آشکارسازی روند ابرناکی براساس داده های مشاهداتی و ماهواره ای در حوضه آبریز دریاچه ارومیه

Introduction:

Clouds are one of the most important climate factors affecting water systems on Earth's because, on the one hand, they transfer variable amounts of ocean moisture to land, and on the other side, they play a decisive role in the distribution of rainfall on the earth's level. Also, due to their influence on the amount of solar radiation and the extraction of energy from the Earth’s surface, they are the controllers of the energy outflows on the Earth's surface. Thus, any change in time and space in the clouds can affect other climate factors and complicate the effects of climate change. The basin of Urmia Lake is one of the most important and largest ecosystems in the northwest of Iran, whose change has notable impacts on the local climate and economic, social, and hydrological conditions. The basin of Urmia Lake has been hit by a severe low-water crisis in recent years, which has led to a significant drop in the lake’s water level and a worrying drop in its level. The basin is considered to be one of the crucial poles for the slaughter of debris and various agricultural products, so cloud coverage and its association with other climate parameters such as temperature and rain can have a constructive impact on the lives and economies of its inhabitants. Then, in the current study, the supernatic process of the sky was carried out using the reductive analysis of the observation data of weather stations for the first time in Iran and the world to reveal supernatic changes in the sky in the basin of Urmia Lake.



Materials and methods:

To reveal supernovaic changes in the basin of Urmia Lake, data on the total daily coverage of the sky for the statistical period of 71 years (1951–2021) for five selected stations were taken from the Meteorological Organization Statistics Center. Satellite data from Moody’s Three for 22 years (2001–2022) and Moody's Aqua for the 20-year period (2003–2022) were also extracted on a monthly scale from NASA’s site for overall supernova coverage of the sky. For the purpose of analyzing the cloud spread in the study area, the analysis of data obtained using the Ridit analysis method was made, and the meaningful Mann-Kendall test was used. The cloudiness of the sky was classified into five classes (0 to 8 octaves). For the cloudiness of the sky, the data of the hours of the day 09, 12, 15, and 06 were analyzed. Due to the nature of satellite data and observations, two different methods were used to analyze the trend. Because the cloudiness data is ranked and the cloudiness of the sky is classified into nine classes (0 to 8 octaves), the only statistical method that can correctly obtain the cloudiness trend is the Ridit analysis method, but to check the cloudiness trend Because the satellite data are distant, the Mann-Kendall method was used. Ridit analysis is a statistical method of analysis that was first introduced by Bross in 1958 in the statistical literature. It is a method for comparing the distribution of ordinal (rank) scale variables and is similar to non-parametric statistical techniques that require the calculation of changes for successive classes. This method compares year-to-year changes relative to a reference distribution. If it increases over time compared to the values, there is a probability of an increasing trend compared to the reference distribution, but if it decreases compared to the values, there is a probability of a decreasing trend compared to the reference distribution. Ridit analysis is used to express volatility relative to the reference distribution. Annual outputs of Ridit analysis were used to analyze the trend. If the output of Ridit analysis is drawn as a graph, the trend can be shown, and the existence of the trend can be determined with the trend test. For this purpose, the non-parametric Mann-Kendall test was used to test the significance of the trend.



Result and discussion:

In this research, the aim is to reveal changes in the overall cloudiness of the sky based on observational and satellite data in the basin of Urmia Lake. The findings of the research showed that the results of the analysis of Reddit and Mann Kendall on an annual and seasonal basis indicate a negative trend and a decrease in the overall cloudiness of the sky in this basin. So all five stations annually and in the winter season have a decreasing and decreasing trend of cloudiness, and in the autumn season, the stations of Urmia, Saqez, and Khoy have an increasing trend, and Tabriz and Maragheh have a decreasing trend. In the spring and summer seasons, three out of five stations show a decreasing trend, which indicates a decrease in the amount of cloud cover in these seasons, which can be the reason for the increase in temperature and the decrease in relative humidity in the spring and summer. The results of both Aqua and Tera satellites are the same annually and seasonally, so the cloudiness of the sky in Urmia station has a positive trend and insignificant increase, but in Tabriz, Khoy, Saqez, and Maragheh stations, it has a negative trend and insignificant decrease. The results obtained from the analysis of Ridit and the data of two satellites, Aqua and Tera, on an annual and seasonal basis also show the greatest agreement between the results obtained from the analysis of Ridit and the data of Aqua and Tera satellites on an annual basis, but also seasonally, respectively. They are most appropriate in summer, autumn, and winter. But in the spring, except for Urmia and Khoy stations, the rest of the stations do not have compliance. According to the obtained results, the compatibility of the results of the Ridit analysis with the satellite data was confirmed, and the correctness of the results obtained from the Ridit analysis was proved.



Conclusion:

Generally, the results are obtained from observational and satellite data, indicating a reduction in all cloud days and overall supernova coverage of the sky at the stations studied. So the largest percentage of total supernovaic coverage of the sky must belong to cloudless, nebulous, and semi-nebulous levels that may be caused by a decrease in moisture entry into the area studied. Also, since the rainfall in the northwest of Iran, in which the basin of Urmia Lake is affected by periods due to decreased temperature, increased relative humidity, and the introduction of cooling systems, occurs more in the autumn and winter periods, the reduction of all cloud days and overall supernatural coverage of the sky in all segments, especially in the fall and winter, can create drier climate conditions and have a noticeable impact on the local climate and economic-social and hydrological conditions of the basin of Urmia Lake.