Spatiotemporal temperature trends over homogenous climatic regions of Pakistan during 1961–2017

Rising temperature has increased the frequency, severity, length, and timing of temperature extremes around the globe. The current study examined the spatiotemporal variation of Tmin, Tmax, Tmean, and diurnal temperature range (DTR) over homogeneous climatic zones of Pakistan, using observed monthly datasets from fifty stations for the period 1961–2017. The nonparametric modified Mann–Kendall (MMK), Sen’s slope estimator (SSE), and sequential Mann–Kendall (SQMK) tests were utilized to investigate the spatiotemporal trends. Cluster analysis and the L-moment approach were used to identify the homogenous climatic regions. In general, seasonal and annual Tmin, Tmax, Tmean, and DTR increased significantly in most sub-regions and the whole country, whereas JJA observed significant decreasing trends in Tmin, Tmax, and Tmean in most sub-regions during 1961–2017. Furthermore, decreasing trends prevailed in seasonal and annual Tmin in most sub-regions and the whole country during 1961–1989, whereas increasing trends were evident during 1990–2017. Tmean exhibited increasing trends on the seasonal and annual time scale in both periods except significant decrease in JJA at –0.16 and –0.20 °C/decade in the first and second periods, respectively. Tmax, Tmean, and DTR inferred decreasing trends in JJA at –0.42, –0.20, and –0.46 °C/decade, respectively, while Tmax and DTR had significant decrease in SON at –0.30 and –46 °C/decade, respectively, in the whole country during 1990–2017. The SQMK results indicate that Tmin, Tmax, Tmean, and DTR observed an increasing trend in DJF and MAM from 1985 onwards, and most of the regions observed significant trends from mid-2000. A negative correlation was observed between annual Tmin and Tmean with elevation, whereas a positive correlation was observed between annual Tmax and DTR with elevation. Pakistan has experienced numerous extreme events like heatwaves and droughts recently. Therefore, future research should investigate changes in air fluxes caused by zonal circulation and anticyclone conditions to explain the temperature variability.