Abstract
Abstract. River flow is a reflection of the input of moisture and its transformation in storage and transmission over the catchment. In the Upper Indus Basin (UIB), since high-altitude climate measurement and observations of glacier mass balance are weak or absent, analysis of trends in magnitude and timing in river flow provides a window on trends and fluctuations in climate and glacier outflow. Trend analysis is carried out using a Mann–Kendall nonparametric trend test on records extending from 1960 to 1998. High-level glacial catchments show a falling trend in runoff magnitude and a declining proportion of glacial contribution to the main stem of the Indus. Elsewhere annual flow has predominantly increased with several stations exhibiting statistically significant positive trends. Analysis of timing using spring onset date (SOT) and centre of volume date (CoV) indicated no clear trends – in direct contrast to what has been observed in western North America. There is, however, a consistent relationship between CoV and annual runoff volume. A consistently positive correlation was also found between SOT and CoV for all the stations, implying that initial snowpack conditions before the onset of runoff influence timing throughout the season. The results of the analysis presented here indicate that the magnitude and timing of streamflow hydrograph is influenced both by the initial snowpack and by seasonally varied trends in temperature. The study contributes to the understanding of the links between climate trends and variability and river runoff and glacier mass balance and runoff. The Upper Indus Basin is predominantly influenced by winter precipitation; similar trend analysis applied to summer-monsoon-dominated catchments of the central Himalaya is recommended.
Highlights
1.1 Context and objectiveThe now-refuted statements (WWF, 2005; IPCC, 2007) concerning the predicted rapid retreat and disappearance of Himalayan glaciers and consequent drastic reduction in downstream river flows has spurred vigorous debate on changes in glacier mass balance (Berthier et al, 2007; Eriksson et al, 2009) and river flow, and the nature and role of climate trends and variability (Immerzeel et al, 2008; Bookhagen and Burbank, 2010)
Limited attention has been paid to historic changes in river flow, which can provide a reflection of the climatic input of moisture and its transformation in storage and transmission over the river
This paper extends the number of stations to nineteen for assessment of trends with the aim of identifying trends and other patterns of change in both magnitude and timing of runoff response for flow-gauging stations in Upper Indus Basin (UIB) (Fig. 1)
Summary
The now-refuted statements (WWF, 2005; IPCC, 2007) concerning the predicted rapid retreat and disappearance of Himalayan glaciers and consequent drastic reduction in downstream river flows has spurred vigorous debate on changes in glacier mass balance (Berthier et al, 2007; Eriksson et al, 2009) and river flow, and the nature and role of climate trends and variability (Immerzeel et al, 2008; Bookhagen and Burbank, 2010). Concerns about the potential impacts of climate change on flow in the Indus (Rees and Collins, 2006), given temperature changes in line with global climate change projections (Cruz et al, 2007), have given rise to expectations of dramatic decreases in river flow volume (Briscoe and Qamar, 2007; Immerzeel et al, 2008). Limited attention has been paid to historic changes in river flow, which can provide a reflection of the climatic input of moisture and its transformation in storage and transmission over the river
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