Comparison of land-atmosphere interaction at different surface types in the mid-to lower reaches of the Yangtze River valley

Abstract

The mid-to lower reaches of the Yangtze River valley are located within the typical East Asian monsoon zone. Rapid urbanization, industrialization, and development of agriculture have led to fast and complicated land use and land cover change in this region. To investigate land-atmosphere interaction in this region where human activities and monsoon climate have considerable interaction with each other, micrometeorological elements over four sites with different surface types around Nanjing, including urban surface at Dangxiao (hereafter DX-urban), suburban surface at Xianling (XL-suburb), and grassland and farmland at Lishui County (LS-grass and LS-crop), are analyzed and their differences are revealed. The impacts of surface parameters of different surface types on the radiation budget and land surface-atmosphere heat, water, and mass exchanges are investigated and compared. The results indicate the following. (1) The largest differences in daily average surface air temperature (Ta) surface skin temperature (Ts), and relative humidity (RH), which are found during the dry periods between DX-urban and LS-crop, can be up to 3.21°C, 7.26°C, and 22.79 %, respectively. The diurnal ranges of the above three elements are the smallest at DX-urban and the largest at LS-grass, XL-suburb, and LS-crop. (2) Differences in radiative fluxes are mainly reflected in upward shortwave radiation (USR) that is related to surface albedo and upward longwave radiation (ULR) that is related to Ts. When comparing four sites, it can be found that both the smallest USR and the largest ULR occur at the DX-urban site. The diurnal variation in ULR is same as that of Ts at all four sites. (3) The differences in daily average sensible heat (H) and latent heat (LE) between DX-urban and LS-crop are larger than 45 and 95Wm-2, respectively. The proportion of latent heat flux in the net radiation (LE/Rn) keeps increasing with the change in season from the spring to summer. (4) Human activities have obvious effects on microclimate. The urban heat island (UHI) effect results in a Ta2°C higher at the urban site than other sites in the nighttime. At the crop site, LE is dominant due to irrigation, and negative H is observed since evaporation cooling leads to low Ts. Although Ts is higher at XL-suburb than that at LS-grass, there is no large difference in Ta between the two sites due to the distinct effects of the planted forest.