1.?Introduction .Since the pre-industrial, global mean surface temperature has increased by about 0.87 °C with a more remarkable warming in global land surface temperature (1.53 °C) (IPCC 2018 ). Confronted by climate change, the frequency, intensity and/or duration of droughts has increased in some regions including the Mediterranean, North Africa and Middle East (Vicente-Serrano et al2014 , Spinoni et al2015 , Dai and Zhao 2017 , Páscoa et al2017 ), north-eastern China ...