Data-treatment.md

+# Monthly runoff into annual
+```
+if file_name == "mrunoff.nc":
+        #convert number of months to years
+        nb_year = int(len(years)/12)
+        tmp = np.zeros([nb_year,len(latitudes),len(longitudes)])
+        #calculation of the sum over each year
+        for k in range(0,nb_year,1):
+            tmp[k] = np.sum(data[k*12:k*12+12],axis=0)
+        data = tmp
+```
+years,latitudes,longitudes = list from the file reading
+data = numpy array from the reading of the file [months,latitudes,longitudes]
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