Journal of Earth System Science ( IF 1.9 ) Pub Date : 2020-11-20 , DOI: 10.1007/s12040-020-01494-x Grace Nengzouzam , Sanayanbi Hodam , Arnab Bandyopadhyay , Aditi Bhadra
Abstract
A high resolution (0.25°×0.25°) daily gridded dataset was analysed to study the spatial and temporal trend in various regions of India during the period of 1901–2013. The non-parametric Mann–Kendall (MK) test has been applied to the time series (1901–2013) rainfall data in order to detect the trends for both rainfall depth and number of rainy days. Sen slope estimator test was also used to find out the magnitude of the trend. In addition, Pettitt–Mann–Whitney (PMW) test was employed so as to determine the probable change year. The results of trend analysis of rainfall depth showed maximum number of grid points having increasing trend in summer months, while the dry months showed higher grid points with significant decreasing trend. Jammu and Kashmir, in particular, was found to have increasing trend in all months for all three levels of significances, i.e., 1%, 5%, and 10%, while NE (northeastern) region continuously reported significant decreasing trends. The annual trend analysis of the 30-year moving window of rainfall depth showed higher number of grid points with significant increasing trend during 1901–1950, decreasing trend during 1931–1980, and increasing trend again during 1961–2013. The PMW test for the rainfall depth and number of rainy days for 1901–2010 showed 1961 and 1974 as the most probable change point years with about 339 and 284 grid points agreeing upon it, respectively. The maximum increasing significant trends in rainfall was observed during south-west monsoon months. Recent years also reported an increase in rainfall intensity leading to probable increase of extreme events like floods and droughts.
Research Highlights
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MK test and Sen slope estimation were carried out to analyse the trend and magnitude of trends for rainfall depth over India for the period of 113 years (1901–2013) wherein the wet months were found to show positive trends while the dry months were characterized more by negative trends.
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Pettitt–Mann–Whitney test was also carried out for both the rainfall depth and number of rainy days to detect the change year wherein the years 1961 and 1974 were found as the most probable change point years, respectively.
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A 30-year moving window was used for both rainy days and rainfall depth to represent the climatic conditions of the region. Thus, the total 113 years daily rainfall data from 1901 to 2013 were divided into 10 sections, viz., 1901–1930, 1911–1940, 1921–1950, 1931–1960, 1941–1970, 1951–1980, 1961–1990, 1971–2000, 1981–2010, and 1991–2013.
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Upon analysing the trend of rainfall depth, on seasonal scale, maximum significant increasing trends were reported during the periods 1961–1990 and 1971–2000 in all seasons except the post-monsoon months. This indicated that maximum change in trend took place during these periods justifying the outcome of PMW test carried out.
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There might be an increase in the intensity of rainfall on the rainy days as opposed to prolonged dry periods leading to increase in extreme events like floods and droughts in the recent years. It is also clearly visible that the country is experiencing a huge shortage of rainwater during the recent years accentuating the need for conservation of water to satisfy the country’s increasing demand.
中文翻译：
印度高分辨率栅格化降雨数据的时空趋势
摘要
分析了高分辨率（0.25°×0.25°）的每日网格数据集，以研究1901–2013年期间印度各个地区的时空趋势。非参数Mann-Kendall（MK）测试已应用于时间序列（1901-2013）降雨数据，以检测降雨深度和雨天数的趋势。Sen斜率估计器检验也用于找出趋势的幅度。此外，还使用了Pettitt–Mann–Whitney（PMW）检验来确定可能的变更年份。降雨深度趋势分析结果显示，夏季最大网格点数量呈上升趋势，而干旱月份则网格数量最大，呈明显下降趋势。查和克什米尔，尤其是 被发现在所有三个显着性水平的所有月份中都有上升趋势，即1％，5％和10％，而东北地区则连续报告了显着的下降趋势。降雨深度30年移动窗口的年度趋势分析显示，网格点数量更多，1901–1950年间趋势显着增加，1931–1980年间趋势下降，而1961–2013年再次趋势增加。对1901-2010年降雨深度和雨天数的PMW测试表明，1961年和1974年是最可能的变化点年，分别有大约339个和284个网格点。在西南季风月份观测到最大的最大上升趋势。
研究重点
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进行了MK检验和Sen斜率估计，以分析印度113年间（1901-2013年）降雨深度的趋势和趋势量，其中发现潮湿月份显示出正趋势，而干燥月份的特征更为明显。负面趋势。
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还对降雨深度和雨天数进行了Pettitt–Mann–Whitney试验，以检测变化年份，其中1961年和1974年分别被认为是最可能的变化点年份。
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在下雨天和降雨深度都使用了30年的移动窗口，以表示该地区的气候条件。因此，将1901年至2013年的总共113年的每日降雨数据划分为10个部分，即1901–1930、1911-1940、1921-1950、1931-1960、1941-1970、1951-1980、1961-1990， 1971–2000、1981–2010和1991–2013。
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在分析降雨深度的趋势后，在季节性尺度上，报告了除季风后月份以外的所有季节在1961–1990年和1971–2000年期间最大的显着增长趋势。这表明在这些时期内发生了最大的趋势变化，证明了进行PMW测试的结果是合理的。
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在雨天降雨强度可能增加，而不是长时间的干旱，导致近年来发生诸如洪水和干旱之类的极端事件增加。同样显而易见的是，近年来，该国正经历着雨水的严重短缺，这加剧了对节水的需求，以满足该国不断增长的需求。
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