On the attribution of historical and future dryness/wetness changes in China incorporating surface resistance response to elevated CO2

Considering impacts of elevated CO2-induced increases in surface resistance on potential evapotranspiration (PET), to revisit and attribute the changes in dryness/wetness is necessary for accurately understanding evolutions of the historical and future drying and wetting conditions. Therefore, we comprehensively investigated the historical (1965–2011) and future (2019–2098; including four scenarios) annual dryness/wetness changes through incorporating CO2 effect into the Food and Agriculture Organization of the United Nations' report 56 (FAO-56) Penman-Monteith and the self-calibrating Palmer Drought Severity Index. During the historical and future periods, China experienced significant wetting (p < 0.05), and moreover the wetting trends prevailed across most (> 70%) of China, especially for each future scenario with >50% of China with significant (p < 0.05) wetting. A joint-solution method with multiple sensitivity experiments was used to separate each driving factor's contribution to annual dryness/wetness changes. Results showed that for the whole China increased precipitation was responsible for the historical and future wetting trends. However, the determinant factors varied spatially. Across China, the historical major contributors were precipitation, wind speed, air temperature and net solar radiation, totally accounting for 97.6% of China. The annual dryness/wetness across China could be attributed to precipitation, air temperature and net solar radiation for SSP1–2.6 and SSP2–4.5, but precipitation and air temperature for SSP3–7.0 and SSP5–8.5. Moreover, through comparing attributions of the annual dryness/wetness changes with and without CO2 effect, we found that the CO2 effect could change the determinant factors mainly in eastern China, and the corresponding area percentages increased with the gas emissions, particularly for SSP3–7.0 and SSP5–8.5 with the largest values above 42%. This finding highlighted that the CO2 effect should be considered when conducting attribution analysis of the changes in dryness/wetness.