WorkBlock 5 - Feedbacks between Hydrology and Climate

Co-ordinator: Eleanor Blyth, Centre for Ecology and Hydrology (NERC)
Deputy co-ordinator: Ronald Hutjes, Wageningen University (WUR)

The main objective of Workblock 5 is to provide a global and regional analysis of feedbacks between the land surface and climate system using a fusion of models and data.

This work block will quantify those feedbacks from hydrological processes and the climate system, that are currently not (sufficiently) accounted for in climate models, and that are likely to impact on water cycle components. The feedbacks addressed include soil moisture feedbacks, sub-grid scale processes, feedbacks associated with ecosystem processes, snow and vegetation, and feedbacks associated with anthropogenic modification of land cover and soil moisture (e.g. irrigation).

In essence, it identifies the main process mismatches within the modelling framework of WATCH which result from using hydrological models off-line from the climate models. On the one hand, these off-line impact models generally contain more information about changes to the land surface due to anthropogenic activity than the climate models. On the other, hydrological models do not contain representation of some key vegetation and surface energy balance processes which may affect the global water cycle components.

The work is divided into three work packages:

  • WP5.1 this work package aims to build up a picture of the location and strength of "feedback hotspots" across the globe, using data sources in an innovative way. As part of this overview, it will bring together the results from the feedback studies in the other two work packages, WP5.2 and WP5.3. As an interim measure, we will create a new correction map to allow the feedbacks to be fed into the water resources analysis in WB6
  • WP5.2 will investigate interactions between ecosystem processes and the climate and how these affect the water resources
  • WP5.3 Addresses feedbacks associated with changes in land use. The impact and feedbacks into the global water cycle of changes in the land-cover (irrigated land and increases in cultivated land in sensitive areas)

 

The “Koster et al map” indicating the land-atmosphere coupling strength diagnostic for boreal summer (the difference, dimensionless, describing the impact of soil moisture on precipitation), averaged across the 12 models participating in GLACE.

Figure: The “Koster et al map” indicating the land-atmosphere coupling strength diagnostic for boreal summer (the  difference, dimensionless, describing the impact of soil moisture on precipitation), averaged across the 12 models participating in GLACE. (Insets) Areally averaged coupling strengths for the 12 individual models over the outlined, representative hotspot regions. No signal appears in southern South America or at the southern tip of Africa. (image taken from the science paper of Koster et al., 2004 (DOI 10.1126/science.1100217))

Work Performed and Results achieved during Year 2 (February 2008 – 31 January 2009)
The focus of the second year of Work Block 5 has been on confirming methods for assessing feedbacks in the water cycle and its impact on global water resources. Initial analyses have been carried out in some areas such as irrigation, CO2 fertilisation and rainfall feedbacks due to convective rainfall triggering. Plans for further work have been agreed on other aspects such as global land cover change, evaporation demand feedback and impact of local wetlands on rainfall. There have been meetings to discuss ways to bring together the results of the projects across this workblock, resulting in an agreed method for including feedbacks in water resources studies. These meetings have resulted in reports summarising the outcomes.

Achievements have included: