Evaluating the Performance of Standardized Precipitation Evapotranspiration Index in Cold Climate Regions using Trend Analysis

Drought monitoring is crucial for water resource management in cold climate regions. For drought monitoring, different drought indices are used. Some drought indices, only consider precipitation and ignore temperature-driven evapotranspiration, which face significant limitations in cold regions. SPEI index provides a more comprehensive and adaptable tool by integrating temperature-driven evapotranspiration and water balance analysis. So, this index performance is worth evaluating in cold climate and mountainous regions. So, this study aims to compare the performance of Standardized Precipitation Evapotranspiration Index (SPEI) in two mountainous and cold climate regions in Iran and the United States (US). The Mann-Kendall Test was employed to assess the trend in the Upper Colorado River Basin (UCRB) in the US and Lorestan province. The results revealed a predominantly decreasing trend in drought occurrences across Lorestan, especially in southern and southwestern areas with lower elevations. In contrast, the UCRB showed a positive trend, indicating a wet period. The western parts of the UCRB were predominantly affected by drought. Among the studied stations, Khorram Abad station exhibited the most statistically significant trend at the 99% confidence level (Z > 2.57). The temporal trend analysis of drought revealed more positive and negative abrupt changes in the UCRB than in Lorestan. This indicates a higher degree of small-scale variability in the UCRB compared to Lorestan. This study provides a temperature-responsive method for drought assessment, supporting the development of adaptive strategies that address snowmelt variability, seasonal water availability, and shifting drought patterns in cold regions.