Abstract：
Uncertainty and uneven distribution of monsoonal rainfall and its consequences on crop production is a matter of serious concern in India, specifically, in the Indo-Gangetic plain region. In this study, drought patterns were investigated through standardised precipitation index (SPI) of varying timescales, using the India Meteorological Department (IMD) precipitation data (1901-2021). We analysed the spatio-temporal pattern of different drought characteristics (frequency, duration, severity, intensity) of the Indian Gangetic basin using run theory. The bivariate copula method has been incorporated to combine two drought properties (severity and duration). Copula integrates multivariate distribution and considers the dependency rate among the variables. The five most widely used copulas from various copula families, elliptical (normal, t-copula) and Archimedean (Clayton, Gumbel, Frank), were estimated for modelling, and the best fit copula was selected. The study revealed that seasonal drought is more frequent and intense in the Upper and Middle Gangetic Plain, whereas annual drought is quite scattered in nature. It is worthy to mention that downward drought trends were observed in this agricultural belts significantly after 1965; specifically, in the Upper, Middle, and Trans Gangetic Plain regions. With increasing drought duration and severity, the drought return period raised, but the frequency decreased gradually. Most of the droughts characterised by less duration and severity occurred with a return period below 10 years for the whole region. The major 100 + years return period droughts were to be found after 1960 and their frequencies were significantly higher after 2000. The most recent remarkable droughts with more than 100 years of return occurred during 2008-2011 and 2016-2018 in the Upper and Middle Gangetic plains, whereas in the Lower Gangetic plain, a hundred-year return period drought was occurred during 2010-2013. This study provides agroclimatic-zones-wise significant information of drought characteristics and its nature of occurrence in the Indian Ganga Basin. The results enhance the understanding of drought management and formulation of adaptive strategies to mitigate the adverse impact of droughts.
摘要：
季风降雨的不确定性和分布不均及其对作物生产的影响在印度是一个令人严重关切的问题,具体来说,在印度恒河平原地区。在这项研究中,通过不同时间尺度的标准化降水指数(SPI)调查干旱模式，使用印度气象部门(IMD)降水数据(1901-2021)。我们分析了不同干旱特征的时空格局(频率，持续时间,严重程度,强度)使用运行理论对印度恒河盆地进行分析。结合了双变量copula方法，以结合两种干旱特性（严重程度和持续时间）。Copula整合了多变量分布，并考虑了变量之间的依赖率。来自不同科普拉家族的五种最广泛使用的科普拉，椭圆(正常，t-copula)和阿基米德(克莱顿，Gumbel,Frank),被估计用于建模，并选择了最适合的copula。研究显示,上上中区恒河平原的季节性干旱更为频繁和强烈,而年度干旱在自然界中相当分散。值得一提的是，在1965年之后，该农业带出现了明显的干旱趋势；具体来说，在上层,中间,和跨恒河平原地区。随着干旱持续时间和严重程度的增加，干旱重现期延长，但频率逐渐降低。大多数干旱的持续时间和严重程度都较短，整个地区的重现期低于10年。1960年以后发现了100多年的主要回归期干旱，2000年以后的频率明显更高。最近一次超过100年的重大干旱发生在2008-2011年和2016-2018年期间，在恒河上游和中部平原，而在下恒河平原，2010-2013年期间发生了百年重现期干旱。这项研究为印度恒河盆地的干旱特征及其发生性质提供了农业气候区方面的重要信息。结果增进了对干旱管理的了解，并制定了减轻干旱不利影响的适应性战略。
