Modelling shortwave and longwave downward radiation and air temperature driving ablation at the Forni Glacier (Stelvio National Park, Italy)

We focus here on modelling the meteorological parameters most influencing snow/ice melting over an alpine glacier. Specifically, we consider shortwave and longwave downward radiation, and air temperature. We set up and test a methodology for their accurate distribution at the glacier surface, which can be applied whenever: i) supraglacial meteoro-logical measurements are available or ii) weather data are acquired from a station quite close to the glacier. As a suitable site to test our approach we selected the Forni Glacier, in the Italian Alps, where an Automatic Weather Station (AWS) has been running since autumn 2005 thus giving a robust dataset for developing a field based modeling approach. First, we modelled and distributed the incoming solar radiation by taking into account actual atmospheric conditions, glacier topography and shading. Then, we modelled the incoming longwave radiation considering cloud-cover and air temperature. Third, we investigated a local lapse rate to depict the yearly variability of the vertical air temperature gradient, to assess the actual thermal conditions at different elevations. Finally, we compared the modeled values against data collected on the field. The results display that during the glacier ablation period (i.e.: May-September): i) our approach provides a good depiction of both point incoming solar and infrared radiation fluxes, ii) the spatial distribution of the incoming solar radiation we developed is satisfactory, iii) our tests suggest that the incoming longwave fluxes can be considered constant over the whole glacier ablation area thus neglecting its spatial distribution, and iv) the application of a local lapse rate provides a good distribution of air temperature at the glacier surface

Future Hydrological Regimes in the Upper Indus Basin: A Case Study from a High-Altitude Glacierized Catchment

The mountain regions of the Hindu Kush, Karakoram, and Himalayas (HKH) are considered Earth’s “third pole,” and water from there plays an essential role for downstream populations. The dynamics of glaciers in Karakoram are complex, and in recent decades the area has experienced unchanged ice cover, despite rapid decline elsewhere in the world (the Karakoram anomaly). Assessment of future water resources and hydrological variability under climate change in this area is greatly needed, but the hydrology of these high-altitude catchments is still poorly studied and little understood. This study focuses on a particular watershed, the Shigar River with the control section at Shigar (about 7000 km2), nested within the upper Indus basin and fed by seasonal melt from two major glaciers (Baltoro and Biafo). Hydrological, meteorological, and glaciological data gathered during 3 years of field campaigns (2011–13) are used to set up a hydrological model, providing a depiction of instream flows, snowmelt, and ice cover thickness. The model is used to assess changes of the hydrological cycle until 2100, via climate projections provided by three state-of-the-art global climate models used in the recent IPCC Fifth Assessment Report under the representative concentration pathway (RCP) emission scenarios RCP2.6, RCP4.5, and RCP8.5. Under all RCPs, future flows are predicted to increase until midcentury and then to decrease, but remaining mostly higher than control run values. Snowmelt is projected to occur earlier, while the ice melt component is expected to increase, with ice thinning considerably and even disappearing below 4000 m MSL until 2100

Future hydrological regimes and glacier cover in the Everest region: The case study of the upper Dudh Koshi basin

Assessment of future water resources under climate change is required in the Himalayas, where hydrological cycle is poorly studied and little understood. This study focuses on the upper Dudh Koshi river of Nepal (151 km2, 4200–8848 m a.s.l.) at the toe of Mt. Everest, nesting the debris covered Khumbu, and Khangri Nup glaciers (62 km2). New data gathered during three years of field campaigns (2012–2014) were used to set up a glacio-hydrological model describing stream flows, snow and ice melt, ice cover thickness and glaciers' flow dynamics. The model was validated, and used to assess changes of the hydrological cycle until 2100. Climate projections are used from three Global Climate Models used in the recent IPCC AR5 under RCP2.6, RCP4.5 and RCP8.5. Flow statistics are estimated for two reference decades 2045–2054, and 2090–2099, and compared against control run CR, 2012–2014. During CR we found a contribution of ice melt to stream flows of 55% yearly, with snow melt contributing for 19%. Future flows are predicted to increase in monsoon season, but to decrease yearly (− 4% vs CR on average) at 2045–2054. At the end of century large reduction would occur in all seasons, i.e. − 26% vs CR on average at 2090–2099. At half century yearly contribution of ice melt would be on average 45%, and snow melt 28%. At the end of century ice melt would be 31%, and snow contribution 39%. Glaciers in the area are projected to thin largely up to 6500 m a.s.l. until 2100, reducing their volume by − 50% or more, and their ice covered area by − 30% or more. According to our results, in the future water resources in the upper Dudh Koshi would decrease, and depend largely upon snow melt and rainfall, so that adaptation measures to modified water availability will be required

Gli effetti del cambiamento climatico sul regime idrologico nelle Alpi

Il cambiamento climatico influenzerà il ciclo idrologico e la diponibilità di risorsa idrica nelle Alpi. Qui si studia la potenziale evoluzione futura del ciclo idrologico (2045-2054) per un fiume alpino italiano, in funzione di scenari di cambiamento climatico: il Serio (circa 300 km2). Essendo infatti l’idrologia di questo bacino fortemente dipendente dal ciclo della copertura nivale, vi saranno molto probabilmente rilevanti variazioni in risposta ai cambiamenti climatici. Si è qui stato calibrato e validato un modello idrologico, in grado di simulare il regime della risorsa idrica fluviale. E’ stata eseguita una procedura di disaggregazione temporale dei dati di temperatura e precipitazione future, ottenuti da due modelli di circolazione generale GCM, che sono stati quindi utilizzati come input per il modello idrologico, al fine di ottenere i regimi idrologici proiettati per diverse sezioni a differenti altitudini del bacino. Gli scenari e le storylines dei diversi GCM adottati differiscono l’uno dall’altro per quanto riguarda le proiezioni dell’ammontare di precipitazione e temperatura, ma concordano su una diminuzione delle prime e su un aumento delle seconde. Tutti gli scenari idrologici concordano nel prospettare un ritiro della copertura stagionale di neve, dovuta a un aumento delle temperature, oltre che un incremento delle portate autunnali e invernali, come conseguenza dell’aumento delle precipitazioni liquide. Portate più basse sono invece previste durante la primavera e l’estate, in vista di una diminuzione delle piogge e dello scioglimento nivale. Il modello CCSM3 prevede infatti l’anticipazione della stagione di scioglimento nivale di un mese. Nei bacini in quota il fenomeno è più evidente poiché l’incremento delle portate invernali cresce più che proporzionalmente

Climate change will affect hydrological regimes in the Alps

Climate change will affect hydrological cycle and water resources in the Alps. Here we sketched potential future (2045-2054) hydrological cycle under prospective climate change scenarios within an Alpine river of Italy: Serio (ca. 300 km2). Therein, hydrology is highly dependent upon snow cover cycle, very likely to be affected by climate changes. We set up and validated a hydrological model able to mimic water resources regime of the river. We then use downscaled future temperature and precipitation from two general circulation models GCMs to feed the hydrological model and obtain projected hydrological regimes, at flow sections at different altitudes within the catchment. The scenarios and storylines from the adopted GCMs differ from one another with respect to projected precipitation and temperature amount, but agree upon decrease of the former and increase of the latter. All hydrological scenarios agree upon prospective shrinkage of seasonal snow cover due to increased temperature, and upon prospective increase of Fall and Winter stream flows as due to increased liquid precipitation. Lower discharges are projected during Spring and Summer, in view of decreased rainfall and snow cover at thaw, and the CCSM3 model provides shifting of thaw season to one month earlier. Higher catchments are more impacted because Winter flows increase more proportionally