Alps with less snow, Austrian-Italian border. Credit: Martina

2021-22 snow deficit in Italy leads to serious drought

1 January 2022 00:00 UTC–25 July 2022 23:00 UTC

Region

Italy

Satellites

Meteosat, Sentinel-2, Terra/Aqua

Instruments

SEVIRI, MODIS

Channels/Products

Multi-channel, H SAF product H10 – SE-E-SEVIRI

While Italy is suffering an intense drought, we take a look at how H SAF snow products contributed to the monitoring of the winter snow deficit.

Last Updated

21 February 2023

Published on

01 August 2022

By Francesco Avanzi, Simone Gabellani, Luca Pulvirenti, Alexander Toniazzo, Alessandra Mascitelli, Silvia Puca, and the H SAF team

Between Autumn 2021 and Winter 2021/22, Italy experienced a markedly dry and warm period, which led to a significantly negative anomaly in snow accumulation. Even Spring 2022 saw an intense precipitation deficit, which caused one of the most severe droughts in Italy over the recent decades. Satellite observations contributed to the monitoring of this deficit in real time.

Such events substantiate that monitoring snow from a quantitative perspective is crucial to support decision-makers in identifying anticipatory actions. Reliable information, in this sense, can only come from the integration of multiple data sources: ground observations, dynamic modelling, and satellites.

Satellite-based snow observations, as delivered from H SAF products, effectively contributed to the monitoring of water accumulated as snow in the Italian Alps during Winter 2021/22, as part of the operational snow monitoring service S3M-Italy, operated by the CIMA Research Foundation for Italian Civil Protection.

S3M-Italy daily map of snow depth — Figure 1: An example output of S3M Italy: real-time snow depth map for 26 November 2021, published on myDEWETRA platform

S3M-Italy provides daily maps of snow depth, Snow Water Equivalent (SWE), snow liquid water content, and cumulative daily melt water at 200m resolution across Italy. The system also includes estimates of snow albedo and glacier melting, and is driven by meteorological inputs derived from the interpolation of thousands of ground stations of precipitation, air temperature, radiation, and relative humidity. S3M-Italy also assimilates real-time measurements of snow depth from hundreds of in-situ measurement stations and satellite maps from Sentinel-2, MODIS, and H SAF (SE-E-SEVIRI).

From a snow perspective, Autumn 2021 yielded an average snow pack across the Italian Alps until mid-December. Subsequently, S3M-Italy detected a clear deficit in the amount of water stored in the snow pack (that is, SWE), which has remained stable below the first quartile of the 2010–2021 climatology. As a result of this deficit, snow has depleted much earlier than usual.

S3M-Italy water stored in snow pack (SWE) — Figure 2: Normalized Snow Water Equivalent in northern Italy: the black line is 2021-2022, while the red area delimits the first and third quartiles of the 2010-21 climatology.

This deficit was particularly significant across the north-western Italian Alps (even –80% or more), while it remained less intense across the north-eastern Italian Alps and the Apennines, but still showed a deficit of at least 36% compared the period 2010 - 2021

Mean SWE anomaly — Figure 3: Snow water equivalent anomaly for 2021-2022 v 2010-21

In addition to water deficit, scarce winter snow implied that, as early as June, many Italian glaciers had already lost snow cover and were, therefore, subject to early melt. Figure 4 shows an example from the Miage glacier (Mont Blanc massif): on the left, snow water equivalent for 8/6/22; on the right, mean snow water equivalent (2010-21).