LIAISE

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. 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. 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)

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:

1. What are the key natural and anthropogenic semi-arid surface processes that modulate or control infiltration and runoff and govern turbulent fluxes and their spatial heterogeneity?
2. How does anthropization impact boundary layer development, mesoscale circulations and potentially precipitation recycling over this region via feedbacks with the atmosphere?
3. What is the sustainability of ground water and reservoirs in the face of expanding agricultural and farming activities, especially in light of projected future warming and drying over this region?

      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.

Field campaign

This is the last field campaign of the HyMeX project, and is a core activity leading into HyMeX phase 2. 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): April through September 2021

      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 multiple representative Mediterranean land cover types, including a small lake. 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. This network will enable us to evaluate the ability of land surface models (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) Special Observation Period (SOP): July, 2021

      The SOP is planned for July, when contrasts between irrigated and natural surfaces are at their maximum. The SEB stations will be complimented by additional biogeophysical measurements and trublence estimates, such as those from scintillometers. The SEB network will be complemented by extensive measurements of the lowest 4 km of the atmosphere using captive balloons, frequent radio-sounding releases, UHF wind profilers, lidars and approximately 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, solar-induced fluorescence (SIF) and surface soil moisture estimates will be aquired from instruments onboard the ATR42.