Abstract
Grassland, as the primary vegetation on the Qinghai-Tibet Plateau, has been increasingly influenced by water availability due to climate change in last decades. Therefore, identifying the evolution of drought becomes crucial to the efficient management of grassland. However, it is not yet well understood as to the quantitative relationship between vegetation variations and drought at different time scales. Taking Qinghai Province as a case, the effects of meteorological drought on vegetation were investigated. Multi-scale Standardized Precipitation Evapotranspiration Index (SPEI) considering evapotranspiration variables was used to indicate drought, and time series Normal Difference Vegetation Index (NDVI) to indicate the vegetation response. The results showed that SPEI values at different time scales reflected a complex dry and wet variation in this region. On a seasonal scale, more droughts occurred in summer and autumn. In general, the NDVI presented a rising trend in the east and southwest part and a decreasing trend in the northwest part of Qinghai Province from 1998 to 2012. Hurst indexes of NDVI revealed that 69.2% of the total vegetation was positively persistent (64.1% of persistent improvement and 5.1% of persistent degradation). Significant correlations were found for most of the SPEI values and the one year lagged NDVI, indicating vegetation made a time-lag response to drought. In addition, one month lagged NDVI made an obvious response to SPEI values at annual and biennial scales. Further analysis showed that all multiscale SPEI values have positive relationships with the NDVI trend and corresponding grassland degradation. The study highlighted the response of vegetation to meteorological drought at different time scales, which is available to predict vegetation change and further help to improve the utilization efficiency of water resources in the study region.
Highlights
Drought is generally defined as “a period of abnormally dry weather long enough to cause a serious hydrological imbalance” [1]
The objectives of this study were to (1) investigate the frequency and intensity of drought in Qinghai Province based on Standardized Precipitation Evapotranspiration Index (SPEI) at different scales to study the spatio-temporal and multi-scale characteristics of drought in this region; (2) analyze the spatio-temporal characteristics and changing trend of vegetation based on Normal Difference Vegetation Index (NDVI) from 39 main meteorological stations in Qinghai Province, combining the Mann-Kendall method and Hurst index; and (3) explore the correlation between multiscale SPEI, NDVI with different time-lags, and NDVI trends, which provided the scientific basis for the efficient management and protection of vegetation
The values of SPEI 6 showed a relatively large fluctuation amplitude owing to the impact of temperature and RemotepSreencs.ip2i0t1a7t,io9,n1,3w29hich indicated that the semi-annual frequency of drought is high in Qinghai
Summary
Drought is generally defined as “a period of abnormally dry weather long enough to cause a serious hydrological imbalance” [1]. The SPEI retains the advantages of the PDSI, but it is suitable for making multi-spatial and multi-temporal scale comparisons. It takes into account both potential evapotranspiration (PET) and precipitation in determining the degree of drought [13,14]. Studies showed that the SPEI reaches higher correlation with crop yields than the SPI [9]. This index can capture the impact of temperatures on water demand, which makes it into a useful tool to monitor and evaluate the degree of drought. The relationship between low frequency drought and climate index in Beijing was identified by using a series of values of the SPEI [18]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call