Upwind moisture sources shape drought vulnerability of major forest carbon stocks

Forest-based climate mitigation depends on the long-term stability of forest carbon uptake, yet resilience under shifting hydroclimatic conditions remains uncertain. While forest management and reporting largely operate within national borders, forest water supply is regulated by atmospheric moisture transport across large and often transboundary source regions. This creates a scale mismatch between governance structures and the physical processes that sustain carbon sequestration.

We develop a global framework linking (i) governance-relevant sink units (countries) with (ii) physically defined upwind moisture source regions to assess the hydroclimatic vulnerability of major forest carbon stocks. Large forest carbon stocks are mapped from satellite-based aboveground biomass products, and hydroclimatic stress is quantified using drought indices alongside carbon-uptake proxies. Areas are classified as vulnerable where increasing drought stress co-occurs with weakening carbon uptake signals over recent decades.

Using an Eulerian atmospheric moisture tracking model (WAM2layers), we quantify each sink region’s seasonal dependence on terrestrial versus oceanic upwind moisture sources and the spatial concentration of key source areas. Initial results indicate strong geographic and seasonal variation in upwind moisture dependence, showing that atmospheric teleconnections can influence drought exposure of forest carbon sinks beyond national boundaries.