Dominant Climatic Factors Associated with Reconnaissance Drought Index Variability Using Principal Component Analysis

Drought is a major hydroclimatic hazard in semi-arid regions, where limited precipitation and high atmospheric water demand intensify water scarcity. This study investigates the relationships among precipitation, reference evapotranspiration (ET₀), and the Reconnaissance Drought Index (RDI) in the Darreh Dozdan River Basin, Lorestan Province, Iran. Meteorological data from the Kuhdasht synoptic station for ۱۹۹۸–۲۰۲۲ were analyzed. Reference evapotranspiration was estimated using the FAO-۵۶ Penman–Monteith method, and drought conditions were characterized using the RDI framework. Principal component analysis (PCA) was applied to standardized annual precipitation, ET₀, and the log-transformed RDI ratio to identify the dominant multivariate hydroclimatic pattern. The first principal component (PC۱) explained ۶۷.۷۷% of the total variance, while PC۲ explained ۳۱.۷۴%. Precipitation (۰.۸۷) and the log-transformed RDI ratio (۱.۰۰) showed strong positive loadings on PC۱, whereas ET₀ exhibited a moderate negative loading (−۰.۵۳). Normalization of the squared PC۱ loadings of precipitation and ET₀ yielded relative loading shares of ۷۲.۹۳% and ۲۷.۰۷%, respectively. These values indicate that precipitation is more strongly represented than ET₀ within the dominant drought-related component; they should not be interpreted as a causal decomposition of RDI variance. Overall, the results show that annual drought variability in the study basin is more strongly associated with fluctuations in precipitation than with reference evapotranspiration, while atmospheric evaporative demand remains an important secondary component of drought variability.

کلیدواژه ها:

Reconnaissance Drought Index ، Principal component analysis ، Precipitation ، Reference Evapotranspiration ، Semi-arid basin