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1.
Effect of spatial correlation on regional trends in rain events over India   总被引：2，自引：0，他引：2  
The regional trends are evaluated in the frequency of various rain events using the daily gridded (1°?×?1°) rainfall dataset for the time period 1901–2004, prepared by the India Meteorological Department (IMD). In terms of intensity, the events are classified as low, moderate, heavy and extreme heavy, while short and long spells are classified on the basis of duration of rainfall. The analytical (parametric) and the empirical (bootstrap) techniques were used to incorporate the impact of spatial correlation in regional trends. It is observed that, consideration of spatial correlation reduces the significance level of the trends and the effective number of grid points falling under each category. Especially, the noticeable cross-correlation have reduced the significance of the trends in moderate and long spell rain events to a large extent, while the significance of trends in the extreme heavy and short spell events is not highly affected because of small cross-correlation.  相似文献   

2.
Summary The present study is an analysis of the observed extreme temperature and precipitation trends over Yangtze from 1960 to 2002 on the basis of the daily data from 108 meteorological stations. The intention is to identify whether or not the frequency or intensity of extreme events has increased with climate warming over Yangtze River basin in the last 40 years. Both the Mann-Kendall (MK) trend test and simple linear regression were utilized to detect monotonic trends in annual and seasonal extremes. Trend tests reveal that the annual and seasonal mean maximum and minimum temperature trend is characterized by a positive trend and that the strongest trend is found in the winter mean minimum in the Yangtze. However, the observed significant trend on the upper Yangtze reaches is less than that found on the middle and lower Yangtze reaches and for the mean maximum is much less than that of the mean minimum. From the basin-wide point of view, significant increasing trends are observed in 1-day extreme temperature in summer and winter minimum, but there is no significant trend for 1-day maximum temperature. Moreover, the number of cold days ≤0 °C and ≤10 °C shows significant decrease, while the number of hot days (daily value ≥35 °C) shows only a minor decrease. The upward trends found in the winter minimum temperature in both the mean and the extreme value provide evidence of the warming-up of winter and of the weakening of temperature extremes in the Yangtze in last few decades. The monsoon climate implies that precipitation amount peaks in summer as does the occurrence of heavy rainfall events. While the trend test has revealed a significant trend in summer rainfall, no statistically significant change was observed in heavy rain intensity. The 1-day, 3-day and 7-day extremes show only a minor increase from a basin-wide point of view. However, a significant positive trend was found for the number of rainstorm days (daily rainfall ≥50 mm). The increase of rainstorm frequency, rather than intensity, on the middle and lower reaches contributes most to the positive trend in summer precipitation in the Yangtze.  相似文献   

3.
A new technique for identifying regional climate events, the Objective Identification Technique for Regional Extreme Events(OITREE), was applied to investigate the characteristics of regional heavy rainfall events in China during the period1961–2012. In total, 373 regional heavy rainfall events(RHREs) were identified during the past 52 years. The East Asian summer monsoon(EASM) had an important influence on the annual variations of China's RHRE activities, with a significant relationship between the intensity of the RHREs and the intensity of the Mei-yu. Although the increase in the frequency of those RHREs was not significant, China experienced more severe and extreme regional rainfall events in the 1990 s. The middle and lower reaches of the Yangtze River and the northern part of South China were the regions in the country most susceptible to extreme precipitation events. Some stations showed significant increasing trends in the southern part of the middle and lower reaches of the Yangtze River and the northern part of South China, while parts of North China, regions between Guangxi and Guangdong, and northern Sichuan showed decreasing trends in the accumulated intensity of RHREs.The spatial distribution of the linear trends of events' accumulated intensity displayed a similar so-called "southern flooding and northern drought" pattern over eastern China in recent decades.  相似文献   

4.
The contribution of Cut-off Lows (CoLs) to precipitation and extreme rainfall frequency in South Africa has been quantified from 402 station records over the period 1979–2006. Firstly, 500 hPa CoL trajectories over Southern Africa and surrounding oceans were determined and their features thoroughly analyzed. In a second step, using daily precipitable water, outgoing long wave radiation data and station rainfall records, an area was defined where the occurrence of CoLs is associated with rainfall over South Africa. CoLs transiting in the 2.5°E–32.5°E/20°S–45°S are more likely to produce precipitation over the country. When 500 hPa CoLs are centered just off the west coast of the country (around 15°E/32.5°S) their impact is substantial in term of daily rainfall intensity and spatial coverage. CoL rainy days have been studied and it is shown that they significantly contribute to precipitation in South Africa, more strongly along the south and east coasts as well as inland, over the transition zone between the summer and winter rainfall domains where they contribute between 25 to more than 35 % of annual accumulation. At the country scale, CoL rainfall is more intense and widespread in spring than during other seasons. Over the analyzed period, a significant trend in annual CoLs’ frequency shows an increase of about 25 %. This increase is mainly realized in spring and in a lesser extent in summer. This trend is accompanied by a significant increase in the frequency of CoL rainy days specifically along the south coast and over the East of the country during the spring–summer period. In parallel, it is shown that from late spring until summer CoLs’ frequency varies significantly accordingly with large scale circulation modes of the Southern Hemisphere such as the Pacific South American pattern (PSA). This positive trend in CoLs’ frequency may be related with the positive trend in the PSA during the spring–summer period over the three last decades.  相似文献   

5.
利用2010-2019年浙江省暖季(5-9月)1426个国家站和区域站小时雨量数据和NCEP 1° X 1°逐日4次再分析资料,分析了浙江省暖季短时强降水、极端短时强降水时空分布特征及区域性短时强降水事件,结果表明:①近10年暖季短时强降水频次呈增多趋势,降水强度变化平稳;8月(上旬)降水频次最多,9月(中旬)强度最强...  相似文献   

6.
研究大陆或次大陆尺度日降水长期趋势变化规律,对于检测、理解区域气候和陆地水循环对全球气候变暖的响应特征十分重要。利用美国国家气候资料中心(NCDC)和中国基准气候站、基本气象站网降水观测资料,在对该站点资料进行基本质量控制基础上,选取东亚地区619个站1951～2009年日降水数据,按照百分位阈值对降水进行分级,共分为弱、中、强、极强4个级别,用经纬度网格面积加权平均方法构建区域平均的时间序列,分析了各类降水事件长期变化趋势的时空特征。结果表明:东亚地区近59年平均总降水量表现出不显著下降趋势,降水日数没有出现趋势性变化,平均日降水强度略有减小;区域平均的年降水量、降水日数和日降水强度在中国北方大部、蒙古东部、俄罗斯远东地区南部和日本列岛多呈减少趋势,而在俄罗斯中西伯利亚南部、朝鲜半岛南部和中国长江中下游流域一般表现为增加。从季节上看,近59年东亚区域平均的冬、春季降水量、降水日数和日降水强度均呈增加趋势,而夏、秋季一般呈减少趋势,仅夏季日降水强度略有增加。降水的年内分配出现均匀化趋势。从不同级别降水事件看,近59年来东亚区域平均的各级别降水量均为下降趋势,中降水、强降水和极强降水日数也呈现下降趋势,弱降水日数表现出较明显增加;仅有全区秋季强降水量、日数减少趋势和冬季中降水量、日数增加趋势通过了显著性水平检验。分析还发现,近30年(1980～2009年)东亚地区日降水趋势变化出现了新的特征,主要表现为大部分地区降水日数呈现增加,日降水强度减少,45°N以南多数台站降水量也增加,全区降水有向非极端化方向发展趋势。  相似文献   

7.
Using the high-quality observed meteorological data, changes of the thermal conditions and precipitation over the North China Plain from 1961 to 2009 were examined. Trends of accumulated temperature and negative temperature, growing season duration, as well as seasonal and annual rainfalls at 48 stations were analyzed. The results show that the accumulated temperature increased significantly by 348.5℃ day due to global warming during 1961-2009 while the absolute accumulated negative temperature decreased apparently by 175.3℃ day. The start of growing season displayed a significant negative trend of -14.3 days during 1961- 2009, but the end of growing season delayed insignificantly by 6.7 days. As a result, the length of growing season increased by 21.0 days. The annual and autumn rainfalls decreased slightly while summer rainfall and summer rainy days decreased significantly. In contrast, spring rainfall increased slightly without significant trends. All the results indicate that the thermal conditions were improved to benefit the crop growth over the North China Plain during 1961-2009, and the decreasing annual and summer rainfalls had no direct negative impact on the crop growth. But the decreasing summer rainfall was likely to influence the water resources in North China, especially the underground water, reservoir water, as well as river runoff, which would have influenced the irrigation of agriculture.  相似文献   

8.
Various hydrological and meteorological variables such as rainfall and temperature have been affected by global climate change. Any change in the pattern of precipitation can have a significant impact on the availability of water resources, agriculture, and the ecosystem. Therefore, knowledge on rainfall trend is an important aspect of water resources management. In this study, the regional annual and seasonal precipitation trends at the Langat River Basin, Malaysia, for the period of 1982–2011 were examined at the 95 % level of significance using the regional average Mann–Kendall (RAMK) test and the regional average Mann–Kendall coupled with bootstrap (RAMK–bootstrap) method. In order to identify the homogeneous regions respectively for the annual and seasonal scales, firstly, at-site mean total annual and separately at-site mean total seasonal precipitation were spatialized into 5 km?×?5 km grids using the inverse distance weighting (IDW) algorithm. Next, the optimum number of homogeneous regions (clusters) is computed using the silhouette coefficient approach. Next, the homogeneous regions were formed using the K-mean clustering method. From the annual scale perspective, all three regions showed positive trends. However, the application of two methods at this scale showed a significant trend only in the region AC1. The region AC2 experienced a significant positive trend using only the RAMK test. On a seasonal scale, all regions showed insignificant trends, except the regions I1C1 and I1C2 in the Inter-Monsoon 1 (INT1) season which experienced significant upward trends. In addition, it was proven that the significance of trends has been affected by the existence of serial and spatial correlations.  相似文献   

9.
Accurately predicting precipitation trends is vital in the economic development of a country. Ground observed data from the Nigeria Meteorological Agency (NIMET) was analyzed to study the long-term spatio-temporal trends of rainfall on annual and seasonal scales for 23 stations in Nigeria during a 40-year period spanning from 1974 to 2013. After testing the presence of autocorrelation, Mann–Kendall (modified Mann–Kendall) test was applied to non-autocorrelated (autocorrelated) series to detect the trends in rainfall data. Theil and Sen’s slope estimator test was used to find the magnitude of change over a time period. Pettitt’s test, Standard Normal Homogeneity Test, and Buishand’s test were further used to test the homogeneity of the rainfall series. The results show an increasing trend in annual rainfall; however, only nine stations have a significant increase during the period of study. On the seasonal time scale, a significant increasing trend was observed in the pre- and post-monsoon seasons, while only nine stations show a significant increasing trend in monsoon rainfall and a significant decreasing trend in the winter rainfall over the last 40 years. During the study period, 15.4 and 13.90 % increase were estimated for annual and monsoonal rainfall, respectively. Furthermore, seven stations exhibit changes in mean rainfall while majority of the stations considered (Eighteen stations) exhibit homogeneous trends in annual and seasonal rainfall over the country. The performance of the different tests used in this study was consistent at the verified significance level.  相似文献   

10.
Alpine and Mediterranean areas are undergoing a profound change in the typology and distribution of rainfall. In particular, there has been an increase in consecutive non-rainy days, and an escalation of extreme rainy events. The climatic characteristic of extreme precipitations over short-term intervals is an object of study in the watershed of Lake Maggiore, the second largest freshwater basin in Italy (located in the north-west of the country) and an important resource for tourism, fishing and commercial flower growing. The historical extreme rainfall series with high-resolution from 5 to 45 min and above: 1, 2, 3, 6, 12 and 24 h collected at different gauges located at representative sites in the watershed of Lake Maggiore, have been computed to perform regional frequency analysis of annual maxima precipitation based on the L-moments approach, and to produce growth curves for different return-period rainfall events. Because of different rainfall-generating mechanisms in the watershed of Lake Maggiore such as elevation, no single parent distribution could be found for the entire study area. This paper concerns an investigation designed to give a first view of the temporal change and evolution of annual maxima precipitation, focusing particularly on both heavy and extreme events recorded at time intervals ranging from few minutes to 24 h and also to create and develop an extreme storm precipitation database, starting from historical sub-daily precipitation series distributed over the territory. There have been two-part changes in extreme rainfall events occurrence in the last 23 years from 1987 to 2009. Little change is observed in 720 min and 24-h precipitations, but the change seen in 5, 10, 15, 20, 30, 45, 60, 120, 180 and 360 min events is significant. In fact, during the 2000s, growth curves have flattened and annual maxima have decreased.  相似文献   

11.
In this paper, temperature and rainfall data series were analysed from 34 meteorological stations distributed throughout Bangladesh over a 40-year period (1971 to 2010) in order to evaluate the magnitude of these changes statistically and spatially. Linear regression, coefficient of variation, inverse distance weighted interpolation techniques and geographical information systems were performed to analyse the trends, variability and spatial patterns of temperature and rainfall. Autoregressive integrated moving average time series model was used to simulate the temperature and rainfall data. The results confirm a particularly strong and recent climate change in Bangladesh with a 0.20 °C per decade upward trend of mean temperature. The highest upward trend in minimum temperature (range of 0.80–2.4 °C) was observed in the northern, northwestern, northeastern, central and central southern parts while greatest warming in the maximum temperature (range of 1.20–2.48 °C) was found in the southern, southeastern and northeastern parts during 1971–2010. An upward trend of annual rainfall (+7.13 mm per year) and downward pre-monsoon (?0.75 mm per year) and post-monsoon rainfall (?0.55 mm per year) trends were observed during this period. Rainfall was erratic in pre-monsoon season and even more so during the post-monsoon season (variability of 44.84 and 85.25 % per year, respectively). The mean forecasted temperature exhibited an increase of 0.018 °C per year in 2011–2020, and if this trend continues, this would lead to approximately 1.0 °C warmer temperatures in Bangladesh by 2020, compared to that of 1971. A greater rise is projected for the mean minimum (0.20 °C) than the mean maximum (0.16 °C) temperature. Annual rainfall is projected to decline 153 mm from 2011 to 2020, and a drying condition will persist in the northwestern, western and southwestern parts of the country during the pre- and post-monsoonal seasons.  相似文献   

12.
Changes in climatic parameters are often given in terms of global averages even though large regional variability is generally observed. The study of regional tendencies provides not only supplementary conclusions to more large-scale oriented results but is also of particular interest to local policy-makers and resource managers to have detailed information regarding sensible and influential climatic parameters. In this study, changes in precipitation for the Balearic Islands (Spain) have been analyzed using data from 18 rain gauges with complete daily time series during the period 1951–2006 and two additional sites where only monthly totals were available. Tendencies for maximum and minimum 2-m temperatures have also been derived using data from three thermometric stations with daily time series for the period 1976–2006. The thermometric stations are located at the head of the runways in the airports of the three major islands of the archipelago, where urbanization has arguably not had a relevant impact on the registered values. The annual mean temperature in the mid-troposphere and lower stratosphere has also been analyzed using the Balearics radiosonde data for the period 1981–2006. Results show there is a negative tendency for annual precipitation (163 mm per century) with 85% significance on the sign of the trend. An abrupt decrease in mean yearly precipitation of 65 mm is objectively detected in the time series around 1980. Additionally, the analysis shows that light and heavy daily precipitation (up to 4 mm and above 64 mm, respectively) increase their contribution to the total annual, while the share from moderate-heavy precipitations (16–32 mm) is decreasing. Regarding the thermometric records, minimum temperatures increased at a rate of 5.8°C per century during the 31 years and maximum temperatures also increased at a rate of 5.0°C per century, both having a level of statistical significance for the sign of the linear trend above 99%. Temperatures in the mid-troposphere decreased at a rate of ??5.4°C per century while a tendency of ??7.8°C per century is found in the lower stratosphere. The level of statistical significance for the sign of both the tropospheric and stratospheric linear trends is above 98% despite the great inter-annual variability of both series.  相似文献   

13.
A methodology has been applied to investigate the spatial variability and trends existent in a mid-twentieth century climatic time series (for the period 1943–1977) recorded by 58 climatic stations in the Albert–Victoria water management area in Uganda. Data were subjected to quality checks before further processing. In the present work, temporal trends were analyzed using Mann–Kendall and linear regression methods. Heterogeneity of monthly rainfall was investigated using the precipitation concentration index (PCI). Results revealed that 53 % of stations have positive trends where 25 % are statistically significant and 45 % of stations have negative trends with 23 % being statistically significant. Very strong trends at 99 % significance level were revealed at 12 stations. Positive trends in January, February, and November at 40 stations were observed. The highest rainfall was recorded in April, while January, June, and July had the lowest rainfall. Spatial analysis results showed that stations close to Lake Victoria recorded high amounts of rainfall. Average annual coefficient of variability was 19 %, signifying low variability. Rainfall distribution is bimodal with maximums experienced in March–April–May and September–October–November seasons of the year. Analysis also revealed that PCI values showed a moderate to seasonal rainfall distribution. Spectral analysis of the time components reveals the existence of a major period around 3, 6, and 10 years. The 6- and 10-year period is a characteristic of September–October–November, March–April–May, and annual time series.  相似文献   

14.
In this study, 43-year (1965–2007) monthly and annual rainfall time series of ten rainfall stations in a semi-arid region of western India are analyzed by adopting three tests for testing normality and by applying autoregressive technique for exploring persistence. Gradual trends are identified by three tests, and their magnitudes are assessed by the Sen’s slope estimator. Also, abrupt changes are detected by using four tests and they are further confirmed by two tests. Box-whisker plots revealed that the rainfalls of June and September are right skewed for all the stations. The annual rainfalls of Bhinder, Dhariawad, and Gogunda stations are found considerably right skewed. The normality tests indicated that the rainfall of July does not deviate from the normal distribution at all the stations. However, the annual rainfall is found non-normal at five stations. The monthly rainfalls of June, July, and August have persistence respectively at three (Mavli, Salumber, and Sarada), two (Kherwara and Sarada), and one (Mavli) stations, whereas the annual rainfall has persistence at Girwa and Mavli stations. Significantly increasing trend is detected at Mavli in the rainfall of July and in the annual rainfall (p value?>?0.05), while the negative trend in August rainfall at Dhariawad is found significant (p value?>?0.10). This study revealed that the presence of serial correlation does not affect the performance of the Mann-Kendall test. Mean values of trend magnitudes for the rainfalls of June, July, August, and September are 0.3, 0.8, ?0.4, and 0.4 mm year?1, respectively, and the overall mean value for the annual rainfall is 0.9 mm year?1. It is found that the standard normal homogeneity test and the Pettitt test are biased towards the end of the series to locate a change point. Conversely, the Bayesian test has a tendency to look for a change point in the beginning of time series. Confirmed abrupt changes in the rainfall time series are found in the year 2003 (Bhinder) in June; years 1974 (Mavli) and 1989 (Dhariawad and Salumber) in July; years 1972 (Sarada), 1990 (Dhariawad), and 2003 (Mavli) in August; years 1977 (Dhariawad), 1991 (Sarada), and 2004 (Kotra) in September; and in the year 1972 (Mavli and Sarada stations) in the annual series. It is emphasized that the significantly increasing trend of rainfall may have linkages with climate change and/or variability. Finally, this study recommends use of multiple statistical tests for analyzing hydrologic time series in order to ensure reliable decisions.  相似文献   

15.
利用地面实况资料及NCEP再分析资料(1°×1°),选取2016年、2010年及2011年发生在天津市的3次强降水天气过程,分析其天气形势及水汽条件,并应用湿位涡理论对3次暴雨天气进行了诊断分析。分析结果表明:3次暴雨过程均发生在典型的东高西低的环流形势下,低空低涡是主要的影响系统之一。低涡的动力结构及水汽条件的差异对应不同的降水强度。正涡度区强度越强、维持时间越长,降水强度越大。2016年过程水汽通量散度明显强于另两次过程的,与其降水强度相匹配。湿位涡的时空演变可以很好地描述天津地区暴雨的发生发展。天津上空MPV_1负值区标志着不稳定能量的急剧增加,MPV_1负值区出现在降水发生前3 h至6 h,提前预示了天津地区暴雨天气的发生。MPV_1正值区对应强降水的区域。过程降水前MPV_2绝对值的激增,表明大气的斜压性增强,有利于气旋性涡度发展。MPV_2绝对值的激增基本同步于降水的发生。  相似文献   

16.
Frequency, intensity, areal extent (AE) and duration of rain spells during summer monsoon exhibit large intra-seasonal and inter-annual variations. Important features of the monsoon period large-scale wet spells over India have been documented. A main monsoon wet spell (MMWS) occurs over the country from 18 June to 16 September, during which, 26.5 % of the area receives rainfall 26.3 mm/day. Detailed characteristics of the MMWS period large-scale extreme rain events (EREs) and spatio-temporal EREs (ST-EREs), each concerning rainfall intensity (RI), AE and rainwater (RW), for 1 to 25 days have been studied using 1° gridded daily rainfall (1951–2007). In EREs, ‘same area’ (grids) is continuously wet, whereas in ST-EREs, ‘any area’ on the mean under wet condition for specified durations is considered. For the different extremes, second-degree polynomial gave excellent fit to increase in values from distribution of annual maximum RI and RW series with increase in duration. Fluctuations of RI, AE, RW and date of occurrence (or start) of the EREs and the ST-EREs did not show any significant trend. However, fluctuations of 1° latitude–longitude grid annual and spatial maximum rainfall showed highly significant increasing trend for 1 to 5 days, and unprecedented rains on 26–27 July 2005 over Mumbai could be a realization of this trend. The Asia–India monsoon intensity significantly influences the MMWS RW.  相似文献   

17.
We analyzed trends, interdecadal variability, and the quantification of the changes in the frequency of daily rainfall for two thresholds: 0.1 mm and percentile 75th, using high quality daily series from 52 stations in the La Plata Basin (LPB). We observed increases in the annual frequencies in spatially coherent areas. This coherence was more marked in austral summer, autumn, and spring, during which the greatest increases occurred in southern Brazil, especially during extreme events. In winter, the low and middle basins of the Río Uruguay and Río Paraná showed negative trends, some of which were significant. Interdecadal variability is well defined in the region with more pronounced positive jumps west of the basin between 1950 and 2000. This variability was particularly more marked during periods of extreme rainfall in summer, autumn, and spring, unlike in winter when extreme daily rainfall in the lower Rio Paraná basin decreased by up to 60%. The changes in the past century during extreme rainfall produced modifications in the annual rainfall cycle. The annual cycle of both indices was broader during the last period which is mainly explained by the strong decreases in winter.  相似文献   

18.
In this study, the multifractal detrended fluctuation analysis method is employed to determine the thresholds of extreme events. Subsequently, the characteristics of extreme temperatures have been analyzed over Northeast China during 1961–2009. Approximately 58 % of stations have negative interdecadal trends of ?2.2 days/10 years to 0 days/10 years in extreme low minimum temperature (ELMT) frequency. Notable positive trend of 0–2.5 days/10 years in extreme high maximum temperature (EHMT) frequency of about 94 % stations are found. Approximately 58 % of stations have decreasing trend in ELMT intensity, whereas 69 % of stations have increasing trend of EHMT intensity. The trends are the range of ?0.72 °C/10 years to 0 °C/10 years and 0–0.7 °C/10 years, respectively. We propose the extreme temperatures indices, ELMT index (ELMTI) and EHMT index (EHMTI), which combined the frequency and intensity of extreme temperatures to represent the order of severity of extreme temperatures. According to this approach, serious ELMT mainly occur in the Songliao Plain and the Sanjiang Plain, especially in the Songliao Plain. Serious EHMT distinctly occur in the Sanjing Plain, and the southwestern and northwestern regions of Northeast China in recent five decades.  相似文献   

19.
Annual series of light rainfall, moderate rainfall and heavy rainfall are computed for 4 zones arranged from south to north in Nigeria: Coastal, Guinea-Savanna, Midland and Sahelian zones. Daily rainfall data for the period 1919–85 are utilized. Each series is examined for evidence of change in structure in terms of pattern of decrease and increase in dry and wet years, the overall trend, and the occurrence of runs of dry and wet years. The northern Nigeria (Midland and Sahel) heavy rainfall series and the Sahel moderate rainfall series are found to depict evidence of climatic change as defined by Landsberg (1975) that climatic conditions must change to a new equilibrium position with the values of climatic elements changed significantly. On the other hand Landsberg's definition of climatic fluctuations as involving temporary deflection which can revert to earlier conditions is found to fit the 4 regional light rainfall series and the Midland area moderate rainfall series. The southern Nigeria moderate and heavy rainfall series are found to depict only evidence of high frequency oscillations about a stable long-term mean. The recent drought in Nigeria north of about 9° N is shown to be associated with a large decline in moderate and heavy rainfalls over this part of the country.  相似文献   

20.
This paper provides an insight into the long-term trends of the four seasonal and annual precipitations in various climatological regions and sub-regions in India. The trends were useful to investigate whether Indian seasonal rainfall is changing in terms of magnitude or location-wise. Trends were assessed over the period of 1954?C2003 using parametric ordinary least square fits and non-parametric Mann?CKendall technique. The trend significance was tested at the 95% confidence level. Apart from the trends for individual climatological regions in India and the average for the whole of India, trends were also specifically determined for the possible smaller geographical areas in order to understand how different the trends would be from the bigger spatial scales. The smaller geographical regions consist of the whole southwestern continental state of Kerala. It was shown that there are decreasing trends in the spring and monsoon rainfall and increasing trends in the autumn and winter rainfalls. These changes are not always homogeneous over various regions, even in the very short scales implying a careful regional analysis would be necessary for drawing conclusions regarding agro-ecological or other local projects requiring change in rainfall information. Furthermore, the differences between the trend magnitudes and directions from the two different methods are significantly small and fall well within the significance limit for all the cases investigated in Indian regions (except where noted).  相似文献   

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