# From Climate Conditions to the Numerical Slope Stability Analysis of Surface Coal Mines
## 3 Baseline Climate Description--Past Events  
Greece is located in the southern part of the Balkan peninsula, in southeastern Europe. It mainly presents a typical Mediterranean climate (Figure 2) with mild, rainy winters, warm, dry summers, and extended periods of sunlight [36]. The area of Megalopoli is representative of this climate; in contrast, the region of Western Macedonia presents a climate similar to continental Europe [37]. The climate of Megalopoli is categorized as Cas (hot summer Mediterranean) according to the Koppen-Geiger climate classification, having hot summers and mild winters [35] (Figure 2). Most rainfall days are recorded during fall and winter with an annual average precipitation of 800 mm; the driest month is July, and the wettest is December, with an average monthly precipitation of 9 mm and 147 mm, respectively [38]. The average temperature in Megalopoli is 14.9 \({}^{\circ}\)C.  
The climate of Ptolemais is classified as Cfb (temperate oceanic) according to the Koppen-Geiger climate classification, having intense winters and mild summers with a very low number of dry days ([PERSON], 2018) (Figure 2). Rainfall in plain areas ranges from 600-800 mm/year [39]. There are 108.3 average rainfall days, with August being the driest month, with 30 mm of rain, and November the wettest, with 60.3 mm of average precipitation. The mean annual temperature is 11.5 \({}^{\circ}\)C.  
The quantification of past and current climate conditions depends on the measurements obtained from several weather stations in an area. Figure 3 presents the precipitation for these two regions for the last 30 years (1990-2019) (data provided by the Hellenic National Meteorological Service). Both regions present fluctuations, but they are practically constant in these 30 years. Megalopoli's precipitation level is overall higher and presents more sharp fluctuations than the Ptolemais one. For example, the maximum mean monthly precipitation difference between two consecutive years was 33 mm for Ptolemais (2013-2014) and 51 mm for Megalopoli (2004-2005). For Ptolemais, the mean precipitation per month is 37 mm, and for Megalopoli, 56 mm. Assuming this precipitation falls in one day, the rainfall intensity is 1.5 mm/h in Ptolemais and 2.3 mm/h in Megalopoli, denoting light rain. By obtaining the maximum mean monthly precipitation of 64 mm in Ptolemais and 88 mm in Megalopoli and making the same assumption, one obtains 2.7 mm/h and 3.7 mm/h, respectively, denoting a moderate rain intensity. Figure 3: Measurements of the last 30 years of mean monthly precipitation from 1990–2019. More detailed data for the precipitation in these areas were obtained from the National Observatory of Athens up to ten years ago, for two meteorological stations different but close to previous ones (data publicly available). They do not cover the 30 years that is the classical period used for describing a climate (World Meteorological Organization) but are more detailed in terms of rainfall activity. Figure 4 presents the maximum mean monthly precipitation per year (the x-axis refers to the month with the highest mean precipitation) and the maximum daily precipitation per year (the x-axis refers to the day with the highest precipitation) for the past ten years. Figure 4a shows that the maximum mean monthly precipitation per month can be four times larger than the mean monthly one. For instance, in 2019, for Ptolemais, the mean monthly precipitation was 30.8 mm and the maximum 92.6 mm, and for Megalopoli, 88 mm and 381 mm, respectively. These observations denote that more extreme rains than assessed by the mean monthly values are possible; if these maximum mean monthly rains are assumed to fall in one day, that would dictate 4 mm/h and 16 mm/h. Figure 4b presents maximum daily rains similar to the mean monthly precipitation, supporting the assumption that the mean monthly precipitation can fall in one day.