Snow survey hopes for avalanche of data

More accurate snowfall measurements could improve climate models and estimates of water resources.
 

Mountains are barometers of climate change, but some of the simplest questions about them are the hardest to answer. How much snow coats their peaks and slopes, for example? And how do these frosty shrouds alter from year to year? This week, an international programme kicks off to answer those questions.

In a two-year project called the Solid Precipitation Intercomparison Experiment (SPICE), spearheaded by the World Meteorological Organization (WMO), climate scientists will deploy a suite of state-of-the-art snow gauges at 15 sitesin geographically and climatically diverse countries around the world, up to 4,318 metres above sea level (see أ¢â‚¬ثœWhite noiseأ¢â‚¬â„¢). The goal is to make accurate measurements of snow depth and snowfall أ¢â‚¬â€‌ the most fragile form of precipitation, which can elude or clog simple collecting devices أ¢â‚¬â€‌ and come up with recommendations for the best ways to do snow surveys in different parts of the world. The results could improve climate models and help to predict permafrost stability, ecosystem changes and the availability of water resources in the coming decades.

أ¢â‚¬إ“Snowfall is an important part of the global hydrological cycle,أ¢â‚¬آ‌ says Roger Atkinson, acting head of the WMOأ¢â‚¬â„¢s Instruments and Methods of Observation Programme in Geneva, Switzerland. أ¢â‚¬إ“If we canأ¢â‚¬â„¢t accurately measure the amount of snowfall, then we wonأ¢â‚¬â„¢t be able to know how much water we have and how it will change in the future.أ¢â‚¬آ‌

Snowfall also أ¢â‚¬إ“partly determines whether a glacier grows or retreats,أ¢â‚¬آ‌ says Zhang Yinsheng, a climate scientist at the Chinese Academy of Sciencesأ¢â‚¬â„¢ Institute of Tibetan Plateau Research in Beijing, who is not involved in the SPICE project. أ¢â‚¬إ“People have been debating the fate of Himalayan glaciers for a long time, but we donأ¢â‚¬â„¢t have a proper grasp of even the basics.أ¢â‚¬آ‌

Although researchers can accurately assess some climate parameters such as temperature, pressure, wind speed and humidity, measuring snowfall remains challenging. Snowflakes are light and drift with the wind, and weather conditions can dramatically affect what proportion of snowfall is actually captured by researchersأ¢â‚¬â„¢ cylindrical metal gauges, says climate scientist Rodica Nitu at Environment Canada in Gatineau, who leads the project. And when the temperature is around freezing, the damp snow tends to stick to the rim of the container, soon forming a cap and preventing further collection.

أ¢â‚¬إ“Undercatch is a serious problemأ¢â‚¬آ‌, says Roy Rasmussen, a climate scientist at the US National Center for Atmospheric Research in Boulder, Colorado. This is particularly the case with automatic gauges, which can capture as little as 20% of the actual snowfall, he says.

Unreliable snow readings introduce one of the greatest unknowns to climate models, hampering the ability to predict future changes in water resources and mountain hazards, says Rasmussen. And snowfall, like other forms of precipitation, is expected to increase as the globe warms. Better snow data could help modellers to predict the increase in snowfall, and whether it will be sufficient to offset the increased melting of glaciers.

The last major international effort to measure snow was more than 20 years ago, and أ¢â‚¬إ“there has been a lot of progress since thenأ¢â‚¬آ‌, says Rasmussen. One of the main aims of the project is to test the range of recently developed sensors, gauges and windshields. For example, field observations show that shields to reduce the horizontal wind speed above the gauge increase collection enormously. أ¢â‚¬إ“Itأ¢â‚¬â„¢s the most important factor for accurate snow measurements,أ¢â‚¬آ‌ says Rasmussen.

New ways of heating the measuring gauges should also prevent snow capping without causing evaporation or air turbulence that blows the snow away. The field is also switching from manual to automated instruments, enabling continuous measurements over large, hard-to-access areas. Relating the two data sets will make records of snow measurements continuous over time, says Nitu.

Zhang says that the project is timely and important, but that it misses crucial regions such as the Himalayas, where SPICE doesnأ¢â‚¬â„¢t have a testing site. Early next year, Zhang and his colleagues will set up a network of stations across the Tibetan plateau and surrounding mountain ranges, at altitudes up to 6,000 metres, which will gather accurate snow measurements across the region that could augment SPICEأ¢â‚¬â„¢s results.

In the longer term, however, أ¢â‚¬إ“there will never be enough ground measurements to cover an entire mountainأ¢â‚¬آ‌, says Michael Lehning, a climate scientist at the Swiss Federal Institute for Snow and Avalanche Research in Davos-Dorf, who is involved in the project. Results from SPICE will be used to calibrate airborne and satellite-based sensors, which use techniques such as microwave, radar and laser ranging to survey much larger areas.

أ¢â‚¬إ“The idea is to push remote sensing to be accurate enough for use in mountains,أ¢â‚¬آ‌ says Lehning. أ¢â‚¬إ“Itأ¢â‚¬â„¢s still a long way off, but SPICE is a good starting point.أ¢â‚¬آ‌