Development of a nonparametric spatial standardized precipitation–temperature index for regional drought characterization

Drought is one of the most damaging natural hazards, caused by prolonged shortages of precipitation and changes in temperature that reduce water availability. Reliable assessment of drought conditions across space is essential for sustainable water resource management and effective climate adaptation. However, most existing drought indices are designed for temporal analysis and often rely on probability distribution assumptions that may not adequately capture the spatial variability of drought-related variables. This study proposes a new drought monitoring framework, the Spatial Standardized Precipitation–Temperature Index (SSPTI), for assessing drought conditions across space. The index is based on a precipitation–temperature drought variable and employs a nonparametric standardization procedure applied independently at each time step. To examine the suitability of distribution-based standardization, several probability distributions and three component GMM were evaluated. The results showed considerable variation in distributional behavior over time, indicating that probabilistic framework may not consistently represent the spatial drought variable. The proposed methodology was applied to monthly precipitation and temperature records from 42 spatial locations across Pakistan for the period 1981–2021. Variogram analysis revealed clear seasonal differences in spatial dependence, while geostatistical interpolation techniques were used to generate continuous drought maps. The resulting SSPTI provides a simple, flexible, and distribution-free measure of relative spatial dryness and wetness conditions. By avoiding restrictive distributional assumptions, the proposed framework provides a practical tool for drought monitoring and spatial drought assessment over large geographical regions.