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LIAISE - Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment


One of the largest challenges facing environmental science is understanding future changes in the terrestrial water cycle and the subsequent impact on water resources. It has also been recognized by international organizations such as the World Climate Research Programme (WCRP) that human activities are playing a key role in modifying the continental water cycle, and therefore must be accounted for in projections. As highlighted by the WCRP Grand Challenge on “Water for the Food Baskets of the World,” this issue is especially critical in bread basket regions where water resources are already limited, such as the Mediterranean basin. Understanding the processes that drive the hydrological cycle in this region is a key aim of the international HYdrological cycle in the Mediterranean Experiment (HyMeX). Climate projections from the Coupled Model Intercomparison Project phase 5 (CMIP5) predict that the Mediterranean region will be a so-called climate change “hot spot” during the twenty-first century. However, semi-arid regions are also hot spots for biases in climate model variables, in particular land surface temperature (LST) and components of the surface energy balance. The Mediterranean basin is also characterized by highly heterogeneous land cover in terms of both natural and anthropized surfaces. Since rainfall is essentially limited to winter and mountainous areas, human management of the natural river systems is required to provide water for crops and an ever-increasing population. Dams and extraction for irrigation modify the amount and timing of the water flowing into the ocean. Irrigation is also known to significantly impact local atmospheric boundary layer (ABL) growth and structure, in addition to modifying near surface atmospheric conditions and increasing convective activity and clouds downwind of irrigated areas. The understanding of the impact of anthropization and its representation in models have been inhibited due to a lack of consistent and extensive observations. Here we present the plans for a project which will bring together ground-based and airborne measurements with modeling studies including data assimilation of remotely-sensed data to improve our understanding of key natural and anthropogenic land processes and the subsequent feedbacks with the Mediterranean boundary layer and basin-scale hydrological cycle.

Objectives and science questions

The overall objective of this new activity, the Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) project, is to improve our understanding of the impact of anthropization on the water cycle in terms of land-atmosphere-hydrology interactions, and the limitations of models to represent all aspects of the terrestrial water cycle in a semi-arid environment on the Iberian peninsula. The main science questions can be summarized as:
Field Campaign: 2020

This is the last field campaign of the HyMeX project. The study domain for LIAISE is the Ebro basin in northeastern Spain, which is bound to the north by the Pyrenees and to the south by the Iberian System. Surface heterogeneity has grown due to the presence of human society, which has been altering the hydrological cycle and the landscape mainly through intense agricultural activity. There are 2 observation periods :

1) Intensive Observation Period (IOP) from early April through September 2020

A network of surface energy budget (SEB) observing stations will be installed within an approximately 10 km radius centered over the Urgell and Plà d’Urgell (Lleida) region of the Ebro basin. This area is selected since it encompasses several representative Mediterranean land cover types. This location will also allow us to benefit from the dense local meteorological station and radar data from the Spanish State Meteorological Agency (AEMET) and the Meteorological Service of Catalonia (SMC), along with an existing extensive observation site run by the Institute of Agrifood Research and Technology (IRTA), which includes weighing lysimeters in apple orchards. This network will enable us to evaluate the ability of LSMs to simulate fluxes, especially evapotranspiration, over irrigated sites and to contrast the fluxes with those from natural surfaces. These sites will be maintained at least through entire growing season. State-of-the-art soil moisture products [such as that from the Soil Moisture and Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) missions] will be combined with in situ soil moisture observations from an existing network in collaboration with the Ebro Observatory and private irrigation-monitoring companies for use in assimilation into the LSMs and/or for evaluation. Field-scale actual and potential evapotranspiration will be evaluated using two-source energy balance (TSEB) models, which combine thermal observations from Sentinel-3 satellites and optical observations from Sentinel-2 satellites.

2) 2 Special Observation Periods (SOP)

The first SOP will be during a 5-day period during the dry down of soil moisture in the spring. Throughout this period, radiosondes will be launched at regular periods to add to atmospheric and flux profiles along a 50 m mast. These data will be used to study the impact on interactions with the lower part of the boundary layer and the contrast in the surface fluxes between the sites with natural dry down and the irrigated sites. A number of LSMs will be confronted with the data. The second SOP is planned for mid July, when contrasts between irrigated and natural surfaces are at their maximum. The SEB network will be complemented by extensive measurements of the lowest 4 km of the atmosphere using captive balloons, frequent radio-sounding releases, a UHF wind profiler, lidars and up to five flights by the French Office of Aircraft Instrumented for Environmental Research (SAFIRE)/ATR42 aircraft. Measured atmospheric fluxes and state variables will be used in conjunction with fully coupled, non-hydrostatic mesoscale models to study the impact of irrigation on the spatial variability of the ABL, the basin scale circulation and water budget and interactions between the irrigated and natural surfaces. In addition, high-resolution land surface temperature and surface soil moisture estimates will be aquired from instruments onboard the ATR42.

Anticipated outcomes

LIAISE addresses the GEWEX Science Questions and contributes to WCRP's Grand Challenges, notably how a warming world will affect available fresh water resources globally, specifically in the food basket regions, and how it will change human interactions with these resources and their value to society. Another key GEWEX Science Question addressed by LIAISE pertains to improving our understanding of the effects and uncertainties of water and energy exchanges in the current and changing climate and how to convey this information to society. The improvement of the representation of anthropogenic effects in models will form the foundation for water resource impact studies under future climate change. These results will be communicated to water management services within the Ebro basin. A comprehensive database, consisting of surface-based and aircraft measurements of surface and hydrological fluxes and states and properties of the ABL, will be integrated into the Mediterranean Integrated STudies at Regional And Local Scales (MISTRALS)/HyMeX database, which can accessed upon request by interested researchers. This database of observations will form the basis for a number of international modeling experiments that will cut across many areas of interest to GEWEX, ranging from theability of LSMs to capture soil moisture dry down, the representation of heterogeneity and how this interacts with the atmospheric boundary layer, the impacts of human influence on land surface fluxes, land/atmosphere interactions the terrestrial water cycle of semi-arid environments.


Organizational meetings

Boone, A., M. Best, J. Cuxart, J. Polcher, P. Quintana, J. Bellvert, J. Brooke, G. Canut-Rocafort, J. Price, 2019: Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE). Gewex News, (in press for the February issue).

Conference or workshop presentations

A. Boone, J. Polcher, M. Zribi, S. Garrigues, Y. Tramblay, C. Albergel, S. Bastin, J.-C. Calvet, G. Canut-Rocafort, J. Cuxart, S. Donier, P. Fanise, M. Haeffelin, L. Jarlan, P. LeMoigne, M. LePage, P. Quintana Segui, 2018 : Human Iimprint on Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (HILIAISE), 11th HyMeX Workshop, Lecce, Italy, 2018

Polcher, J., A. Boone, M. Best, J. Cuxart, P. Quintana-Segui, S. Garrigues, Y. Tramblay, M. Zribi, C. Albergel, S. Bastin, A. Bourdon, J. Brooke, G. Canut-Rocafort, J.-C. Calvet, S. Donier, M. Haeffelin, L. Jarlan, P. Le Moigne, M. Le Page, F. Lohou, M. Lothon, 2018 : Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) Project, 11-12 December in ESA -ESRIN Frascati, Italy, 2018.

A. Boone, M. Best, J. Cuxart, J. Pocher, P. Quintana-Segui, F. Lohou, Y. Tramblay, M. Zribi, C. Albergel, S. Bastin, A. Bourdon, J. Brooke, G. Canut-Rocafort, J.-C. Calvet, A. Dabas, S. Donnier, F. Gibert, S. Garrigues, M. Haeffelin, L. Jarlan, O. Merlin, M. Lothon, P. Le Moigne, S. Munier and M. Le Page, 2019: Land surface Interactions with the Atmosphere over the Iberian Semi-arid Environment (LIAISE) Project. MetMed, Palma, Spain, 4-6 March, 2019

Core Group Members