Improved understanding on flash droughts: from a perspective of the rapid intensification rate

The rapid intensification rate and short duration are currently two different notions in defining flash droughts. Here we make a thorough evaluation on these two approaches and illustrate which approach can provide more accurate information of flash drought and why. Based on the conception of intensification rate, a new method focusing on soil moisture depletion during the onset-development phase is proposed, and its performance in monitoring flash drought events, their onset time and spatial dynamics are compared with those from the short-duration method. Results show that the proposed rapid-intensification approach is superior to the short-duration approach in capturing the continuous evolution process of drought. Since the short-duration approach ignores the change of soil moisture with time, it can hardly ensure the identified flash drought events all have the rapid evolving characteristic. Meanwhile, the miss monitoring for flash drought onset is also observed for the short-duration approach. The unreasonable selections of hydro-meteorological variables and corresponding thresholds, particularly refers to that of temperature, is the main reason for the poor behavior of the short-duration approach.