Study of snow precipitation changes trend in North West of Iran

In recent years the phenomenon of climate change and global warming, the gradual increase in average temperature in most parts of the earth, cause drastic changes in the amount and type of precipitation in different regions of the world. In many parts of the world, solid precipitation as rain instead of snow and the amount of snow has fallen and this position has caused changes in the hydrological system. Because of the importance of the issue, many studies have been conducted in Iran and the world in this regard. Among the studies can be Lehning and et al (2002) in Switzerland, Laternser and Schneebeli (2003) in the Swiss Alps, and Huntington (2004) in England, Cabe and Clark (2005) in US, noted. Several studies in the snow zone in relation to monitoring has been conducted. Most of these studies are based on remote sensing and statistical methods are rarely used. Such studies can be Dini and et al (1385) stuck in the snow levels in Central Alborz, Hosseini and Porhmmat (1386), in the catchment Taleghan, Matkan and et al (1387) in Karaj Dam catchment and Latyan, ghorbanizadeh and et al (1388), in doses, Rasouli and Adhami (1386) cited. In this study, given the lack of statistical studies in the context of changes in snow in Iran, is trying to change in the North West of Iran, have been studied and the average increase in temperature fluctuations in the snow in the North West of Iran, will be assessed. 

Data used in this study, data include daily rainfall and average annual snowfall of 15 synoptic stations in the North West of Iran. Method used in this study, the relative time series analysis of annual snowfall, which is equivalent to the following: (1), (2), (3), (4)In Equation 2, the relative reduction in the behavior of some of the real and if the behavior increases, more of the actual shows. In Equation 3, the situation is reversed, While in Equation 4, the average of the two previous and it seems more appropriate model for the process is relative. But this test, only general estimates of the variables of the show. There are so linear, second-grade science test to be judged. For trend analysis, linear or parabolic well, the polynomial model has been used: (5) In this study, to test the significance of the methods of Spearman, Kendall and Pierson used. 

Climate change is possible in some areas, rainfall can not find a regime change. Change the falling snow, the total annual precipitation, rainfall is one form of regime change. Therefore, to determine how changes in rainfall, the relative amount of snow to total precipitation of the stations is considered. The results of this study showed that, this parameters relative trend for stations in Mahabad, Meianeh, Piranshahr and Sardasht is increasing and decreasing the remaining stations. To examine the relative significance of Kendall and Spearman correlations has been used. Correlation between these parameters with time and error rate calculated for each of the stations showed that only correlation stations Tabriz, Ahar, Khalkhal, Maku is a significant reduction of the 5 stations. The stations with significant trend line fitted patterns are also evaluated. The evaluation results is also show a linear trend of decrease of this parameter in the four stations, Ahar, Khalkhal, Maku and Tabriz. 

Analysis of annual total snowfall data trend showed that, there are meaningful decline in the station of Urmia, Tabriz, Ahar, Khalkhal, Piranshahr and the reducing trend of the snow at these stations. Also, the proportion of total annual snow precipitation relative trend, excluding stations Mahabad, Meianeh, Piranshahr and Sardasht were increasingly trend. In other stations, the state showed a reducing trend. The line fitted to the equation, represents a significant decline are in the station of Tabriz, Ahar, Khalkhal, Maku. Results of the comparison between the total snowfall and Percent of total annual precipitation as snow with trend temperature changes s howed Stations in the Urmieh, Tabriz, Ahar, Khalkhal Maku and Piranshahr the increase in annual average temperatures, snowfall rates of decline is significant and this could indicate a gradual warming in the North West's negative effects on the precipitation changes from snow to rain and regime change on precipitation from snow to rain and severe loss of water resources is dependent on snow melts gradually.