by Judith Curry
A new publication in Nature Geoscience projects an increase in runoff from Himalayan catchmants during the 21st century, despite a decline in glacier size.
Rising river flows throughout the 21st century in two Himalayan glacierized watersheds
W.W. Immerzeel, F. Pelliciotti, M.F.P. Bierkens
Abstract. Greater Himalayan glaciers are retreating and losing mass at rates comparable to glaciers in other regions of the world. Assessments of future changes and their associated hydrological impacts are scarce, oversimplify glacier dynamics or include a limited number of climate models. Here, we use results from the latest ensemble of climate models in combination with a high-resolution glacio-hydrological model to assess the hydrological impact of climate change on two climatically contrasting watersheds in the Greater Himalaya, the Baltoro and Langtang watersheds that drain into the Indus and Ganges rivers, respectively. We show that the largest uncertainty in future runoff is a result of variations in projected precipitation between climate models. In both watersheds, strong, but highly variable, increases in future runoff are projected and, despite the different characteristics of the watersheds, their responses are surprisingly similar. In both cases, glaciers will recede but net glacier melt runoff is on a rising limb at least until 2050. In combination with a positive change in precipitation, water availability during this century is not likely to decline. We conclude that river basins that depend on monsoon rains and glacier melt will continue to sustain the increasing water demands expected in these areas.
Nature Geoscience, doi:10.1038/ngeo1896, 2013. [link] to abstract
From the Utrecht University press release:
One of the big unknowns of climate change predictions — and one that has led to considerable contention — lies in knowing the future of water runoff from the Himalayas. The snow- and ice-rich region supplies water for billions of people in Asia and is sometimes referred to as the Earth’s “Third Pole.”
A study out yesterday in Nature Geoscience by Walter Immerzeel, a physical geographer at Utrecht University, suggests that, in at least two major Himalayan watersheds, river flows and runoff should rise until 2100.
They found that in both watersheds, runoff from glaciers should increase until the 2040s or 2060s, later than previous estimates, depending on which climate scenarios are applied.
There is still considerable uncertainty in the finding that runoff will increase through 2100, Immerzeel noted, because global climate models vary widely in their projections for future precipitation in the region.
In the paper, Immerzeel points out that his new finding contradicts previous work he has published, suggesting that runoff in the Indus and Ganges basin would decrease. At least for now, this is good news for people and farmers who rely on that water, he said.
“Strong increases in water demand are projected in the Indus as the food production needs to grow to feed the quickly rising population,” Immerzeel said. “An increased water availability from the mountains may help to sustain this growing demand.”
Immerzeel plans to research how the timing of water availability might shift in his own future research. The researcher also pointed to the need to examine how extremes, such as floods, landslides and glacier lake outburst floods might change along with the climate.
Webster and Jian
Addressing some of the Immerzeel’s future research interests, Peter Webster published a paper several years ago in Proc. Roy. Soc. entitled Environmental prediction, risk assessment, and extreme events: adaptation strategies for the developing world. The relevant excerpt from the abstract:
Based on imperfect models and scenarios of economic and population growth, we further suggest that flood frequency and intensity will increase in the Ganges, Brahmaputra and Yangtze catchments as greenhouse gas concentrations increase. However, irrespective of the climate change scenario chosen, the availability of fresh water in the latter half of the 21st century seems to be dominated by population increases that far outweigh climate change effects. Paradoxically, fresh water availability may become more critical if there is no anthropogenic climate change.
Circum Himalayan Riparian Threats
Several years ago, my company CFAN wrote a report on this topic for Office of the Secretary of Defense; the material may be somewhat outdated, but here is the intro paragraph:
Major rivers originating in the Himalayas include the Ganges, Indus, Brahmaputra, Yangtze, Mekong, Irrawaddy, and Yellow Rivers. Their combined drainage basin is home to 3 billion people, including Afghanistan, China, India, Pakistan, and Bangladesh. The headwaters of these rivers lie in the Himalayas in Tibet, parts of which are under the control of the People’s Republic of China. Given the large and growing population of South and Southeast Asia and the increasing demand for water for irrigated farming and industry, transboundary disputes over water are ongoing and are significant and growing concerns, particularly if a major drought looms in the future. These disputes are central to food security, energy needs and resources and the future of water resources in the region. Riparian security issues are key for two major rivers in the region – the Ganges and Brahmaputra Rivers – and climate change (particularly drought) might act as a threat accelerant in riparian conflicts in South Asia.
Text from my 2010 Congressional Testimony:
Arguably the biggest global concern regarding climate change impacts is concerns over water resources. This concern is exacerbated in regions where population is rapidly increasing and water resources are already thinly stretched. China and South Asia (notably India, Pakistan, and Bangladesh) are facing a looming water crisis arising from burgeoning population and increasing demand for water for irrigated farming and industry. China has been damming the rivers emerging from Tibet and channeling the water for irrigation, and there is particular concern over the diversion of the Brahmaputra to irrigate the arid regions of Central China. China’s plans to reroute the Brahmaputra raises the specter of riparian water wars with India and Bangladesh.
The IPCC AR4 WGII makes two statements of particular relevance to the water situation in central and south Asia:
“Freshwater availability in Central, South, East and South-East Asia . . . is likely to decrease due to climate change, along with population growth and rising standard of living that could adversely affect more than a billion people in Asia by the 2050s (high confidence).”
“Glaciers in the Himalaya are receding faster than in any other part of the world and, if the present rate continues, the likelihood of them disappearing by the year 2035 and perhaps sooner is very high if the Earth keeps warming at the current rate. Its total area will likely shrink from the present 500,000 to 100,000 km2 by the year 2035 (WWF, 2005).”
The lack of veracity of the statement about the melting Himalayan glaciers has been widely discussed, and the mistake has been acknowledged by the IPCC. However, both of these statements seem inconsistent with the information in Table 10.2 of the IPCC AR4 WG II and the statement:
“The consensus of AR4 models . . . indicates an increase in annual precipitation in most of Asia during this century; the relative increase being largest and most consistent between models in North and East Asia. The sub-continental mean winter precipitation will very likely increase in northern Asia and the Tibetan Plateau and likely increase in West, Central, South-East and East Asia. Summer precipitation will likely increase in North, South, South-East and East Asia but decrease in West and Central Asia.”
Based on the IPCC’s simulations of 21st century climate, it seems that rainfall will increase overall in the region (including wintertime snowfall in Tibet), and the IPCC AR4 WGII does not discuss the impact of temperature and evapotranspiration on fresh water resources in this region. The importance of these omissions, inconsistencies or mistakes by the IPCC is amplified by the potential of riparian warfare in this region that supports half of the world’s population.
For the past week, the climate news world has been abuzz on the topic of climate change and conflict. A question that needs to be asked is what is the risk of highly confident consensus statements about future climate change impacts, like the Himalayan glaciers melting in 2035, of provoking conflicts? And if these confident projections turn out to be wrong . . .
As a I stated in my recent Congressional Testimony:
I have found that the worst prediction outcome is a prediction issued with a high level of confidence that turns out to be wrong; a close second is missing the possibility of an extreme event.
Owing to the high population that is rapidly growing and the high level of societal vulnerability, the South Asian region ranks among the most volatile in terms of potential adverse climate variability/change impacts. Immerzeel and colleagues have done a careful study on topic having substantial socioeconomic and security implications. Immerzeel has carefully stated the uncertainties, and provides context for the uncertainty in terms of his previous paper that found the opposite conclusion.
IMO, the IPCC AR4 got off pretty lightly for its error regarding the Himalayan glaciers, given the potential for this disastrously wrong forecast to have caused conflict in the region. I hope that especially WGII will be more careful next time.