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.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |