Abstract
Abstract. Largely depending on the meltwater from the Hindukush–Karakoram–Himalaya, withdrawals from the upper Indus Basin (UIB) contribute half of the surface water availability in Pakistan, indispensable for agricultural production systems, industrial and domestic use, and hydropower generation. Despite such importance, a comprehensive assessment of prevailing state of relevant climatic variables determining the water availability is largely missing. Against this background, this study assesses the trends in maximum, minimum and mean temperatures, diurnal temperature range and precipitation from 18 stations (1250–4500 m a.s.l.) for their overlapping period of record (1995–2012) and, separately, from six stations of their long-term record (1961–2012). For this, a Mann–Kendall test on serially independent time series is applied to detect the existence of a trend, while its true slope is estimated using the Sen's slope method. Further, locally identified climatic trends are statistically assessed for their spatial-scale significance within 10 identified subregions of the UIB, and the spatially (field-) significant climatic trends are then qualitatively compared with the trends in discharge out of corresponding subregions. Over the recent period (1995–2012), we find warming and drying of spring (field-significant in March) and increasing early melt season discharge from most of the subregions, likely due to a rapid snowmelt. In stark contrast, most of the subregions feature a field-significant cooling within the monsoon period (particularly in July and September), which coincides well with the main glacier melt season. Hence, a decreasing or weakly increasing discharge is observed from the corresponding subregions during mid- to late melt season (particularly in July). Such tendencies, being largely consistent with the long-term trends (1961–2012), most likely indicate dominance of the nival but suppression of the glacial melt regime, altering overall hydrology of the UIB in future. These findings, though constrained by sparse and short observations, largely contribute in understanding the UIB melt runoff dynamics and address the hydroclimatic explanation of the Karakoram Anomaly.
Highlights
Hydropower generation has a key importance in minimizing the ongoing energy crisis in Pakistan and meeting the country’s burgeoning future energy demands
We present a first comprehensive and systematic hydroclimatic trend analysis for the upper Indus Basin (UIB) based on 10 stream flow, 6 low-altitude manual and 12 high-altitude automatic weather stations
The observed cooling phenomenon is generally attributed to the incursions of the South Asian summer monsoonal system and its precipitation (Cook et al, 2003) into the Karakoram and the UIB-West, which presently seems to be accelerated in view of the observed increase in cloud cover, precipitation and number of wet days (Bocchiola and Diolaiuti, 2013)
Summary
Hydropower generation has a key importance in minimizing the ongoing energy crisis in Pakistan and meeting the country’s burgeoning future energy demands. Seasonal water availability from the upper Indus Basin (UIB), which contributes to around half of the annual average surface water availability in Pakistan, is indispensable for exploiting 3500 MW of installed hydropower potential at the country’s largest reservoir, Tarbela, immediately downstream. Withdrawals from the UIB further contribute to the country’s agrarian economy by meeting extensive irrigation water demands. The earliest water supply from the UIB after a long dry period (October to March) is obtained from melting of snow (late May to late July), the extent of which largely depends upon the accumulated snow amount and the concurrent temperatures (Fowler and Archer, 2005; Hasson et al, 2014b). Snow and glacier melt runoffs, originating from the Hindukush–Karakoram–Himalaya (HKH) ranges, together constitute around 70–80 % of the mean annual water available from the UIB (SIHP, 1997; Immerzeel et al, 2009). Unlike major river basins of South and Southeast Asia that feature extensive summer monsoonal wet regimes downstream, the lower Indus Basin is mostly arid and hyper-arid and much relies upon the meltwater from the UIB (Hasson et al, 2014b)
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