Abstract
Abstract. The snowpack over the Mediterranean mountains constitutes a key water resource for the downstream populations. However, its dynamics have not been studied in detail yet in many areas, mostly because of the scarcity of snowpack observations. In this work, we present a characterization of the snowpack over the two mountain ranges of Lebanon. To obtain the necessary snowpack information, we have developed a 1 km regional-scale snow reanalysis (ICAR_assim) covering the period 2010–2017. ICAR_assim was developed by means of an ensemble-based data assimilation of Moderate Resolution Imaging Spectroradiometer (MODIS) fractional snow-covered area (fSCA) through an energy and mass snow balance model, the Flexible Snow Model (FSM2), using the particle batch smoother (PBS). The meteorological forcing data were obtained by a regional atmospheric simulation from the Intermediate Complexity Atmospheric Research model (ICAR) nested inside a coarser regional simulation from the Weather Research and Forecasting model (WRF). The boundary and initial conditions of WRF were provided by the ERA5 atmospheric reanalysis. ICAR_assim showed very good agreement with MODIS gap-filled snow products, with a spatial correlation of R=0.98 in the snow probability (P(snow)) and a temporal correlation of R=0.88 on the day of peak snow water equivalent (SWE). Similarly, ICAR_assim has shown a correlation with the seasonal mean SWE of R=0.75 compared with in situ observations from automatic weather stations (AWSs). The results highlight the high temporal variability in the snowpack in the Lebanese mountain ranges, with the differences between Mount Lebanon and the Anti-Lebanon Mountains that cannot only be explained by hypsography as the Anti-Lebanon Mountains are in the rain shadow of Mount Lebanon. The maximum fresh water stored in the snowpack is in the middle elevations, approximately between 2200 and 2500 m a.s.l. (above sea level). Thus, the resilience to further warming is low for the snow water resources of Lebanon due to the proximity of the snowpack to the zero isotherm.
Highlights
The hydrological processes related to mountain areas are essential for the water supplies for a large part of humanity (Viviroli et al, 2007)
The use of Intermediate Complexity Atmospheric Research model (ICAR) is justified as it is computationally inexpensive compared to similar Weather Research and Forecasting model (WRF) simulations, while retaining a physical basis to enable simulations in regions lacking observations
It was not expected that the parent WRF simulation would need to be improved with ICAR, but the increase in resolution was necessary as the snowpack simulations require higher resolutions
Summary
The hydrological processes related to mountain areas are essential for the water supplies for a large part of humanity (Viviroli et al, 2007). Despite the relatively mild temperature of the Mediterranean climates, mountains there often exhibit deep and long-lasting snowpacks accumulating more than 3 m and an average snow season of 5 months at the summit areas (Alonso-González et al, 2020b; Fayad et al, 2017b). Mediterranean snowpacks are characterized by a high interannual variability, which affects the amount and seasonality of river flows (LópezMoreno and García-Ruiz, 2004). Despite this variability, the thickness and high density exhibited by the snowpack in the Mediterranean climate (Fayad et al, 2017b) makes them an effective water storage system. The fact that snowpack conditions are close to isothermal during most of the snow season makes them highly sensitive to the current climate warming (Alonso-González et al, 2020a; López-Moreno et al, 2017; Yilmaz et al, 2019)
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