Trend analysis of five important daily rainfall characteristics at Urmia Lake basin

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DINPASHOH Y.; Sedighpour R.

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Journal: IRANIAN WATER RESEARCH JOURNAL Year:2020 | Volume:13 | Issue:4 (35) Page(s): 63-72

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Title

Trend analysis of five important daily rainfall characteristics at Urmia Lake basin

Author(s)

DINPASHOH Y. | Sedighpour R. | Issue Writer Certificate

Keywords

Mann-KendallQ1

Sen’s estimatorQ1

trendQ1

Urmia Lake basinQ1

Abstract

Urmia Lake basin is one of the main important cereal production areas of Iran. In recent years, climate change affected the elements of the hydrological cycle in the basin. Better management of available water requires good understanding of trends in water budget elements in the basin. In recent years, many studies conducted on trends in rainfall depths in Urmia Lake basin. However, less attempt were done on understanding the trends in the number of days (NOD) with rainfall (R) in this watershed. This study tries to fill this gap by classifying the rainfall depths into the five distinct classes and analyzing the trends in NOD with rainfall in Urmia Lake basin. Therefore, the aim of this study is to detect trends in the number of days with different rainfall depths (received in 24 hours) and in five distinct classes, in Urmia Lake basin. In order to detect trends, the information of the twenty five stations having at least 10 years consecutive daily rainfall data were used. Data of daily rainfall depths provided from IRIMO. In each year the number of days with rain in the five distinct classes counted for every site. Therefore, for each station the NOD with R in a certain class created. trends of the mentioned time series detected using the non-parametric Mann-Kendall (MK1) method. We considered the significant autocorrelation coefficients in trend analysis. For this purpose the modified version of MK method by Hamed and Rao (1998) was used. Moreover, slopes of trend lines estimated using the Sen's estimator approach. In order to analyze the spatial trends for each of the time series, some relevant maps prepared in which the stations having significant trends were shown by markers. This could facilitate the interpretation of trends in the area under study. Results showed that the slope of trend lines for the NOD with R between 0. 1 and 1 mm is often positive. About 84% of the stations had upward trend line. The five stations located in the southern part of the basin experienced significant upward trend (in level of 10% or less) in the NOD with R between 0. 1 and 1 mm. The slope of trend lines for the case of the NOD with R between 1 and 5 mm were almost negative. In the case of days with rain between 1 and 5 mm, the 15 stations had downward trend lines, which five of them showed significant trend; whereas the remaining stations had upward trend line slopes (insignificant at 10% level). However, the slope of trend lines for the NOD with R between 5 to 10 mm in 44% of the stations were negative, in which only four of them were significant (in 10% level). trend line slopes in 40% of the station were positive, in which only one station experienced significant trend at ten percent level. The steepest positive trend magnitude belonged to the station namely Herris, with β = 1. 633 (day/year). For the NOD with R between 10 and 15 mm, about 32% of the stations had negative trend line slopes. However, only three stations experienced negative significant trends. About 26% of stations had positive trend line, in which only one section (Maraghe) exhibited significant trend in 1% level. The steepest slope of the trend lines belonged to the station Shahindezh with β = 0. 585 (days/year). The slopes of trend lines for the NOD with R greater than 15 mm were positive for 52% of the stations. However, only one of them experienced significant trend (in 10% level). Moreover, 24% of the stations had negative trend in the mentioned class. Among the total of 25 selected stations only one section (Maraghe) had significant negative trend. The steepest slope of the trend lines belonged to the station Herris with β = 0. 464 (days/year). In general, trends of the NOD with R less or equal one mm in Urmia Lake basin were upward. But trends for the time series of the NOD with R in the classes of 1-5, 5-10 and 10-15 mm were downward. This means that light storms events in the study area are going to be occur frequently but heavy rains is going to be rare. It can be concluded that the number of light raining days in a year had increasing trend. This implies that such light rains can not to be utilized by crops and trees, because such rains immediately can be lost by evaporation process after ceasing the rain. However, heavy rains which showed increasing trends for most of the selected stations produce large floods in the rivers discharging Urmia Lake.

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APA: Copy

DINPASHOH, Y., & Sedighpour, R.. (2020). Trend analysis of five important daily rainfall characteristics at Urmia Lake basin. IRANIAN WATER RESEARCH JOURNAL, 13(4 (35) ), 63-72. SID. https://sid.ir/paper/159875/en

Vancouver: Copy

DINPASHOH Y., Sedighpour R.. Trend analysis of five important daily rainfall characteristics at Urmia Lake basin. IRANIAN WATER RESEARCH JOURNAL[Internet]. 2020;13(4 (35) ):63-72. Available from: https://sid.ir/paper/159875/en

IEEE: Copy

Y. DINPASHOH, and R. Sedighpour, “Trend analysis of five important daily rainfall characteristics at Urmia Lake basin,” IRANIAN WATER RESEARCH JOURNAL, vol. 13, no. 4 (35) , pp. 63–72, 2020, [Online]. Available: https://sid.ir/paper/159875/en

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