From river basins like the Okavango Basin (Hughes et al., 2011) to mountain ranges all over the world, water resources in all types of ecologies will likely be dramatically affected by global climate change. Mountain water sources are particularly important because they also have huge impacts on the lowlands below them. Much of the demand for water by farmers and households in lowland areas is met by a supply from mountain ranges, and 53% of mountainous areas worldwide are considered essential components of downstream water supply. High altitude regions redistribute winter precipitation in the form of runoff in the spring and summer, reducing variability of water flows and contributing to the level of water available in resevoirs. Stream-flow variability is also positively correlated with basin elevation, making mountain basins among the most vulnerable environments in terms of climate change. Although several past studies have indirectly pointed to the vital role of mountains for global water resources, no studies had yet been focused exclusively on this topic. Viveroli et al. (2011) discuss the impacts of climate change on mountain resources and give suggestions for future research, management, and policy. By studying eleven different case studies and attempting to integrate information from each, the researchers were able to conclude that global generalizations about the impact of climate change on mountain water supply cannot be drawn. Instead, research and management must work on a regional scale because of the many interactions between topography, vegetation, and soil composition with water supply. The authors suggest that the most important conclusion to be drawn is that further monitoring, research, and policy implementation is essential to helping mountain regions and their lowland dependants cope with the challenges that future climate change will pose to water resources.
Viviroli, D., Archer, D. R., Buytaert, W., Fowler, H. J., Greenwood, G. B., Hamlet, A. F., Huang, Y., Koboltsching, G., Litaor, M. I., Lopez-Moreno, J. I., Lorentz, S., Schadler, B., Schreider, H., Schwaiger, K., Vuille, M., and Woods, R., 2011. Climate change and mountain water resources: overview and recommendations for research, management, and policy. Hydrology and Earth System Sciences 15, 471-504. GSSS: mountain water (2011)
For the purposes of simplification, this paper focuses on surface water while largely ignoring groundwater, even though groundwater will likely play a large role in future water resources as well. Instead of going into great depth of detail about all the various factors that might affect water resources in mountain regions, therefore, this study seeks to see what we already know and what we need to find out in order to suggest management and policy as well as further research and monitoring. One of the most important pieces of information that the study gleaned was that different mountain regions are at differing risk for climate change impact. Climate change is a challenge everywhere, but regional variance in the type of difficulty that a warming climate will present makes it so that regional, not global, plans must be made to cope with these changes. In each region, researchers look at what they refer to as “water stress,” or how much of the available water is used up by the demand in that region. A level of 0.4 or higher indicates a large amount of water stress. Water stress computations also take into account land use change, economic development, population growth, and the ability of water management to adapt to climate change. For instance, dry areas are likely to continue getting even drier in a warming scenario, but may be better equipped to deal with this change because their infrastructure is already set up to cope with high water stress. On the other hand, subtropical climate zones have both vulnerability to water scarcity and high dependence on mountain water resources, making them face a very high level of water stress. In general, areas with low GDP, high growth rates, and a high dependence on mountain runoff in the lowlands face the highest projected water stress from climate change.
One aspect of mountain water resources that is common among many regions is the importance of snow and glacial melt. The study projects that in a warming climate there will likely be less ice and therefore less runoff, meaning a lower water yield as a whole in high altitude areas. Expected seasonal shifts will also greatly impact the runoff patterns and water supply from snow. This is a particularly disturbing trend, as one-sixth of the world’s population currently lives within a snowmelt-dominated region where 75% of summer runoff is generated by glacial or ice melting. Glaciers and snow also act as “storage,” creating a way for water resources to be saved up during cold and wet years and later released during dry, hot years. Less snowmelt, therefore, means more variability in water availability with climate change. In order to see if other storage mechanisms could combat this change, the authors compare simulated annual runoff from snowmelt in the regions studied to the capacity of existing reservoirs to see if the storage capacity was available to buffer seasonal shifts in runoff. Their findings suggest that these reservoirs are helpful in reducing variability, but cannot act on the same scale as glacial water storage. In addition, the models project an increase in precipitation falling as rain rather than snow in the winter, and earlier timing for snowmelt in the spring. These issues compound the problem with disappearing glacial and ice-bound sources of water in the mountains.
In order to combat these challenges, the authors devote a large part of the paper to suggesting mechanisms for future change. Firstly, future research and monitoring must be increased and undertaken on a much larger scale. Currently, there is little monitoring of mountain areas, as they are often inconvenient to run labs in because of their isolation and often freezing temperatures. The data gleaned from these monitoring bases must then be shared between scientists and water resource managers or policymakers in the region to ensure that conclusions from scientific studies can have a practical application in preparing for climate change. One way to ensure increased communication, according to the authors, is to put some of the monitoring responsibilities in the hands of those who are most invested: the farmers and people living in these mountain and lowland communities whose lives will be directly impacted by future climate changes. This will also help studies remain at a regional scale where they can be most effectively utilized. It is important to remember, however, that ecological regions can and often do cross national borders, and it is therefore essential for different countries to work together to combat future climate change challenges in water resource management. Finally, the authors point out that solutions to these challenges in mountainous regions must be interdisciplinary in scope, and attempts to integrate climate change with other challenges such as economic growth will be essential to helping save the world’s mountain water resources.
Hughes, D. A., Kingston, D. G., Todd, M. C., 2011. Uncertainty in water resources availability in the Okavango River basin as a result of climate change. Hydrology and Earth System Sciences 15, 931–941.