A new surface solar radiation database of 74 daily series is set up for the Piedmont region (northwest Italy) for the 1990-2016 period. All the series are subjected to a detailed quality control, homogenization and gap-filling procedure and are transformed into relative annual/seasonal anomaly series. Finally, a gridded version (0.5°x0.5°) of the database is generated. The resulting series show an increasing tendency of about +2.5% per decade at annual scale, with strongest trend in autumn (+4% per decade). The only exception is winter, showing a negative but not significant trend.Considering the plain and mountain mean series, the trends are more intense for low than for high elevations with a negative vertical gradient of about -0.03% per decade per 100m at annual scale and values up to -0.07% per decade per 100m in spring.Focusing on clear days only (selected by CMSAF-COMET satellite data over the 1991-2015 period), trend significance strongly increases and both low and high elevation records exhibit a positive trend in all seasons. However, the trends result slightly lower than for all-sky days (with the only exception of winter). The differences observed under clear-sky conditions between low and high elevations are more pronounced in winter, where the trend shows a negative vertical gradient of about -0.1% per decade every 100m.Overall, this paper shows how a high station density allows, performing a more detailed quality control thanks to the higher performances in detecting the inhomogeneities with higher data availability and capturing regional peculiarities otherwise impossible to observe.

Abstract. Our changing climate is expected to affect ice core records as cold firn progressively transitions to a temperate state. Thus, there is a need to improve our understanding and to further develop quantitative process modeling, to better predict cold firn evolution under a range of climate scenarios. Here we present the application of a distributed, fully coupled energy balance model, to simulate cold firn at the high-alpine glaciated saddle of Colle Gnifetti (Swiss–Italian Alps) over the period 2003–2018. We force the model with high-resolution, long-term, and extensively quality-checked meteorological data measured in the closest vicinity of the firn site, at the highest automatic weather station in Europe (Capanna Margherita, 4560 m a.s.l.). The model incorporates the spatial variability of snow accumulation rates and is calibrated using several partly unpublished high-altitude measurements from the Monte Rosa area. The simulation reveals a very good overall agreement in the comparison with a large archive of firn temperature profiles. Our results show that surface melt over the glaciated saddle is increasing by 3–4 mm w.e. yr−2 depending on the location (29 %–36 % in 16 years), although with large inter-annual variability. Analysis of modeled melt indicates the frequent occurrence of small melt events (<4 mm w.e.), which collectively represent a significant fraction of the melt totals. Modeled firn warming rates at 20 m depth are relatively uniform above 4450 m a.s.l. (0.4–0.5 ∘C per decade). They become highly variable at lower elevations, with a marked dependence on surface aspect and absolute values up to 2.5 times the local rate of atmospheric warming. Our distributed simulation contributes to the understanding of the thermal regime and evolution of a prominent site for alpine ice cores and may support the planning of future core drilling efforts. Moreover, thanks to an extensive archive of measurements available for comparison, we also highlight the possibilities of model improvement most relevant to the investigation of future scenarios, such as the fixed-depth parametrized routine of deep preferential percolation.

Abstract. Our changing climate is expected to affect ice core records as cold firn progressively transitions to a temperate state. Thus there is a need to improve understanding and further develop quantitative process modeling, to better predict cold firn evolution under a range of climate scenarios. Here we present the application of a distributed, fully coupled energy balance model, to simulate high-alpine cold firn at Colle Gnifetti over the period 2003–2018. For the first time, we force such a model with high-resolution, long-term and extensively quality-checked meteorological data measured in closest vicinity of the firn site, at the Capanna Margherita (4560 m a.s.l.). The model incorporates the spatial variability of snow accumulation rates, and is calibrated using several, partly unpublished high-altitude measurements from the Monte Rosa area. The simulation reveals a very good overall agreement in the comparison with a large archive of firn temperature profiles. The rate of firn warming at 20 m depth is estimated at 0.44 °C per decade. Our results show that surface melt over the glaciated saddle is increasing by 3–4 mm w.e. yr−2 depending on the location (29–36 % in 16 years), although with large inter-annual variability. Analysis of modeled melt indicates a marked tendency towards small melt events (

&lt;p&gt;Cold firn is progressively transitioning to a temperate state under a changing climate. This process is expected to affect ice core records and the mass balance of cold and polythermal glaciers. Thus there is a need to gain better understanding of this transition and develop quantitative, physical models, to predict cold firn evolution under a range of climate scenarios.&lt;/p&gt;&lt;p&gt;Here we present the application of a distributed, fully coupled energy balance and sub-surface model, to simulate high-alpine cold firn at Colle Gnifetti over the period 2003&amp;#8211;2018. For the first time, we force such a model with high-resolution, long-term, quality-checked meteorological data measured in closest vicinity of the firn site, at the highest weather station in Europe (Capanna Margherita, 4560 m a.s.l.). The model includes the spatial variability of snow accumulation rates, and is calibrated using several, partly unpublished high-altitude measurements from the Monte Rosa area.&lt;/p&gt;&lt;p&gt;Overall, the simulated firn temperature profiles reach a very good agreement in comparison with a large archive of borehole measurements. Our results show a 20 m-depth firn warming rate of 0.44 &amp;#176;C per decade. Moreover, we find that surface melt over the glaciated saddle is increasing by 3&amp;#8211;4 mm w.e. yr&lt;sup&gt;-2&lt;/sup&gt; (+29&amp;#8211;36 % in 16 years) depending on the location, although with a large inter-annual variability. The simulation also indicates that atmospheric humidity is a prominent control over melt occurrence, with considerable amounts of sublimation taking place in dry conditions. Hourly-resolution analysis of the melt dynamics reveals a marked tendency towards frequent, small melt events (&lt; 4 mm w.e.): these collectively represent a significant fraction of the total amounts.&lt;/p&gt;