Abstract
Abstract. This study estimated the effects of projected variations in precipitation and temperature on snowfall-snowmelt processes and subsequent river discharge variations in the Tagliamento River in Italy. A lumped-parameter, non-linear, rainfall-runoff model with 10 general circulation model (GCM) scenarios was used. Spatial and temporal changes in snow cover were assessed using 15 high-quality Landsat images. The 7Q10 low-flow probability distribution approximated by the Log-Pearson type III distribution function was used to examine river discharge variations with respect to climate extremes in the future. On average, the results obtained for 10 scenarios indicate a consistent warming rate for all time periods, which may increase the maximum and minimum temperatures by 2.3 °C (0.6–3.7 °C) and 2.7 °C (1.0–4.0 °C), respectively, by the end of the 21st century compared to the present climate. Consequently, the exponential rate of frost day decrease for 1 °C winter warming in lower-elevation areas is approximately three-fold (262%) higher than that in higher-elevation areas, revealing that snowfall in lower-elevation areas will be more vulnerable under a changing climate. In spite of the relatively minor changes in annual precipitation (−17.4 ~ 1.7% compared to the average of the baseline (1991–2010) period), snowfall will likely decrease by 48–67% during the 2080–2099 time period. The mean river discharges are projected to decrease in all seasons, except winter. The low-flow analysis indicated that while the magnitude of the minimum river discharge will increase (e.g. a 25% increase in the 7Q10 estimations for the winter season in the 2080–2099 time period), the number of annual average low-flow events will also increase (e.g. 16 and 15 more days during the spring and summer seasons, respectively, in the 2080–2099 time period compared to the average during the baseline period), leading to a future with a highly variable river discharge. Moreover, a consistent shift in river discharge timing would eventually cause snowmelt-generated river discharge to occur approximately 12 days earlier during the 2080–2099 time period compared to the baseline climate. These results are expected to raise the concern of policy makers, leading to the development of new water management strategies in the Tagliamento River basin to cope with changing climate conditions.
Highlights
Observed and projected increases in temperature and precipitation variability are perhaps the most influential climatedriven changes to impact water systems (Parry et al, 2007)
The output from the band combination method and the normalized difference snow index (NDSI) index reveals that snowmelt begins in the low-elevation areas of the catchment, where, the snow cover is generally thin and the air temperature is high
This study used 10 general circulation model (GCM) scenarios for three future time periods to evaluate the hydrological response of the Tagliamento River for probable variations in temperature and precipitation patterns
Summary
Observed and projected increases in temperature and precipitation variability are perhaps the most influential climatedriven changes to impact water systems (Parry et al, 2007). Precipitation largely occurs as snow during the winter, which accumulates on the ground until adequate solar energy is available to start the melting process in spring and summer This melting water sustains the river level downstream when rainfall decreases and when demand is high. According to the meteorological records from 1980 to because changes in the future climate are projected 2010, the annual average temperature near the catchment to be more intense, many concerns have been raised regard- outlet was approximately 10.9 ◦C, and the temperature deing the potential burden that may be imposed on hydrological creased with elevation at an average rate of 4.2 ◦C per processes in the Tagliamento valley. The daily average winter (December–February) temperature was close to the melting point (2.1 and 1.0 ◦C near the catchment outlet and at Forni Avoltri station, respectively), which may adversely affect seasonal snow cover changes under a changing climate. The geology of the catchment area mainly consists of limestone and flysch, which is occasionally intermixed with layers of gypsum (Tockner et al, 2003)
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