Paper Reviewed
Farhan, S.B., Zhang, Y., Ma, Y., Guo, Y. and Ma, N. 2015. Hydrological regimes under the conjunction of westerly and monsoon climates: a case investigation in the Astore Basin, Northwestern Himalaya. Climate Dynamics 44: 3015-3032.

Introducing the rationale for their study, Farhan et al. (2015) write that it is "difficult to develop a clear understanding of climate-change impacts in the Hindukush-Karakoram-Himalaya region" of the Tibetan Plateau because of "substantial variability of glacier changes within the region (Fujita and Nuimura 2011), uncertainties related to the contribution of glaciers to runoff (Immerzeel et al. 2011), variable retreat rates (Kumar et al. 2008) and strong spatial variations in glacier behavior related to topography and climate (Scherler et al. 2011)." They also note that "uncertainties in projections of glacier changes (Cogley 2011; Lutz et al. 2012), controversial and erroneous reports stated by IPCC (2007) and revealed by Cogley et al. (2010), lack of knowledge, paucity of long term records (Kaser et al. 2006), unsuitable or uncertain data and methods, failure to publish existing data (Barnett et al. 2005), very limited mass balance records particularly in the Upper Indus River Basin (UIB) (Bhutiyani 1999), and even excessive classification and secrecy regarding fundamental hydrological data collectively make these problems much worse."

Against this backdrop, the five scientists engaged in a new effort to reduce these uncertainties by investigating the impacts of climate change on this glaciated region. In doing so, they focused on the Astore Basin, a high-altitude 4,000 km² sub-catchment of the Upper Indus River Basin located in the northwestern Himalayan region of Pakistan, analyzing the relationship between various meteorological, hydrological and satellite remote sensing data sets over the past four decades.

Among the many findings of their study, Farhan et al. report that trend analysis of the mean monthly snow cover area revealed "no significant depletion trends" over the period 2003-2010, which was "mainly because of the fact that there was also no trend in the summer mean temperature during that period." In addition, they write that statistical analyses reveal the annual stream flow fluctuations in the Astore River over the period 1980-2010 were "predominantly influenced by variations in precipitation rather than the alteration in catchment temperatures; consequently, the stream flow fluctuations were not governed by enhanced glacier ablation and retreat."

With respect to glaciers, Farhan et al. note that of the 98 glaciers in this region covering an area greater than one square kilometer, temporal image analysis for the period 1973-2013 showed that 28 glaciers experienced minor increases, 45 slightly decreased, and the remaining 25 appeared to be in a stable state. Not surprisingly, therefore, the overall total glacier area experienced an insignificant decrease of 0.3 percent over the four-decade period, which the authors describe as a minor change in the range of data accuracy and which suggests "quite stable conditions of Astore basin glaciers." What is more, laser altimetry data of glacier thickness changes over the period 2003-2008 "also revealed stability or even a slightly growing trend."

In summing up their findings, Farhan et al. state that the observed stability of Astore basin glaciers represents "a different response to global warming" in which "summer temperature reductions and positive trends in winter precipitation imply reduced ablation and increased accumulation ... which may lead to balanced and/or positive glacier ice mass balance ... and may explain one of the reasons for their relative insensitivity to warming."

References
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Bhutiyani, M.R. 1999. Mass-balance studies on Siachen Glacier in the Nubra valley, Karakoram-Himalaya. India 45: 112-118.

Cogley, J.G. 2011. Present and future states of Himalaya and Karakoram glaciers. Annals of Glaciology 52: 69-73.

Cogley, J.G., Kargel, J.S., Kaser, G. and van der Veen, C.J. 2010. Tracking the source of glacier misinformation. Science 337: 522.

Fujita, K. and Nuimura, T. 2011. Spatially heterogeneous wastage of Himalayan glaciers. Proceedings of the National Academy of Sciences, USA 108: 14011-14014.

Immerzeel, W.W., Beek, L.P.H., Konz, M., Shrestha, A.B. and Bierkens, M.F.P. 2011. Hydrological response to climate change in a glacierized catchment in the Himalayas. Climatic Change 110: 721-736.

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Kaser, G., Cogley, J.G., Dyurgerov, M.B., Meier, M.F. and Ohmura, A. 2006. Mass balance of glaciers and ice caps: consensus estimates for 1961-2004. Geophysical Research Letters 33: 1-5.

Kumar, K., Dumka, R.K., Miral, M.S., Satyal, G.S. and Pant, M. 2008. Estimation of retreat rate of Gangotri glacier using rapid static and kinematic GPS survey. Current Science 94: 258-262.

Lutz, A.F., Immerzeel, W.W., Gobiet, A., Pellicciotti, F. and Bierkens, M.F.P. 2012. New climate change scenarios reveal uncertain future for Central Asian glaciers. Hydrology and Earth System Sciences Discussions 9: 12,691-12,727.

Scherler, D., Bookhagen, B. and Strecker, M.R. 2011. Spatially variable response of Himalayan glaciers to climate change affected by debris cover. Nature Geoscience 4: 156-159.