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Increasing Drought Under Global Warming?

Reference
Dai, A. 2012. Increasing drought under global warming in observations and models. Nature Climate Change doi:10.1038/NCLIMATE1633.
There is a growing concern among many climate scientists about the potential for increasing world-wide droughts due to the warming of the Earth's climate, both in the present and in the future. In a new paper exploring this issue, Dai (2012) analyzes historical records of precipitation, streamflow and drought indices since about 1950. The paper further makes a comprehensive analysis of model-simulated soil moisture, drought indices and "precipitation - evaporation" differences to conclude that "observed global aridity changes up to 2010 (since 1950) are consistent with model predictions, which suggest severe and widespread droughts in the next 30-90 years over many land areas resulting from either decreased precipitation and/or increased evaporation"

More specifically, Dai analyzes coupled climate model simulations ( CMIP3- Coupled Model Inter-comparison Project phase 3 and new phase CMIP5) under increasing greenhouse gases, demonstrating how most climate models show decreases in soil-moisture content (in the top 10-cm layer) during the 21st century over most of the Americas, Europe, southern Africa, most of the Middle East, southeast Asia and Australia. Furthermore, because SST (Sea Surface Temperature) patterns largely influence land precipitation and drought, the author also conducts a maximum covariance analysis of SSTs and PDSI (Palmer Drought Severity Index) and documents spatial and temporal patterns to reinforce the conclusion about an increasing severity of future drought.

The interannual and decadal variability of dry and wet periods, either regionally or globally, has been a topic of extensive research by many scientists. A paper by the same author (Dai, 2012) discusses precipitation variability over the contiguous USA during 1920-2010 and documents large multi-decadal oscillations which appear to be linked to the Inter-decadal Pacific Oscillation (commonly identified as PDO-Pacific Decadal Oscillation). For the monsoonal climate of south Asia, another recent paper (Hsu Pang-chi et al., 2012) suggests there is a robust signal for increasing global monsoon area as well as precipitation amounts. Another recent study (e.g., Cherchi et al., 2011) also suggests an enhancement of global monsoon due to increased levels of CO2. And, a study by Mahajan et al. (2012) analyzes the statistical significance of heavy precipitation events over the contiguous USA in the context of model simulation (see Heavy Precipitation Over the US: Has it Increased as Some have Predicted it Should?). In view of these and several other modeling studies, which suggest "increasing precipitation in future in a warming world" Dai's conclusion about 'exacerbation of future droughts' appears contradictory and may need to be re-evaluated.

Additional Reference
Dai, A. 2012. The influence of the Inter-decadal Pacific Oscillation on US precipitation during 1923-2010. Climate Dynamics DOI 10.1007/s00382-012-1446-5.

Cherchi, A., Alessandri, A., Mesina, S. and Navara, A. 2011. Effects of increased CO2 levels on monsoons. Climate Dynamics 37: 83-101.

Hsu, P., Li, T., Luo, J.-J., Murakami, H., Kitoh, A. and Zhao, M. 2012. Increase of global monsoon area and precipitation under global warming: A robust signal? Geophysical Research Letters 39: L06701, doi:10.1029/2012GL051037.

Archived 25 September 2012