Apocalypse delayed – Himalayan researchers reverse earlier predictions of water shortages

I sense that some of the alarmism and the apocalyptic futures always associated with global warming hysteria are beginning to moderate.

Earlier predictions of water shortages due to the shrinkage of Himalayan glaciers are being reversed by new research which now predicts increased water flow in two Himalayan watersheds.

W. W. Immerzeel, F. Pellicciotti & M. F. P. Bierkens, Rising river flows throughout the twenty-first century in two Himalayan glacierized watersheds, Published online 04 August 2013, Nature Geoscience  (2013) doi:10.1038/ngeo1896

EnergyWire comments:

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.”

For years, scientists struggled to understand how precipitation will change in these mountains (ClimateWire, Oct. 24, 2011). They have also had difficulty determining how much glacier melt from the mountains contributes to water supply. 

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.

“We show that the peak in meltwater is later than we previously thought, which in combination with a projected increase in precipitation results in an increase in water availability until the end of the century,” he said.

The two watersheds Immerzeel reports on in the paper are those of the Baltoro and Langtang glaciers, which feed the Indus and Ganges rivers, respectively. In the Baltoro watershed, this is largely due to more glacier runoff from melt. In the Langtang, increased precipitation drives the extra runoff.

Immerzeel and his co-authors used the output of the latest global climate models from the Coupled Model Intercomparison Project (CMIP5) to look at temperature and precipitation projections. They combined that data with a hydrologic model of glacier responses to climate change.

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.

….. 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.”

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.

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