Determining the Seasonality of Monthly Rainfall using the Markham Method in the Ardabil Province Rain Gauge Stations

The spatial and temporal fluctuations of the climatic element of precipitation and severe changes will lead to changes in atmospheric patterns. Therefore, the study of precipitation trends in different time and space scales is considered as a topic of interest in climatology. The purpose of this study was to calculate the seasonal precipitation index, using the Markham method in 28 rain gauge stations of Ardabil province during the 30-year recorded period. In this regard, daily rainfall data were analyzed and the Markham method was used to calculate the mean time of occurrence and the seasonality index (SI) of the components S, C and PR (average annual rainfall vector). In the next step, the Seasonality Index (SI) obtained from the PR ratio to the total annual rainfall for all rain gauge stations over the study area. According to the results, the lowest amount of seasonality is related to Sanin and Shamshirkhani stations with a value of 0.18. While the highest seasonality value is calculated for the Sarein Station with a value of 0.39. Based on the seasonal pattern of monthly rainfall values, the mean occurrence time of rainfall of 20 rain gauge stations falls into winter season, and the 6 rain gauge stations experience the highest rainfall during spring season and the 2 remaining stations had a rainy autumn season. Distinguishing seasonality pattern of monthly and seasonal rainfall can be used for the prediction of water balance changes, cultivation timing, and flood/drought events in finer time scales.