The transfer of phosphorus from terrestrial to aquatic ecosystems is a key route through which climate can influence aquatic ecosystems. A number of climatic factors interact in complex ways to regulate the transfer of phosphorus and modulate its ecological effects on downstream lakes and reservoirs. Processes influencing both the amount and timing of phosphorus export from terrestrial watersheds must be quantified before we can assess the direct and indirect effects of the weather on the supply and recycling of phosphorus. Simulation of the export of phosphorus from the terrestrial environment is complicated by the fact that it is difficult to describe seasonal and inter-annual variations by existing process-based and empirical models. These variations are also strongly influenced by the history of the weather and by the frequency of extreme weather events. For example, the effects of storm runoff on the export of phosphorus can be very sensitive to levels of soil saturation and soil moisture, which are in turn influenced by the past history of precipitation and evapotranspiration. Inclusion of effects such as these is impossible using simple empirical models and difficult using process based models when model parameterization changes in response to antecedent conditions.