Streamflow Variations in Monthly, Seasonal, Annual and Extreme Values Using Mann-Kendall, Spearmen’s Rho and Innovative Trend Analysis

The present study investigates the variations in the monthly, seasonal and annual streamflow timeseries at twenty (20) stations over the upper Indus river basin (UIRB) by using Mann-Kendall (MK), Spearman’s rho (SR) and innovative trend analysis (ITA) methods. Moreover, variations in extreme flows were investigated by dividing the daily streamflow timeseries into two categories; extremely low (<10th percentile) and extremely high (>90th percentile) flows. At monthly time scale, 240 timeseries were investigated, out of which 134, 138 and 159 timeseries manifested significant trends by using MK, SR and ITA methods, respectively. Whereas, seasonal and annual flows showed significant trends over 57, 62 and 75 timeseries based on MK, SR and ITA methods, respectively. Extremely low flows exhibited significant increasing trends over seven (07) stations and significantly decreasing trends over three (03) stations whereas, four (04) stations exhibited significantly decreasing trends in extremely high flows. Therefore, it may be concluded that the variations in the extremely low flows will be more pronounced compared to extremely high flows in the future. This may constitute constant pressure on water resources availability in the lower Indus plains where most of the country’s population is dependent on agricultural activities.