Prevailing climatic trends and runoff response from Hindukush–Karakoram–Himalaya, upper Indus Basin

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)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012) and, separately, from six stations of their long-term record . 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 , 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".

A Hydrometeorological Perspective on the Karakoram Anomaly Using Unique Valley‐Based Synoptic Weather Observations

“…This explanation is much more likely than the possibility of anthropogenic consumption of summer season river discharge, as no major diversions or storage developments exist upstream of Tarbela Dam that could account for the 6.3% observed decrease in summer season contribution. Similar negative trends for summer season discharge above Pertab Bridge are reported by Hasson et al ().…”

“…The increase in annual percentage of winter and autumn discharge can be related to the increase in winter season annual percentage precipitation and increases in winter and autumn daytime temperatures (Figures a and b). However, the 11% decrease in spring season precipitation is accompanied by a 4.5% increase in discharge, indicating that rising temperatures (Asad et al, ; Fowler & Archer, ; Hasson et al, ; Iqbal et al, ) have caused the snowfields to become more vulnerable to melt during the spring (Figures a, b, and f). In summer, the 7% increase in precipitation is accompanied by a 6.3% decrease in discharge, indicating that the regional hydrological mass balance is actually positive during the summer, in spite of the fact that this is when most of the annual melting takes place.…”

“…So far, the availability of long‐term in situ meteorological observations is limited mainly to valley‐based sites that are (for the most part) situated away from the glaciers (Immerzeel et al, ; Winiger et al, ). Consequently, previous explanations of the Karakoram anomaly have been based mainly on analyses of long‐term temperature, precipitation, and river flow records (Archer, ; Archer & Fowler, ; Cook et al, ; Forsythe et al, ; Fowler & Archer, ; Hasson et al, ; Tahir et al, ; Zafar et al, ).…”

Investigating Snow Cover and Hydrometeorological Trends in Contrasting Hydrological Regimes of the Upper Indus Basin

“…A total of 630 images of MODIS, MOD10A2 snow product were downloaded (https://modis.gsfc.nasa.gov/data/dataprod/mod10.php) for the 15-year period from 2001-2015 for the Astore and Hunza sub-basins. The cloud cover was removed by using a validated non-spectral cloud removal technique [41] in Erdas Imagine software (ver. 2014).…”

Rising mean and extreme near‐surface air temperature across Nepal

“…However, temperature trend characteristics vary depending on the season, region, and temperature variable (maximum or minimum). For instance, the greater Himalayan region of Pakistan (north of 35°N latitude) exhibits a summer cooling and a decrease in warm nights (Sheikh et al ., ; Hasson et al ., ), which contrasts with the general warming trend (Klein Tank et al ., ; Caesar et al ., ; Sheikh et al ., ). Likewise, prominent increase observed in maximum temperature over central and western Himalayan mountains (Shrestha et al ., ; Bhutiyani et al ., ; Kattel and Yao, ; Nayava et al ., ) is in direct contrast to prominent increase observed in minimum temperatures over South Asia, India, China, and Tibet in recent decades (Alexander et al ., ; Klein Tank et al ., ; Panda et al ., ; Ding et al ., ; Tong et al ., ).…”