The lagged effect and impact of soil moisture drought on terrestrial ecosystem water use efficiency

Water use efficiency (WUE) is an ecological indicator reflecting the link between carbon and water cycles in terrestrial ecosystems, which is often affected by drought disturbance. However, knowledge about the influences of soil moisture drought on WUE is still lacking. Therefore, this paper aims to quantify the lagged effect and impact of soil moisture drought on terrestrial ecosystem WUE from 1982 to 2018 using ERA5 and Global Land Surface Satellite (GLASS) datasets. Drought conditions are described by the soil moisture anomaly percentage index (SMAPI). The lagged effect of drought on WUE is measured by the month with the maximum significant correlation between SMAPI and WUE. The impact of drought on WUE is estimated through the relative change of WUE during drought and non-drought periods. The results showed that: (1) Drought had an approximately 4-month lagged effect on WUE, which was observed in 70.87% of the global vegetated areas. The lagged effect of drought on WUE was a short period (1–4 months) for shrubland and sparse vegetation, middle and long periods (5–12 months) for forest. (2) When drought occurred, WUE decreased by 36.95% in the Tibetan Plateau and 24.93% in West Africa, while WUE in North Europe, Alaska/N.W. Canada, and West Asia increased by 14.64%, 8.83%, and 8.53%, respectively. The negative and positive impacts of drought on WUE in each vegetation type were commensurate. Our results provide useful information for understanding the response of ecosystem carbon and water cycles to drought..