  Environmental fluid mechanics underlies a wealth of natural, industrial and,
by extension, societal challenges. In the coming decades, as we strive towards
a more sustainable planet, there are a wide range of grand challenge problems
that need to be tackled, ranging from fundamental advances in understanding and
modeling of stratified turbulence and consequent mixing, to applied studies of
pollution transport in the ocean, atmosphere and urban environments. A workshop
was organized in the Les Houches School of Physics in France in January 2019
with the objective of gathering leading figures in the field to produce a road
map for the scientific community. Five subject areas were addressed: multiphase
flow, stratified flow, ocean transport, atmospheric and urban transport, and
weather and climate prediction. This article summarizes the discussions and
outcomes of the meeting, with the intent of providing a resource for the
community going forward.
