Twenty first century climatic and hydrological changes over Upper Indus Basin of Himalayan region of Pakistan

Abstract

This study is based on both the recent and the predicted twenty first century climatic and hydrological changes over the mountainous Upper Indus Basin (UIB), which are influenced by snow and glacier melting. Conformal-Cubic Atmospheric Model (CCAM) data for the periods 1976-2035, 2041-2070, and 2071-2100 and Regional Climate Model (RegCM) data for the periods of 2041-2050 and 2071-2080 with RCP8.5 are used for climatic projection and, after bias correction, the same data are used as an input to the University of British Columbia (UBC) hydrological model for river flow projections. The projections of all of the future periods were compared with the results of 1976-2005 and with each other. Projections of future changes show a consistent increase in air temperature and precipitation. However, temperature and precipitation increase is relatively slow during 2071-2100 in contrast with 2041-2070. Northern parts are more likely to experience an increase in precipitation and temperature in comparison to the southern parts. A higher increase in temperature is projected during spring and winter over southern parts and during summer over northern parts. Moreover, the increase in minimum temperature is larger in both scenarios for all future periods. Future river flow is projected by both models to increase in the twenty first century (CCAM and RegCM) in both scenarios. However, the rate of increase is larger during the first half while it is relatively small in the second half of the twenty first century in RCP4.5. The possible reason for high river flow during the first half of the twenty first century is the large increase in temperature, which may cause faster melting of snow, while in the last half of the century there is a decreasing trend in river flow, precipitation, and temperature (2071-2100) in comparison to 2041-2070 for RCP4.5. Generally, for all future periods, the percentage of increased river flow is larger in winter than in summer, while quantitatively large river flow was projected, particularly during the summer monsoon. Due to high river flow and increase in precipitation in UIB, water availability is likely to be increased in the twenty first century and this may sustain water demands.

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

“…These findings are largely in agreement with the earlier future water availability projections for the UIB under warmer climates as typically but inconsistently projected by the climate models under a variety of anthropogenic forcing [5][6][7][8], as explained in Section 1. The results of far-future water availability are further consistent with earlier studies focusing on the sub-basins of the UIB.…”

“…It is pertinent to mention here that though CORDEX-SA experiments provide high resolution present and future climate simulations, however, their ability to reproduce the observed hydro-climatology over the steep HKH topography is by hardly any means better than their forcing CMIP5 GCMs, which being consistent to their older versions and downscaled experiments, substantially over-(under-) estimate precipitation (temperatures) and fail to reproduce summer cooling [7,15,16,[82][83][84][85][86][87]. Such cold and wet biases in the CORDEX-SA and their CMIP5 forcing experiments are larger than their projected end of 21st century climatic changes under RCP8.5, indicating huge climatic uncertainty over the UIB [16].…”

“…Such finding is largely consistent with the prevailing changes depicted from the long-term observed streamflow record ( Figure 5) and with the reports of anomalously positive or stable glacial mass balances and extents [20,22,[27][28][29]31,[33][34][35], increasing snow covers and falling end-of-summer regional snow line altitudes [20,22,25,26], and subsequent reduction in the melt season discharges [4,19]. On the other hand, a decrease in the glacier melt and in the overall discharge is in direct contrast to the reports from earlier studies, which addressing only partially the climatic uncertainty over the UIB assess its future water availability under warmer climates [5][6][7][8]90], and suggest rather enhanced glacial melt and rise in the water availability throughout the 21st century. Such contradictory findings of rise in the near-future water availability, lacking the relevance of near-future climate change in accordance with the prevailing hydroclimatic trends, are quite misleading for the immediate freshwater resources management in Pakistan.…”

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

“…The increase of flows during the P2 period can be explained by the large increase of rainfall over the catchment during this period for the RCP8.5 scenario [9]. Similar results were obtained by [52,53] in the Indus basin in Pakistan. Ref.…”

Climate Change Impacts on the Upper Indus Hydrology: Sources, Shifts and Extremes

“…Analysis with regional climate models (RCM) reveals consistent warming until the end of the century with greater warming in the upper Indus than in the lower Indus. Precipitation projections show a non-uniform change with increases projected for the upper parts and decreases for the lower parts [44,45]. However care needs to be taken in using RCMs directly in impact studies.…”