For most of the groups, the period from 1967 to 1973 was that of consistently below average seasonal rainfall. However, the
timing and extent of the decline varied with location. Common to stations in four of the six groups was a negative trend in
seasonal rainfall for the period considered. The geographic variation in seasonal rainfall trends has tremendous agricultural
significance since there are indications that the reliability of the season is decreasing from the humid forest zone with
positive seasonal trends to the arid/semi-arid savanna with significant negative seasonal trends.
Received June 24, 1998 Revised December 18, 1998 相似文献
8.
Exploring the climate problems of Brazil’s Nordeste: a review 总被引：1，自引：0，他引：1
Stefan Hastenrath 《Climatic change》2012,112(2):243-251
This article reviews the exploration of the climate dynamics of Brazil’s Nordeste in the course of a century. The drought-prone and semi-arid northern Nordeste of Brazil experiences a short rainy season around March–April, when the interhemispheric gradient of sea surface temperature (SST) in the tropical Atlantic is weakest and the Intertropical Convergence Zone (ITCZ) reaches its southernmost position in the course of the annual cycle. The recurrent Secas (droughts) have a severe socio-economic impact. During drought years, the interhemispheric SST gradient in the tropical Atlantic is steep and the ITCZ stays far North, while the waters of the eastern equatorial Pacific tend to be anomalously warm. Based on the extensive diagnostic exploration of the circulation mechanisms of interannual climate variability, empirical methods have been developed for the forecasting of the Nordeste rainy season. These have been applied in the real-time prediction of seasonal rainfall anomalies throughout the last decade of the 20th century. 相似文献
9.
This paper applies the newest emission scenarios of the sulfur and greenhouse gases, namely IPCC SRES A2 and B2 scenarios, to investigate the change of the North China climate with an atmosphere-ocean coupled general circulation model. In the last three decades of the 21st century, the global warming enlarges the land-sea thermal contrast, and hence, causes the East Asian summer (winter) monsoon circulation to be strengthened (weakened). The rainfall seasonality strengthens and the summer precipitation increases significantly in North China. It is suggested that the East Asian rainy area would expand northward to North China in the last three decades of the 21st century. In addition, the North China precipitation would increase significantly in September. In July, August, and September, the interannual variability of the precipitation enlarges evidentlv over North China. implying a risk of flooding in the future. 相似文献
10.
文章比较了各种气候模式对温室效应的估计，及其可能对中国气候的影响。分析和预测了太阳活动与火山活动的长期变化，在此基础上估计了未来可能产生的自然气候变化。结果表明，在未来50年中太阳活动和火山活动均可能使气候变冷。因此，可能在一定程度上抵消因温室效应加剧而产生的变暖。但在2010年之后，温室效应可能逐步占据主导地位，到2030年全球平均气温可能比1961～1990年平均上升0.6℃以上，东亚地区的增温，可能比全球平均稍强。气候变暖后，东亚地区降水可能增加。但在我国北方，夏季干旱程度可能加大。 相似文献
11.
Intraseasonal oscillation of the rainfall variability over Rwanda and evaluation of its subseasonal forecasting skill 
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下载免费PDF全文 非洲中东部地区的经济主要依靠自给农业支撑,该地区农业经济对降水的变化尤为敏感.本文以卢旺达为例,观测分析指出卢旺达的次季节降雨主要集中在10-25天;根据次季节尺度降水变率的单点相关方法,发现卢旺达的次季节降水变率和周围区域变化一致;进一步合成结果显示该地区次季节降水变率与异常西风有关,这可追溯到赤道地区西传的赤道Rossby波.最后,本文评估了当前动力模式ECMWF对 卢旺达地区(即非洲中东部)次季节降水变率的预报能力,发现EC模式在对该区域降水和相关风场指数的预报技巧都在18天左右,且预报技巧表现出一定的年际差异,这可能与热带太平洋的背景海温信号有关.该工作增进了当 前对非洲中东部地区的次季节降水变率和预测水平的认知,并且对该地区国家粮食安全和防灾减灾具有启示性意义. 相似文献
12.
Summary Preliminary climatological statistics of extreme weather events over the southern Africa region are established through analysis of daily weather maps of the South African Weather Bureau for a twenty year peiod, 1973–1992. Influences of global warming and inter-annual variability imposed by El Nino events, amongst others, are sought. Notable trends include a decrease in the frequency of station days with rainfall > 70 mm and an increase in station days with temperature > 38°C. Correlations offer some insights to extreme climate associations. Lows over the land in the west and over the sea to the east display consistent interannual variability, despite opposing rainfall regimes. Agreement in extreme temperature statistics in all regions suggest that drought is widespread over southern Africa. Rainfall in the north is negatively related to lows over the sea to the south. A potential mechanism underlying the inverse relationship between midlatitude and sub-tropical storminess is the development of a vorticity dipole associated with the westerly jet stream. This is investigated in an El Nino-influenced case study.With 9 Figures 相似文献
13.
14.
A possible linkage in the interdecadal variability of rainfall over North China and the Sahel 总被引：8，自引：0，他引：8
1. Introduction The capital city of China, Beijing, and other largecities, such as Tianjin and Shijiazhuang are all locatedin North China (roughly the region 35?–40?N, 110?–125?E), a region with a very large population. In thepast several decades, the rainfall decreased remarkablyin North China. Nevertheless, the amount of waterdemanded by agriculture and industry and the popu-lation at large has increased. These two trends havemade the de?ciency of water resources in North Chinabeco… 相似文献
15.
Summary Variability of rainfall in the semi-arid regions can cause problems in evaluating experimental trials. To describe the spatial rainfall patterns over a large experimental station, rainfall was monitored during the 1986 and 1987 rainy seasons using 18 raingages over the 500 ha experimental station of ICRISAT Sahelian Center, in Niger, West Africa. Average relative variability of individual rain storms, defined as the percentage deviation from the mean, varied from 2 to 62%, while the variability over the rainy season was 17.1%. Isohyetal patterns of individual rain storms as well as seasonal totals showed distinct coherence in the spatial pattern over the station. The effects of total volume, duration, direction and intensity of storms and the time of year on the spatial correlations were analyzed. Storm value showed a large influence on the correlation decay with distance. Correlations in the W — E and SW — NE directions were higher in comparison to those in the N — S and NW — SE directions. Point rainfall measurements were better correlated with the network average rainfall than with the rainfall recorded at the meteorological station. Variograms among raingages revealed that the distance of independence was approximately 1 000 m for almost all storms. Use of a network of raingages over agricultural experiment stations reduces the average relative variability of areal rainfall estimates and provides a means to develop simple relations for estimation of point rainfall for individual applications.With 8 Figures 相似文献
16.
Precipitation extremes in a karst region: a case study in the Guizhou province, southwest China 总被引：3，自引：2，他引：1
Qiang Zhang Chong-Yu Xu Zengxin Zhang Xi Chen Zhaoqing Han 《Theoretical and Applied Climatology》2010,99(1-2):53-65
The topography of hilly landscapes modifies crop environment changing the fluxes of water and energy, increasing risk in these vulnerable agriculture systems, which could become more accentuated under climate change (drought, increased variability of rainfall). In order to quantify how wheat production in hilly terrain will be affected by future climate, a newly developed and calibrated micro-meteorological model for hilly terrain was linked to a crop growth simulation model to analyse impact scenarios for different European regions. Distributions of yield and growing length of rainfed winter wheat and durum wheat were generated as probabilistic indices from baseline and low (B2) and high (A2) emission climate scenarios provided from the Hadley Centre Regional Climate Model (HadRM3). We used site-specific terrain parameters for two sample catchments in Europe, ranging from humid temperate (southeast UK) to semi-arid Mediterranean (southern Italy). Results for baseline scenario show that UK winter wheat is mainly affected by annual differences in precipitation and yield distributions do not change with terrain, whilst in the southern Mediterranean climate yield variability is significantly related to a slope × elevation index. For future climate, our simulations confirm earlier predictions of yield increase in the UK, even under the high emission scenario. In the southern Mediterranean, yield reduction is significantly related to slope × elevation index increasing crop failure in drier elevated spots but not in wet years under baseline weather. In scenarios for the future, the likelihood of crop failure rises sharply to more than 60%, and even in wet years, yields are likely to decrease in elevated spots. 相似文献
17.
Impacts of Present and Future Climate Change and Climate Variability on Agriculture in the Temperate Regions: North America 总被引：2，自引：0，他引：2
The potential impact of climate variability and climate change on agricultural production in the United States and Canada
varies generally by latitude. Largest reductions are projected in southern crop areas due to increased temperatures and reduced
water availability. A longer growing season and projected increases in CO2 may enhance crop yields in northern growing areas. Major factors in these scenarios analyzes are increased drought tendencies
and more extreme weather events, both of which are detrimental to agriculture. Increasing competition for water between agriculture
and non-agricultural users also focuses attention on water management issues. Agriculture also has impact on the greenhouse
gas balance. Forests and soils are natural sinks for CO2. Removal of forests and changes in land use, associated with the conversion from rural to urban domains, alters these natural
sinks. Agricultural livestock and rice cultivation are leading contributors to methane emission into the atmosphere. The application
of fertilizers is also a significant contributor to nitrous oxide emission into the atmosphere. Thus, efficient management
strategies in agriculture can play an important role in managing the sources and sinks of greenhouse gases. Forest and land
management can be effective tools in mitigating the greenhouse effect. 相似文献
18.
Future projections of winter rainfall in southeast Australia using a statistical downscaling technique 总被引：1，自引：0，他引：1
Much of southeast Australia has experienced rainfall substantially below the long-term average since 1997. This protracted
drought is particularly noticeable in those parts of South Australia and Victoria which experience a winter (May through October)
rainfall peak. For the most part, the recent meteorological drought has affected the first half of the rainfall season May–June–July
(MJJ), while rainfall during the second half August–September–October (ASO) has been much closer to the long term average.
The recent multi-year drought is without precedent in the instrumental record, and is qualitatively similar to the abrupt
decline in rainfall which was observed in the southwest of Western Australia in the 1960 and 1970s. Using a statistical downscaling
technique, the rainfall decline is linked to observed changes in large-scale atmospheric fields (mean sea level pressure and
precipitable water). This technique is able to reproduce the statistical properties of rainfall in southeast Australia, including
the interannual variability and longer time-scale changes. This has revealed that the rainfall recent decline may be explained
by a shift to higher pressures and lower atmospheric precipitable water in the region. To explore the likely future evolution
of rainfall in southeast Australia under human induced climate change, the same statistical downscaling technique is applied
to five climate models forced with increasing greenhouse gas concentrations. This reveals that average rainfall in the region
is likely to decline in the future as greenhouse gas concentrations increase, with the greatest decline occurring during the
first half of winter. Projected declines vary amongst models but are generally smaller than the recent early winter rainfall
deficits. In contrast, the rainfall decline in late winter–spring is larger in future projections than the recent rainfall
deficits have been. We illustrate the consequences of the observed and projected rainfall declines on water supply to the
major city of Melbourne, using a simple rainfall run-off relationship. This suggests that the water resources may be dramatically
affected by future climate change, with percentage reductions approximately twice as large as corresponding changes in rainfall. 相似文献
19.
There is an increasing need to understand what makes vegetation at some locations more sensitive to climate change than others. For savanna rangelands, this requires building knowledge of how forage production in different land types will respond to climate change, and identifying how location-specific land type characteristics, climate and land management control the magnitude and direction of its responses to change. Here, a simulation analysis is used to explore how forage production in 14 land types of the north-eastern Australian rangelands responds to three climate change scenarios of +3°C, +17% rainfall; +2°C, ?7% rainfall; and +3°C, ?46% rainfall. Our results demonstrate that the controls on forage production responses are complex, with functional characteristics of land types interacting to determine the magnitude and direction of change. Forage production may increase by up to 60% or decrease by up to 90% in response to the extreme scenarios of change. The magnitude of these responses is dependent on whether forage production is water or nitrogen (N) limited, and how climate changes influence these limiting conditions. Forage production responds most to changes in temperature and moisture availability in land types that are water-limited, and shows the least amount of change when growth is restricted by N availability. The fertilisation effects of doubled atmospheric CO2 were found to offset declines in forage production under 2°C warming and a 7% reduction in rainfall. However, rising tree densities and declining land condition are shown to reduce potential opportunities from increases in forage production and raise the sensitivity of pastures to climate-induced water stress. Knowledge of these interactions can be applied in engaging with stakeholders to identify adaptation options. 相似文献