Australia: The Land Where Time Began

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Global Drought Changes in the 21st Century – Magnitude and Causes Under a Low-Moderate Emissions Scenario

According to Zhao & Dai in the 21st century drying over land is expected to increase as a result of atmospheric demand for moisture and it is expected that the number of dry days will increase. In this study Zhao & Dai investigated the magnitude and key drivers of this drying by the use of model simulations under a low-moderate scenario, RCP4.5. The self-calibrated Palmer drought severity index with the Penman-Monteith potential evapotranspiration (PET) (sc_PDSI_pm), top 10-cm soil moisture (SM), and runoff (R) from 14 models are analysed. It has to be found that the change patterns are comparable while the magnitude differs among these measurers of drought. It has been suggested that the frequency of the SM-based moderate (severe) agricultural drought could possibly increase by 50-100 % (100%-200%) in a relative sense by the 2090s over most of the Americas, Europe, and southern Africa and parts of East and West Asia as well as Australia. In spite of increases in the mean frequency of runoff-based hydrological drought could also increase by 10%-50% over most land areas. The probability density functions (PDFs) flatten, which enhances the increases of drought induced primarily by decreases in the mean. The SM change is contributed to by precipitation (P) and evapotranspiration (E) changes; whereas sc_PDSI_pm decreases are the result of PET increases of 10%-20% with contributions from decreased P over subtropical areas. Most of the PET increase is explained by rising temperatures and vapour deficits, which in turn explains most of the E increases over Asia and northern North America while decreased SM leads to lower E over the rest of the world. There are radiation and wind speed changes that have only small effects on the future PET and drought. On a global scale runoff ratio changes little while there are increases in P, E and R of about 4%-5% in the 21st century.

Sources & Further reading

  1. Zhao, T. and A. Dai (2015). "The Magnitude and Causes of Global Drought Changes in the Twenty-First Century under a Low–Moderate Emissions Scenario." Journal of Climate 28(11): 4490-4512.


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