Critical Zone:An Emerging Research Area for Sustainability

In the era of Anthropocene, characterized by a dramatic increase in anthropogenic pressure, global changes are challenging the capacity of planet Earth to sustain the development of human societies in the long term. In the past two decades, this concern has fostered worldwide efforts to develop integrated studies of the ‘critical zone’ (CZ), the outer skin of the Earth, extending from the canopy top to the bottom of the aquifer, hosting the continental biosphere and providing basic human needs such as water, food, energy and ecosystem services¹ . Environmental processes within the CZ, such as energy and mass exchange, formation of soil, streamflow and evolution of landscape are critical to sustain biodiversity as well as humanity ^2,3 . However, with rapid socio-economic development, the CZ is subjected to increasing stress from anthropogenic forcings such as the growth in human and livestock populations, increase in land use, global environmental changes, and expanding consumption patterns⁴ . The expanding needs for sustainable development call for understanding, predicting and managing the complexity as well as dynamics within the CZ and to study its feedback with other compartments of the environmental systems^5,6 . The main challenge faced by the CZ research is to integrate effectively the multiple disciplines at stake, from geosciences, biological sciences, ecology, hydrology, soil science to social sciences, working within a wide range of temporal and spatial scales^7,8 . The interdisciplinary and multiscale study of terrestrial ecosystem processes can be best addressed by critical zone observatories (CZOs), where domain experts across different disciplines study various aspects of the CZ. This will lead to holistic understanding of complex systems 8 .