BackgroundBangladesh is known as a deltaic plain at the confluence of the Ganges, Brahmaputra and Meghna River Basins (GBM) and their tributaries. The rainfall pattern of northeastern part of Bangladesh is changing along with the discharge pattern of Surma River. In this study, the changes in precipitation of Sylhet and river discharge of Surma River and the relationship between them were investigated. The study emphasizes on the influence of climatic component (rainfall) on the hydro-characteristics of river. The time series data from 1973 to 2016 (44 years) of rainfall and river discharge of Surma River were collected and analyzed. The basic hydro-characteristics, including arithmetic mean, variability, skewness, distribution type, persistence, dependence, trend, and correlation have been studied through various statistical methods, including coefficient of variation, Mann–Kendall test, Sen’s slope estimator, and Pearson’s coefficient of correlation.ResultsThe rainfall trend shows moderate year-to year variability although there is an indication of declining rainfall trend. As with rainfall, the river discharges show moderate year to year variations that are related to the variability in rainfall. The decreasing rate is 1.53 mm for rainfall and − 1.51 m3/s for discharge (Mann–Kendall test). The rainfall was increasing from 1973 to 1989 but after 1990 it is reduced. The mean discharge of Surma River was 845.99 M3/s. The rainfall started to fall down extremely from 1990 to 2016 but before that the rainfall showed an increasing trend with modest slope. It is possible that the declining trend in rainfall observed in Sylhet is a result of climate change which causes the declining of Surma River discharge. Over these 44 years analysis, the rainfall and discharge shows a very decreasing trend and both rainfall and discharge were highly related for most of the time.ConclusionIn conclusion, it can be noticed that the rainfall in Sylhet has been reduced from the time 1973 to 2016 which directly affects the discharge of Surma River. Consequently, this result might be the indication about the effect of climatic change in the local as well as global level.

中文翻译：

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孟加拉东北部苏尔马河地区的降雨和流量趋势：理解气候变化影响的方法

背景孟加拉国被称为恒河、雅鲁藏布江和梅格纳河流域 (GBM) 及其支流汇合处的三角洲平原。孟加拉东北部的降雨格局随着苏尔马河的流量格局发生变化。本研究对锡尔赫特降水与苏尔马河河流流量的变化及其相互关系进行了研究。研究重点研究气候成分（降雨）对河流水文特征的影响。收集并分析了1973年至2016年（44年）苏尔马河降雨和河流流量的时间序列数据。通过各种统计方法研究了基本的水文特征，包括算术平均值、变异性、偏度、分布类型、持续性、依赖性、趋势和相关性，包括变异系数、Mann-Kendall 检验、Sen 斜率估计和 Pearson 相关系数。结果降雨趋势显示出中等的逐年变化，尽管有降雨趋势下降的迹象。与降雨量一样，河流流量显示出与降雨量变化有关的年际变化。降雨的下降率为 1.53 毫米，排放的下降率为 - 1.51 立方米/秒（Mann-Kendall 测试）。从 1973 年到 1989 年降雨量增加，但在 1990 年之后减少。苏尔马河平均流量为845.99 M3/s。1990-2016年降雨量开始急剧下降，但在此之前降雨量呈上升趋势，坡度不大。在锡尔赫特观察到的降雨量下降趋势可能是气候变化导致苏尔马河流量下降的结果。在这44年的分析中，降雨量和流量呈明显下降趋势，大部分时间降雨量和流量高度相关。结论综上所述，可以看出锡尔赫特的降雨量从1973年到2016年有所减少直接影响苏尔马河的流量。因此，这一结果可能表明气候变化对当地和全球水平的影响。可以看到，锡尔赫特的降雨量从 1973 年到 2016 年有所减少，直接影响了苏尔马河的流量。因此，这一结果可能表明气候变化对当地和全球水平的影响。可以看到，锡尔赫特的降雨量从 1973 年到 2016 年有所减少，直接影响了苏尔马河的流量。因此，这一结果可能表明气候变化对当地和全球水平的影响。