Contrasting roles of interception and transpiration in the hydrological cycle
Abstract
The contribution of land evaporation to local and remote precipitation (i.e., moisture recycling) has been extensively studied and is found to be of significant importance for water resources, agriculture and ecosystems. Our paper is the first research to present moisture recycling metrics for partitioned evaporation. We use a new land surface model (STEM) to compute land evaporation partitioned into canopy and ground interception (i.e., the fast feedbacks), and transpiration and open water evaporation (i.e., the slow feedbacks). We also use a numerical moisture tracking model (WAM-2layers, with atmospheric variables taken from ERA-Interim) to track the components of land evaporation separately, backward as well as forward in time. Moreover, we include age tracers to study the lifetime of these components. The origin and fate of the fast and slow vapor feedbacks appear to be very different. Global maps indicate that evaporated interception is more likely to return as precipitation on land than transpired water. On average, evaporation from interception is found to have an atmospheric residence time of nine days, while transpiration typically resides ten days in the atmosphere. In the figure it can be seen that interception evaporation recycling has much shorter length scales than transpiration evaporation recycling, thus interception generally precipitates closer to its evaporative source. We conclude that interception mainly works as an intensifier of the local hydrological cycle during wet spells. On the other hand, transpiration is very active during dry spells and is transported over much larger distances downwind where it can act as an important source of moisture, especially during the onset and decline of the rainy period. Land use changes (e.g., forest to cropland conversion) were already known to have an impact on the magnitude of moisture recycling, but here we show that even when total annual evaporation remains equal, a different partitioning will result in different moisture recycling patterns and hence a redistribution of water resources. As such, this research highlights that land use changes can have complex effects on the atmospheric part of the hydrological cycle.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFM.H13L..02V
- Keywords:
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- 1843 HYDROLOGY Land/atmosphere interactions;
- 1631 GLOBAL CHANGE Land/atmosphere interactions;
- 1655 GLOBAL CHANGE Water cycles;
- 1818 HYDROLOGY Evapotranspiration