Sensitivity of planetary boundary layer atmosphere to historical and future changes of land use/land cover, vegetation fraction, and soil moisture in Western Kentucky, USA

Abstract

Changes in land use land cover (LULCC), vegetation fraction (FV), and soil moisture affects land surface atmosphere interactions, characteristics of planetary boundary layer (PBL), and near surface atmospheric moisture content. Previous studies have investigated impacts of LULC, FV, and soil moisture changes on atmosphere separately. The present study investigates the combined impacts of changes in LULC, FV, and soil moisture, on PBL atmosphere and near surface atmospheric moisture content. The study is set in western region of Kentucky, USA. We have used the Noah land surface scheme and MM5 model for this purpose. The study used two nested domains. The current land use land cover of the inner domain was changed to grass, forest, and bare soil to represent historical changes and potential near future modifications. Subsequently, FV and soil moisture were systematically changed for each of the land uses. The simulations have found that changes of current land use to grass within the inner domain increases latent heat flux, dew point temperature, relative humidity, and equivalent potential temperature. It was found that height of the PBL was reduced and development of circulation cells was visible along land use land cover discontinuity. Changes in horizontal and vertical wind field were also reported. FV changes for grass further magnified these impacts. For example, decrease or increase in FV has decreased or increased latent heat flux. Similar response of other PBL parameters could be found for changes in FV along with LULC. It was also found that if we replaced forest with lower FV by grass with higher FV, the impacts could cancel each other. Changes to forest and bare soil land use types and lower FV for forest also produced generally similar types of responses. Soil moisture changes, particularly drying, further impacted these responses. This study finds that increase in FV counteracts impacts of soil moisture reduction up to a level. Overall, grass produced moister PBL and lowered the height of PBL and LCL. It is interesting to note that during nighttime the impacts of LULC, FV and soil moisture changes were diminished. These changes not only modified meso-scale wind fields but also potential for convective development. It was concluded that similar experiments needed to be undertaken for convectively conducive environments to better understand the combined impacts of changes in LULC, FV and soil moisture.