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

third stations globally during 1950–2018. Frich et al. [34] investigated about the possible changes in climate extreme over the whole glob using observed data for the duration of 1946–1999. They noted a significant increase and a decrease in the number of warm summer nights and the num- ber of frost days, respectively, and a significant increase in heavy precipitation events. Sheikh et al. [35] derived climate extremes for temperature (for the duration of 1971–2000) and precipitation (for the duration of 1961–2000) using observed data over Pakistan, India, Bangladesh, Nepal and Sri Lanka. Their results indicate an increase in precipitation extremes in South Asia, consistent with the global average. Rizvi et al. [36] investigated temperature and precipitation extreme at four meteorological stations (Islamabad, Muree, Jhelum and Mian- wali) using observed data for the duration of 1960–2013. Their findings concluded that most of the temperature extremes have positive trend except FDO at Islamabad and Jhelum stations. Glaciers play significant role in terms of water availability in the mountainous regions in the world [37,38]. Most of the mountain glaciers worldwide are losing mass [39,40]. In con- trast, Glaciers in the Karakoram and adjacent Kunlun Shan seem to be stable or even growing in the recent past [41–43]. The glaciers stability is consistent with temperature trends in the Upper Indus Basin (UIB) between 1961 and 2000, investigated by Fowler et al. [44], indicating decreasing summer temperatures and runoff. These studies used somehow outdated climate

data till 2000 and call for updated investigation. With the recently recorded climate data, it can update the recent trends and potentially explain the Karakoram anomaly. In addition, spatio- temporal trend analysis of precipitation and temperature extremes can provide information about the frequency, intencity and duration of extremes events like floods, heatwaves and droughts etc. Towards this end, a special section is presented to investigate climate change and significance of the temperature and precipitation extremes at each meteorological station in the northern part of Pakistan. Various studies conducted recently explored a relationship between heatwaves, high-tem- perature extremes, and population exposure during the 21st Century. For instance, Iyakaremye et al. [45] concluded that by the mid of 21st century, the population exposure is expected to increase by ~ 28% (25%) in comparison to the baseline duration under SSP5-8.5 (SSP2-4.5) in Africa. May parts of Africa has experienced intensified and more frequent hot days and nights recently which clearly indicating a shift in the African climate [46]. Projected results about pre- cipitation suggested uncertainties over Pakistan [47,48], however, some studies suggested that precipitation has mixed trend (decreasing trend for some time periods and increasing trend for other time periods) over the northern Pakistan in the future. This demonstrate that it is imperative to understand better the condition of climate change and extremes, particularly in

the UIB as it will have impacts on water availability, hydropower generation, agriculture and the livelihood of inhabitants downstream. In addition, this can assist policy makers in terms of planning for better mitigation and adaptation measures in the future. A different approach is adapted in contrast to the previous studies to investigate climate change signals and climate extremes’ analysis over Pakistan for the duration of 1962–2019 (making two time slices, i.e., 1962–1990 and 1991–2019). Initially, the change in the mean val- ues for precipitation and temperature between two-time slices is tested for possible signifi- cance separately. The spatio-temporal trend analysis of climate extremes is then performed zone wise for each time duration. A comparison is made between the two time periods to see the possible changes in climate change and climate extremes. The assessment is drawn by using various statistical techniques, e.g., probability density functions, spatio-temporal trend analysis and testing the significance of climate extremes. The major aims of this study are: (1) to test the significance of changing climate in two-time durations for each climate zone in Pakistan and each station in the HKH (Hindukush-Karako- ram-Himalaya) region; (2) spatio-temporal trend analysis of climate extremes in each climate 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 3 / 27