Water balances differ enormously in qualitative and quantitative terms at different scales. The percentage of runoff of a plot on a slope is in general much higher than the total runoff of the slope. Although variability in soil properties and rain characteristics can explain some of the differences, other processes need to be considered to explain the apparent reduction of the runoff coefficient. The soil surface storage capacity is expected to vary with scale as the roughness of a field differs, but also interferes with the irregular folding forms of the slope.
Experimental fields were designed of different slope lengths and the different components of the water balance were measured. Results were compared with findings in literature. Different methods were developed or applied to approach the calculation of soil surface storage capacity in relation to scale. To verify the calculations and find patterns in soil surface storage capacity in relation to scale, a theoretical approach was established.
Between the plots of 2 x 2 m, 2 x 4 m and 2 x 6 m no significant scale difference could be found because of problems in experimental plot-design and poor measuring equipment amplified by the extreme tropical rainfall conditions. But the definition of the term fractional runoff and of runoff-scenarios proved to be useful analytical tools. Not the soil surface storage capacity turned out to be the main reason for the reduction in runoff coefficient with increasing slope length, but the increased residence time of the surface water. For improved water use efficiency and related to this nutrient use efficiency and soil conservation the spatial interrelationship should be acknowledged. Modeling and simulation of the dynamic system processes can improve the understanding of these hillslope systems and provide powerful tools for sustainable land use planning.