Assessing the resilience of the terrestrial water cycle

 The green water components of the terrestrial water cycle - transpiration, surface soil moisture, and land precipitation - are critical for Earth system stability and ecosystem productivity. However, complex and accelerating human pressures are altering the land surface and water cycle at vast spatial scales. Changes to the terrestrial water cycle can have wide-reaching impacts on ecological (e.g., affecting biodiversity, ecosystem structure and function), and social systems (e.g., affecting crop yields). Despite evidence of considerable and widespread change globally, the resilience of green water variables, or their ability to absorb and recover from disturbances, is not yet well understood. Here, we assess green water resilience using early warning signals (EWS) applied to global satellite-derived time series of green water variables. We map where and how green water resilience is changing, and empirically evaluate these estimates against past abrupt changes to understand where and when EWS are effective.

We show that EWS provide limited but non-negligible additional skill in anticipating abrupt transitions when combined with environmental context. We also find that a wider portfolio of context-appropriate EWS is needed to capture heterogeneous water-vegetation dynamics across eco-hydrological systems. For example, Critical Slowing Down suggests transpiration resilience loss in arid to sub-humid ecosystems, while signals of Critical Speeding Up and flickering are more common in high-latitude and sub-humid systems. Our results highlight emerging risks to terrestrial water cycle dynamics under ongoing anthropogenic pressures.