Determination of the Precipitation Regime and the Seasonality Index Variations in the Central Part of the Ardabil Province

Precipitation is the most important climatic factor, particularly in dry lands and its regime characteristics is affected by the change in climate. The precipitation regime is a result of physical, spatial and temporal interactions. The seasonality index (SI) specifies the distribution of monthly rainfall over the year and evaluates the seasonal variations of the rainfall regime. The present study was conducted to determine the precipitation regime and to detect the trend of precipitation SI at the central part of the Province of Ardabil. The rainfall data of 24 stations were collected for the 1989–2012 period. Descriptive statistics of monthly precipitation data were presented both graphically and statistically, and the spatial-temporal variations were estimated using the SI and coefficient of variation (CV). The trend of precipitation SI at different rain gauge stations was determined using the Mann-Kendall test. The results showed that the highest CV belonged to the Sad-Ghorichay and Lay Stations (65 and 63%), and the lowest was related to the Shamsir Khani Station (36%). Based on the precipitation SI of monthly data, two main regimes were determined: a short dry-season (SI= 0.2–0.3), and a wet-season having the SI value of 0.6. The results of the Mann-Kendall test showed that most stations had either negative or positive trends in the precipitation SI. The increasing trend in the study area was more than the decreasing trend; only in some stations was the trend statistically significant. Also, assessing the CV of precipitation data showed that the uniformity of monthly precipitation values had decreased during the study period. Increasing the CV and precipitation SI indicate a change in precipitation regime; consequently, an increase in the severity of possible droughts in the study area.