Monthly and annually wind speed data from nine meteorological stations over Heihe River Basin

observed by the China Meteorological Administration from 1960to 2009

were used to analyze the spatial and temporal variability of average wind speed.Mann-Kendall methods

inverse distance weighted(IDW)

and correlation analysis were employed.The result showed a decreasing trend in annual average wind speed during the past 50years

and theβvalue was-0.01.Decreasing tendency in wind speed occurred in four seasons(spring

summer

autumn and winter)as well

and theβvalues were-0.012

-0.011

-0.007 and-0.008

respectively.Interdecadal change of wind speed in the 1960sand 1970sshowed positive anomalies

while a negative anomaly was showed since 1980s.The intra-annual variation of wind speed appeared as partial bimodal.Meanwhile

these two peaks existed in April and November

respectively

and the first peak was much larger than the second one.Spatially

slightly increasing trend was showed in the upper reaches with an average rate of 0.01m/s

while decreasing trend were showed in the middle and lower reaches with an average rate of 0.005and0.029m/s

respectively.At the same time

the trends in different regions varied significantly in four seasons.Abrupt change in annual wind speed occurred in 1985

while abrupt change in four different seasons occurred in 1986

1984

1983and 1985

respectively.Decreasing trend in annual and spring wind speed was correlated with average temperature

average maximum temperature

average minimum temperature and potential evapotranspiration

but this correlation declined in summer and autumn.Only potential evapotranspiration in winter affected wind speed significantly at the 0.01level.All this indicated that

decreased wind speeds was the main factor that leading to the decrease of potential evapotranspiration in Heihe River Basin in recent 50years.