Following on from the previous blog post, a paper by Archer et al. (2010) looks quite broadly at how the sustainability of water resources in the Indus basin might be altered by future changes in climate, as well as changes in socio-economic conditions. As was noted by the Indus water commissioner in the previous post, climate change effects on glacier shrinkage were suggested to be the primary cause of water scarcity. However, in this paper by Archer et al. it is argued that the impact of glacier retreat may be limited, especially when compared with other physical and socio-economic factors downstream of the Himalayan glaciers.
Agriculture in Pakistan is very much reliant on water which originates in the mountain sources of the upper Indus. As the authors note, these water resources are already highly stressed and are likely to get worse with projected rises in population. The paper considers the impact of climate change on these water resources in terms of three distinct hydrological regimes: a nival regime (dependent on melting winter snow), a glacial regime, and a rainfall regime. The mountainous sources of water are known to be affected by changes in temperature and in precipitation. The authors note that this is due to most of the runoff being derived from the melting of seasonal glacier snow and ice. Thus, any ablation of glaciers could quite easily affect water scarcity downstream.
Figure 1. The Indus basin
However, as the paper importantly notes, there is a great deal of uncertainty regarding how climate change might affect glaciers and river flow in the region. It cites several studies, which show regional conflicts with global patterns. Firstly, that summer temperatures (key for glacial melt) have actually fallen in the Karakoram between 1961 and 2000. Secondly, similar falls in temperature were found for the monsoon and pre-monsoon periods (April to May) in the Karakoram. Thirdly, that there have been significant increases in Upper Indus precipitation (both winter and summer) between 1961 and 1999. Fourthly, that extensive glacial mass balance records do not show shrinking glaciers. And finally, that in the late 1990s, there was widespread evidence of glacier expansion in the Karakoram.
With such conflicting evidence in the upper region of the Indus basin, it is unknown whether climate change will have a positive or negative effect on water resources in the region. The authors state that the hypothesis of reduced water resources relies on two assumptions: firstly that temperature and glacier melt are the primary impact on water resources, and secondly, that temperatures in the Upper Indus will rise in line with global climate predictions. As a result of this, they state that both of these assumptions are questionable. In particular, it is stated that river flow has been shown to not depend uniquely on glacier melt, but also rely on seasonal snowmelt and rainfall. This thus gives us the three hydrological regimes: nival, glacial and rainfall.
In the nival regime, the area of seasonal snow melt gives the largest contribution to downstream flow. This comes largely because the area of seasonal snow is much bigger than the perennial snow and ice. Of course, however, the area greatly reduces during the melt season. For this regime, winter precipitation has been shown likely to have the most significant impact on summer runoff. And unlike the glacial regime, there is a significant negative relationship between runoff and temperature on nival regimes. Archer et al. state that this:
“Can be explained by greater evaporative losses from the snow cover under higher temperatures and thus reduced runoff.”
As a result, the authors estimate that for a 2oC rise in summer temperature, there would be an 18 percent reduction in runoff. However, the observed Karakoram decline in summer temperature would produce increased summer runoff.
In the glacial regime, the contribution to flow in the very high catchments is significant. However, the combined flow of these high catchments into the Indus represents an average of less than 30 percent. Here, there is a significant positive correlation between summer runoff and temperature. As well as this, winter precipitation doesn’t have such an influence. As such, spring and summer temperatures have the greatest impact on runoff. In this regime, runoff will rise initially with increased global temperature, but reduce sharply with declining glacier mass.
However, the findings of falling summer temperatures in the region mean that with this positive correlation between runoff and summer temperature, there is presently a downward trend in flow. The present and past behaviours of the Karakoram glaciers are noted in the paper:
“...glacier recessions were observed in almost all Karakoram glaciers for most of the 20th century until the mid-1990s. However, at lower elevations glaciers continued to decline. This seems to confirm that glacier loss is reduced in the Karakoram compared both with the neighbouring Himalaya and the Pamir mountains to the west.”
Finally, in the monsoon rainfall regime, the main influence falls over the southern plains and foothills of the Himalaya. Here, seasonal volume of runoff (as a result of rainfall) is lower than in the glacial and nival regimes. However, the monsoon rainfall produces more intense runoff and therefore highest flooding in the region. Therefore, this regime can be very important for water resources in the Indus basin. Yet as the paper states, the IPCC indicate that estimates of precipitation change hold great uncertainty, and that the impact of climate change on monsoon precipitation cannot be safely assumed.
In summary, based on the three regimes identified for the upper Indus basin, the paper shows that there appears to be little evidence for reductions in runoff and thus availability of water resources in the region. It must also be accepted, however, that much of this relies on uncertainty over glacier response to climate change in the Karakoram. Indeed, more recent past climate may not be a reliable guide to future change as well.
Whilst not the focus of this blog, it is important to mention briefly, the overall findings of the paper when physical and socio-economic conditions downstream are considered. Whilst the authors found inconclusive evidence of climate change causing reductions in runoff, they did find that several other factors had much greater influence on water resources further down in the Indus basin. Firstly, that urban growth and industrialisation will increase and demand further shares of the scarce water resources. Thus, economics plays an important role in water resource management, as large investment is needed to provide practical solutions whilst balancing the needs of security, health and education. Secondly, reservoir sedimentation means that water resources will diminish as storage is taken up by sediment. This problem will not reduce unless new reservoirs are built. Finally, the alternative of using groundwater in the spring for agriculture may soon have no practical use when the water tables fall from over pumping.
As can be seen, the issue of water scarcity in Pakistan’s Indus basin is very complex. The presence of and future changes to glaciers upstream is a very important part of the highly stressed water scarcity issues here. Only with greater knowledge of how these regional glaciers will react to global climate change, using past records and future modelling, will a truly certain answer be able to be given for these problems.
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