Climate change could trigger more landslides in High Mountain Asia

High Mountain Asia storesmore fresh water in its snow and glaciers than any place on Earth outside thepoles, and more than a billion people rely on it for drinking and irrigation.The study team used satellite estimates and modeled precipitation data toproject how changing rainfall patterns in the region might affect landslidefrequency.

The study team found thatwarming temperatures will cause more intense rainfall in some areas, and thiscould lead to increased landslide activity in the border region of China andNepal. More landslides in this region, especially in areas currently covered byglaciers and glacial lakes, could cause cascading disasters like landslide damsand floods that affect areas downstream, sometimes hundreds of miles away,according to the study. The study was a collaboration between scientists fromNASA's Goddard Space Flight Center in Greenbelt, Maryland; the National Oceanicand Atmospheric Administration (NOAA) in Washington; and Stanford University inPalo Alto, California. High Mountain Asia stretches across tens of thousands ofrugged, glacier-covered miles, from the Himalayas in the east to the Hindu Kushand Tian Shan mountain ranges in the west. As Earth's climate warms, HighMountain Asia's water cycle is changing, including shifts in its annual monsoonpatterns and rainfall. Heavy rain, like the kind that falls during the monsoonseason in June through September, can trigger landslides on the steep terrain,creating disasters that range from destroying towns to cutting off drinkingwater and transportation networks.

In summer 2019, monsoonflooding and landslides in Nepal, India and Bangladesh displaced more than 7million people. In order to predict how climate change might affect landslides,researchers need to know what future rainfall events might look like. But untilnow, the research making the landslide predictions has relied on records ofpast landslides or general precipitation estimate models. Other studies haveeither addressed this relationship very locally, or by adjusting the precipitationsignal in a general way, said Dalia Kirschbaum, a research scientist at NASA'sGoddard Space Flight Center. Our goal was to demonstrate how we could combineglobal model estimates of future precipitation with our landslide model toprovide quantitative estimates of potential landslide changes in this region.The study team used a NASA model that generates a nowcast estimating potentiallandslide activity triggered by rainfall in near real-time. The model, calledLandslide Hazard Assessment for Situational Awareness (LHASA), assesses thehazard by evaluating information about roadways, the presence or absence ofnearby tectonic faults, the types of bedrock, change in tree cover and thesteepness of slopes.

Then, it integrates currentprecipitation data from the Global Precipitation Measurement mission. If theamount of precipitation in the preceding seven days is abnormally high for thatarea, then the potential occurrence of landslides increases. The study teamfirst ran LHASA with NASA precipitation data from 2000-2019 and NOAA climatemodel data from 1982-2017.

They compared the resultsfrom both data sets to NASA's Global Landslide Catalog, which documentslandslides reported in the media and other sources. Both data sets comparedfavorably with the catalog, giving the team confidence that using the modeledprecipitation data would yield accurate forecasts. Finally, the study team usedNOAA's model data to take LHASA into the future, assessing precipitation andlandslide trends in the future (2061-2100) versus the past (1961-2000). Theyfound that extreme precipitation events are likely to become more common in thefuture as the climate warms, and in some areas, this may lead to a higherfrequency of landslide activity.

Most significantly, theborder region of China and Nepal could see a 30-70% increase in landslideactivity. The border region is not currently heavily populated, Kirschbaumsaid, but is partially covered by glaciers and glacial lakes. The combinedimpacts of more frequent intense rainfall and a warming environment couldaffect the delicate structure of these lakes, releasing flash floods andcausing downstream flooding, infrastructure damage, and loss of waterresources. The full human impact of increasing landslide risk will depend onhow climate change affects glaciers and how populations and communities change.When they evaluated their model projections in the context of five potentialpopulation scenarios, the team found that most residents in the area will beexposed to more landslides in the future regardless of the scenario, but only asmall proportion will be exposed to landslide activity increases greater than20%. The study demonstrates new possibilities for research that could helpdecision-makers prepare for future disasters, both in High Mountain Asia and inother areas, said Kirschbaum.

Our hope is to expand ourresearch to other areas of the world with similar risks of landslides,including Alaska and Appalachia in the United States, said Sarah Kapnick,physical scientist at NOAA's Geophysical Fluid Dynamics Laboratory andco-author on the study. We've developed a method, figured out how to worktogether on a specific region, and now we'd like to look at the U.S. tounderstand what the hazards are now and in the future.