Open AccessCO2-plant effects do not account for the gap between dryness indices and projected dryness impacts in CMIP6 or CMIP5
Author(s) -
Jacob Scheff,
Justin S. Mankin,
Sloan Coats,
Haibo Li
Publication year - 2021
Publication title -
environmental research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.37
H-Index - 124
ISSN - 1748-9326
DOI - 10.1088/1748-9326/abd8fd
Subject(s) - dryness , environmental science , evapotranspiration , surface runoff , climatology , precipitation , aridity index , arid , index (typography) , vegetation (pathology) , climate change , atmospheric sciences , water content , meteorology , ecology , geography , geology , medicine , surgery , geotechnical engineering , pathology , world wide web , computer science , biology
Recent studies have found that terrestrial dryness indices like the Palmer Drought Severity Index (PDSI), Standardized Precipitation Evapotranspiration Index (SPEI), and Aridity Index calculated from future climate model projections are mostly negative, implying a drying land surface with warming. Yet, the same models’ future runoff and bulk soil moisture projections instead show regional signals of varying sign, and their vegetation projections show widespread greening, suggesting that the dryness indices could overstate climate change’s direct impacts. Most modeling studies have attributed this gap to the indices’ omission of CO 2 -driven stomatal closure. However, here we show that the index-impact gap is still wide even in future-like model experiments that switch off CO 2 effects on plants. In these simulations, mean PDSI, Aridity Index, and SPEI still decline broadly with strong warming, while mean runoff, bulk soil moisture, and vegetation still respond more equivocally. This implies that CO 2 -plant effects are not the dominant or sole reason for the simulated index-impact gap. We discuss several alternative mechanisms that may explain it.