Evaluation of the trend of extreme temperature and precipitation indices in the central desert of Iran

The activities of humanity on Earth have significantly changed over the past hundred years. The increase in greenhouse gas concentrations has led to global warming and, as a result, has caused changes in climate indices. Assessing extreme temperature and precipitation values is of great importance in agricultural planning and water resource management policies. In this study, using daily temperature and precipitation data from 18 synoptic stations located on the periphery of the central desert of Iran, 12 extreme indices, including 6 temperature indices and 6 precipitation indices defined by ETCCDMI, were evaluated for the time period from 1991 to 2020. For trend and magnitude determination of the indices, the Mann-Kendall test and Sen's slope estimator were used. The research results indicate an increasing trend in warm extreme indices and a decreasing trend in cold extreme indices in the study area. The Alborz Mountains factor has some influence on these indices, with the decreasing trend in cold extreme indices being less pronounced in the northern part of the region, which is closer to the Alborz Mountains, compared to the southern part. For instance, the Shahroud station and warm extreme indices in the southern part of the region show a significant increasing trend compared to the north. Furthermore, the diurnal temperature range index in the northern part of the region, which is close to the southern slopes of the Alborz Mountains, exhibits the highest increasing trend, while in the southern part, this index shows a decreasing trend. Regarding the 6 precipitation indices, no significant trend was observed in most of the stations.