Spatiotemporal Trend Analysis of Minimum, Mean, and Maximum Air Temperature in the Kashkan River Basin Using Cloud Computing and Modified Mann–Kendall Tests

This study investigates the spatiotemporal trends of minimum, mean, and maximum temperature in the Kashkan Basin using nonparametric time series tests, including the Mann–Kendall test modified by the PW_MK, VCA, and TFPW approaches, along with Sen’s slope estimator. The results indicate that, at the annual scale, all three temperature variables exhibit statistically significant increasing trends. Specifically, mean temperature increased at a Sen’s slope of 0.053 °C per year, minimum temperature at 0.051 °C per year, and maximum temperature at 0.056 °C per year. The Mann–Kendall test statistics for the annual data also confirm the high significance of these trends, showing a very high confidence level for all variables.

At the seasonal scale, increasing trends dominated most months and seasons, although their magnitude and statistical significance differed among variables. For mean temperature, the strongest increasing trends were observed in winter months and late spring, particularly in Esfand (March), Bahman (February), and Khordad (June), where high Z values and confidence levels confirmed warming. For minimum temperature, the greatest increases occurred during the warm months and in summer; Tir (July), Mordad (August), Shahrivar (September), and the summer season showed notable upward trends. Maximum temperature also displayed increasing trends in most months, with more pronounced increases in winter and early spring. Only in a few limited periods, such as Shahrivar (September) or Mordad (August) in some indices, decreasing or non significant trends were observed.

A comparison of the different trend test methods shows that the overall pattern of temperature change in the Kashkan Basin is robust and consistently upward. The concurrent increases in minimum and maximum temperatures, in line with mean temperature, indicate an intensification of regional warming. Overall, the findings suggest that the Kashkan Basin has experienced a widespread and statistically significant warming trend in recent decades, which may have important implications for water resources, evapotranspiration, heat stress, and ecosystem stability in the region.