Modeling Hydrological Impacts of Climate and Irrigation Changes in a Mediterranean Catchment

Catchment responses to climate and irrigation changes in a semi-arid climate

The ongoing climate change will have important impacts on hydrological processes, especially in semi-arid regions, where water resource is limited. The prediction of these impacts is necessary to adapt to the new conditions, but is complicated by our limited understanding of catchment sensitivity to temperature and precipitation changes. To improve this understanding, hydrological models are often used. These models are calibrated in present climate with measured data. Inputs are then modified based on various climate scenarios. Outputs of the models run in present conditions are finally compared with the outputs of the models run in future conditions.

Various hydrological models have been used for this purpose, from simple conceptual models to distributed, integrated models. However, integrated hydrological models have only rarely been used in climate-impact studies because of the long simulation time associated with this type of model [Goderniaux, 2011]. These models could however bring interesting insights into the estimation of climate change impacts, notably because of their distributed representation of water exchanges between the surface and subsurface.

Consequently, the goal of this study is to estimate and to improve the usefulness of integrated hydrological models in climate-impact studies.

Model calibration is a necessary step to apply a hydrological model to a catchment. The speed of the calibration depends on the duration of the simulation and the number of model parameters. Integrated hydrological model often have long simulation times and a large number of parameters. Hence, parameter calibration of these models is a long and tedious process in many practical cases. Consequently, model calibration is often limited to a trial-and-error process.

To accelerate model calibration, we propose a new calibration method based on a set of computational grids of increasing resolution. Model using fine grids have longer simulation time. Hence, the computational grid must be as coarse as possible but the grid must also be fine enough to represent run-off and peak-flow. However, base flow and hydraulic heads are represented acceptably in coarser grids. We propose to first calibrate the model on base flow and hydraulic heads in coarser grids and to calibrate the model on peak flow using finer grids afterwards. This method accelerates model calibration by a factor of eight in our case study.

Presentation CMWR 2014 
Grid simplication to accelerate calibration of integrated catchment models: Accuracy vs. effciency

Extreme events, such as droughts, have often stronger impacts on the hydrology than average climatic changes. However, droughts can be difficult to characterize. Many droughts indices, that is, summary metrics representing the dryness level, have been developed to quantify droughts. However, because comparisons between drought indices are rare, the choice of a particular drought index can be difficult. To simply this process, we compare seven well-known drought indices to the outputs from our hydrological model in present and future conditions. We compare the correlation between modelled hydrological variables (discharge, water deficit, and hydraulic heads) and drought indices. Then, we analyze the relationships between each drougth index and the hydrological variables. Correlation coefficient are similar for all irrigation scenarios in present and future cliamtes. However, the relationships between hydrological variables and the drougth indices are sensitive to climate change.

Poster AGU 2015
Integrated Modeling of Climate Change Impacts in an Irrigated, Semi-arid Catchment (Lerma, Spain)

• [Abrahao, 2011] Abrahao, R.; Causapé, J.; García-Garizábal, I. & Merchán, D. Implementing irrigation: Water balances and irrigation quality in the Lerma basin (Spain), Agricultural Water Management, 2011, 102, 97-104
• [Goderniaux, 2011] Goderniaux, P.; Brouyère, S.; Blenkinsop, S.; Burton, A.; Fowler, H. J.; Orban, P. & Dassargues, A.Modeling climate change impacts on groundwater resources using transient stochastic climatic scenarios Water Resour. Res., AGU, 2011, 47, W12516
• [Merchan, 2013] Merchan, D.; Causapé, J. & Abrahao, R. Impact of irrigation implementation on hydrology and water quality in a small agricultural bassin in Spain, Hydrological Sciences Journal, 2013, 58, 1400-1413
• [Milano, 2013] Milano, M.; Ruelland, D.; Dezetter, A.; Fabre, J.; Ardoin-Bardin, S. & Servat, E. Modeling the current and future capacity of water resources to meet water demands in the Ebro basin Journal of Hydrology, 2013, 500, 114-126
• [Pérez, 2011] Pérez, A.; Abrahão, R.; Causapé, J.; Cirpka, O. & Bürger, C. Simulating the transition of a semi-arid rainfed catchment towards irrigation agriculture Journal of hydrology, 2011, 409, 663-681

• von Gunten, D., Wöhling, T., Haslauer, C., Merchán, D., Causapé, J., Cirpka, O.A. (2016): Using an integrated hydrological model to estimate the usefulness of meteorological drought indices in a changing climate. Hydrol. Earth Syst. Sci., doi: 10.5194/hess-20-4159-2016
• von Gunten, D., Wöhling, T., Haslauer, C., Merchán, C., Causapé, J., Cirpka, O.A. (2015): Estimating Climate-Change Effects on a Mediterranean Catchment under Various Irrigation Conditions. J. Hydrol. Reg. Stud., 4, 550-570, doi: 10.1016/j.ejrh.2015.08.001
• von Gunten, D., Wöhling, T., Haslauer, C., Merchán, C., Causapé, J., Cirpka, O.A. (2014): Efficient Calibration of a Distributed Pde-based Hydrological Model Using Grid Coarsening. J. Hydrol. 519, 3290-3304, doi: 10.1016/j.jhydrol.2014.10.025