Update Urban Morphology Morphometric Calculator (Grid).rst

docs/source/pre-processor/Urban Morphology Morphometric Calculator (Grid).rst

@@ -103,6 +103,7 @@ Urban Morphology: Morphometric Calculator (Grid)
 * Remarks
       All DSMs need to have the same extent and pixel size.
       Polygon grids must be squared (or rectangular) and allinged with the CRS used. This will be fixed in future versions so that any shaped grid can be used (see issue #12 in the `repository <https://github.com/UMEP-dev/UMEP/issues>`__).
+      Units of wai is non dimensional (area building walls / total horizontal area).
 
 * References
       -  Kent CW, CSB Grimmond, J Barlow, D Gatey, S Kotthaus, F Lindberg, CH Halios 2017: Evaluation of urban local-scale aerodynamic parameters: implications for the vertical profile of wind and source areas Boundary Layer Meteorology 164 183–213 doi: [10.1007/s10546-017-0248-z https://link.springer.com/article/10.1007/s10546-017-0248-z]