## 3 Data and Methods  
### Satellite Data  
MODIS data acquired in the first two bands (i.e., channel 1, VIS, at 0.62-0.67 \(\upmu\)m and channel 2, NIR, at 0.841-0.876 \(\upmu\)m) at 250 m of spatial resolution were used in this work. In more detail, imagery acquired by the sensor onboard the Aqua satellite in the 12:00-14:00 GMT temporal range, for the month of December in the 2002-2016 period have been investigated. MODIS Level 1B (MYD02 QKM) and geolocation (MYD03)  
Figure 1: Localization of the Region of Interest (ROI). In the background, the Landsat Enhanced Thematic Mapper Plus (Landsat 7 ETM+) false-color (R = Short Wave InfraRed-SWIR; G = NIR; B = RED) composite image of 5 December 2013 at 9:31 GMT. The red box is the area used in the text.  
data directly produced at the satellite receiving station of the Institute of Methodologies for Environmental Analysis (IMAA), located in Tito Scalo (Basilicata region, southern Italy), have been processed. These data have been produced by running the Community Satellite Processing Package (CSPP) software with antenna data directly acquired. Level 1B and geolocation data downloaded from the Level-1 and Atmosphere Archive & Distribution System (LAADS) Distributed Active Archive Center (DAAC) archive [26] have been also used to fill any gaps in the analyzed historical series.  
Similarly, for VIIRS, data collected in the first two imagery bands (i.e., I1, VIS, at 0.60-0.68 um and I2, NIR, at 0.85-0.88 um) and the thermal infrared (TIR) imagery one (I5, TIR, at 10.5-12.4 um) at 375 m of spatial resolution were investigated. In particular, acquisitions coming from the SNPP satellite in the same daily temporal range of Aqua were considered for the month of December in the 2012-2016 period. Also for VIIRS, the SNPP Sensor Data Record (SDR) and the I-band terrain-corrected geolocation (GITCO) data directly produced at the Institute of Methodologies for Environmental Analysis (IMAA) receiving station, which was downloaded from the NOAA Comprehensive Large Array-data Stewardship System (CLASS) archive [27], have been exploited to populate the historical series.  
Finally, in absence of in situ ground truth data, the Landsat 7 ETM+ image acquired on 5 December 2013 at 9:31 GMT over the ROI and downloaded from the U.S. Geological Survey (USGS) portal [28] (Figure 1), was used to assess the accuracy of the achieved results. The RGB false color (R = SWIR, 1.55-1.75 um; G = NIR, 0.775-0.90 um; B = RED, 0.63-0.69 um) of such an image, related to the ROI, is shown in Figure 1. In order to better highlight the area most affected by the water presence, the Normalized Difference Vegetation Index (NDVI) has been computed, looking for values below zero, which should correspond to water affected areas [29], including both flooded pixels and permanent water. A Boolean (water/no water) mask was produced and shown in Figure 2.  
An area of about 105 km\({}^{2}\) has been recognized as affected by water presence, including permanent waters related both to rivers and the San Giuliano Lake included within the ROI.  
Figure 2: In green, the pixels of the Landsat 7 ETM+ image, shown in Figure 1, recognized as water affected are depicted (see text).