A snow cover climatology for the Pyrenees from MODIS snow products

Abstract

Abstract. The seasonal snow in the Pyrenees is critical for hydropower production, crop irrigation and tourism in France, Spain and Andorra. Complementary to in situ observations, satellite remote sensing is useful to monitor the effect of climate on the snow dynamics. The MODIS daily snow products (Terra/MOD10A1 and Aqua/MYD10A1) are widely used to generate snow cover climatologies, yet it is preferable to assess their accuracies prior to their use. Here, we use both in situ snow observations and remote sensing data to evaluate the MODIS snow products in the Pyrenees. First, we compare the MODIS products to in situ snow depth (SD) and snow water equivalent (SWE) measurements. We estimate the values of the SWE and SD best detection thresholds to 40 mm water equivalent (w.e.) and 150 mm, respectively, for both MOD10A1 and MYD10A1. κ coefficients are within 0.74 and 0.92 depending on the product and the variable for these thresholds. However, we also find a seasonal trend in the optimal SWE and SD thresholds, reflecting the hysteresis in the relationship between the depth of the snowpack (or SWE) and its extent within a MODIS pixel. Then, a set of Landsat images is used to validate MOD10A1 and MYD10A1 for 157 dates between 2002 and 2010. The resulting accuracies are 97 % (κ = 0.85) for MOD10A1 and 96 % (κ = 0.81) for MYD10A1, which indicates a good agreement between both data sets. The effect of vegetation on the results is analyzed by filtering the forested areas using a land cover map. As expected, the accuracies decrease over the forests but the agreement remains acceptable (MOD10A1: 96 %, κ = 0.77; MYD10A1: 95 %, κ = 0.67). We conclude that MODIS snow products have a sufficient accuracy for hydroclimate studies at the scale of the Pyrenees range. Using a gap-filling algorithm we generate a consistent snow cover climatology, which allows us to compute the mean monthly snow cover duration per elevation band and aspect classes. There is snow on the ground at least 50 % of the time above 1600 m between December and April. We finally analyze the snow patterns for the atypical winter 2011-2012. Snow cover duration anomalies reveal a deficient snowpack on the Spanish side of the Pyrenees, which seems to have caused a drop in the national hydropower production.

Daily gridded datasets of snow depth and snow water equivalent for the Iberian Peninsula from 1980 to 2014

“…The original granules were mosaicked and reprojected from the sinusoidal system to the Universal Transverse Mercator (UTM) reference system. Then, we ran a gapfilling algorithm, using the binary snow product to avoid data losses due to cloud cover (Gascoin et al, 2015). This provided gap-free daily maps showing the presence and absence of snow in each mountain range from 2000 to 2014.…”

On the Use of Hydrological Models and Satellite Data to Study the Water Budget of River Basins Affected by Human Activities: Examples from the Garonne Basin of France

“…As it contains a complex network of dams used for hydropower, the observed discharge is not representative of natural processes (in particular snow melt). Recently, Gascoin et al (2015) built a snow cover dataset based on the space-based MODIS products, MOD10A1 and MYD10A1 (Hall et al, 2007), for the Pyrenees. This dataset provides snow cover extent at a daily time step over the region since 2000, with 500 m resolution.…”

Snow observations in Mount Lebanon (2011–2016)

“…All available tiles from 1 September 2011 to 31 August 2016 were assembled and resampled to 500 m with a nearest-neighbor method in UTM 36N using the MODIS reprojection tool over a rectangular spatial subset (upper left x = 730 km, y = 3830 km; lower right x = 850 km, y = 3680 km). Then we ran a gap-filling code which is fully described in Gascoin et al (2015) to interpolate the missing information mostly caused by cloud cover. The algorithm utilizes the topographic information (elevation and aspect) from the ASTER global digital elevation map, which was resampled to the same resolution.…”