Future Water Availability from Hindukush-Karakoram-Himalaya upper Indus Basin under Conflicting Climate Change Scenarios

Abstract

Future of the crucial Himalayan water supplies has generally been assessed under the anthropogenic warming, typically consistent amid observations and climate model projections. However, conflicting mid-to-late melt-season cooling within the upper Indus basin (UIB) suggests that the future of its melt-dominated hydrological regime and the subsequent water availability under changing climate has yet been understood only indistinctly. Here, the future water availability from the UIB is presented under both observed and projected-though likely but contrasting-climate change scenarios. Continuation of prevailing climatic changes suggests decreased and delayed glacier melt but increased and early snowmelt, leading to reduction in the overall water availability and profound changes in the overall seasonality of the hydrological regime. Hence, initial increases in the water availability due to enhanced glacier melt under typically projected warmer climates, and then abrupt decrease upon vanishing of the glaciers, as reported earlier, is only true given the UIB starts following uniformly the global warming signal. Such discordant future water availability findings caution the impact assessment communities to consider the relevance of likely (near-future) climate change scenarios-consistent to prevalent climatic change patterns-in order to adequately support the water resource planning in Pakistan.

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

“…Thus, field-significant results for the whole Karakoram are mainly dominated by the contribution of relatively large number of stations from the western Karakoram. Nevertheless, reports of increasing end-ofsummer snow cover and falling regional snow line altitudes (Minora et al, 2013;Hasson et al, 2014b;Tahir et al, 2016), increasing or stable glacial extents (Hewitt, 2005;Scherler et al, 2011;Bhambri et al, 2013;Minora et al, 2013), and possibly a non-negative glacier mass balance within eastern and central Karakoram (Gardelle et al, 2013 -in contrast to a shorter period - Kääb et al, 2015), local climate change narratives (Gioli et al, 2013) and overall simulated reduced near-future water availability for the UIB (Hasson, 2016b) reinforce our presented findings.…”

“…These seasonally distinct changes place emphasis on the separate assessments of snow and glacier melt regimes, for which an adequate choice is the hydrological models, which are able to independently simulate snow and glacier melt processes, e.g., the University of British Columbia (UBC) watershed model. Based on the UBC model, Hasson (2016b) recently confirmed our findings that the continuation of prevailing early melt season warming will yield an increased and early snowmelt runoff, but in stark contrast, mid-to late melt season cooling will result in a decreased and delayed glacier melt runoff in the near future. Such changes in both snow and glacier melt regimes all together can result in a sophisticated alteration of the hydrological regimes of the UIB and, subsequently, the timings of the downstream water availability.…”

Assessment of Future Water Resources Availability under Climate Change Scenarios in the Mékrou Basin, Benin

“…Ref. [54] also found a high variability in future flows due to the variability of the various components of the hydrological cycle in the same catchment. As with rainfall, the significant runoff increases were obtained mostly from August to November.…”

Bias Correction of High‐Resolution Regional Climate Model Precipitation Output Gives the Best Estimates of Precipitation in Himalayan Catchments

“…Additionally, given their rather coarse spatial resolution and dependence on the assimilation of meteorological observations, precipitation estimates over the HKKH region from global atmospheric reanalysis datasets such as ERA-Interim (Dee et al, 2011) are also unsuitable for forcing hydrological models (Ma et al, 2009). Using a regional climate model to dynamically downscale coarse-resolution reanalysis or global climate model data to high spatial resolution (<10 km) over data-sparse mountainous regions is one method for providing sufficiently detailed precipitation information for driving hydrological and water resources models and estimating precipitation extremes for impact assessments (e.g., Akhtar et al, 2008;Ali et al, 2015;Ghosh & Dutta, 2012;Narula & Gosain, 2013;Li et al, 2016;Nepal, 2016;ul-Hasson, 2016;Sanjay et al, 2017]. Subsequent biases in the downscaled precipitation output can be reduced using postprocessing techniques that correct important statistical properties of the simulated precipitation distribution so that they match the available observations, resulting in realistic forcing data for hydrological streamflow simulations (Teutschbein & Seibert, 2012).…”