Scenarios of Drought Impact on River Discharge
Introduction
Figure 1. Dryness in Lake Klöntal, Switzerland. Credits: Sarah Loetscher
Droughts are one of the main water-related geophysical hazards in Europe1. An area of particular concern is the Mediterranean region due to an increase in the occurrence of these events2. While the impact of droughts on food security is acknowledged, its effects span the entire economy at different levels3.
Precipitation and temperature are the main factors that influence the occurrence of droughts. On the one hand, liquid precipitation or rainfall (hereinafter referred to as precipitation) contributes to the river discharge over a short time-span. On the other hand, rising temperatures lead to increasing evapotranspiration, culminating in the reduction of the available water.
Snow is a crucial variable in mountain environments. In the Alps, a substantial proportion of winter and early spring precipitation falls as snow above an altitude of 1,000 meters, which remains stored in the snowpack, and it is slowly released during the warmer months supplying water from April to September. Consequently, the accumulation of snow can alleviate or exacerbate the effects of droughts.
Understanding the behaviour of snow helps to anticipate whether the current season will either experience a shortage, average conditions, or an abundant water availability. This knowledge informs decision-making processes, facilitating the adequate water management and implementation of preventive actions to optimize water availability. As a result, snow cover estimation is one of the main indicators to predict possible drought conditions4, also playing a pivotal role in operational flood forecasting5.
Droughts can also be caused by human activities in the river basins, such as hydroelectric production, civil water distribution, and irrigation. These activities causing water extraction or restitution, disrupt the natural flow of water within a catchment. Consequently, such operations decrease or increase water availability at specific areas within the basin.
In the following pages, a river discharge and drought tool for decision-making is presented. The selected area to show-case the capabilities of the tool is the Sarca river basin in Italy. The data used in the pipelines of the models that feed into the platform correspond to the period 2002 – 2022, enabling the user to run scenarios of water availability for a given month between April and September based on total averages over the reference period (2002 - 2022).
1 Markonis, Y., Kumar, R., Hanel, M., Rakovec, O., Máca, P., & AghaKouchak, A. (2021). The rise of compound warm-season droughts in Europe. Science advances, 7(6), eabb9668.
2 M. Hoerling, J. Eischeid, J. Perlwitz, X. Quan, T. Zhang, P. Pegion, On the increased frequency of mediterranean drought. J. Climate 25, 2146–2161 (2012).
3 K. Stahl, I. Kohn, V. Blauhut, J. Urquijo, L. De Stefano, V. Acácio, S. Dias, J. H. Stagge, L. M. Tallaksen, E. Kampragou, A. F. Van Loon, L. J. Barker, L. A. Melsen, C. Bifulco, D. Musolino, A. de Carli, A. Massarutto, D. Assimacopoulos, H. A. J. Van Lanen, Impacts of European drought events: insights from an international database of text-based reports. Nat. Hazards Earth Syst. Sci. 16, 801–819 (2016).
4 Staudinger, M., Stahl, K., and Seibert, J. (2014), A drought index accounting for snow, Water Resour. Res., 50, 7861– 7872, doi:10.1002/2013WR015143.
5 Rössler, O., Froidevaux, P., Börst, U., Rickli, R., Martius, O., and Weingartner, R.: Retrospective analysis of a non forecasted rain-on-snow flood in the Alps – a matter of model limitations or unpredictable nature?, Hydrol. Earth Syst. Sci., 18, 2265–2285, https://doi.org/10.5194/hess-18-2265-2014, 2014.