Compound hot-dry events greatly prolong the recovery time of dryland ecosystems

Previous studies have reported that the damage to ecosystems caused by compound hot-dry events was generally more severe than that of dry events, such as greater loss of vegetation productivity and higher tree mortality. With the continuous global warming, the probability and severity of compound hot-dry events are expected to increase further; however, the dynamics of ecosystem recovery from compound hot-dry events are not yet clear, which is not conducive to drought adaptation and protection of ecosystems. This study clarified the difference between the recovery time of compound hot-dry and dry events, revealed the negative impact of increased VPD on ecosystem recovery in the compound hot-dry and dry environment, and warned that the ecosystems may face more severe recovery pressure due to warming in the future.

They reported that the average recovery time of global ecosystems to compound hot-dry events was more than 5 months, and the average recovery time was about 4 months to dry events. This meant that the compound hot-dry events extended the recovery time of ecosystems by more than 1 month on average compared to dry events. The difference in recovery time (ΔRT) between compound hot-dry and dry events decreased with the increase of aridity index (the ratio of precipitation to potential evapotranspiration), indicating that the extended recovery time was more severe in the drylands than in the humid regions. In humid regions, the mean ΔRT based on NDVI and LAI was 0.93 and 0.90 months, respectively; however, the ΔRT was 1.54 months and 1.20 months in drylands, respectively.

The canopy conductance (G_c) and maximum photosynthetic assimilation rate (A_max) of compound hot-dry and dry events calculated based on the FLUXNET2015 dataset show that compound hot-dry events lead to more severe stomatal closure, limiting the material production required for the vegetation recovery process.

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