Paper Reviewed
Damberg, L. and AghaKouchak, A. 2014. Global trends and patterns of drought from space. Theoretical and Applied Climatology 117: 441-448.

Damberg and AghaKouchak (2014) note that "numerous studies argue that the Earth's climate is changing rapidly, especially during the second half of the twentieth century," citing Trenberth (2001) as a prime example of this point of view, as well as Trenberth (1999) as an example of this viewpoint as it applies to the planet's hydrologic cycle. Not convinced of the extreme nature of these contentions, however, they decided to analyze "changes in areas under droughts over the past three decades." However, they say that "unlike most previous global-scale studies that have been based on climate models," their study was "based on satellite gauge-adjusted precipitation observations." So what did the two U.S. researchers thereby learn?

As they write near the end of their paper, "several areas, such as the southwestern United States, Texas and the Gulf of Mexico region, parts of the Amazon, the Horn of Africa, northern India, and parts of the Mediterranean region, are among areas showing significant drying trends over the past three decades." On the other hand, they say that "central Africa, Thailand, Taiwan, Central America, northern Australia, and parts of eastern Europe show a wetting trend during the same time span." And, last of all, they report that a Mann-Kendall test of the satellite data reveal that "the area of global land under drought conditions does not show a significant trend over the past three decades."

In further commenting on what they learned, Damberg and AghaKouchak state that the results of their satellite-based study "disagree with several model-based studies (e.g., Dai, 2012) that indicate droughts have been increasing over land." However, as they state in the concluding paragraph of their paper, their findings concur with those of several observation-based studies, such as those of Sheffield et al. (2012).

References
Dai, A. 2012. Increasing drought under global warming in observations and models. Nature Climate Change 2: 52-58.

Sheffield, J., Wood, E. and Roderick, M. 2012. Little change in global drought over the past 60 years. Nature 491: 435-438.

Trenberth, K. 1999. Conceptual framework for changes of extremes of the hydrological cycle with climate change. Climatic Change 42: 327-339.

Trenberth, K. 2001. Climate variability and global warming. Science 293: 48-49.