Droughts will become the 'new normal' in a quarter of the world by 2050 - including parts of the Mediterranean - according to new research. Global warming will increase the intensity and frequency in many regions, say scientists.
It will reduce water supplies - impacting agriculture and energy systems. Current management strategies may be insufficient, warns the international research team.
By the middle of the century, increases are statistically significant in 25 and 28 per cent of land under low and high greenhouse gas emissions, respectively. Specific areas show substantial increases of more than double the current rate.
Under both scenarios, so-called hotspots include the Mediterranean, southern and central South America and Australia.
Lead author Professor Yusuke Satoh, of the Korea Advanced Institute of Science & Technology, Daejeon, said: "Some regions exhibit steady increases in drought frequency. The projected increases are highly likely by the middle of this century compared to the historical period. Drought conditions will become more frequent, thereby creating a new normal."
The study in Nature Communications estimates periods in which droughts will shift to an "unprecedented" state. It evaluated changes for 59 global subcontinental regions until the end of the 21st Century.
Co-author Dr Tokuta Yokohata, of the National Institute for Environmental Studies (NIES), Tsukuba, Ibaraki, said: "Regarding precipitation and temperature, preceding studies report the timing at which the impact of climate change emerges. However, no study had successfully estimated the timing in terms of drought focusing on river discharge at a global scale.
"A temporal evaluation about future drought conditions in comparison to our historical experiences is essential to take appropriate climate change strategies, especially for climate adaptations, in the long term and in time."
Dr Yokohata and colleagues calculated the time of first emergence (TFE) - onset beyond the largest historical variability from 1865 to 2005. For instance, TFE5 indicates the regional drought frequency remains higher than the maximum value during the period for more than five years.
The scientists analysed river discharge simulation data derived from combinations of five global hydrological and four climate model projections. They also considered low and high greenhouse gas concentrations scenarios to work out the consequences of society’s decisions on the climate mitigation pathway.
Prof Yusuke Satoh said: "The projected impacts of warming show significant regional disparities in their intensity and the pace of their growth over time."
The study, published in the journal Nature Communications, detects TFE5 in 18 out of 59 regions by 2100 under high greenhouse gas concentrations. Even for a low greenhouse gas concentration scenario that assumes stringent mitigation strategies, 11 regions are projected to reach TFE5 within the century.
Co author Dr Hideo Shiogama, also from NIES, said: "Under high and low greenhouse gas concentration scenarios, respectively, seven and five regions show TFE5 in approximately 30 years, which is before or around an expected climate stabilisation in case of the low climate change scenario. Importantly, the results imply unavoidable unprecedented states in these regions."
In particular, southwestern South America and the Mediterranean regions consistently show early and robust TFE5 in both scenarios. On the other hand, the differences between greenhouse gas concentration scenarios indicate our choice of mitigation strategies produces a noticeable difference in the timing and robustness of the projection.
Prof Satoh added: "Appropriate and feasible climate mitigation and adaptation plans are essential for overcoming the expected extraordinarily severe dry conditions. Particularly regarding adaptation, it is crucial to improve our preparedness in the given time horizon before unprecedented drought conditions emerge."
