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1.
Tiganadaba Lodoun Moussa Sanon Alessandra Giannini Pierre Sibiry Traoré Léopold Somé Jeanne Millogo Rasolodimby 《Theoretical and Applied Climatology》2014,117(3-4):485-494
In the Sahel region, seasonal predictions are crucial to alleviate the impacts of climate variability on populations' livelihoods. Agricultural planning (e.g., decisions about sowing date, fertilizer application date, and choice of crop or cultivar) is based on empirical predictive indices whose accuracy to date has not been scientifically proven. This paper attempts to statistically test whether the pattern of rainfall distribution over the May–July period contributes to predicting the real onset date and the nature (wet or dry) of the rainy season, as farmers believe. To that end, we considered historical records of daily rainfall from 51 stations spanning the period 1920–2008 and the different agro-climatic zones in Burkina Faso. We performed (1) principal component analysis to identify climatic zones, based on the patterns of intra-seasonal rainfall, (2) and linear discriminant analysis to find the best rainfall-based variables to distinguish between real and false onset dates of the rainy season, and between wet and dry seasons in each climatic zone. A total of nine climatic zones were identified in each of which, based on rainfall records from May to July, we derived linear discriminant functions to correctly predict the nature of a potential onset date of the rainy season (real or false) and that of the rainy season (dry or wet) in at least three cases out of five. These functions should contribute to alleviating the negative impacts of climate variability in the different climatic zones of Burkina Faso. 相似文献
2.
Boubacar Ibrahim Harouna Karambiri Jan Polcher Hamma Yacouba Pierre Ribstein 《Climate Dynamics》2014,42(5-6):1363-1381
Sahelian rainfall has recorded a high variability during the last century with a significant decrease (more than 20 %) in the annual rainfall amount since 1970. Using a linear regression model, the fluctuations of the annual rainfall from the observations over Burkina Faso during 1961–2009 period are described through the changes in the characteristics of the rainy season. The methodology is then applied to simulated rainfall data produced by five regional climate models under A1B scenario over two periods: 1971–2000 as reference period and 2021–2050 as projection period. As found with other climate models, the projected change in annual rainfall for West Africa is very uncertain. However, the present study shows that some features of the impact of climate change on rainfall regime in the region are robust. The number of the low rainfall events (0.1–5 mm/d) is projected to decrease by 3 % and the number of strong rainfall events (>50 mm/d) is expected to increase by 15 % on average. In addition, the rainy season onset is projected by all models to be delayed by one week on average and a consensus exists on the lengthening of the dry spells at about 20 %. Furthermore, the simulated relationship between changed annual rainfall amounts and the number of rain days or their intensity varies strongly from one model to another and some changes do not correspond to what is observed for the rainfall variability over the last 50 years. 相似文献
3.
The evolution of seasonal cycle and interannual rainfall, the number of rainy days and daily rainfall types, dry spells frequency of occurrence, onset/cessation/length of rainy season, sowing dates, and the duration of the cropping period, are investigated at local (individual sites) and sub-regional scales (four different rainfall zones) using daily records of station data (83 sites) over Senegal. In the limits of a case study, these analyses complement and update previous studies conducted in the extreme Western Sahel (11?C16° N and 20° W?C10° E). The results unveil noticeable evolution of some of these rain-based factors in the recent periods as compared to the previous dry years. In the regions recording less than 800?mm/year (Sudan and Sahel sub-regions), the positive and statistically significant trends of rainfall amount are associated with new features of increasing frequency of short dry spell category, increasing number of some classes of extreme daily rainfall amounts and shifts in the peak number of rainy days. At sub-regional scales, the starting years (or change points) the magnitude and the signs of the new trends are unevenly distributed in the period post-1990. Earlier and higher amplitude changes are found at local scales and not less than one third of the sites in each sub-regional network are significantly affected. The extreme Southern sub-region exhibits no significant changes. Statistically significant trends are not observed on daily rain records ??10?mm, onset/cessation dates, successful sowing dates, rainy season length, cropping period, medium and extreme dry spell categories. Rather, some of these factors such as the successful sowing date and the cropping season length exhibit significant variability. The onset (cessation) dates of the rainy season are followed (preceded) by extreme dry spell episodes. In the perspectives of climate impact assessments on the local agriculture a sub-regional periodic synopsis of the major rain-based factors of interest to agricultural applications are provided at the end the paper. They document some important internal variability patterns to reckon with in a multi-decadal work over the 1950?C2008 period for this region. 相似文献
4.
基于对汛期的理解和认识, 利用Samel等人设计的半客观统计分析方法、Mann-Kendall突变分析、滑动t检验等方法, 通过分析和研究1957—2006年华北台站的日降水资料, 确定了华北汛期起讫的日期。结果表明:华北汛期始于6月30日, 止于8月18日, 持续期为50d。华北汛期的起讫日期、持续天数以及空汛发生的频次, 具有鲜明的地域特征:冀北山地汛期开始最早, 结束较迟, 持续天数较长, 空汛发生频次最少; 黄土高原汛期开始较迟, 其北部汛期结束最迟, 持续期也最长, 发生空汛的频次也比较多; 黄河下游地区汛期开始比较早, 结束最早, 汛期最短, 发生无大汛的频次较大; 河北平原地区, 汛期开始最迟, 结束较迟, 汛期较长, 发生无大汛的频次最多。与华北汛期开始和结束日相对应的东亚大气环流特征是:当西太平洋西部上空500hPa存在正的位势高度距平, 华北上空存在负的位势高度距平, 同时地面为“东高西低”的异常海平面气压场配置时, 异常偏南风到达30°N, 华北汛期开始; 当华北上空500hPa为较小的位势高度正距平, 日本海为位势高度正距平, 而地面上, 我国大陆和西太平洋之间为“西高东低”的异常海平面气压场配置时, 异常偏北风控制我国东部地区, 华北汛期结束。 相似文献
5.
This study was targeted at evaluating the performance of six Regional Climate Models (RCMs) used in Coordinated Regional Climate Downscaling Experiment (CORDEX). The evaluation is on the bases of how well the RCMs simulate the seasonal mean climatology, interannual variability and annual cycles of rainfall, maximum and minimum temperature over two catchments in western Ethiopia during the period 1990–2008. Observed data obtained from the Ethiopian National Meteorological Agency was used for performance evaluation of the RCMs outputs. All Regional Climate Models (RCMs) have simulated seasonal mean annual cycles of precipitation with a significant bias shown on individual models; however, the ensemble mean exhibited better the magnitude and seasonal rainfall. Despite the highest biases of RCMs in the wet season, the annual cycle showed the prominent features of precipitation in the two catchments. In many aspects, CRCM5 and RACMO22 T simulate rainfall over most stations better than the other models. The highest biases are associated with the highest error in simulating maximum and minimum temperature with the highest biases in high elevation areas. The rainfall interannual variability is less evident in Finchaa with short rainy season experiencing a larger degree of interannual variability. The differences in performance of the Regional Climate Models in the two catchments show that all the available models are not equally good for particular locations and topographies. In this regard, the right regional climate models have to be used for any climate change impact study for local-scale climate projections. 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.
Mark R. Jury 《Theoretical and Applied Climatology》2010,101(1-2):29-40
Ethiopian decadal climate variability is characterized by application of singular value decomposition to gridded rainfall data over the period 1901–2007. Two distinct modes are revealed with different annual cycles and opposing responses to regional and global forcing. The northern zone that impacts the Nile River and underlies the tropical easterly jet has a unimodal rainy season that is enhanced by Atlantic Multidecadal Oscillation warm phase. This rainfall mode is linked with the Atlantic zonal overturning circulation and exhibits 10–12-year cycles through much of the twentieth century. The southern zone has a bimodal rainy season that is enhanced by Pacific Decadal Oscillation cool phase and the southern meridional overturning circulation. Multiyear wet and dry spells are characterized by sympathetic responses in the near-equatorial trough extending from Central America across the African Sahel to Southeast Asia. The interaction of Walker and Hadley cells over Africa appears to be a key feature that modulates Ethiopian climate at decadal frequency through anomalous north–south displacement of the near-equatorial trough. 相似文献
8.
During the last 30 years, the climate of the West African Sahel has undergone various changes, especially in terms of rainfall. This has large consequences for the poor-resource farmers depending mainly on rainfed agriculture. This paper investigates the impacts of current climate variability and future climate change on groundnut and cowpea production in Niger for three major agricultural regions, including the groundnut basin.Niger was one of the largest West African groundnut producing and exporting countries. Groundnut production – as a cash crop – dropped fromabout 312,000 tons in the mid 1960s (about 68% exported) to as low as 13,000tons in 1988 and increased again to 110,000 tons in 2000. Cowpea, a food crop, showsa different tendency, going from 4,000 tons in the mid fifties to a maximum of 775,000 tons in 1997, and its cultivated area is still increasing. It is also a cash crop in local economies (especially for women).To highlight the impact of climate change on groundnut and cowpea production (significantly determined by rainfall in July, August and September), the following components of the rainfall regime were calculated for the period 1951–1998: mean annual and monthly rainfall, beginning, end and lengthof the rainy season, number of rainy days per month, amount of rainfall per rainy day and the maximum length of dry spell per month. Three sub-periods whose duration varied per region were defined: for Dosso 1951–1968,1969–1984 and 1985–1998; for Maradi 1951–1970, 1971–1987 and1988–1998; and for Zinder 1951–1966, 1967–1984 and 1985–1998. A change in rainfallregime components was observed between the three sub-periods, which were characterized in chronological order by wet, dry and intermediate conditions. To assess the impact of climate variability and change on groundnut and cowpea production, a statistical modeling approach has been followed, based on thirteen predictors as described and discussed in the preceding paper. Climate change is mimicked in terms of reduced total amount of rainfall for the three main rainfall months and an increased temperature, while maintaining other significant predictors at a constant level. In 2025,production of groundnut is estimated to be between 11 and 25% lower, while cowpeayield will fall maximally 30%. Various strategies to compensate thispotential loss are presented for the two crops. 相似文献
9.
Variations of Meiyu Indicators in the Yangtze-Huaihe River Basin during 1954-2003 总被引：1，自引：0，他引：1 
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下载免费PDF全文 1. IntroductionThe primary physical manifestation of the EastAsian summer monsoon is persistent, heavy precipita-tion identified with a coherent, well-defined rainband.Generally, such rainband movement is characterizedby a stepwise northward advance from southern Chinaand the western North Pacific in early-mid May to theYangtze River valley and southern Japan in mid-June,then to north China and the Yellow Sea as well as thesouthern Japan Sea in late July (Ding, 1992, 1994;Tao and Chen, … 相似文献
10.
辽宁雨季和多雨季标准的划分研究 总被引：4，自引：0，他引：4
遵循针对性、可靠性、实用性和可操作性的原则,对1951—2005年降水量和副热带高压脊线资料进行了统计分析。结果表明:采用降水量作为雨季划分标准,以副热带高压脊线位置作为多雨季划分标准,可得出辽宁各地雨季、多雨季常年起止时间,历年最早、最晚起止时间,从而使雨季、多雨季得以定时、定量预报,进而为防灾、减灾工作提供气象依据。同时得出,辽宁平均雨季降水量占全年平均降水量的60.8%,95%的区域性暴雨(暴雨站数大于等于3)出现在雨季时段内,雨季日数与雨季期间暴雨次数相关系数为0.97,与雨季期间总降水量相关系数为0.98;较强降水过程、重大洪涝灾害集中在多雨季,多雨季时段内辽宁大范围区域性暴雨(暴雨站数大于等于10)次数占全年总次数的70%。多雨季日数的长短一定程度上决定了大范围区域性暴雨的次数,同时决定了多雨季期间的总降水量。 相似文献
11.
Caribbean Sea rainfall variability during the rainy season and relationship to the equatorial Pacific and tropical Atlantic SST 总被引：1，自引：1，他引：0
The present study investigates the Caribbean Sea rainfall variability during the early and late rainy seasons and its association with sea surface temperature (SST) and air?Csea interaction based on observational estimates, the NCEP Climate Forecast System (CFS) and Global Forecast System (GFS) simulations, and the CFS retrospective forecasts. Analysis of the observational estimates indicates that air?Csea interaction is important over the Caribbean Sea, whereas the atmospheric forcing of SST dominates over the Gulf of Mexico. The CFS simulation captures the basic elements of this observed air?Csea relationship. The GFS simulation produces spurious SST forcing of the atmosphere over the Gulf of Mexico largely due to prescribing SST. The CFS forecasts capture the air?Csea relationship in the late rainy season (August?COctober), but cannot reproduce the SST forcing of atmosphere over the Caribbean Sea in the early rainy season (May?CJuly). An empirical orthogonal function (EOF) analysis indicates that the leading modes of percent anomalies of the rainy season precipitation have the largest loading in the southern Caribbean Sea in observations. The model simulations and forecasts skillfully reproduce the spatial pattern, but not the temporal evolution. The Caribbean Sea rainfall variability in the early rainy season is mainly due to the tropical North Atlantic (TNA) SST anomalies in observations, is contributed by both the TNA and eastern equatorial Pacific (EEP) SST anomalies in the CFS simulation, and has an overly large impact from the EEP SST anomalies in the GFS simulation and the CFS forecasts. The observed Caribbean Sea rainfall variability in the late rainy season has a leading impact from the EEP SST anomalies, with a secondary contribution from the TNA SST anomalies. In comparison, the model simulations and forecasts overestimate the impacts of the EEP SST anomalies due to an earlier development and longer duration of the El Ni?o-Southern Oscillation in the CFS compared to observations. 相似文献
12.
Intraseasonal oscillation of the rainfall variability over Rwanda and evaluation of its subseasonal forecasting skill 下载免费PDF全文
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
13.
14.
Simulation and Projection of Changes in Rainy Season Precipitation over China Using the WRF Model 总被引：2，自引：0，他引：2
The Weather Research and Forecasting (WRF) model is used in a regional climate model configuration to simulate past precipitation climate of China during the rainy season (May-September) of 1981-2000, and to investigate potential future (2041-2060 and 2081-2100) changes in precipitation over China relative to the reference period 1981-2000. WRF is run with initial conditions from a coupled general circulation model, i.e., the high-resolution version of MIROC (Model for Interdisciplinary Research on Climate). WRF reproduces the observed distribution of rainy season precipitation in 1981-2000 and its interannual variations better than MIROC. MIROC projects increases in rainy season precipitation over most parts of China and decreases of more than 25 mm over parts of Taiwan and central Tibet by the mid-21st century. WRF projects decreases in rainfall over southern Tibetan Plateau, Southwest China, and northwestern part of Northeast China, and increases in rainfall by more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River during 2041-2060. MIROC projects further increases in rainfall over most of China by the end of the 21st century, although simulated rainfall decreases by more than 25 mm over parts of Taiwan, Guangxi, Guizhou, and central Tibet. WRF projects increased rainfall of more than 100 mm along the southeastern margin of the Tibetan Plateau and over the lower reaches of the Yangtze River and decreased rainfall over Southwest China, and southern Tibetan Plateau by the end of the 21st century. 相似文献
15.
Besides sea surface temperature (SST), soil moisture (SM) exhibits a significant memory and is likely to contribute to atmospheric
predictability at the seasonal timescale. In this respect, West Africa was recently highlighted as a “hot spot” where the
land–atmosphere coupling could play an important role, through the recycling of precipitation and the modulation of the meridional
gradient of moist static energy. Particularly intriguing is the observed relationship between summer monsoon rainfall over
Sahel and the previous second rainy season over the Guinean Coast, suggesting the possibility of a soil moisture memory beyond
the seasonal timescale. The present study is aimed at revisiting this question through a detailed analysis of the instrumental
record and a set of numerical sensitivity experiments. Three ensembles of global atmospheric simulations have been designed
to assess the relative influence of SST and SM boundary conditions on the West African monsoon predictability over the 1986–1995
period. On the one hand, the results indicate that SM contributes to rainfall predictability at the end and just after the
rainy season over the Sahel, through a positive soil-precipitation feedback that is consistent with the “hot spot” hypothesis.
On the other hand, SM memory decreases very rapidly during the dry season and does not contribute to the predictability of
the all-summer monsoon rainfall. Though possibly model dependent, this conclusion is reinforced by the statistical analysis
of the summer monsoon rainfall variability over the Sahel and its link with tropical SSTs. Our results indeed suggest that
the apparent relationship with the previous second rainy season over the Guinean Coast is mainly an artefact of rainfall teleconnections
with tropical modes of SST variability both at interannual and multi-decadal timescales. 相似文献
16.
Summary Groundnut production strongly contributes to Senegal’s economy. Interannual variations of groundnut yield for the country
as a whole, and their relationship with rainfall amounts, are examined for the 31-yr period 1960–1990. It is shown that on
that scale, and after removing decadal trends, almost half of the variance is explained by rainfall variability, especially
that of the early part of the rainy season (July–August). Given the high spatial coherence of seasonal rainfall in the region,
teleconnections with global- and regional-scale climate dynamics, including sea-surface temperatures, are assessed. Though
some features are similar to the rest of the Sahel, others are more specific, such as the higher sensitivity to ENSO (El-Ni?o
Southern Oscillation) and to coupled ocean-atmosphere climate anomalies over the nearby Tropical North Atlantic Ocean, which
are associated to the latitudinal location of the ITCZ over the ocean. Lag-correlations with pre-season SST are also discussed.
Some of these teleconnections are used to define preliminary empirical models for rainfall and groundnut yield prediction
for Senegal.
Received March 23, 1998 Revised January 11, 1999 相似文献
17.
18.
Assessment of a climate model to reproduce rainfall variability and extremes over Southern Africa 总被引：1，自引：1，他引：0
It is increasingly accepted that any possible climate change will not only have an influence on mean climate but may also significantly alter climatic variability. A change in the distribution and magnitude of extreme rainfall events (associated with changing variability), such as droughts or flooding, may have a far greater impact on human and natural systems than a changing mean. This issue is of particular importance for environmentally vulnerable regions such as southern Africa. The sub-continent is considered especially vulnerable to and ill-equipped (in terms of adaptation) for extreme events, due to a number of factors including extensive poverty, famine, disease and political instability. Rainfall variability and the identification of rainfall extremes is a function of scale, so high spatial and temporal resolution data are preferred to identify extreme events and accurately predict future variability. The majority of previous climate model verification studies have compared model output with observational data at monthly timescales. In this research, the assessment of ability of a state of the art climate model to simulate climate at daily timescales is carried out using satellite-derived rainfall data from the Microwave Infrared Rainfall Algorithm (MIRA). This dataset covers the period from 1993 to 2002 and the whole of southern Africa at a spatial resolution of 0.1° longitude/latitude. This paper concentrates primarily on the ability of the model to simulate the spatial and temporal patterns of present-day rainfall variability over southern Africa and is not intended to discuss possible future changes in climate as these have been documented elsewhere. Simulations of current climate from the UK Meteorological Office Hadley Centre’s climate model, in both regional and global mode, are firstly compared to the MIRA dataset at daily timescales. Secondly, the ability of the model to reproduce daily rainfall extremes is assessed, again by a comparison with extremes from the MIRA dataset. The results suggest that the model reproduces the number and spatial distribution of rainfall extremes with some accuracy, but that mean rainfall and rainfall variability is under-estimated (over-estimated) over wet (dry) regions of southern Africa. 相似文献
19.
The characteristics of rainfall regime and its variability in the sub-humid region of mid-Ghana is analyzed using daily rainfall data from the Wenchi, 1950–2000. Prior research in the area, suggests that climatic variability occurs at lower frequencies than the typical ENSO signal and may be more closely related to noted shifts in global climatic patterns. Fifty-six possible starting dates encompassing the traditional growing season, extending from late January to early November, at 5 day increments, are used to define temporal units of varying lengths, variable temporal units (VTUs). Rainfall characteristics in each unit are described by two variables: total rainfall and number of rainy days. Given the widely noted global climatic shift in the 1970s and the results of regional analyses, the 50 year record is sub-divided into two 20 year periods, 1950–1969 (period 1) and 1980–2000 (period 2). The means and variances of the two variables in each VTU are compared to identify any times when the changes in rainfall characteristics are most noticeable within the rainfall regime between periods. Both variables yield results consistent with the main rainy season and the long dry season being relatively unchanged, however the short dry spell is becoming wetter and the minor rainy season (September/October) has become significantly drier and shorter. The observations are consistent with the general north–south erosion of the bi-modal regime in West African which is associated with the southward shift of the ITCZ and the monsoonal system. This phenomenon is believed to be ongoing for the last 10,000 years in step with the hypothesized shift of the perihelion into the boreal winter. The use of independent arbitrary starting dates and durations (VTU) advances the understanding of temporal variability of rainfall, at a scale appropriate to agricultural practices in the study area. 相似文献
20.
J. A. Mabbutt 《Climatic change》1989,15(1-2):191-221
Tropical semi-arid climates occur between 10 and 35 deg latitude and are characterised by highly variable summer rainfall of between 300 and 750 mm in a rainy season of at least 4 months, generally adequate for rainfed cropping but with considerable drought risk. They support a mesic savanna vegetation. They have a land extent of 4.5 million km2, mainly occupied by Third World nations with rapidly increasing populations which in the main are predominantly rural and largely agricultural with low per capita incomes, consequently vulnerable to climate change. A doubling of atmospheric CO2 by the year 2030 is predicted to cause a rise in equilibrium mean temperature of 1–3 °C; however there is continuing uncertainty regarding the consequences for rainfall amount, variability and intensity, length of rainy season or the frequency of extreme rainfall events. Two scenarios are considered, with reduction and increase in rainfall respectively, involving corresponding latitudinal shifts in present climatic boundaries of about 200 km. Because of their variability, a clear signal of the greenhouse effect on these climates may be delayed, whilst regional responses may differ. Vegetational and hydrological responses under the alternative scenarios are considered. The possible consequences for rainfed and irrigated agriculture, water and energy supplies and disease and pest ecology are discussed. Lands of the semi-arid tropics are already extensively desertified, with consequent lowered productivity and heightened vulnerability to drought, and the possible impacts of greenhouse warming on desertification processes and on measures for land rehabilition to the year 2030 are reviewed. Measures to conserve the biological diversity of savanna lands in face of greenhouse warming are discussed. 相似文献