Impact of Groundwater in Earth system Models – I-GEM

Our international consortium offers a unique opportunity to compare the sensitivity of simulated climate to different GW parameterizations within three different climate models: the French IPSL and CNRM-GAME climate models, and the American NCAR climate model CESM, modified and used here by the Taiwanese team.

The project is organized into 4 successive scientific tasks, each relying on specific simulations:
T1. Sensitivity to fixed water table depths (WTD), to identify the patterns of “active WTD”, below which GW do not impact regional climate
T2. Dynamic WTD over the recent period, to assess the potential of realistic GW parametrizations to improve the simulated climate, with a focus on land/atmosphere feedback and the persistence/memory in the Earth system
T3. Dynamic WTD and climate change, with two complementary questions: (1) What is the influence of GW on the climate change trajectory? (2) What is the impact of climate change on water resources (including GW)?
T4. Dynamic WTD with withdrawals, which artificially increase soil moisture via irrigation, with potential impacts on climate until water resources get exhausted.

We will also organize two workshops with international experts of the modeling and observation of groundwater at large scales, to brainstorm on the priorities to incorporate groundwater in climate models.

Task 1 allowed us to propose a new diagnostic of the sensitivity of the evapotranspiration to the water table depth, called the critical water table depth, which facilitates the comparison between models and regions. This critical water table depth show a large similarity in the three models compared in this project; in particular, it is maximum in arid and semi-arid zones, where it is important that climate models account for the link between soils and deep groundwater, at least where aquifers are known to exist.

Our work will improve the groundwater parametrization in three climate models, and make them closer to real Earth system models, allowing integrated studies of global change impacts on water resources. We will also try to devise indicators of groundwater failure to sustain water withdrawals, which could be very useful for elaborating adaptation strategies.

Ducharne, Lo, Decharme, Wang, Cheruy, Ghattas, Chien, Lan, Colin, Tyteca (2016). Groundwater-soil moisture-climate interactions: lessons from idealized model experiments with forced water table depth. Geophysical Research Abstracts, Vol. 18, EGU2016-8541, EGU General Assembly, Wien.

Groundwater (GW) constitutes 30% of the fresh water resources, which are subjected to increasing withdrawals. When shallow enough, it can also sustain soil moisture, thus increase evapotranspiration, with potential impact on the climate system (in particular temperatures and precipitation). Its large residence time can also increase the Earth system’s memory, with consequences on the persistence of extreme events, hydro-climatic predictability, and anthropogenic climate change, particularly the magnitude of regional warming.
Our main goal is to explore the impacts of GW on regional and global climate, and its links to water resources availability, through model analyses. To this end, our Franco-Taiwanese consortium offers a unique opportunity to compare the sensitivity of simulated climate to different GW parametrizations within 3 different climate models: the French IPSL and CNRM-GAME climate models, and the American NCAR climate model (CESM), modified and used here by the Taiwanese team.
All teams have experience in international intercomparison projects, and they have all recently emerged as important actors of the research on groundwater in climate models: the IPSL team and Min-Hui Lo have pioneered the analysis of the sensitivity of global simulated climate to GW, while the CNRM-GAME team achieved significant advances regarding the global-scale parameterization of GW and its coupling with rivers and land surfaces.
The project includes two transversal tasks: T0. Coordination; T5. International workshops; and the research program is organized into 4 successive scientific tasks:
T1. Sensitivity to fixed water table depths (WTD), to identify the patterns of “active WTD”, below which GW do not impact regional climate
T2. Dynamic WTD over the recent period, to assess the potential of realistic GW parametrizations to improve the simulated climate, with a focus on land/atmosphere feedback and persistence/ memory in the Earth system
T3. Dynamic WTD and climate change, with two complementary questions: (1) What is the influence of GW on the climate change trajectory? (2) What is the impact of climate change on water resources (including GW)?
T4. Dynamic WTD with withdrawals, which artificially increase soil moisture via irrigation, with potential impacts on climate until water resources get exhausted.
I-GEM is also intended to consolidate the potential of France and Taiwan in the interdisciplinary research field of the global water cycle, by tightening the links between these two countries, and by federating the French community (IPSL and CNRM-GAME). We also aim at enhancing the visibility of French and Taiwanese teams, by developing closer links with European and North-American leaders in large-scale modeling of GW. To this end, we want to organize two international workshops on the role of GW in climate models, one in Taiwan and one in France, with a broad audience (T5).