Shows the occurrence of atmospheric (low humidity and high air temperatures) and soil drought conditions "Drought directly limits terrestrial water availability and carbon uptake through low soil moisture (SM) and/or high vapor pressure deficit (VPD) 6,7 , and extreme water stress can substan- tially reduce agricultural production 8,9 and bring about wide- spread vegetation mortality 10,11 . Specifically, drought suppresses photosynthetic assimilation rates by reducing stomatal conduc- tance and related enzyme activity 6,12 and inducing leaf senes- cence and abscission as well 13 , resulting in reduced gross primary productivity (GPP) at the ecosystem scale. When water is limited, compound droughts (CDs) characterized by concurrent low SM and high VPD would cause even greater reductions in GPP than soil drought (low SM) or atmospheric aridity (high VPD) alone 14,15 . Low SM and high VPD tend to occur simultaneously over much of the global land surface, as SM deficits reduce evapotranspiration and increase sensible heat flux, resulting in a drier and warmer atmosphere and a higher VPD, and the high VPD in turn enhances evaporative water loss and accelerates reduction in SM16,17 . " Here on models: CDs are projected to become more frequent and more extreme, which could greatly reduce land carbon sink and compromise climate mitigation efforts 3,14 . However, assessments of past and future changes in CDs largely focus on extreme events from a statistical perspective 4,17,18 without taking into account whether these events cause adverse impacts on the environment. Risks of VCDs have been greatly underestimated as the widely adopted quantile-based approach identifies only 11% of VCDs and 26% of global GPP anomalies due to VCDs. The frequency and intensity of VCDs and their adverse impacts on carbon uptake are projected to increase further, irrespective of whether the CO2 fertilization effect on vegetation growth and photosynthesis is considered or not.
Next massive model error gets confirmed: Serious underestimation of reduced carbon uptake due to vegetation compound droughts
The error will develop a non-linear nature as the underlying processes not included in models behave non-linear...
#CMIP6 #CMIP5 #climate #extremeevents #uöäü1sinks
