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Reliable predictions for monsoonal r...

May 11, 2016

Photo: MARUM, University of Bremen; M. Mohtadi
MARUM scientists provide an overview of current monsoon research

Reliable forecasting is crucial in reducing the possible catastrophic impacts of changes in monsoon patterns. Improving the prognoses at the regional scale is a great challenge in monsoon research. In a summary article appearing in the online issue of the professional journal Nature on 12 May 2016, scientists from MARUM, the Center for Marine Environmental Sciences at the University of Bremen, give an overview of the various mechanisms that can control changes in monsoon systems. They combine data from measurements and climate archives with the results of computer models.
Monsoons impact climate in the tropics and subtropics and influences regions in which, taken all together, more than two thirds of the world population live. Changes in the strength, duration or time of the monsoon precipitation often produce catastrophic consequences in the form of drought or flooding. Prognoses of the summer monsoon are thus of crucial importance for billions of people, although the precipitation is still difficult to predict.

“The problem is that changes in a monsoon system can be controlled by a variety of driving forces on very different time scales – ranging from months to hundreds of thousands of years. Each individual monsoon system reacts differently, however, to the same stimulus,” explains MARUM scientist Dr. Mahyar Mohtadi. The marine geologist is first author of an overview article that has recently appeared online in the professional journal Nature.

Together with his colleagues Dr. Matthias Prange and Dr. Stephan Steinke, Mohtadi takes the approach of identifying different causes for a monsoon, and investigating how these change or have changed through time. These include, for example, the tilt of the Earth’s axis, but also marine currents or the effect of greenhouse gases in the atmosphere. Every monsoon region reacts individually to these stimuli. If the ocean’s surface water warms due to global climate change, the result would be an increase in precipitation on land in the North African monsoon region. The same impetus in the Indian monsoon region, however, would result in a tendency for the clouds to release their rain over the sea, so that it would become drier on the land.

The Nature study incorporates results from over 1000 scientific publications on monsoon research from recent years, whereby the MARUM scientists have combined direct measurements and climate reconstruction data with results from computer models. They have come to the conclusion that the data from climate archives provide valuable insights into the regional dynamics of a monsoon system that can help researchers to better understand the internal feedback mechanisms. “These paleoclimate data provide clues to how a system has reacted in the past and how sensitively it has reacted to various driving forces. They can help monsoon researchers to improve the computer models and thus reduce uncertainty in their predictions,” says Mohtadi. The challenge in monsoon research, which can also be viewed as an opportunity, is the expansion of interdisciplinary research in this field.

Palaeoclimatic insights into forcing and response of monsoon rainfall
Mahyar Mohtadi, Matthias Prange & Stephan Steinke
Published online in Nature, 12 May 2016, doi:10.1038/nature17450

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Diagram: Significant components of a summer monsoon and its driving forces. Summer solar radiation warms the land faster than the ocean, producing monsoon winds that transport moisture from the sea to the land. PDO = Pacific Decadal Oscillation, temperature variation in the Pacific; AMO = Atlantic Multi-decadal Oscillation, circulation fluctuations in ocean currents in the North Atlantic; AMOC = Atlantic Meridional Overturning Circulation (Diagram: MARUM, University of Bremen; M. Mohtadi, M. Prange and S. Steinke)

Hong Kong harbor during the rainy period (Photo: Torsten Bierstedt)