The relevance of the residence time of water vapor in the atmosphere for the study of the effect of climate change on the global hydrological cycle

Nesta revisión, os e as autoras discuten a relevancia do tempo de residencia como un indicador clave de variacións importantes no ciclo hidrolóxico presente e futuro
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Professor Luis Gimeno heads the international team that prepared the work.

Four years ago was the international congress of the European Geophysical Union that took place in Ourense, organized by lecturers and researchers from the Ourense campus, Luis Gimeno and Raquel Nieto. In this congress practically all the leading scientists in the transport of moisture in the atmosphere participated and the need to work as a priority on the residence time of water vapor in the atmosphere became evident. “It is a fundamental component in the knowledge of the hydrological cycle, and it is an essential indicator of how the hydrological cycle is altered by dynamic and thermodynamic processes related to climate change,” explains the professor of the Department of Applied Physics of the UVigo Luis Gimeno, who along with Raquel Nieto leads the article. “The residence time of water vapor in the atmosphere” published today in the journal Nature Reviews Earth and Environment (NREE). “The researchers who participated in October 2016 in the international congress worked since then independently within their groups and after four years Nature decided that the topic is very relevant to climate change and invited us” clarifies the researcher of the EPhysLab CIM-UVigo group on the origin of the work, in which also participated researchers from the ETH (Polytechnic Institute of Zurich), the University of Illinois in the USA, the University of Costa Rica, the Technical University of DElf in the Netherlands and the University of Bergen in Norway, in addition to the lecturer of the University Center of Defense in Marin and associate researcher of EPhysLab Jorge Eiras-Barca.

In this review, the authors discuss the relevance of residence time as a key indicator of important variations in the present and future hydrological cycle, putting into context the research work of the different groups and giving guidelines for future research, especially in the implications it has as a relevant parameter for quantifying climate change in the global hydrological cycle. “The residence time of water vapor in the atmosphere is a recurring theme in our field, in fact directly or indirectly it is something that we need in other to evaluate other parameters such as moisture sources, a topic on which we have been working for more than a decade,” says Luis Gimeno, who recalls that last year they published an article in another journal of the Nature Scientific Data group with a database on this parameter, which was updated this year in another publication of the same journal.

An indicator that varies as the climate changes
Gimeno stresses the importance of NREE’s decision to publish the work of the team he leads on a parameter that he says will be decisive in the coming years when studying the effect of climate change on the global hydrological cycle, “because it is summary of the whole cycle and very, very sensitive to global warming,” he says. The residence time of water vapor also varies, he explains, as the climate changes, so that vapor increases by about 7% per degree of surface warming for purely thermodynamic causes, while global precipitation increases by only about 2% as a result of energy constraints, resulting in an increase in water vapor residence time with global warming.

“This came to occur, both in models, as well as in observations, so a future increase is expected in a high emissions scenario,” explains Luis Gimeno.

A key element in understanding extreme precipitation changes
The residence time of water vapor in the atmosphere, the researchers confirm, is important not only from a theoretical point of view, but also because of its influence on other key parameters of the hydrological cycle, such as those related to the determination of moisture sources and sewers, linking evaporation and precipitation at different spatial scales. “It is also a key element in the understanding of extreme precipitation changes and in the relationship between oceanic versus terrestrial sources of precipitation over the continents,” explains Luis Gimeno, who points out that the discrepancies in the different quantifications of the residence time of global water vapor are quite surprising, varying from four to five days, to the more usual eight to ten days.
The paper published today in Nature Reviews Earth and Environment highlights that the regional scale residence time is highly variable, because it depends on many different physical processes that result in different residence time values associated with different system patterns. “Therefore, there is a spectrum of regional residence times, from short times close to four or five days in the tropics or in extratropical regions of passing squalls, to times greater than ten days in polar regions,” says the professor.

Source: DUVI