Document Type : Research Article
Authors
1
PhD candidate in water resources engineering, Department of Water Engineering, University of Tabriz, Tabriz, Iran
2
Professor of Water Engineering, Department of Water Engineering, University of Tabriz, Tabriz, Iran
3
Professor of Climatology, Department of Geography, University of Tabriz, Tabriz, Iran
Abstract
The study of different rainfall patterns in different stations is crucial from the perspective of the hydrological process. In the present study, by using the 564 storms recorded in three rain gauge stations**, namely** Sari, Abbas Abad, and Firuzjah, the Huff curves were plotted in three rainfall classes**: i)** less than 6 hrs, ii) 6-12 hrs, and iii) more than 12 hrs. According to the 50% Huff curves, the storms were analyzed using the quartile approach. Then, the design storm hyetographs were plotted for the selected stations in different rainfall classes. Next, to investigate the variability of the storms, a new method was used based on the vertical distances obtained between the Huff curves of 80% and 20% (V), and also the values of 50% Huff curve (d₅₀) in three different percentages of time (25%, 50%, and 75%).
Results showed that the types of most storms in different rainfall classes were in the second quartile. Also, the results indicated that in most of the classes, a significant percentage of precipitation (more than 80%) falls by the seventh decile of the duration. By moving towards the last deciles, the percentage of rainfall decreased. According to the results, it was found that the highest variability of storms in the rainfall classes of less than 6 hrs, 6-12 hrs, and more than 12 hours was related to stations Sari, Abbas Abad, and Firuzjah, respectively. It seems that the results of this study will be helpful in the scientific management of water resources and timely warning of floods in the region
Extended Abstract
Introduction:
A deep understanding of storm patterns in any region is useful in water resources management. Many researchers have studied rainfall storm patterns in different parts of the world. The pioneer researcher in this regard is the American researcher Huff (1967). He studied storm patterns using data from 261 recorded storms in the eastern USA. Pilgrim & Cordery (1975) derived hyetographs for storms using data from 50 storms in Australia. Spatiotemporal patterns of rainfall were analyzed in Canada by Loukas & Quick (1994). In Calabria, located in southern Italy, rainfall patterns were investigated using data from 45,533 storms. To our knowledge, rainfall storm patterns in Mazandaran province, located in northern Iran, have not been investigated yet. Therefore, the four objectives of this study are: i) Illustration of Huff curves for the selected stations in Mazandaran province, Iran; ii) Detection of storm types using the quartile method; iii) Extraction of design hyetographs based on median Huff curves; and iv) Using an innovative approach based on vertical distances of 20% and 80% Huff curves (denoted here by V) in three distinct times of storm duration, namely 25%, 50%, and 75%.
Material and Methods
The study area is Mazandaran province, located in northern Iran. Three stations, namely Sari, Abbasabad, and Firouzjah, were selected in the province for further analysis. Figure 1 shows the location of the sites and study area. Recorded daily rainfall data were gathered from the Iran Water Resources Management Company in digital form. In this study, rainfall events with cumulative rainfall depth ≥5 mm were selected for analysis. The minimum time interval between two consecutive rain events was set at 60 minutes. Storms were divided into three duration classes: i) 1-6 hours; ii) 6-12 hours; and iii) more than 12 hours. The number of storms varied from 151 in Abbasabad to 241 in Firouzjah. In this study, the Huff curves were plotted for each of the three sites, separately. Moreover, these curves were plotted for the three aforementioned duration classes and are shown in Figure 2.
Results and Discussion
Table 2 shows the percentage of rainfall received in each of the four time quartiles in the selected stations, for three distinct rainfall durations. Results showed that in all three stations, the maximum portion of rain in the 1-6 hour class was received in the second quartile. In the 6-12 hour duration class, the maximum portion of rain in Sari was received in the first quartile, while it was the second quartile for the other two stations (i.e., Abbasabad and Firouzjah). In the >12 hour class, the maximum portion of rain in stations Sari and Abbasabad was received in the second quartile, while it was the first quartile in Firouzjah station. Figure 5 shows the histogram of the mean percentage of rainfall received in different quartiles for distinct rainfall duration classes in the selected stations. Hyetographs for the selected sites were prepared for each of the three classes. Figure 6 shows the design storm hyetographs for the selected sites for the three distinct classes. Additionally, Figure 7 shows statistical details including d₂₀, d₅₀, d₈₀, and V=d₈₀-d₂₀ for Abbasabad station in the 1-6 hour duration. The obtained values of these statistics are presented in Table 3.
Conclusion
In this study, using data from 564 recorded storm events from rain gauges in three stations, the Huff curves were plotted for three distinct duration classes: 1-6 hours, 6-12 hours, and >12 hours. Results indicated that the shapes of the Huff curves varied among sites and across different durations. Furthermore, results showed that the Huff curve types for the stations were predominantly the second type (except for two cases). A considerable portion of rain (>80%) was received before the seventh decile of the rain duration. According to the innovative method, most storm variability in the 1-6 hour class occurred at Sari station, while it occurred at Abbasabad station for the 6-12 hour class, and at Firouzjah station for the >12 hour class. These findings will support optimum management of water resources in Mazandaran province. We recommend conducting similar research in other provinces of Iran.
Acknowledgment
The authors acknowledge the Iran Water Resources Management Company for providing the data used in the study.
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