Assessing Spatial-Temporal Changes of Rainfall Variability Indices in Ardabil Province Rain gauge stations

The rainfall is one of the main elements of the climate in each region. One of the characteristics of arid and semi-arid regions is a low rainfall with high fluctuations. Hence, changes in rainfall patterns, including spatial and temporal changes in rainfall, are of particular importance. The patterns of rainfall distribution, determine the rainfall during the time. The purpose of the present study was to investigate spatial and temporal changes of rainfall variability indices in the gauge stations of Ardabil province.

In this study to determine the rainfall variability from the monthly rainfall with a 24-year period from the year of 1989 to 2013 (based on current statistics) in the watersheds of Ardabil province has been used. In order to calculate the quantitative variability of rainfall in the studied stations, Shannon, Simpson, Index of variability, rainfall variability index (RVI), MCIntosh, Berger-Parker, Rainfall anomaly Index (RAI) were used. After calculating these indices, the spatial variations of the indices at the studied stations were performed using the interpolation methods and the Inverse Distance Weighting method in the Arc Map software, and also the non-parametric Mann-Kendall method was used to determine the temporal variation of the values ​​of rainfall variability indices.

According to the results of the interpolation of these indices, the spatial variations of the Simpson, Index of Variability, McIntosh and the Berger-Parker indices are similar to the one in which the high variation values ​​in the eastern regions include stations of Aladizgeh, Namin, Niaraq, Abi Beiglu and Khosh Abad and the northern part of the province are observed.

In general, it can be said that regions of the province, in the proximity of the provinces of Gilan and East Azerbaijan, have more variability in rainfall values due to the impact of the air masses and rainfall of the Caspian and Mediterranean fronts. Also, the results of the trend test indicated a significant increase in rainfall variability indices that could lead to a change in the seasonal distribution pattern of rainfall values ​​in different months and the results show similar behavior in most of the indices.