Tropical forests are characterized by high annual precipitation and high evapotranspiration and therefore contribute immensely to rewgulation of precipitation (rainfall), water recharge, run off, etc. in a riverwater basin. Nevertheless, it may be subjected to seasonal variations in rainfall inputs, partly driven by atmospheric movements related to the monsoon or latitudinal changes in the inter-tropical conversion zone, that is common in most tropical regions around the world.  Such seasonality implies various changes of the availability of resources, such as water and light, necessary to tree development and to forest functioning.

Some climatic variables (mainly water stress, water saturation and temperature) are expected to play a role in forest dynamics regarding the tree’s physiological processes. All these issue have been particularly important in the face of currently ongoing global warming and accompanied climate change. 

haudralic conductance, xylem and pholem vessel size.  specific root length, root diameter, stomatal conductance.  there are probably more.  all of which are a bit harder to measure than conventional functional traits.  

Nature of foliage (e.g. whether hydrophobic or nor), extent of canopy closure, bark characteristics (rough/ smooth/ epiphytic) influence the amount of interception of precipitation, and thus the amount of runoff.