There exists lake-land breeze that wind blowing onshore from lake to land during the day and offshore in the evening around lake area, due to differences in air pressure mainly caused by different heat capacities between lake and land. Generally speaking, the closer to the lake, the more remarkable the lake climate effects. For studying the lake climate effects, it is not only important for understanding the characteristics of local climate and atmospheric circulation, but also helpful for analyzing and forecasting meso-and micro-scale weather processes. Miyun Reservoir (MYR), which located at 15 km north of Miyun District of Beijing city, is the largest artificial lake in North China. Up to now, there are seldom reports on the influence of MYR on local weather and climate. Based on hourly observation data obtained by 77 automatic weather stations surrounding MYR from 2011 to 2015, local climate effects of MYR were explored and discussed in the present work. The results showed that: 1) comparing with peripheral plains, climate effects of MYR were characterized by the facts that lower air temperature, higher humidity, slightly weaker wind speed and larger rainfall. As far as regional climate was concerned, the MYR had a modulate effect on the local climate and the spatial extent of the effect is about 10 km. The closer to the MYR, the more notable the MYR climate effects. 2) The MYR climate effects were mainly occurred in the summer, especially for temperature and rainfall. In detail, averaged air temperature was lower of 0.96℃ and averaged rainfall amount was higher of 13.3% in MYR than in the adjacent plains, where has the same elevation with MYR away from 10km. In addition, there were significant differences in diurnal variations of meteorological factors between the south and north regions of the MYR. 3) Excluding the impact of the large-scale background wind field, local wind presented the characteristics of monthly variation, i.e., mountain breeze was dominant from April to September, especially in summer; while in other months, valley breeze was more prevailing, especially in the wintertime. In general, annual averaged local wind speed was about 0.14 m/s in the east-west direction, which was slightly larger than that of 0.10 m/s in the north-south direction around the MYR. 4) In summer, there existed significant differences in wind vectors at the south and north regions of the MYR, due to the influence of local circulation. In most time of the whole day, component anomalies were usually in the same phase, while component anomalies presented out of phase at the south and north regions of the MYR. Lake-land breeze and mountain-valley breeze had the same/opposite directions at the north/south regions of the MYR, and thus these correspondingly formed the overlaying/counteractive effects. Due to lake-land differences in heat capacities and topography effects, lake-land breeze and mountain-valley breeze in the areas around MYR usually existed at the same time, which mainly caused the differences in seasonal and diurnal variations of meteorological elements at different locations around the MYR region.
