Temporal Variability and Trend Analysis of Thom's Discomfort Index in Jos Plateau, Nigeria: A Mann-Kendall and Sen's Slope Estimation Approach

This study evaluates the spatiotemporal variability and trend dynamics of Thom's Discomfort Index (DI) in Jos Plateau, Nigeria, using 30 years of monthly meteorological data spanning 1996 to 2025. The DI was computed from mean air temperature and relative humidity following Thom (1959), and trend analysis was conducted using the non-parametric Mann-Kendall test and Sen's slope estimator. Results revealed a mean annual DI of 20.12°C, with monthly values ranging from 17.67°C (January) to 22.33°C (April–May). Approximately 70.8% of monthly observations fell within the comfortable zone (DI < 21), while 28.6% indicated conditions of reduced comfort (21 ≤ DI < 24). The Mann-Kendall test detected a statistically non-significant positive trend in annual DI (Z = 1.53, p = 0.125, τ = 0.200), with Sen's slope of 0.013°C per year. At the monthly scale, significant upward trends were identified in May (Z = 1.963, p = 0.050), July (Z = 2.105, p = 0.035), and November (Z = 2.105, p = 0.035). Decadal analysis confirmed an upward shift in mean DI from 20.06°C (1996–2005) to 20.32°C (2016–2025). These findings suggest a gradual intensification of thermal stress in a region historically considered thermally temperate, with significant implications for human health, outdoor productivity, and climate-sensitive urban planning in the Jos Plateau.