Revisiting the evolution of the 2009–2011 meteorological drought over Southwest China

With intensifying climate change, droughts over Southwest China (SWC) are drawing increasing interest. The droughts of 2009–2011 have attracted special concern. However, the roles of atmospheric evaporative demand [reflected by reference evapotranspiration (ET0)] and precipitation (P) anomalies in drought evolutions are still unclear. To that end, we revisited the evolution of the 2009–2011 SWC meteorological droughts quantitatively and comprehensively by quantifying the ET0 and P impacts. In terms of three drought parameters [i.e., drought intensity (DI), area (DA), and duration (DD)], SWC experienced the second most severe drought of the 1961–2012 period in 2009. Evident differences existed among the drought conditions in different months, i.e., more severe droughts occurred in February–March 2009, September 2009 to March 2010, and June–October 2011. Based on the annual means over drought regions, the 2009 and 2011 DI (DA) could be attributed to lower P, but the P and ET0 impacts [P, ET0, and P-and-ET0 (which reflects drought occurrence due to their combined impacts only)] were comparable in 2010. In addition, P reduction was responsible for DD during 2009–2011. Except in January–March, which were dominated mostly by P, DI (DA) was generally dominated by ET0 (ET0 or P-and-ET0) over the three years. While P dominated spatially and temporally for the majority of the 36 months for DI (DD), some areas were mainly affected by ET0 (ET0 or P-and-ET0). Therefore, to better understand drought evolutions and improve drought monitoring and forecasting, the impacts of ET0 anomalies should be fully considered. The results of this study provide an important reference framework for comprehensively understanding the underlying mechanisms of droughts not only in SWC but also in other regions around the world.