Trend Analysis and the Relationship Between Flow Variability, Precipitation, and River Sediment Load (Case Study: Selected Stations of Iran's Main Basins)

Modares, Fatemeh; Farajzadeh, Manuchehr; Shah Hossini, Majid

doi:10.61882/jeer.405.1.1

year 16, Issue 1 (Spring 2026) E.E.R. 2026, 16(1): 1-21 | Back to browse issues page

‎ 10.61882/jeer.405.1.1

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Modares F, Farajzadeh M, Shah Hossini M. Trend Analysis and the Relationship Between Flow Variability, Precipitation, and River Sediment Load (Case Study: Selected Stations of Iran's Main Basins). E.E.R. 2026; 16 (1) :1-21
URL: http://magazine.hormozgan.ac.ir/article-1-895-en.html

Trend Analysis and the Relationship Between Flow Variability, Precipitation, and River Sediment Load (Case Study: Selected Stations of Iran's Main Basins)

Fatemeh Modares

, Manuchehr Farajzadeh ^*

, Majid Shah Hossini

Physical Geography, Faculty of Humanities, University of Tarbiat Modares, Tehran , farajzam@modares.ac.ir

Abstract: (494 Views)

1- Introduction
Changes in precipitation, discharge, and sediment load in rivers and water resources are crucial parameters in water resource management studies. This study analyzes the trends of discharge, precipitation, and sediment in the watershed areas of Zarrineh River, Qareh Sou, Kashaf Rud, and Dez over a 30-year period (2023-1994) using the non-parametric Mann-Kendall test and Pearson correlation method. The findings indicate a significant correlation between discharge and sediment without any delay, with correlation coefficients ranging from 0.68 to 0.96. Additionally, a significant correlation between discharge and precipitation is observed only in the Dez and Qareh Sou rivers, with a stronger connection to precipitation from one day prior. The trend analysis of precipitation and discharge across various stations indicates an overall decline in these parameters, except for the Aghdarband station in the Kashaf Rud basin. The highest decreasing Sen's slope for precipitation is noted at the Dez dam station, while significant reductions in discharge are seen at the Samian and Arbab Kandi stations. In other stations, changes appear as short-term fluctuations. An assessment of sediment trends reveals a decrease in sediment levels across most watersheds, excluding the Kashaf Rud basin. These changes are also found to be significant in various stations. Moreover, the Mann-Kendall graphical test indicates a break point and a shift in 1998 and again in 2007, which results in a notable decrease in discharge and sediment in the studied watersheds.

2-Methodology
The study area of this research includes four important watersheds in the country: Qara Su, Zarineh Rud, Dez, and Kashaf Rud. The Qara Su watershed, which is part of the Aras sub-basin, features the longest and most water-rich internal river of Ardabil province, named Qara Su. This river originates from the Talesh highlands. The Zarineh Rud watershed is located in the south and southeast of Lake Urmia and is recognized as the largest sub-basin of Lake Urmia. This watershed contains a river of the same name, which flows through the provinces of Kurdistan and West Azerbaijan and, at 302 kilometers long, is one of the longest and most water-rich rivers in the region. In this research, precipitation, flow, and sediment data were collected from the selected stations, and the trends of these time series data were analyzed using the non-parametric Mann-Kendall test and the Sen's slope estimator. Additionally, to identify points of change and trend breaks, the Mann-Kendall graphical method was employed, and Pearson correlation tests were conducted to examine the relationships between flow, precipitation, and sediment. The Mann-Kendall test is based on the ranks of data in time series and is used to assess trends in hydrological and meteorological data. The slope estimation of the trend line using the Sen method is employed as a non-parametric technique that calculates the median slope by analyzing the differences between observations in a time series. In this method, a slope is calculated for each pair of consecutive data points, and their median represents the slope of the trend line. Moreover, the correlation coefficient serves as a criterion to determine the degree of association between variables and to identify the type, direction, and extent of their linear correlations
3- Results
This study analyzed the trends of annual discharge, precipitation, and sediment load over a 30-year period (1994–2023) in four watersheds: Zarrineh River, Qareh Su, Kashaf rud River, and Dez. Using non-parametric methods like the Mann-Kendall test, Sen’s slope estimator, and regression line slope, the researchers found a significant correlation (p < 0.01) between discharge and sediment load across all basins, with correlation coefficients ranging from 0.68 to 0.96. Discharge and precipitation showed lower correlation coefficients between 0.32 and 0.55, with only the Dez and Qareh Su rivers demonstrating significant correlations. Lagged analysis indicated that discharge correlated most strongly with precipitation from the previous day, except for the Dez River, which correlated with precipitation from two days earlier. Trend analysis found that precipitation and discharge were declining across most of the study period, particularly at Zarrineh River and Dez dam stations, where significant changes were noted (Mann-Kendall statistics of -2.3 and -2.0, respectively). The highest decline in precipitation was observed at Dez dam station with a Sen’s slope of -5.8. In Qareh Su, significant declines in discharge were identified at Samian and Arbab Kandi stations, while some stations exhibited only minor fluctuations. Sediment load trends showed a universal decline across the studied basins, except for the Kashaf rud River. Notable reductions were observed at Samian station in Qareh Su and Taleh Zang station in Dez, both significant at the 1% level. The Mann-Kendall test indicated breakpoints in 1998 and 2007, signaling sustained reductions in discharge and sediment load across most basins throughout the period of study.
4. Discussion & Conclusions
This study investigates and analyzes the relationship and trends of precipitation, discharge, and sediment in the Zarrineh River, Qareh Su, Dez, and Kashf rud River. The amounts of discharge and sediment also follow the trends of precipitation; except for the Agh-Darband station in the Kashf rud River, in other stations, they show a decreasing and negative trend. This decreasing trend has become significant in the three rivers of Qareh Su, Zarrineh River, and Dez. The highest slope of change in discharge and sediment, similar to the precipitation variable, is related to the dam station. In the watersheds of East Azerbaijan, it corresponds to a significant decrease in discharge and sediment. The examination of the points of rupture and break in the changes also revealed that the changes are reducing in the studied variables. This decreasing trend has continued until the end of the studied statistical period. The analysis of the relationship between discharge, sedimentation, and precipitation also showed that there is no strong and significant correlation between discharge and either precipitation or sediment in any of the rivers studied. Therefore, despite a direct relationship, one should not always infer an increase or decrease in sedimentation to be directly related to an increase or decrease in precipitation and discharge. In conclusion, based on the results obtained from the analysis of the annual trends of precipitation, discharge, and sediment in the four rivers studied in different watersheds, it was determined that in most of the examined areas, the mentioned variables demonstrated a decreasing trend. Based on the slope estimator, the annual changes in discharge and sediment are more severe and more pronounced than those in precipitation in the region. The results of this study indicate that if attention is not paid to climatic and hydrological changes.

Keywords: Precipitation, Sen’s Slope, Sediment, Trend, Discharge, Mann-Kendall

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Received: 2025/05/25 | Published: 2026/04/16

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