Enthalpies of Vaporization of Organic Compounds. VII. Some Carboxylic Acids.

Abstract

Partitioning of rainfall into evapotranspiration and runoff is controlled by climate and catchment characteristics. The degree of control exerted by these factors varies with the spatial and temporal scales of processes being modelled. Understanding individual hydrological processes and their relationships with climatic and catchment characteristics is an important step in predicting catchment water balance. However, this does not mean that one should try to incorporate every known process into a model. The interaction and co-evolution of these processes may manifest themselves in such a way that the overall behaviour of the catchment can be described by simple relationships. A top-down approach was used on a whole catchment-scale water balance to determine the minimum level of model complexity required for predicting runoff over a range of time scales. Monthly values of precipitation, potential evapotranspiration, and streamflow from 265 catchments in Australia were used in this study. A model based on the "limits" concept and an index of dryness was adopted and proved to be adequate for the selected catchments. On mean annual basis, the index of dryness defined as the ratio of potential evapotranspiration to precipitation was found to be a dominant factor in determining the water balance. (Figure Presented) At annual time scale, interannual variability in streamflow can be reasonably well estimated from the index of dryness without additional inputs. Results however suggested increased model complexity is required on finer time scale such as monthly. In response to this, the mean annual water balance model was modified to include additional factors and this resulted in a parsimonious lumped conceptual model on monthly time scale. The model was calibrated against the measured runoff and showed encouraging results (Figure 2). The model developed from this study can be applied to ungauged catchments and also be used to investigate the impact of land use and climate change on catchment- scale water balance. (Figure Presented).