Long-term Trend Analysis and the Relationship Between Meteorological and Hydrological Series (Case study: Ilam Dam Watershed)

Rainfall and discharge are the most important climatic and hydrological parameters, the prediction of their behavior is of special importance for water resources management. In this study, the trend of precipitation parameters, maximum, minimum and average temperature and flow over a period of 30 years in Ilam meteorological station and Gol-Gol hydrometric station evaluated. Mann-Kendall and Sen's slope estimator tests were used to determine the trend and Pettitt test was used to determine the change point. To investigate the relationship between discharge and precipitation, SPI and SDI drought indices were calculated and then their relationship in 6 time periods of 3, 6, 9, 12, 24 and 48 months was determined by Pearson correlation method. The results showed that the rainfall trend increased in some months and decreased in others. The average temperature trend and the maximum temperature trend are upward in most months, but the minimum average temperature trend is often downward. Discharge trends are declining in most months. The results of Pearson correlation coefficient showed that there is a significant correlation between SPI and SDI drought indices. According to the results of Pettitt test, the time of change of variables is in the early 80's and the change point in the discharge time series is more than precipitation, which shows that along with climatic factors, human factors have been effective in the discharge rate of the basin.