Climate change and spatio-temporal trend analysis of climate extremes in the homogeneous climatic zones of Pakistan during 1962-2019

Where H0 and HA represent null and alternative hypothesis, respectively. The notation μ1962– 1990 and μ1991–2019 represent the average climatology during 1962–1990 and 1991–2019, respectively. Here the average climatology means average temperature or precipitation for the mentioned time duration. The change between the two time slices is significant at 5% level of significance if the p-value of the test is less than or equal to 0.05. To assess the detailed behav- iors of zone-wise climatology, this analysis was carried out on a seasonal as well as on annual basis. 3.3. Trend analysis For trend analysis, a non-parametric test, the modified version of MK (mMK) test has been used initially proposed by [59] and widely uses in hydrology and climatology for trend analysis (e.g., [60,61]). The null hypothesis in MK test is “no monotonic trend is present in the data”. Which means that if the p-value of the test is less than or equal to 0.05, then it is concluded that there is a trend in the data at 5% level of significance. For further details about the test sta- tistic and calculation of the MK test, we refer to [62]. 3.4. Climate extremes analysis Climate extremes related to temperature and precipitation were calculated for both time slices. To assess the changes in climate extremes, probability density functions were drawn for both time slices and a comparison is made between them. To investigate spatial variability and changes, the changes in climate extremes were interpolated to the target location by using a

geostatistical interpolation method called Kriging. The analysis provides information about the changes in climate extremes during the two-time slices over the full domain. Finally, the statistical significance of the climate extremes was performed by using a 5% level of signifi- cance. A comparison was made between climate extremes in both time slices for temperature and precipitation in each climate zone in terms of statistical significance. For definition and unit of measurement of climate extremes, we refer to [63,64]. A summary of the climate extremes used in this study is given in Annex-01. 3.5. Climate change assessment and extremes’ analysis in HKH region HKH comprises one of the world’s largest non-polar glaciers [65–67], therefore, climate change and extremes can have significant impacts on snow and glacier melt which can further alter the hydrological regime of this region. Different studies conducted about trends in tem- perature, precipitation and extremes over Pakistan recently. For instance, the results of Bhatti et al. [68] suggested that the linear trend of all precipitation extreme indices showed an increasing tendency over Pakistan during 1980–2016. The study of Ullah et al. [69] illustrated that the spatial distributions of Tmin and Tmax showed a warming trend over the whole coun- try, however, the seasonal and annual Tmin (Tmax) exhibited sharp increasing trends in the southern, southwestern and southeastern (northern and southwestern mountainous) regions of Pakistan. Elevation dependent significant fluctuations have been noted in long-term precip-

itation trend (during 1980–2016) in Pakistan with these categories: decreases in 500–1000m and 1000–1500m elevation zones; significant increasing trend in elevation zones of �500m and�1500 m [70]. Strong variability has been noted in precipitation during 1986–2005 over Pakistan, particularly in the northern parts of the country. For instance, a positive trend in the precipitation variability was noted during the winter season in Himalaya and Karakorum region while a negative trend was noted during pre-monsoon season in the Karakorum and Himalayas regions [71]. Studies related to extremes analysis suggested that the precipitation and temperature extremes like warm nights, summer days, warm days, warmest day, and PLOS ONE Climate change and extremes analysis using observed data (1962-2019) over Pakistan PLOS ONE | https://doi.org/10.1371/journal.pone.0271626 July 27, 2022 6 / 27