Tracking atmospheric water pathways by direct evaporation tagging: A case study for West Africa

Abstract

[1] One of the central questions in hydrological research is where and to what extent evaporated water of a region returns as precipitation in another region. This study addresses this question and presents a detailed process-based approach implemented into a regional climate model. It allows tagging and tracking of the moisture evaporating from a given region into the atmosphere until it returns to the land surface as precipitation. Our approach is fully three-dimensional and enables the detailed consideration of vertical transport mechanisms for tagged water. We present a case study for the region around Lake Volta in West Africa. The simulation demonstrates the performance of the regional model and the implemented tagging mechanism. It shows the evolution of the tagged moisture field and reveals details of the transport: Moisture evaporated from Lake Volta is initially transported predominantly to the east and north, lifted by convective processes and then transported in upper layers to the west far away from the source of evaporation. The results indicate that the coupling between boundary layer and higher levels through convective processes can be essential for the fate of tagged water substances. Detailed analysis for a 2 month period in the rainy season 1998 shows that locally up to 6% of precipitating water originates from the Lake Volta region. Less than 2% of the evaporated water is locally recycled as precipitation in the source area. A further 10% precipitates in the rest of the Volta Basin.Citation: Knoche, H. R., and H. Kunstmann (2013), Tracking atmospheric water pathways by direct evaporation tagging: A case study for West Africa,

Variability of West African monsoon patterns generated by a WRF multi-physics ensemble

“…These studies demonstrate the skill of the WRF model and its predecessor, the Mesoscale Meteorology model 5 (MM5, Grell et al 1994) in representing specific features of the West African climate (Vizy and Cook 2002;Bliefernicht et al 2013;Hagos and Cook 2007;Sijikumar et al 2006), for RCM-based climate projections (Jung and Kunstmann 2007;Vigaud et al 2011), for the investigation of tropical storms triggered over the region (Vizy and Cook 2009;Druyan et al 2009;Chiao and Jenkins 2010) and for evaporation tagging (Knoche and Kunstmann 2013). These studies either simply mention which model configurations were employed, or include a pragmatic testing of model physics to minimize the bias against observations.…”

A mathematical framework for analysis of water tracers: Part 1: Development of theory and application to the preindustrial mean state

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