Spatiotemporal Impact of Temperature and Precipitation on the Cryosphere of Pakistan in Changing Climate

Abstract

This research thesis is mainly focused to assess changes in the daily observed temperatures and precipitation over the Hindukush, Karakoram and Himalaya mountains of the northern Pakistan (HKNP) which is a permanent source of fresh water (in the form of large glacial bodies with perennial snow cover) for Pakistan’s largest Indus River system that fulfills a large fraction of the water demand for agricultural land of the country as well as hydropower generation and other domestic purposes. The current research work has three aspects: Firstly, spatiotemporal variability in the observed daily maximum temperature (Tmax), minimum temperature (Tmin) and mean temperature (Tmean) for a recent 30year period (1986–2015) is examined from a total of 18 different weather stations in the HKNP region by employing probability distribution functions (PDFs) on annual and seasonal basis. The observed river discharge is used to assess the impact of temperature variations on the glaciers and snow covers of the HKNP region. The temperature based PDFs show a significant mean decadal warming of 0.45 C, 0.03 C, and 0.25 C, in Tmax, Tmin and Tmean of the region, on annual basis, respectively. However, the observed river discharges based PDFs of the region show a mean negative decadal shift of −40.15 m3/s on annual basis. The negative decadal shift in river discharge in warm climate is discussed in terms of percentile based analysis which quantifies temperature changes for each percentile. The results revealed that the decadal changes in Tmin percentiles are more correlated with river discharge than decadal changes in Tmax and Tmean percentiles, on annual basis. The seasonal analysis showed a significant positive decadal shift of 1.93 C for Tmax in spring season, whereas winter season showed a significant negative decadal shift of −0.56 C in Tmin of the HKNP region, from first decade (1986–1995) to third decade (2006–2015), respectively. The rest of seasons (i.e., summer and autumn) displayed high variability in the Tmax, Tmin and Tmean in the HKNP region. A high observed (non-parametric) correlation between the observed total cloud cover (TCC) and temperatures of the region indicates that changes in regional cloud cover might have influenced the regional temperatures. Secondly, spatiotemporal variability in the observed daily diurnal temperature range (DTR) is assessed for same weather stations for 30-year period (1986–2015) both on seasonal and annual basis. The DTR is a difference of Tmax and Tmin. The regional mean DTR is 13.27 °C on annual basis, with a maximum in autumn (14.63 °C) and minimum in winter (11.81 °C). On annual basis, the regional DTR has increased significantly at a rate of 0.34 °C per decade, during the 30-year study period at p ≤ 0.05, based on Mann-Kendall test. On seasonal basis, the DTR displays an increasing trend in all four seasons with largest significant increase in the winter season at a rate of 0.32 °C per decade. The DTR is positively correlated with Tmax of the region on seasonal and annual basis. A strong negative correlation is found between the DTR and observed TCC in all seasons, indicating that variability in TCC has a considerable impact on the variation of DTR in this region. The statistically significant increasing DTR trend along with statistically significant decreasing trend of TCC in spring season suggests an early melt of snow and ice cover in the region, consequently changing the hydrological cycle of the region that demands a better water resource management in the HKNP region. Thirdly, spatiotemporal variability in the observed daily precipitation is assessed by employing the precipitation based PDFs that show a significant positive mean decadal shift of 0.13 mm/day from 1996–2005 to 2006–2015 in the HKNP region, on annual basis. The seasonal analysis shows a positive mean decadal shift of 0.18, 0.18, and 0.16 mm/day for precipitation of the region, in winter, summer and autumn season, from 1996–2005 to 2006–2015, respectively. It is further observed that the intensity of extreme precipitation events also increases progressively (from 213.8 to 257.0 mm/day) during 1986–1995 to 2006–2015 for summer season in the HKNP region. Along with temporal shifts, spatial positive (negative) precipitation shifts are also noticed in the western (eastern) parts of the HKNP region. The percentile based analysis shows that wet days (< 2.5 mm/event) are directly correlated with seasonal snow cover distribution that shows increasing trend for summer season in changing climate in the north eastern part of the HKNP region. A progressively increasing high observed non-parametric correlation from 0.54 to 0.71 between the observed precipitation and river discharge of the region is observed in recent decade (2006–2015) which requires a more strategic water resource management in the HKNP region in the coming years in line with earlier findings in this thesis research. Cumulatively, the thesis work is an effort to highlight the outcomes generated by employing frequency distribution based methods on the recent daily observed temperatures and precipitation in the HKNP region. These methods were ignored in previous research studies conducted specifically in the HKNP region. The outcomes of these methods not only provide a more detailed assessment of climate change impacts on the cryosphere of the HKNP region, but also provide a reference document for many related applied research aspects in the coming days.