Abstract:
Precipitation fluctuations caused by the climate changes of the last century have caused a significant impact on the weather conditions of our country.In order to better manage water resources, knowing the process of these changes can be helpful. In this regard, in the present research, after examining the rainfall statistics of Talar Basin stations in Mazandaran province in terms of statistical duration, the uniformity of the statistics of different years and the absence of years without statistics, as well as the appropriate distribution at the sections of the basin, the number of 9 river stations for the study of rainfall trends , they were selected monthly, quarterly and annually. Precipitation trend of selected stations in four seasons of spring, summer, autumn and winter and in annual scale in total of 9 stations of Talar basin with the length of statistical periods available for each station was calculated and analyzed by non-parametric Mann-Kendall test. It should also be mentioned that the Sen test was used to determine the magnitude of this trend. In a general conclusion, the results obtained from this research show the fluctuations of the precipitation trend in the area. Considering that precipitation is the fundamental factor of agricultural and environmental activity, these fluctuations can affect the precipitation cycles of this area. Therefore, better management of water resources and planning to adapt to this change in rainfall conditions can guarantee the future of agriculture in the region. So that in times of high water, excess water can be stored with watershed management methods and used in times of drought.


EXTENDED ABSTRACT

Introduction

Temporal and spatial changes of precipitation are very important as one of the most important components of climate in the water cycle of the basin. The first step in applying the correct management of water resources is to study the factors affecting these resources, including climatic changes. The amount of precipitation and its spatial pattern varies in each region. These fluctuations are normal in different cases or are repeated periodically. Various statistical methods are used to accurately check the changes in rainfall trends, because statistical tests determine whether the increase or decrease in rainfall in an area is normal or whether these changes are abnormal and statistically significant.various parametric and non-parametric statistical methods have been developed in order to study the trend in time series, which have been widely used by various researchers, but it should be noted that non-parametric methods have often been used in hydrological studies. Perhaps the main reason for this issue is to pay attention to the fact that non-parametric tests are more suitable for data series whose statistical distribution is not normal or which have missing data. Unlike parametric methods, these tests do not show much sensitivity to data outside the range. Trends in meteorological time series can be caused by gradual natural changes or climate change. It should be noted that the significant trend in a precipitation time series does not in itself constitute clear evidence of the occurrence of climate change in a region, but only reinforces the hypothesis of its occurrence that this characteristic is related to multiple factors controlling the climate.

Materials and methods
Mann-Kendall Test was originally presented by a scientist named Mann (1945) and later developed by Kendall (1975).One of the advantages of this test is that it is suitable for time series whose statistical distribution is not defined. Apart from this, another useful feature of using this method is the very low effectiveness of this method for limit type values, which in some cases are found time series. Considering the usefulness and abilities of this test, which can help to detect time series changes of climate variables, it has been of great interest to climate change researchers. Using Kendall's non-parametric test, the null hypothesis of the absence of trends in time series can be investigated and the points of sudden change of trends can be determined. In order to achieve the goals of this research, the required climatic data was also prepared from the General Directorate of Meteorology of Mazandaran Province.

Results and discussion
According to the investigations, 9 important and suitable stations of the region were selected, which had longer statistics and no statistical defects. In this research, the trend of rainfall fluctuations of the above-mentioned selected stations in the four seasons of spring, summer, autumn and winter and in the annual scales in all 9 selected stations of the hall area with the length of the mentioned statistical periods was investigated with the non-parametric Mann-Kendall test. Age test was also used to determine the magnitude of this process. The weather pattern in the region indicates the impact of climate changes and changes in rainfall conditions on the studied area, and these climate fluctuations can cause more climate anomalies. So that in some cases it causes floods and in other cases it causes drought, which can affect the agricultural and environmental pattern of the region. The results obtained from this research in other mountain and plain stations investigated in this area show minor or major changes in the rainfall trend of this area.

Conclusion
In a general conclusion, the results obtained from this research show the fluctuations of the precipitation trend of the area. Considering that precipitation is the fundamental factor of agricultural and environmental activity, these fluctuations can affect the rainfall cycles of this area. Therefore, better management of water resources and planning to adapt to this change in rainfall conditions can guarantee the future of agriculture in the region. So that in times of high water, excess water can be stored with watershed management methods and used in times of drought. Due to the increase in population in recent years and the development of the tourism industry and the pressure on the river ecosystem, the issue of water resources planning seems more sensitive and important. Lack of detailed planning for the agricultural sector can disrupt the process of droughts due to the increase in the population on the banks of this river and more water consumption in agriculture. According to the correct cultivation pattern and as it was said, the use of new watershed management methods can be helpful.