Assertion: drought's characteristic | /r/HasProperty | assessed at the surface
Facets:
value: to determine
type: PURPOSE
Source sentences:
text: At the surface, the spatial and temporal characteristics of vegetative state (in terms of water stress) for major vegetation types (crops and boreal zones), soil moisture, stream network, river flows, lake levels, wetlands, depression storage, groundwater and sub-surface flows be assessed to determine when and where drought is occurring.