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Tarbiat Modares University , farajzam@modares.ac.ir
Abstract: (39 Views)
In this study, the trend of annual discharge, precipitation, and sediment changes over a 30-year period (1994–2024) in the studied watersheds was examined using statistical tests. The results showed that there is a significant correlation between discharge and sediment at the 0.01 level and the correlation coefficient varies between 0.68 and 0.96. The results of trend analysis also indicated a decrease in precipitation and discharge at most stations during the statistical period, except for Aqdarband station in Kashfrud. This decrease was reported at Zarinehroud and Dez Dam stations with Mann-Kendall statistics of -2.3 and -2 at the 5% level of significance. The sediment trend was also decreasing in most basins, and this trend was found to be significant at the Samian (Qaresu) stations with a value of -1.3 and Telezang (Dez) with a value of -3.4 at the 1 percent level, and at the Zarinehroud and Dez Dam stations at the 5 percent level. In order to complete the statistical analyses, wavelet transformation was also used to examine the time-frequency behavior of fluctuations in precipitation, discharge, and sediment variables. The wavelet results showed that in most stations, an annual pattern in precipitation and discharge is observed as the dominant component. Also, in some stations, medium-term fluctuations with periods of 24 to 36 months were identified, which could be related to climatic phenomena. Sediment behavior was more discontinuous than discharge and precipitation and more dependent on extreme events, such that in some basins such as Dez and Qarasu, sudden increases in wavelet power were observed on short-term scales. These findings highlight the importance of wavelet analysis as a complementary tool alongside traditional statistical methods, as it allows for a more precise and multi-scale examination of the temporal dynamics of hydrological variables.
Received: 2025/05/25
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