Long-term changes in the effect of drought stress on ecosystems across global drylands.

Droughts are one of the climate extremes that occur frequently in drylands, constraining the terrestrial carbon uptake and water cycle processes. Studies about the long-term changes in the effect of drought stress on dryland ecosystems under global warming are still insufficient so far. Here we comprehensively investigate long-term changes in droughts and the effect of drought stresses on ecosystems across global drylands for 1982–2015, and further reveal changes in the configurations of the key meteorological and ecological factors of droughts, by using observation and reanalysis datasets. Climatically, the spatial patterns of intensity, occurrence, duration and severity of all drought categories across global drylands are highly consistent with each other. Associated with severe droughts, drylands witness insufficient precipitation (−12.4 mm mon⁻¹ area-averaged over global drylands), warmer temperature (0.6°C), water deficit (−19.0 mm mon⁻¹), higher atmospheric aridity (0.06 kPa), lower soil moisture (−0.03 m³ m⁻³), suppressed vegetation growth and declined carbon uptake (−0.13 g C m⁻² d⁻¹). The affected area, occurrence, duration and severity for mild to severe droughts in drylands and the anomalies of meteorological and ecological factors for all drought categories have increased significantly during 1982–2015. Specifically, when droughts occur, the precipitation deficit is weakened at a rate of 3.7–9.6 mm mon⁻¹ (30 yr)⁻¹, the higher temperature (atmospheric aridity) is further intensified at 0.71–0.87°C (30 yr)(39–47 Pa (30 yr)⁻¹), the water (soil moisture) deficit is relieved at 1.7–5.1 mm mon⁻¹ (30 yr)⁻¹ (4.1×10⁻³–7.4×10⁻³ m³ m⁻³ (30 yr)⁻¹), and the suppressed vegetation growth is generally alleviated at 0.98×10^−2–1.2×10⁻² (30 yr)⁻¹. Since the 2000s, the increasing trend in the suppressed vegetation growth during droughts tends to stagnate over about 50% of the dryland area. By checking the probability density function, the configurations of the key meteorological and ecological factors of droughts show significant differences between the periods before and after 2000. The probability of drought stress caused by precipitation and soil moisture deficit has decreased by 20% and 10%, respectively, while that caused by higher temperature and atmospheric aridity has been doubled, and increased by 26% and 15%, respectively. Thus, the impact of drought stress on dryland ecosystems caused by atmospheric aridity are increasing under global warming. [ABSTRACT FROM AUTHOR]