The "Guidelines" for estimating wind speed variations in boundary-layer flo
w over hills and other terrain features as well as within internal boundary
layers downstream of changes in surface roughness were developed by Taylor
and Lee and Walmsley, Taylor and Salmon. We revisit the problem and propos
e new formulations based on results of our MSFD and NLMSFD calculations of
flow over hills. The effects of surface roughness and non-linearity on frac
tional speed-up are incorporated. Comparisons with experimental data are di
scussed. (C) 2000 Elsevier Science Ltd. All rights reserved.