Spatio-temporal pattern of impacts of vegetation on controlling sand-dust weather in Beijing-Tianjin Sandstorm Source Control Project

Abstract: Sand-dust weather is a weather phenomenon where wind and dust are rolled into the air by strong winds making the air cloudy and visibility reduction. In meteorology, it is divided into three levels of dust, sand and sandstorms according to the intensity of sand-dust weather. Vegetation plays a significant role on controlling the sand-dust weather occurrence. In the past decades, sand-dust weather has a serious impact on people's lives and the socioeconomic development in cities of Beijing and Tianjin, and Hebei province. In order to improve the air quality in Beijing and Tianjin and the surrounding areas, and mitigate the hazards of wind and sand, China launched the Beijing-Tianjin Sandstorm Source Control Project in 2002. Previous studies showed that since implementation of the project, the overall ecological conditions in the region have been improved, and desertification lands and dust weather have been significantly reduced. However, how the vegetation related to the sandstorm weather in the Beijing-Tianjin Sandstorm Source Region (BTSSR) is still unclear. Therefore, we took BTSSR as the study area, which covers 138 counties in six administrative regions (i.e. province, autonomous regions or municipalities) in Beijing, Tianjin, Hebei, Shanxi, Inner Mongolia and Shaanxi Provinces. The data used in this study mainly included numbers of sand-dust weather days (SWD) from China Meteorological Data Service Center (http://data.cma.cn/) and SPOT/VGT Normalized Difference Vegetation Index (NDVI) S10 data from Cold and Arid Regions Science Data Platform of Environmental and Ecological Science Data Center for West China (http://westdc.westgis.ac.cn/). We used the linear trend method to analyze the intra- and inter-annual patterns of sand-dust weather occurrence and vegetation dynamics from 2000 to 2013. The correlation analysis was utilized to explore the relationship between SWD and the monthly NDVI of concurrent/antecedent year. The spatiotemporal pattern of impacts of the vegetation on sand-dust weather was further revealed. The results showed that SWD in BTSSR was high in the west and low in the east. The average SWD of BTSSR was up to 15 days in 2000. The SWD in BTSSR were mainly occurred in spring, which accounted for up to 75.5% of the total. The maximum SWD appeared in 2001, it lasted about 25 days and after that the number of days for SWD decreased significantly till 2013. The NDVI was high in the east and low in the west. The annual NDVI in BTSSR increased smoothly from 2000 to 2013. Correlation analysis showed that the SWD had a more significant correlation with NDVI in concurrent May (R2=0.55，P<0.01) and antecedent August (R2=0.50，P<0.01). The BTSSR was classified into four sub-regions based on the lag effects of vegetation on the SWD. We found that in 19.59% of the BTSSR, the concurrent SWD was significantly correlated with NDVI of the antecedent year, which was mainly located in the sandy zones with vegetation cover of desert grassland and deciduous broad-leaved forest. In the typical steppe such as eastern part and central of typical grassland, the SWD was mainly controlled by the vegetation in the concurrent year. Vegetation, regardless of whether it is alive or withered, they can effectively block the effect of strong winds on the exposed surface, and at the same time reduce wind speed by increasing surface roughness. The main inhibitory effect of dust weather was the remnants of vegetation and withered vegetation in the antecedent year, such as that in Erdos plateau and Horqin sandy. We suggested that in the future, targeted prevention and management measures based on the time-delay characteristics of vegetation impact on sand-dust weather need to be conducted. The results are of great significance to the development and management of vegetation construction in BTSSR.