Regional analysis of trend and non-stationarity of hydro-climatic time series in the Southern Alborz Region, Iran

Analysis of the trend of climatic records is necessary for better climate modelling and subsequently adopting effective planning and management strategies. In this research, the Southern Alborz Range, Iran was selected to analyse the trends and stationarity of hydro-climatic time series. The Mann-Kendall (M-K) classic test was considered to identify the monotonic trend, while trend free pre-whitening approach was applied for eliminating serial correlation from the time series. Meanwhile, time series stationarity was tested by Kwiatkowski-Phillips-Schmidt-Shin (KPSS) test. The results indicated both increasing and decreasing trends for precipitation, mean air temperature and pan evaporation in annual time-scale which were insignificant in most of the stations. The western parts of the area illustrated the highest positive trend (2.018 mm.year(-1)) in annual precipitation; while the south of the study region showed the highest negative trend (-0.999 mm.year(-1)). The highest warming trend belongs to the northern parts of the region (0.035 degrees C.year(-1)); while the western parts show the highest negative trend in temperature variable (-0.07 degrees C.year(-1)); on the other hand, in the entire of the region, an insignificant decreasing trend is observed in most of the evaporation records. Non-stationarity tested with the KPSS suggested annual time series to be significantly stationary after de-trending and removing lag-1 serial correlation. The findings of this investigation may provide important information about the climate of the region and consequently help to implement better management and planning strategies for scarce water resources of the region.