Spatio-temporal trends in snow extent and their linkage to hydro-climatological and topographical factors in the Chitral River Basin (Hindukush, Pakistan)

Abstract

In many parts of the world, including the Hindukush-Karakoram-Himalayan (HKH) region, the population depends on snow and glaciers-melt waters to grow food, generate electricity and store water for their use throughout the year. The annual and seasonal variation in the snow cover area (SCA) due to its response to the climatic variables directly influences the water supplies. The aim of current study is to evaluate the spatio-temporal trends in the annual and seasonal snow cover at basin-wide scale. Impact of topography on the SCA is analyzed by revealing the trends in SCA in different elevation bands. It also investigates the trends in hydro-climatic factors (temperature, precipitation and river flows) in the Chitral River basin (Hindukush region) and their linkage to the SCA variations. Snow cover is estimated using cloud-free 8-day MODIS snow products on 17-year time-period (2000–2016). Hydro-climatic data of the river flow (1989–2014), temperature, and precipitation (1965–2013) were obtained from Water and Power Development Authority (WAPDA), and Pakistan Meteorological Department (PMD). Trend analysis of the SCA and hydro-climatic variables was carried out using Mann-Kendall’s trend test and Sen’s slope. The results reveal: (1) a significant increasing trend in the SCA at basin-wide scale and at all elevation zones i.e. A to E (1471–7708 m ASL), except zone B (2500–3500 m ASL), (2) decreasing and constant trends in the mean temperature and total precipitation, respectively, over the same time-period as SCA indicating possible reasons for increasing SCA, (3) a slight decrease in the mean annual and summer flow (1989–2014) possibly due to the summer cooling, reduced snowmelt and slightly decreasing summer precipitation over this time-period, and (4) strong dependency of the Chitral River flow on snowmelt, driven by the temperature seasonality. Modeling snowmelt runoff under future climate projections in the study area may help to manage the water resources properly.

Keywords:

• Snow cover trends
• hydrological regime
• MODIS snow data
• hydro-climatic trends
• Hindukush region

Acknowledgements

The authors extend their thanks to the Water and Power Development Authority (WAPDA) and the Pakistan Meteorological Department (PMD) for contributing their hydrological and meteorological data, respectively. The authors also thank NASA and USGS for providing SRTM DEM and MODIS data. They are grateful to the anonymous reviewers whose comments and suggestions significantly improved the manuscript. They appreciate the help provided by Dr. Naeem Rashid, Research fellow at KAIST, Republic of Korea (former full-bright postdoctoral fellow at the University of California and winner of the green talent award-2015 at Germany) to revise this manuscript for the English language corrections within a short period of time.

Funding

This work was supported by the National Natural Science Foundation of China (NSFC) and ICIMOD under Grant no. 41761144075.