Abstract
The recent global warming slowdown or hiatus after the big El Niño event in 1997/98 raises the questions of whether terrestrial hydrological cycle is being decelerated and how do the hydrological extremes respond to the hiatus. However, the rapidly developing drought events that are termed as “flash droughts” accompanied by extreme heat, low soil moisture and high evapotranspiration (ET), occurred frequently around the world, and caused devastating impacts on crop yields and water supply. Here, we investigate the long-term trend and variability of flash droughts over China. Flash droughts are most likely to occur over humid and semi-humid regions, such as southern and northeastern China. Flash drought averaged over China increased by 109% from 1979 to 2010, and the increase was mainly due to a long term warming of temperature (50%), followed by the contributions from decreasing soil moisture and increasing ET. There was a slight drop in temperature after 1997, but the increasing trend of flash droughts was tripled. Further results indicate that the decreasing temperature was compensated by the accelerated drying trends of soil moisture and enhanced ET, leading to an acceleration of flash droughts during the warming hiatus. The anthropogenic warming in the next few decades may exacerbate future flash drought conditions in China.
Highlights
Drought is usually a creeping phenomenon that persists for several months or years, and affects the food and water security significantly[1,2], and heatwave usually lasts for a few days with sustained high temperature and notable impacts on human mortality and environment[3]
For each meteorological station and each pentad, a flash drought is defined as the condition in which surface air temperature anomaly is larger than one standard deviation, ET anomaly is positive, and the soil moisture percentile is lower than 40%9
For the water limited regions, ET is very sensitive to soil moisture variations and a moderate dry condition may result in a significant reduction in the ET, reducing the probability of the occurrence of flash droughts according to the definition
Summary
Drought is usually a creeping phenomenon that persists for several months or years, and affects the food and water security significantly[1,2], and heatwave usually lasts for a few days with sustained high temperature and notable impacts on human mortality and environment[3]. The risk of heatwave is increasing[5], and the terrestrial hydrological cycle is expected to be intensified with increasing water vapor feedback[16], leading to the changes in precipitation, soil moisture and ET, as well as characteristics of climate extremes (e.g., droughts). Given the slowdown of temperature and ET, and the uncertain change in soil moisture, it remains unclear what changes have occurred in the flash droughts and whether the hiatus is responsible for the changes. Surface air temperature measurements for the period of 1979–2010 from over two thousand meteorological stations, and soil moisture and ET estimations from three global reanalysis products are used to investigate multidecadal changes in flash droughts over China and the underlying causes
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