Detection of climatic variables trend by using parametric and non parametric statistical tests. (A case study of West Azerbaijan, Iran)

In this study, the trends of annual temperature and precipitation time series were investigated through the West Azerbaijan in Iran during 1968-2008. Two approaches were used to evaluate temporal changes in climatic variables over 40 years-period. The first approach based on a analysis of standardized departures, and second approach based on trend statistical tests. Trend analyses have been made by using both nonparametric Mann–Kendall test (Multiple trend) and parametric (linear regression analysis) procedures. The long historical series of monthly temperature and precipitation data employed in this work have been previously processed through a pre-whitening (PW) technique in order to reduce the autocorrelation of climatic series and its effects on outcomes of trend detection. The Multiple trend are used for identification of an abrupt change in climatic variables time series than a gradual trend. Results state a sudden change of annual temperature and precipitation trend around of 1988 than as a gradual trend. Overall, while the temperature trend is increasing, the precipitation trend is decreasing over 40 years.