Investigation of precipitation trend on the north region of Golestan Province

Precipitation amount is of the most important climate characteristics in each region. The mentioned climate character which shows a lot of variability among other climate parameters, affects seriously on water resources of a region. In some cases, changes in a region precipitation may convert in to the change in precipitation trend and lead to decreasing or even increasing of precipitation, gradually during the time. So, in order to investigate trend in time series, there are some parametric and non-parametric statistical methods. In the presented study, in order to study longtime monthly, seasonal and annual precipitation changes trend in semi arid regions of Golestan Province, least squares and Wald-Wolfowitz tests, have been used. So, some of rain gauge stations had been selected in the north of Golestan Province with at least 30 years records until the end of water years 2006-2007. Then, presence or lack of trend in precipitation amount of the stations had been studied, using above two test methods. The results show that, generally there were all three states of stationary, positive and negative, in stations. On the basis of least of square error test, the positive trend can be established in some more stations, for there more, in some stations amount of precipitation in autumn was increased while this factor was decreased in winter.