Spatiotemporal analysis of precipitation and temperature concentration using PCI and TCI: a case study of Khuzestan Province, Iran

Temperature and precipitation are the basic elements of climate, and their variation can change the water demands of different uses. In this study, the trend of temperature and precipitation of Iran’s largest agricultural products hub (i.e., Khuzestan Province) was examined in monthly, seasonal, and annual timescales in the period 1988–2018 (30 years) in six synoptic stations. The effect of long-term persistence was eliminated, considering the effect of the Hurst coefficient using the fourth version of the Mann–Kendall nonparametric test. The time of occurring sudden change in the time series and concentration of precipitation and the temperature of the study area were also analyzed using the Pettitt test, precipitation concentration index (PCI), and temperature concentration index (TCI), respectively. The results showed that there is a direct relationship between increasing temperature and decreasing precipitation in the study area. The annual temperature has experienced a significant increasing trend, while the annual precipitation has decreased significantly in all stations. Due to the significant trend in the studied series, the Pettitt test detected a total of 94 significant failure points (year of failure) and it was found that sudden changes in air temperature time series began in November 1993 at Ramhormoz station and continued to January 2009. The results of investigating the temperature and precipitation trends in the two sub-periods (1988–2000 and 2001–2018) showed that most of the significant increasing trends in temperature time series were experienced in the first period and most of the significant decreasing trends in precipitation time series were experienced in the second period. In addition to the trend and sudden changes in precipitation and temperature series of the study area, PCI and TCI showed that the climate of the study area is changing and the tendency to climatic irregularities is increasing. Therefore, the trend evaluation of temperature and precipitation at different time and space scales has great importance in planning and managing water resources.