عنوان مقاله [English]
Climate change, as a major global challenge, has attracted the attention of many scholars and has found many types of research (Ghahraman and Gharekhani, 2010). Slight changes in the climate can affect other components in varying degrees, as an important and comprehensive component of the ecosystem. Fluctuations and changes occurring in the region over the short and long term in the climate of a region are the sources of much change in the environment. One of the factors that affect the planet is water vapor. The increase in water vapor yields large positive feedback on the surface temperature (Hansen et al., 1984), which causes rainfall in the middle and high latitudes. Therefore, it is obvious that changes in the content of the vapor barley should be investigated. Since Iran is located in a dry and semi-arid region, it lacks large internal and adjacent water resources to provide its own moisture content. As a result, more rainwater sources should be provided with water levels around it. One of the ways in which it is possible to examine the evolution of specific moisture developments in the past and present is to analyze the process of time series at different time scales. Several statistical methods have been presented to analyze the time series process, which can be categorized into two general categories of parametric and nonparametric methods.
Materials and methods
The study area includes Hormozgan, Sistan and Baluchistan and Kerman provinces, between 25 to 31 degrees north latitude and 54 to 63 degrees east of the Greenwich Meridian. The variables used in this study include specific data (in grams per kilogram) at 1000, 850, 700, and 600 hpa of ERA-Interim data from a series of predefined data from the European Center for the Meteorological Mean of ECMWF is. Parametric methods are mainly based on the regression relationship between the data series. Nonparametric methods have a relatively larger and more significant application than parametric methods. It is more appropriate to use nonparametric methods for series with a certain statistical distribution that is unsuitable for them and a lot of sloping or elongation. The Kendall test is one of the most common and most widely used nonparametric methods of time series analysis. Using the Man-Kendall method, data changes are identified, its type and time are determined. The non-parametric Man-Kendall test was first developed by me (1945) and then developed by Kendal (1975) based on the data rank in a series of times. This method is commonly used in analyzing the hydrological series process and meteorology. The strengths of this method can be attributed to the suitability of its use for series when it does not follow a specific statistical distribution. The negligible influence of this method is the limit values seen in some time series as well as other advantages of using this method. The zero assumption of this test implies the randomness and absence of a trend in the data series, and acceptance of the hypothesis (zero assumption rejection) indicates the trend in the data series.
Results and discussion
Figure 5 shows significant zoning maps of the annual moisture content of stations in the southeast of Iran during the period 2016-1987 based on the index of Man-Kendall. The significant trend at different levels indicates a significant trend at 1000, 850 and 700 hpa in the coastal strip of the Persian Gulf and Oman Sea in the study area and there is no specific trend in the above-mentioned latitudes. Only in two stations of Zahedan (At 1000 hpa) and pomegranate (at 850 and 700 hpa), moisture content have a negative annual trend in the study period.
The significant moisture content at various levels of the atmosphere indicated that the annual humidity trend increased in most southern stations close to the Oman Sea and the Persian Gulf and was decreasing in northern stations. The annual moisture trend of southeast of Iran at different levels of the atmosphere showed a significant trend at 1000, 850 and 700 hpa in the Gulf Coast and Oman Sea in the study area and only at two stations in Zahedan (at 1000 hpa) and Pomegranate (at 850 and 700 hpa) moisture content has a negative annual trend in the studied period. The trend of the average annual moisture content of south-east of Iran at different levels of the atmosphere showed that during the study period, only 1000 hpa positive trend was observed in the average moisture content of southeastern Iran at the significant levels of the test.