Interception is the amount of rainfall, which is ‘intercepted’ and will not infiltrate into the ground or take part in the runoff process. The intercepted rainfall will stay for example on leaves, in the top soil, in small pools on roads or on roofs, etc. and will evaporate within a few days. Evaporation from interception has often been disregarded in hydrological modelling. Reasons for neglecting interception are that the amounts involved are considered small and that it is difficult to measure interception accurately. However, it appears that interception can amount to 20-40% of the precipitation. If interception is disregarded in hydrological models, it will be compensated by another process of the hydrological cycle to meet goodness of fit criteria. This jeopardizes the physical representation of the hydrological model with all its related possible errors.
Moreover if interception is taken into account; it is often considered a constant. Although this is better then completely disregarding interception, the interception process is far from constant and varies in time and space. This is one of the main reasons why measuring interception is difficult.
During my PhD-study (in close cooperation with LIST (formerly CRP-Gabriel Lippmann)) I measured two distinct types of interception:
For the latter I developed a special device to quantify forest floor interception. I investigated interception evaporation on several locations:
- Huewelerbach catchment, Luxembourg: beech trees and forest floor
- Westerbork, The Netherlands: grass/moss
- Botanical garden Delft, The Netherlands: Cedar needles
- Harare, Zimbabwe: Msasa leaves