A Study of Climate Change in Temperature, Cloud, Sunshine Duration and Evaporation in Beijing

Temperature, cloud, sunshine duration and evaporation are key factors of climate system. The increase rate (IR) of annual temperature is 0.77℃/100a(1870-2003) in Beijing. The IR in winter is 1.52℃/100a(1870-2003). The IR of annual temperature range is –0.38℃/10a(1940-2003). The trends of total cloud cover and sunshine duration are all decreasing (1951-2003), out-of-phase pattern is obvious. The sunshine duration (unit: hour) increase rate is -60.9h/10a (1951-2003). The IR of evaporation(unit:mm) is -0.015mm/10a. In recent years the precipitation in Beijing decreased enormously; cloud should be decrease. However sunshine duration and evaporation are decreasing too.

The correlation coefficients (CC) were calculated. The CC between cloud and sunshine is –0.73 in winter and –0.56 in summer, . The CC between annual ，summer mean temperature(Tm) and mean maximum temperature (Tmax) and cloud are higher. In summer the CC of Tmax~cloud is –0.78, the CC of Tm~cloud is –0.72. The CC between annual mean temperature(Tm), annual mean maximum temperature (Tmax) and cloud are –0.59 and -0.65 respectively. All CC between annual ,summer mean minimum temperature and cloud are near –0.40. The CC of Tm~eva(evaporation) and Tmin~Eva are not good. The CC of Tmax~eva is 0.77 in summer. All CC of Cloud~eva are minus, the winter's CC(–0.62) is larger. The CC of Sunshine~eva are 0.65, 0.61 and 0.60 respectively in spring, summer and autumn. The Tmax~cloud's CC is less. In daytime when the cloud is more, the Tmax is lower; but if in the night the cloud is more, the Tmin is higher in summer. The Tmin- cloud's CC and Tmin-eva's CC are low.

The relationship between temperature and sunshine duration in Beijing is not significant. However the CC between temperature range and sunshine (Trange-sunshine) in summer is 0.79, the CC between annual temperature range and sunshine (Trange-sunshine) is 0.78. The CC of Trange~ eva are 0.76 and 0.66 in summer and in spring respectively. As all day has fine visibility in summer., the Tmax is higher and the Tmin is lesser, then the sunshine duration is longer ,the evaporation is larger. So the relationship between temperature range and sunshine duration, evaporation are significant.

Key Words: total cloud cover sunshine duration evaporation