Abstract
In the context of climate change, the intensity, frequency, and duration of drought events have increased significantly, resulting in a profound impact on both natural ecosystems and socio-economic systems. In arid and semi-arid regions, precipitation is the main limiting factor for vegetation growth, and the ecosystems are very sensitive to climate change. Over the past 10 years, the Namibian government has declared national emergencies in 2013, 2016, and 2019 due to extreme drought events. The continued extreme drought has posed serious threat to the country’s food security. Accurately monitoring the continuous drought events in Namibia and assessing their impact on the ecosystem is essential for drought risk management in the region. Based on long-term satellite observation of vegetation index and precipitation, we have evaluated the spatiotemporal dynamics of the three drought events, the vegetation–precipitation relationship across biomes, and the impact of continuous drought events on regional ecosystems. The results suggest that: (1) According to affected area and severity, the drought in 2019 was the most severe one, followed by the drought in 2013; the 2015–2016 drought spread over smaller spatial area, although it continued for two years; (2) Both the accumulated NDVI and precipitation in the growing season in Namibia increased from 2001 to 2010 while showing a significant decreasing trend during 2011–2020; (3) In Namibia, there is a significant correlation between the current season’s accumulated precipitation and the current season’s accumulated NDVI (r = 0.90, p < 0.01). The current season’s accumulated precipitation is also well correlated with the next season’s accumulated NDVI (r = 0.87, p < 0.01), and the correlation between the current season’s accumulated precipitation and the next season’s accumulated NDVI in a wet year is even stronger (r = 0.96, p < 0.01). This indicates that part of the precipitation in the current season may be stored in the soil for the next season’s plant growth, which is more obvious in the northern plains with deep-rooted woody plants; (4) In 2013, the drought event suddenly changed from a long-term relatively humid state to an extremely dry state. During the ecological recovery stage, the NDVI during the growing season could not return to the state before the drought, causing irreversible damage to the Namibian ecosystem. In summary, the continuous extreme drought events during the last decade have caused profound impacts on the regional ecosystem. Much more attention should be paid to whether the extreme drought events will continue into the next decade and how the ecosystem can sustain a new equilibrium under a warmer and drier climate.
Highlights
Drought is a creeping phenomenon caused by prolonged water shortage in which the water supply cannot fulfill the requirements of water demand from different sectors, which may result in profound impacts on the ecosystem, agriculture, and livelihoods [1]
Between 2001 and 2020, Namibia experienced obvious uptrends in both cumulative precipitation and cumulative NDVI in the first ten years, while the cumulative precipitation and cumulative NDVI show a downtrend in the second decade (Figure 2)
The 2018/2019 drought in Namibia is the worst in 90 years, which is much more serious the 2012/2013 drought that is reported as the worst in 30 years [18]. These reports had been confirmed by our results that the dry period captured by Standardized Vegetation Index (SVI) and Standardized Precipitation Index (SPI) of 2018/2019 season are more intensive in terms of both the duration and the spatial extent compared to that of the 2012/2013 season
Summary
Drought is a creeping phenomenon caused by prolonged water shortage in which the water supply cannot fulfill the requirements of water demand from different sectors, which may result in profound impacts on the ecosystem, agriculture, and livelihoods [1]. Drought has long been the world’s costliest natural disaster, and most countries experience serious threat from drought. About 40 million people in southern Africa were affected by drought in the early to mid-1980s, with more than 500,000 deaths [2]. The 1988 drought in the United States caused nearly USD 40 billion in damage, and was the worst natural disaster in U.S history [3]. The 1991–1992 drought in southern Africa affected about 20 million people and caused a shortage of more than 6.7 million tons of grain supplies [2]
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