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Update On Global Drought Patterns (IPCC Take Note)

We are sure you have heard that global warming is causing more frequent and intense droughts throughout the world. Right? The claim is easy to make – higher temperatures increase evaporation rates, soil moisture is depleted, and drought conditions result.

Indeed the Technical Summary of the most recent IPCC assessment includes “More intense and longer droughts have been observed over wider areas, particularly in the tropics and subtropics since the 1970s. While there are many different measures of drought, many studies use precipitation changes together with temperature. Increased drying due to higher temperatures and decreased land precipitation have contributed to these changes”. Further, they write “Although precipitation has increased in many areas of the globe, the area under drought has also increased.

Drought duration and intensity has also increased. While regional droughts have occurred in the past, the widespread spatial extent of current droughts is broadly consistent with expected changes in the hydrologic cycle under warming. Water vapour increases with increasing global temperature, due to increased evaporation where surface moisture is available, and this tends to increase precipitation. However, increased continental temperatures are expected to lead to greater evaporation and drying, which is particularly important in dry regions where surface moisture is limited.”

The bottom line in the table below from the IPCC’s Technical Summary leaves little doubt that the IPCC thinks that droughts have become more frequent, they have been caused in some part by humans, and they will become more frequent in the decades to come.

A major article on global-scale drought has appeared recently in the Journal of Climate by drought experts from Princeton University and the University of Washington; the work was supported by the U.S. Department of Energy the National Oceanic and Atmospheric Administration. We saw an interesting sentence in their abstract as Sheffield et al. wrote “Globally, the mid-1950s showed the highest drought activity and the mid-1970s to mid-1980s the lowest activity.” That does not seem consistent with the story coming from the IPCC.

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