Leicht verschätzt: In Nordamerika schneit es doppelt so viel wie zuvor angenommen

Die Erde erwärmt sich, wie reagiert der Schnee darauf? In den Alpen haben Hüsler et al. 2014 Satellitenbilder ausgewertet und die schneebedeckte Fläche ausgemessen (snow cover area percentage, SCA) . Überraschenderweise hat sich dieser Wert in den letzten 27 Jahren kaum verändert. Abstract:

A satellite-based snow cover climatology (1985–2011) for the European Alps derived from AVHRR data

Seasonal snow cover is of great environmental and socio-economic importance for the European Alps. Therefore a high priority has been assigned to quantifying its temporal and spatial variability. Complementary to land-based monitoring networks, optical satellite observations can be used to derive spatially comprehensive information on snow cover extent. For understanding long-term changes in alpine snow cover extent, the data acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensors mounted onboard the National Oceanic and Atmospheric Association (NOAA) and Meteorological Operational satellite (MetOp) platforms offer a unique source of information.

In this paper, we present the first space-borne 1 km snow extent climatology for the Alpine region derived from AVHRR data over the period 1985–2011. The objective of this study is twofold: first, to generate a new set of cloud-free satellite snow products using a specific cloud gap-filling technique and second, to examine the spatiotemporal distribution of snow cover in the European Alps over the last 27 yr from the satellite perspective. For this purpose, snow parameters such as snow onset day, snow cover duration (SCD), melt-out date and the snow cover area percentage (SCA) were employed to analyze spatiotemporal variability of snow cover over the course of three decades. On the regional scale, significant trends were found toward a shorter SCD at lower elevations in the south-east and south-west. However, our results do not show any significant trends in the monthly mean SCA over the last 27 yr. This is in agreement with other research findings and may indicate a deceleration of the decreasing snow trend in the Alpine region. Furthermore, such data may provide spatially and temporally homogeneous snow information for comprehensive use in related research fields (i.e., hydrologic and economic applications) or can serve as a reference for climate models.

Schnee in den Alpen war auch Thema bei Marty 2013.

Frei et al. 2018 prognostizieren eine Zunahme der Schneefälle in höhergelegenen Gebieten der Alpen im Zuge des Klimawandels.

Ye 2018 untersuchte den Schnee im nördlichen Eurasien und fand einen Bezug zur NAO und Arktischen Oszillation (AO).

Zhong et al. 2018 untersuchten Schneemächtigkeiten im selben Gebiet und fanden interessante Trends:

Spatiotemporal variability of snow depth across the Eurasian continent from 1966 to 2012

Snow depth is one of the key physical parameters for understanding land surface energy balance, soil thermal regime, water cycle, and assessing water resources from local community to regional industrial water supply. Previous studies by using in situ data are mostly site specific; data from satellite remote sensing may cover a large area or global scale, but uncertainties remain large. The primary objective of this study is to investigate spatial variability and temporal change in snow depth across the Eurasian continent. Data used include long-term (1966–2012) ground-based measurements from 1814 stations. Spatially, long-term (1971–2000) mean annual snow depths of >20 cm were recorded in northeastern European Russia, the Yenisei River basin, Kamchatka Peninsula, and Sakhalin. Annual mean and maximum snow depth increased by 0.2 and 0.6 cm decade−1 from 1966 through 2012. Seasonally, monthly mean snow depth decreased in autumn and increased in winter and spring over the study period. Regionally, snow depth significantly increased in areas north of 50° N. Compared with air temperature, snowfall had greater influence on snow depth during November through March across the former Soviet Union. This study provides a baseline for snow depth climatology and changes across the Eurasian continent, which would significantly help to better understanding climate system and climate changes on regional, hemispheric, or even global scales.

Im Februar 2019 hat es auf dem Hohen Peißenberg sehr viel geschneit. SZ am 6.3.2019:

Der starke Schneefall hat Anfang Februar auf dem Hohen Peißenberg zu historisch hohen Messwerten geführt: So fielen an den ersten beiden Tagen des vergangenen Monats 30 Liter pro Quadratmeter Niederschlag. Damit habe sich die Schneehöhe am 4. Februar auf 88 Zentimeter erhöht, heißt es im Rückblick der Wetterwarte auf dem Hohen Peißenberg. An drei Tagen blieb das Temperatur unter null Grad, frostig war es an 14 Tagen.

Auch in Kalifornien gab es im März 2019 jede Menge Schnee. Zur gleichen Zeit soll es auch im Himalaya fürchterlich stark geschneit haben. Schuld hat der Klimawandel, behauptet ein Forscher.

In Denver (Colorado) hat der Schnee in den letzten 7 Jahren zugenommen.

Wie genau kennen die Klimawissenschaftler eigentlich die Schneefälle? Nicht besonders gut, wie die Ohio State University 2018 einräumte:

How much snow accumulates in North America each year? More than scientists thought

There’s a lot more snow piling up in the mountains of North America than anyone knew, according to a first-of-its-kind study. Scientists have revised an estimate of snow volume for the entire continent, and they’ve discovered that snow accumulation in a typical year is 50 percent higher than previously thought.

In the journal Geophysical Research Letters, researchers at The Ohio State University place the yearly estimate at about 1,200 cubic miles of snow accumulation. If spread evenly across the surface of the continent from Canada to Mexico, the snow would measure a little over 7.5 inches deep. If confined to Ohio, it would bury the state under 150 feet of snow. Most of the snow accumulates atop the Canadian Rockies and 10 other mountain ranges. And while these mountains compose only a quarter of the continent’s land area, they hold 60 percent of the snow, the researchers determined.

The research represents an important step toward understanding the true extent of fresh water sources on the continent, explained doctoral student Melissa Wrzesien, lead author on the paper. „Our big result was that there’s a lot more snow in the mountains than we previously thought,“ she said. „That suggests that mountain snow plays a much larger role in the continental water budget than we knew.“

It’s currently impossible to directly measure how much water is on the planet, said Michael Durand, associate professor of earth sciences at Ohio State. „It’s extremely important to know-not just so we can make estimates of available fresh water, but also because we don’t fully understand Earth’s water cycle.“ The fundamentals are known, Durand explained. Water evaporates, condenses over mountains and falls to earth as rain or snow. From there, snow melts, and water runs into rivers and lakes and ultimately into the ocean.

But exactly how much water there is-or what proportion of it falls as snow or rain-isn’t precisely known. Satellites make reasonable measurements of snow on the plains where the ground is flat, though uncertainties persist even there. But mountain terrain is too unpredictable for current satellites. That’s why researchers have to construct regional climate computer models to get a handle on snow accumulation at the continental scale.

For her doctoral thesis, Wrzesien is combining different regional climate models to make a more precise estimate of annual snow accumulation on 11 North American mountain ranges, including the Canadian Rockies, the Cascades, the Sierra Nevada and the Appalachian Mountains. She stitches those results together with snow accumulation data from the plains.

So far, the project has consumed 1.8 million core-hours on NASA’s Pleiades supercomputer and produced about 16 terabytes of data. On a typical laptop, the calculations would have taken about 50 years to complete. Whereas scientists previously thought the continent held a little more than 750 cubic miles of snow each year, the Ohio State researchers found the total to be closer to 1,200 cubic miles.

They actually measure snow-water equivalent, the amount of water that would form if the snow melted-at about a 3-to-1 ratio. For North America, the snow-water equivalent would be around 400 cubic miles of water-enough to flood the entire continent 2.5 inches deep, or the state of Ohio 50 feet deep.

And while previous estimates placed one-third of North American snow accumulation in the mountains and two-thirds on the plains, the exact opposite turned out to be true: Around 60 percent of North American snow accumulation happens in the mountains, with the Canadian Rockies holding as much snow as the other 10 mountain ranges in the study combined. „Each of these ranges is a huge part of the climate system,“ Durand said, „but I don’t think we realized how important the Canadian Rockies really are. We hope that by drawing attention to the importance of the mountains, this work will help spur development in understanding how mountains fit into the large-scale picture.“

What scientists really need, he said, is a dedicated satellite capable of measuring snow depth in both complex terrain and in the plains. He and his colleagues are part of a collaboration that is proposing just such a satellite.

Journal Reference: Melissa L. Wrzesien, Michael T. Durand, Tamlin M. Pavelsky, Sarah B. Kapnick, Yu Zhang, Junyi Guo, C. K. Shum. A New Estimate of North American Mountain Snow Accumulation From Regional Climate Model Simulations. Geophysical Research Letters, 2018; 45 (3): 1423 DOI: 10.1002/2017GL076664