# The Observed Impacts of Wind Farms on Local Vegetation Growth in Northern China
## 1 Introduction  
Wind turbines can modify the surface fluxes of momentum, sensible heat, water vapor, and carbon dioxide by enhancing turbulence, increasing surface roughness, and changing the stability of the atmospheric boundary layer (ABL) [1; 2]. As reported in previous studies, the large establishment of wind farms (WFs) influence the local climate [3; 4]. Based on field campaigns or model simulations, these studies found that large-scale WFs could alter local temperature, reduce precipitation and even mitigate extreme weather [5; 6; 7]. However, due to lack of sufficient observations for validationand the simple parameterization of WFs, the simulated results have significant uncertainties [4; 8]. In addition, field campaigns usually cover a short time span and include only a few measurements, limiting the representativeness of the results. Therefore, due to the limitations of climate models and field campaigns, an increasing number of studies are using remote-sensing data to investigate the effects of WFs on regional climate [9; 10; 11; 12; 13]. Remote sensing data provides global spatial sampling information with high temporal and spatial resolution, and can thus be used to analyze the effects of large-scale WFs. [PERSON] et al. analyzed the effects of WFs on land surface temperature (LST) in Texas and found a nighttime warming effect of 0.31 \({}^{\circ}\)C-0.70 \({}^{\circ}\)C [9; 10]. [PERSON] et al. analyzed the impacts of three WFs in Northern Illinois and provided further observational evidence of a warming effect at night caused by WFs [14].  
Since wind farms can affect local climate [9; 12; 15], changes in local climate, such as temperature and precipitation, may affect local vegetation growth and productivity over WFs [16]. Since the beginning of the 21 st century, China has built enormous wind turbines. In 2010, wind energy capacity in China reached 42.3 GW, exceeding the 40.3 GW capacity of the United States, and ranking first in the world. In 2015, newly-installed wind energy capacity in China amounted to 30.8 GW, accounting for 48.9% of newly-installed capacity worldwide [17]. Within this newly installed wind energy capacity, wind energy development has been fastest in Hebei province and Inner Mongolia [18; 19]. However, the effects of the rapid development of WFs on local climate and vegetation growth in China have not yet been thoroughly evaluated.  
In this paper, we use the moderate-resolution imaging spectroradiometer (MODIS) vegetation index (leaf area index, LAI; normalized difference vegetation index, NDVI; and enhanced vegetation index, EVI) data, MODIS productivity data (gross primary production, GPP; net primary production, NPP), and other auxiliary data (temperature, soil moisture, evapotranspiration, albedo, and wind) to analyze the effects of WFs on summer (June-August, JJA) vegetation growth in the Bashang area of Northern China. The specific objectives of this paper are as follows: (1) to identify whether the WFs in Bashang can influence the summer vegetation growing status and productivity and (2) to further explore the possible processes for the effects of WFs on local vegetation growth.