A study co-written by UCSB scientists demonstrates a link between debris on some Himalayan glaciers and the cessation of glacial melting.

Debris layers of two or more centimeters found on certain Himalayan glaciers have been found to protect them from melting, UCSB professor and co-author of the study Bodo Bookhagen said in a press release. The debris includes pebbles and rocks fallen from nearby mountains, distinguished from other debris such as sand and silt.

Commenting on the novelty of the study, Bookhagen said in the press release that the effect of pebbles and rocks on glacial melting has often been overlooked.

“This parameter has been almost completely neglected in previous Himalayan and other mountainous region studies, although its impact has been known for some time,” Bookhagen said.

According to Bookhagen, the study has contributed to continued controversy regarding an allegedly inaccurate report by the Intergovernmental Panel on Climate Change.

“There are several scientists that have contributed to the IPCC report who are very well aware that the Himalayas are an enormous mountain belt with a large variety of glaciers, topography and climate,” Bookhagen said in an e-mail. “Unfortunately, this knowledge hasn’t been properly conveyed to the public and has been summarized in wrong statements.”

According to Bookhagen, previous data from the more accessible western Himalayas was applied to the entire mountain range, incorrectly lumping together all Himalayan glaciers. The study collected data from the entire range of mountains using high-resolution, remote-sensing images, revealing the diverse glacial responses of various regions within the mountain range.

Whereas glaciers are popularly thought to be in retreat, the study shows glacial activity as more diverse — some are retreating, some are advancing and some remain stagnant.

The abstract of the paper states that the study’s findings regarding the effect of debris on glacial melting and the lack of uniformity in Himalayan glacial responses to climate change have not yet been factored into predictions on future global sea levels or water availability.

Particularly when monsoon rainfall is low, melting glaciers serve as the primary source of water for millions of people who live in the Himalayas and surrounding areas, Bookhagen said.

“In this region, glacial melt waters constitute a major source of water during the pre-monsoon season from April to June,” Bookhagen said. “The central Himalaya would need a large water storage body to keep some of the heavy monsoonal rainfall and distribute it during the remainder of the year.”

Graduate student Dirk Scherler, who contributed research for the project while studying abroad at UCSB, said the findings of the study could aid in providing water for communities downstream.

“We hope that our findings provide an incentive for future studies to gather more … data on actual melt rates and to include aspects like debris cover in models,” Scherler said. “We are also developing a hydrological model for simulating water discharge from Himalayan rivers that explicitly includes the effect of debris cover. But this is ongoing work.”

A paper on the study, co-written by Bookhagen and Scherler, was featured last week in Nature Geoscience.