【環境】全球的な干ばつからの回復パターン

Across diverse ecosystems, drought recovery times are strongly associated with climate and carbon cycle dynamics, according to a paper published in this week’s Nature. Drought is a recurring phenomenon with major impacts on both human and natural systems, and is the most widespread climatic extreme that negatively affects the ‘land carbon sink’, the land’s ability to absorb and store carbon dioxide from the atmosphere.

Recovery time is a critical metric of drought impact that measures the time it takes an ecosystem to revert to its pre-drought functional state. Yet, the factors influencing drought recovery are largely unknown.

Christopher Schwalm and colleagues used a combination of satellite imaging, land surface models, machine learning and analyses from a network of micrometeorological tower sites to evaluate diverse ecosystems. Their data show that post-drought temperature and precipitation conditions were the factors most strongly associated with recovery time, and that drought recovery time was longer for warmer post-drought temperatures. Differences in biodiversity and carbon dioxide concentrations in the atmosphere also influenced recovery time, although to a lesser extent than precipitation and temperature.

The analysis also shows that recovery is longest in the tropics and high northern latitudes (especially in the Russian Far East and Alaska - both of which are vulnerable regions of Earth’s climate system) and that drought impacts increased throughout the twentieth century. If droughts become more frequent, as expected, the time between droughts may become shorter than drought recovery time, leading to permanently damaged ecosystems and widespread degradation of the land carbon sink.