Population movements around the Chinese New Year （CNY）, which are much larger in recent years than before, are the largest annual human migration in the world. However, it is still largely unknown how or to what extent such mass human migration affects urban climate. Here, we investigate the role of mass human migration in influencing Beijing＇s urban heat island （UHI） during the CNY holiday for the period of 2004-2013. We find that the UHI effects expressed as daily mean （ATmean）, maximum （ATmax）, and minimum （ATmin） temperature differences between urban and rural areas show a weakening trend during the CNY week relative to the background period （4 weeks including 2-3 weeks before and 2-3 weeks after the CNY week）. In particular, large reductions occurred during the CNY week for the period of 2009-2013, when nearly half of population left the city before the CNY holiday. △Tmean, △Tmax, and △Tmin averaged over the period of 2009-2013 during the CNY week were 0.64, 0.45, and 0.83 ℃ lower than during the background period, representing relative reductions of 35 %, 66 %, and 27 %, respectively. Our findings highlight the important role of modem mass human migration for urban climate based on a case study in Beijing.
Variations in surface air temperature and precipitation are closely associated because of their thermodynamic relations. The climate shift in the late 1970s and associated changes in precipitation over East Asia have been well reported. However, how the covariability of surface air temperature and precipitation responds to the climate shift is not yet well understood. We used the observed mean（Tmean）, daily maximum（Tmax）, and minimum（Tmin） surface air temperatures and precipitation during the period of 1953–2000 to explore this issue. Results show that the covariability between Tmean and precipitation experienced remarkable changes over certain areas of East Asia after the climate shift with evident seasonal dependencies. In winter, after the climate shift significantly negative correlations occupied more areas over Mongolia and China. By contrast, in summer after the climate shift significantly negative correlations which existed over almost entire East Asia during the pre-shift period were mostly weakened with the exception of enhanced correlations over some small isolated areas. Changes in the covariability of Tmax and precipitation showed a similar spatial pattern to that of the Tmean, whereas the Tmin-precipitation covariability did not. In winter, after the climate shift positive correlations between Tmin and precipitation over southern China were largely weakened, while the areas with significantly negative correlations increased over Mongolia. In summer, changes in Tmin-precipitation covariability appeared to be a negative-positive-negative pattern from south to north over East Asia, with positive changes occurring in the Yangtze-Huai River valley and Korea and negative changes occurring over South China and Japan, and northern part of East Asia.
The urban heat island （UHI） represents one of the most significant human impacts on the earth system. In recent decades, the number of the tourists has a remarkable increase in China and also other regions of the globe. However, it is still unclear whether or to what extent the tourism can affect the UHI. Here, we investigate the role of the tourism for the UHI during the Chinese New Year （CNY） holiday based on a case study in tropical Sanya City, which attracts many tourists for celebrating the CNY and enjoying the warm climate during the holiday. We find that the UHI effects expressed as daily mean （ATmean）, maximum （ATmax）, and minimum （ATmin） surface air temperature differences between urban and nearby nonurban stations averaged over the period of 1995-2004 during the CNY week were 0.48 ℃ （39 %）, 0.66 ℃ （61%）, and 0.42 ℃ （26 %） higher than those averaged over the background period （8 weeks including 4 weeks before and 4 weeks after the CNY week）, respectively. These changes are all significant at the 99 % confidence level. Our findings highlight previously unidentified impact of the tourism on the UHI based on a case study in Sanya City, Hainan Province of China.
Droughts and floods are the two most costly climate disasters over China.However,our ability to predict droughts and floods is limited by poor understanding of the atmospheric response to long memory climate drivers such as sea surface temperature and soil moisture.In this study,we investigate soil moisture feedbacks on summer droughts and floods over eastern China for the1998 and 1999 cases using the Weather Research and Forecasting(WRF)model simulations.Soil moisture climatology,derived from a 20-year-long control run,is used to replace soil moisture evolution in uncoupled simulations for 1998 and 1999 summers.Eastern China experienced severe floods during the summer of 1998,while 1999 summer is characterized by a"southern flood and northern drought"pattern.The WRF model generally simulates relatively well the droughts and floods in the two summers.It is found that land-atmosphere coupling contributes substantially to both droughts and floods over northern China while it plays a relatively small role in precipitation anomalies over southern China.Our findings suggest that soil moisture memory help contribute skill to seasonal prediction of droughts and floods over northern China.
