909 - NEW, COUPLED MARMITES-MODFLOW MODEL IMPROVING SIMULATION OF SUBSURFACE EVAPOTRANSPIRATION

Transcription

1 Session S8.9 - Aqua nd IAH Congress NEW, COUPLED MARMITES-MODFLOW MODEL IMPROVING SIMULATION OF SUBSURFACE EVAPOTRANSPIRATION Alain Pascal Frances ITC, University Twente, Enschede, Netherlands Maciek Waclaw Lubczynski ITC, University Twente, Enschede, Netherlands As subsurface evapotranspiration is poorly simulated in existing hydrological models, a new, coupled model composed of land surface and soil zone MARMITES model and groundwater MODFLOW-NWT model was developed with the aim of incorporating model-based partitioning and sourcing of evapotranspiration (ET), as part of spatio-temporal water balancing at the catchment scale. The partitioning of ET involves its separation into evaporation and transpiration while the sourcing of evaporation and transpiration involves separation of each of the two into soil and saturated zone components. The MARMITES-MODFLOW coupled model was applied to the La Mata catchment (Salamanca, Spain) to demonstrate its capability to simulate complex hydrological systems. The catchment was characterized by a semiarid climate with rainfall 500 mm y -1, granitic bedrock, shallow groundwater and sparse oak woodland. The model was calibrated in transient using daily data of two hydrological years. The water balance results of the partitioning and sourcing of ET involved (in % of rainfall): soil evaporation (34.7%), soil transpiration (8.0%), groundwater evaporation (8.5%) and groundwater transpiration (2.0%). Accordingly, the gross recharge was 28.5% and groundwater exfiltration 17.3%, implying low net recharge 0.7%. The presented MARMITES-MODFLOW model constitutes a powerful tool to analyze catchment water dynamics and water balances in details, accounting separately for impacts of evaporation and transpiration on groundwater resources. The model generates spatio-temporally variable maps of unsaturated and saturated zone fluxes, welldepicting recharge and discharge zones. It can be particularly helpful in analyzing impacts of climate and land cover changes on groundwater resources and for mapping groundwater dependent ecosystems. The MARMITES-MODFLOW is developed in Python, open-source and freely available at: 1

2 NEW, COUPLED MARMITES-MODFLOW MODEL IMPROVING SIMULATION OF SUBSURFACE EVAPOTRANSPIRATION A.P. Francés, M.W. Lubczyński with contributions of E. Balugani, L.Reyes-Acosta, Ch.v.d.Tol ITC, University of Twente Department of Water Resources (WRS)

3 PROBLEM STATEMENT Evapotranspiration partitioning ET = E + T Sourcing E = I + E surf + E soil + E p + E g T = T soil + T p + T g Net recharge (Exf g = 0) R n = R (E g + T g )

4 MARMITES-MODFLOW COUPLED MODEL ET partitioning and sourcing Spatio-temporal water flux assessment 3/13

5 MARMITES-MODFLOW COUPLED MODEL transient and distributed grid-based model land surface hydrological processes meteorological forcing, interception, surface storage, runoff and evaporation from open water soil reservoir / unsaturated zone hydrological processes evaporation, transpiration, percolation and soil moisture driving forces rainfall, potential evaporation and potential transpiration parameterization vegetation, soil, percolation zone and aquifer reservoirs state variables hydraulic heads and soil moisture Python programing language

6 MARMITES-MODFLOW COUPLING 5/13

7 EVAPORATION AND TRANSPIRATION PARTITIONING Vegetation and soil types mapped in each grid cell using remote sensing images Vegetation T = T soil + T p + T g Bare soil E = E soil + E p + E g 6/13

8 EVAPORATION AND TRANSPIRATION SOURCING groundwater evaporation Exponential decay between E g PE g and the depth of groundwater table d (Shah et al, 2007). groundwater transpiration Example of simulated drying tree behavior under water stress (notice, with reduction of soil moisture, first T g increases then decreases with T decline). 7/12

9 LA MATA STUDY CASE semi-arid catchment (~6 km 2 ) weathered and fractured granite shallow water table (~2 m) limited human influence on water resources 2 main tree species >20 years monitoring 8/13

10 LA MATA STUDY CASE water fluxes maps (average of 2 hydrological years) net recharge (Rn) E g gross recharge (Rg) = - T g Exf g

11 LA MATA STUDY CASE water fluxes maps water fluxes time series RAINFALL EVAPORATION TRANSPIRATION 10/13

12 LA MATA STUDY CASE water fluxes maps water fluxes time series RAINFALL RUNOFF RECHARGE EXFILTRATION GW ET 11/13

13 LA MATA STUDY CASE water fluxes maps water fluxes time series scale (Sankey diagrams) water balance at the catchment VEGETATION SURFACE SOIL PERCOLATION GROUNDWATER 12/13

14 Validation - poster ID 939 (S.5.8)

15 CONCLUSIONS MARMITES-MODFLOW: is an open-source code partitioning and sourcing of subsurface evapotranspiration code with spatio-temporally water balance validated with field independent methods (eddy covariance system, sap flow measurements, stable isotopes, evaporation modelling); Introducing processes of partitioning and sourcing of ET into modelling protocol, makes ET simulation more realistic than ever before; more realistic models such as M-M, will improve water management but also can contribute to environmental sciences Development of Earth Observation Methods can stimulate and fully automatize the use of satellite remote sensing data as input for integrated hydrological models 14/13