Glaciochemical Investigations as a Tool for Determining the Spatial and Seasonal Variation of Snow Accumulation in the Central Karakoram, Northern Pakistan

Abstract

Between 70 and 80% of the total annual run-off from the Upper Indus Basin originates from heavy snowfall and glacierized basins at elevations greater than 3500 m a.s.l. However, very little is known concerning the mountainous headwaters of the Indus. This is especially true with respect to the amount of snowfall in the major source area, the high Karakoram. Recent studies of high-altitude alpine glaciers indicate that geochemical dating techniques can accurately and confidently identify seasonal and annual stratigraphy within snow pits and ice cores, and thus can be used to determine the seasonal and annual rate of snow accumulation. In addition, chemical records can usually be employed to determine sources of precipitation. Six snow pits, each 5–10 m deep, were investigated in the accumulation zones of the Biafo and Khurdopin Glacier basins. Both accumulation zones are characterized by broad, open basins separated by steep, narrow ridges in which direct precipitation is the dominant form of nourishment. Seasonal stratigraphy is delineated through an analysis of the seasonal variation in the chemical and physical characteristics of the snow-pack. Annual snow accumulation in the Biafo Glacier basin ranges from 0.9 to 1.9 m water equivalent; maximum accumulation occurs in the elevation band 4900–5400 m a.s.l. Roughly one-third of this snow accumulation occurs during the summer.

Correction and Informed Regionalization of Precipitation Data in a High Mountainous Region (Upper Indus Basin) and Its Effect on SWAT-Modelled Discharge

“…Subsequently, the climatic controls in the UIB are quite different from that in the Himalayas on the eastern side. In fact, over the extent of the UIB, most of the annual precipitation originates in the west, resulting from the mid-latitude western disturbances, and mostly in solid form during winter and spring [20,19,29,30]. Occasional rains are brought by the monsoonal incursions to trans-Himalayan areas [20,29], but even during the summer months, the trans-Himalayan areas do not derive all precipitation from monsoon sources [31].…”

“…Thus the northern valley floors of the UIB are arid, with annual precipitation of only 100-200 mm. These totals increase to 600 mm at 4400 m elevation, and glaciological studies suggest annual accumulation rates of 1500 to 2000 mm at 5500 m altitude [20,32] (see Appendix-A - Figure 5)…”

“…Stream flow is generated by the combination of the storm runoff in the lower part of the upper Indus basin and the snow and glacier runoff from the higher parts of the UIB [33,24] Nearly half of the total annual flow in the Indus basin as a whole is contributed by the UIB, with 86-88% contribution during the summer season while only 12-14% during the winter season [34,35]. The precipitation data of twenty (20) meteorological stations (Figure 1), operative in the study area (UIB) were used in this study. Out of these stations, six (6) are operated by the Pakistan Meteorological Organization (PMD), while fourteen (14), relatively new stations are under the jurisdiction of the Water & Power Development Authority, Pakistan (WAPDA).…”

“…Similarly, while most of the weather stations have become operational after the mid-nineties, long-term data is a rear commodity and only available at a limited number of locations.Owing to the complex orography of the UIB region and to the co-action of different hydro-climatic regimes (which affect the amounts, spatial patterns and the seasonality of precipitation), neither the sparse observed station data (or the gridded data products based on them) nor the sensors-based data, fully represents the precipitation regime of the region [11][12][13][14]. Several studies have pointed out that precipitation in the HKH (Hindu Kush Himalayan) -region exhibits large changes over short distances and has a considerable vertical gradient [15][16][17][18][19][20]. This also explains the fact that the average precipitation amounts over the UIB (based on the sparse and low-altitude climatic station network), are unrealistically low to be able to sustain the observed discharge at the basin outlet.These factors have led many researchers to find ways to assess methods for precipitation correction that may lead to a more realistic water balance [21] in many basins and have also compelled a number of hydrological studies in the UIB region to use, in addition to the observed station data, a variety of other reference climate data from different sources, either directly or with prior modifications and adjustments (e.g.…”

“…Owing to the complex orography of the UIB region and to the co-action of different hydro-climatic regimes (which affect the amounts, spatial patterns and the seasonality of precipitation), neither the sparse observed station data (or the gridded data products based on them) nor the sensors-based data, fully represents the precipitation regime of the region [11][12][13][14]. Several studies have pointed out that precipitation in the HKH (Hindu Kush Himalayan) -region exhibits large changes over short distances and has a considerable vertical gradient [15][16][17][18][19][20]. This also explains the fact that the average precipitation amounts over the UIB (based on the sparse and low-altitude climatic station network), are unrealistically low to be able to sustain the observed discharge at the basin outlet.…”