تحليل روند تغييرات آبدهي رودخانه هاي شمال غرب ايران در سه دهه اخير

Trend Analysis of Streamflow Across the North West of Iran in Recent Three Decades

Trend analysis conducted on streamflow of the Northwest of Iran rivers in three times span namely month, season and annual after removing the effect of all significant serial correlation. Data used were the information of sixteen hydrometric stations selected from 1353 to 1383. Senʹs estimator was used to estimate trend line slope. Three significance levels, 1%, 5% and 10% were used to test trends. Results showed that in annual time scale streamflow of all rivers located in the northwest of Iran had negative trends. The lowest slope of trend line for annual time scale belonged to the Vanyar station, which is equal to -4.49 m3/s/yr. In seasonal time scale, significant negative trends observed for all stations, in which the strongest belonged to spring. In monthly time scale, the numbers of months with negative trends were great than that of the positive trends and about half of the stations had negative trends in the second six months of the year. In general, trends of streamflow of most of stations were statistically negative at 10% level in the three past decades.