Global detection of aridification or increasing wetness in arid regions from 2001 to 2013
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Global detection of aridification or increasing wetness in arid regions from 2001 to 2013 Reiji Kimura1 Received: 29 February 2020 / Accepted: 18 May 2020 © Springer Nature B.V. 2020
Abstract Arid regions are highly vulnerable to climate change and human activity, and global warming in particular has the potential to increase the arid land area. One traditional way to evaluate the extent of climate change in dryland regions is to use the aridity index (AI), defined as the ratio of annual rainfall to annual potential evapotranspiration. However, the AI is a climatic index; it does not represent actual conditions of aridity in arid regions. In contrast, the satellite-based aridity index (SbAI), which is based on day/night land surface temperature changes, is considered to represent actual conditions of moisture availability. Arid regions during 2001–2013 were classified at global scale by comparing the SbAI with the AI, that is, within Turc space, which is based on the water balance concept. In addition, factors contributing to aridification or wetness changes detected in different global regions were examined by comparing the SbAI and AI result with the yearly maximum normalized difference vegetation index and past land use. As a result, dryland regions were newly classified into five zones. In the stable zone, land areas were classified into hyper-arid, arid, semi-arid, or dry sub-humid regions by both the SbAI and the AI. Areas in the transition zone toward dryness are moderately dry. Areas in the transition zone toward wetness include large river basins, oases, and wadis with little rainfall. In the moist zone, rainfed or irrigated farming is being successfully conducted. Many parts of the dry zone, however, are extremely dry. Keywords Aridity index · Desertification · Drylands · Land degradation · Remote sensing
1 Introduction Arid regions are highly vulnerable to climate change, particularly, global warming, because they are highly sensitive to drought, land degradation, and desertification (e.g., Kimura and Moriyama 2019a, b; Feng and Fu 2013; Huang et al. 2016). Moreover, drylands, which occupy about 40% of the Earth’s total land area, are likely to be faced with more and more extreme weather phenomena as global warming advances (IPCC 2013).
* Reiji Kimura rkimura@tottori‑u.ac.jp 1
Arid Land Research Center, Tottori University, Tottori 680‑0001, Japan
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Natural Hazards
Numerical simulations examining the effect of future global warming on aridification and dryland regions (Koutroulis 2019; Greve et al. 2017; Schlaepfer et al. 2017; Scheff and Frierson 2015; Feng and Fu 2013) have indicated that increases in CO2 and temperature and decreases in precipitation in dryland regions will trigger water shortages, drought, and further aridification. Knowledge of how anthropogenic climate change will affect the extent of global drylands is essential for water-resource and land-use management planning in such regions (Feng and Fu 2013). The United Nations Convention to Combat Desert
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