Abstract
An extreme drought event is usually a long-term process with different stages. Although it is well known that extreme droughts that have occurred frequently in recent years can substantially affect vegetation growth, few studies have revealed the characteristics of vegetation responses for different stages of an extreme drought event. Especially, studies should address when the vegetation growth was disturbed and how it recovered through an extreme drought event. In this study, we used the Normalized Difference Vegetation Index (NDVI) and Palmer Drought Severity Index (PDSI) to evaluate the response of vegetation to different stages of a severe drought event during 2009–2010 throughout Southwestern China. The PDSI time series indicated that the drought can be divided into three stages, including an initial stage represented by moderate drought (S1), a middle stage represented by continual severe drought (S2), and a final recovery stage (S3). The results revealed that the drought during the initial stage inhibited the growth of grassland and woody savanna, however, forest growth did not decrease during the first stage of droughts, and there was even a trend towards higher NDVI values. The continual severe drought in the middle stage inhibited growth for all vegetation types, and the woody savanna was affected most severely. In the final stage, all vegetation types underwent recovery, including the grassland that had endured the most severe drought. This study provides observational evidence and reveals that the responses of forest to the extreme drought are different from grassland and woody savanna in the different drought stages.
Highlights
Drought is considered to be a dry spell relative to normal local conditions [1]
The Normalized Difference Vegetation Index (NDVI) data used in this research were from the MODIS vegetation indices product (MOD13A3), which were produced from surface reflectance from which atmospheric effects had been removed [39,40]
Based on the Palmer Drought Severity Index (PDSI) values in the study area, we can separate the drought in the area into three drought stages according to the PDSI values in Table 1: initial stage, middle stage, and final stage, according to the severity degree
Summary
Drought is considered to be a dry spell relative to normal local conditions [1]. Drought can be classified into four types: meteorological, agricultural, hydrological, and socio-economic [2]. The first three types are related to physical phenomena, while the last links drought to the supply and demand of social-economic systems. Increases in the frequency or intensity of severe droughts have been detected over the last several decades, worldwide, and in some cases have been attributed to global climate change [3,4,5]. Extreme drought is a major environmental stress that affects the growth and development of vegetation, subsequently affects the energy balance on the earth’s surface and provides invaluable ecosystem services [6]. It is quite important to monitor and assess the potential impacts of droughts on vegetation response [7,8]
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