W_perm

Considering first $w_{perm}$, converting land use and terrain information into a fractional coverage of breeding areas provided by permanent water bodies is a significant challenge. Wave/ripples action that can drown larvae [#!leprince:27!#] and the presence of predators in larger bodies [#!fillinger:09!#] imply that larvae exist only in a sub-fraction of such water bodies, in pooling that occurs on the edges of lakes and rivers or the shallow edges of ponds. Higher soil moisture in the vicinity of large water bodies can boost available breeding sites by reducing infiltration loss and increasing the lifetime of temporary puddles and ponds. Lastly, rivers and streams can even confound classic relationships between rainfall and vector density by actually providing more breeding sites during drought periods when flow slows or stops altogether [#!haque:10!#]. This remains the subject of current research and the default VECTRI model therefore sets $w_{perm}$ to zero in each grid cell, implying that the breeding site availability is dominated by seasonal ephemeral ponds and malaria incidence will be potentially underestimated in the vicinity of larger semi-permanent water bodies. A user operating the model for a local area with knowledge of permanent water bodies can set this value appropriately in the namelist (default is 1.e-6).

From version 1.9 a optional database is provided for $w_{perm}$ which is derived from a 20m spatially resolved map of water bodies (downloadable at http://2016africalandcover20m.esrin.esa.int/viewer.php). As stated above, large bodies of water are not suitable for vectors, and instead the assumption is made that the enhancement is breeding site availability is instead associated with pond site along lake/river shores. Thus the CCI land cover product has been preprocessed to count all land-water border cells at 20 meter resolution which are then summed over a 5x5km grid to give a permanent breeding site fraction. This fraction is usually much lower than 1%, but can obtain values as high as 10% in swampy/marshland type environments. Note that this derivation is static in time and does not account for the seasonal cycle of emphemeral water bodies. It is recommended to ensure that vector diffusion is switched on when using the spatial map of permanent breeding sites in order to allow vectors to radiate out from these malaria “hot-spots” zones associated with the availability of year-round, perennial water sites. The dataset is available in the file “permanent_breeding_fraction_sentinal_africa.nc” in the data directory. The user will need to project this onto the same grid as the climate driving files and merge the information into the datafile. The standard netcdf name for the field is “wperm”, but a revised name can be specified in the namelist by using the field “wperm_name”.

INCLUDE GRAPHIC OF FRACTION HERE.