The Namib desert is one of the driest regions on Earth, where fog is a prominent climatic feature and an important source of water for ecological processes. The Namib fog is generally of marine origin and advected on shore either directly as fog or as stratus clouds which intercept with the ground at a higher elevation further inland. Correlation between spatial distribution of the flora and fauna and the occurrence of Namib fog is documented in numerous studies. However, knowledge about the spatial and temporal patterns of fog distribution is incomplete and, in particular, the amount of fog water deposition available to the fauna and flora is unknown. Fog precipitation measurements with fog collectors in the Namib have been carried out but no physically sound method to convert them to fog water deposition is available. The lack of observations of cloud physical properties of Namib fog prevents a thorough understanding of fog water deposition processes and their relevance for the water budget.
The proposed sub-project NaFoLiCA-F has two key aspects:
- Characterization of ecosystem water availability in the Namib, with a focus on fog as a source of water. The unsolved question how to scale sampled fog precipitation to fog water deposition is addressed. Fog water deposition is determined with two independent methods, i.e. the eddy covariance approach where the vertical flux of liquid water is directly measured and the use of micro-lysimeters where fog water deposition is derived by weighing a piece of soil. Existing fog collectors and a new fog collector with a higher collection efficiency developed within the project will be calibrated and scaled to give an estimate of fog water deposition. Together with the existing comprehensive micrometeorological data-set (FogNet stations, the UNIBAS flux tower, the BSRN station) and the results of the planned Intensive Observation Period (IOP), we are confident to provide a parameterization for this highly important open question.
- Create a basic data-set from ground-based measurements (permanent stations, one IOP). Provide data to partner projects NaFoLiCA-M and NaFoLiCA-S for the fine- tuning of different empirical parameters for a numerical fog forecast model and for the development and refining of fog related satellite remote sensing techniques.
Process understanding will be advanced by analyzing the life cycle stages of individual fog events, i.e. the temporal and spatial development of fog micro- and macro-physical properties including a characterization of liquid water distribution within the fog vertical profile. The proposed research crosses scales: from the microphysical processes level to the landscape-scale spatial patterns, and from fog property changes within minutes to seasonal patterns and multi-year trends. Taken together, the component projects are expected to greatly improve the understanding of Namib fog as a paradigm of coastal-desert fog phenomena. This will set a basis for improved consideration of fog in regional climate modelling and potential impacts on climate change.