An Application of Wind Rose, Storm Rose, and Sand Rose in the Analysis of Wind Erosion and Determining the Direction of Moving Sands (Case Study Area: Yazd - Ardakan Basin

Yazd -Ardakan basin is one of the areas exposed to wind erosion and dust storms. This basin is
located in the center of Iran, northwest of Yazd. Since analysis of anemometric data has a special
importance for evaluating and distinguishing erosive storm winds, so in this survey, anemometric data
ofa duration period of about 20 years (1982-2000) from synoptic station ofYazd have been taken and
analyzed through different methods. Results obtained from analysis of data through "WRPLOT"(Wind
rose plot software) indicated that the direction of prevailing winds in Yazd basin is generally from
west to north-west (W-NW). The southeast (SE) direction comes next in level. Among the
anemometric data employed in this research, the frequency percentage of calm winds with a velocity
of less than one knot (0.54meter per second) was estimated to be 47.6%. Results obtained, after
determining and drawing storm rose, indicate that based on minimum threshold velocity (about 6.5 mls
on the fine grain plain), dust storm winds in yazd plain have been generally directed northwest. The
other west sector winds, including those towards west and south west direction, were almost of the
same nature, while southeast winds played a less important role. Based on storm rose, frequency of
.wind of less velocity less than 6.5 mls (threshold velocity) is 97% as observed from yazd station. So
the frequency of dust stormy winds is reduced to 3%. The obtained results indicate that the NW, SW
and W winds have the most drift potential (DP) respectively while other winds are of less power for
carrying sands. The resultant drift direction (RDD), has been determined as from southwest-west
(SWW) towards northeast-east (NEE). The angular direction in this respect estimated as is 77 degrees,
measured clockwise from the geographical north.