DDM30 is a raster map which describes the drainage directions of surface water with a spatial resolution of 30’ longitude by 30’ latitude, and covers the land surface of the globe (without Antarctica). In addition to the routing network, DDM30 includes raster maps for basin numbers and slopes.
Here, the DDM30 routing network is mapped to the CRU land surface mask. The DDM30 mask and the CRU land mask do not overlap completely. Numbers of cells in:
• DDM30: 66896
• CRU landmask: 67420
• DDM30 and CRU landmask: 66094
• DDM30, but not CRU landmask: 802
• CRU landmask, but not DDM30: 1326
According to decisions made at the model intercomparison workshop in April 2008, lakes that drains to the sea, but are not included in the CRU land mask, were added to the datasets. These cells should not be included when results are submitted, though, and there should be no runoff added to the river network from these cells. I.e. these cells are included for transportation purposes only (streamflow). This applied to four cells, i.e. Lake Lagoda in the Neva river in Russia (basin number 17012), having coordinates (latitude, longitude) 61.25, 31.25; 60.75, 31.25; 60.75, 31.75; and 60.75, 32.25. The Great Lakes are included in both the CRU land mask and in DDM30. The Caspian Sea, which is included in the DDM30 maps, but not in the CRU land mask, is not included in the provided datasets (all cells in the Caspian Sea are listed as sinks in the original DDM30).
The final number of cells in the provided dataset is hence 67424, which corresponds to the cells in the CRU land mask, in addition to the four cells representing Lake Lagoda. All basins within the mapped flow direction dataset are connected, and have one outlet cell. This required that flow directions were slightly changed for 99 cells in 84 basins.
The 3 provided data sets are:
• Flow direction: ddm30_flowdir_cru_neva.nc (netcdf file) and ddm30_flowdir_cru_neva.asc (arc type ascii file). The flow directions are as follows: 0 - sink or outlet to ocean; 1 - east; 2 - south east; 3 - south; 4 - south west; 5 - west; 6 - north west; 7 - north; 8 - north east; 9 – value given to the 1326 cells included in the CRU land mask that are not included in the original DDM30 flow direction map.
• Basin numbers: ddm30_basins_cru_neva.nc and ddm30_basins_cru_neva.asc. The basins are numbered from 2 to 71326. Basins number 2 through 66896 are included in the original DDM30 map, while each of the 1326 cells included in the CRU land mask and not in the original DDM30 map is given a distinct number from 70001 to 71326.
• Slopes: ddm30_slopes_cru_neva.nc and ddm30_slopes_cru_neva.asc. The 1326 cells in the CRU land mask that are not included in the original DDM30 slope map are all given a value of 0.001. Units: m/m.
