Spatiotemporal Variability of Surface Wind Speed during 1961-2017 in the Jing-Jin-Ji Region,China

Wind speed variations are influenced by both natural climate and human activities.It is important to understand the spatial and temporal distributions of wind speed and to analyze the cause of its changes.In this study,data from 26 meteorological stations in the Jing-Jin-Ji region of North China from 1961 to 2017 are analyzed by using the Mann-Kendall(MK)test.Over the study period,wind speed first decreased by−0.028 m s^-1 yr^-1(p<0.01)in 1961^-1991,and then increased by 0.002 m s^-1 yr^-1(p<0.05)in 1992-2017.Wind speed was the highest in spring(2.98 m s^-1),followed by winter,summer,and autumn.The largest wind speed changes for 1961-1991 and 1992-2017 occurred in winter(−0.0392 and 0.0065 m s^-1 yr^-1,respectively);these values represented 36%and 58%of the annual wind speed changes.More than 90.4%of the wind speed was concentrated in the range of 1-5 m s^-1,according to the variation in the number of days with wind speed of different grades.Specifically,the decrease in wind speed in 1961^-1991 was due to the decrease in days with wind speed of 3-5 m s^-1,while the increase in wind speed in 1992-2017 was mainly due to the increase in days with wind speed of 2-4 m s^-1.In terms of driving factors,variations in wind speed were closely correlated with temperature and atmospheric pressure,whereas elevation and underlying surface also influenced these changes.

On the Increased Precipitation Recycling by Large-Scale Irrigation over the Haihe Plain

Irrigation not only plays an important role in global food security,but it also affects aspects of the regional climate,including precipitation.In this study,we proposed a simple and convenient method to quantify the contribution of large-scale irrigation to precipitation by distinguishing the amount of evaporation generated by irrigation from local evaporation based on the precipitation recycling method.A case study was presented to show the increased precipitation recycling ratio and the contribution of irrigation to precipitation during the main irrigation period in the Haihe Plain from 1961 to 2016.We found that the average precipitation recycling rates in the Haihe Plain are 8.32%,9.74%,and 10.36%in April,May,and June,respectively.The contribution rates of irrigation to precipitation in the Haihe Plain are 3.76%,5.12%,and 2.29%in April,May,and June,respectively.The total contribution of irrigation to precipitation during the main irrigation period is 3.77 mm;the respective contributions in April,May,and June are 0.72,1.70,and 1.35 mm.The contribution of irrigation to local precipitation is relatively small as the inflow of atmospheric moisture during the irrigation period is still the main factor affecting local precipitation.Nevertheless,this part of the precipitation during the irrigation period alleviates the water shortage in the Haihe Plain to some extent.