Project

precipitation; climate change; hydrological cycle; climate models; hydrological sensitivity; observations

Lead
Lay summary
Since the preindustrial period, the concentration of greenhouse gases in the atmosphere is increasing due to human activities. It is well understood that greenhouse gases such as carbon dioxide act to increase the temperature of the atmosphere. Warmer air can consequently hold more moisture, which again results in an increase in precipitation.Global climate models are currently the most powerful tool to investigate the future climate but interestingly, the simulated increase in precipitation is smaller by a factor of two compared to observations. Since changes in precipitation will affect numerous ecosystems as well as food and water security, it is important to understand the reasons for the discrepancy between climate models and observations.On one hand, observations might overestimate the precipitation increase because of too short available time series or inadequacies in measurement systems. On the other hand, climate models might fail at simulating important processes leading to the precipitation formation. In a first step, different observation datasets will be analysed and compared. Then, simulations will be performed with a global climate model in order to investigate the mechanisms leading to precipitation and these results will be compared to already existing model datasets. The proposed project will allow to understand the nature of the discrepancy between climate models and observations. Overall, the project will inform policy makers about the future climate and allow them to agree on adequate adaptation measures.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

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Number	Title	Start	Funding scheme

High-impact and long-term policy decisions are informed by climate model predictions. Despite its relevance for life on Earth, it is still unclear by how much precipitation will change as a result of the projected temperature increase resulting from rising atmospheric greenhouse gas concentrations. Observations show a precipitation increase of up to 6% per Kelvin of surface warming, while the rate found in climate models is between 1 and 3%/K, suggesting a discrepancy of at least a factor two on the global scale. The aim of the proposed research project is to analyze global observations of the hydrological cycle and climate model output to improve process understanding and explain the discrepancies between models and observations. Precipitation trends will first be analyzed in a wide range of observation data sets and in the results of the Coupled Models Intercomparison Program 3 (CMIP3) models as used in the AR4. Then simulations with different setups will be performed with the NCAR Community Climate System Model (CCSM) in order to analyze the response of the hydrological cycle to various factors and processes. Finally, seasonal and spatial differences in precipitation trends will be analysed. In contrast to many previous studies, this project will not only focus on temperature and precipitation but also include other mechanisms and parameters of the hydrological cycle. The results of the project will help to fill a gap in the current understanding of the hydrological cycle and will contribute to a better understanding of precipitation changes, which impact on water resources, ecosystems and global food security.