New approach to detect trends in extreme rain categories by the ITA method in northwest Algeria

A new approach for the modified method of innovative trend analysis (ITA) was applied to the categories of maximum daily rains coming from 41 pluviometric stations of Macta (northwest Algeria) for the period 1970-2010. Six categories of maximum daily rainfall were considered: light: 0-4 mm/day (A); mild to moderate: 4-16 mm/day (B); moderate to heavy: 16-32 mm/day (C-1); heavy: 32-64 mm/day (C-2); heavy to torrential: 64-128 mm/day (D-1); and torrential: equal to or greater than 128 mm/day (D-2). The results show that during the second period (1990-2010), increasing trends were detected in the middle categories B (most frequent: 20.78%), C-1 (17.85%), C-2 (20.21%) and D-1 (4.92%). In addition, migratory movements and rainy events towards the higher categories were detected (in particular towards C-1 (8.84%)). These results show an increase in extreme rains in the Macta watershed during the period 1990-2010.