Simulation of drought processes in Spain
P. Quintana-Seguí (OE)
M.J. Escorihuela (isardSAT)
O. Merlin (CESBIO)
M.C. Llasat (GAMA UB)
G. Míguez-Macho (USC)

The recently started FP7 project eartH2Observe, aims at integrating available global earth observations, in-situ datasets and models to conduct a global water resources re-analysis dataset of significant length. The resulting data will allow for improved insights on the full extent of available water and existing pressures on global water resources in all parts of the water cycle. 

The usability and operational value of the developed data will be verified and demonstrated in a number of case-studies across the world. One of the case studies is set in the Mediterranean area, more specifically, in Spain and Morocco, which are close countries with very different data availability. It will be determined how the global EO products and model results can contribute to drought prediction and management. The work presented in this study corresponds to the Spanish case.

In the Spanish case, we are focused on the reproduction of drought conditions with two different land surface models. The study will be performed with two different forcing datasets, a high resolution dataset based on the SAFRAN meteorological analysis system and a the low resolution global reanalysis produced by the eartH2Observe project.

In this work we present the extension of SAFRAN to the whole of Spain (it currently only covers the NE of the Iberian Peninsula) and the initial efforts to validate one of the two land-surface models used in this case study (SURFEX).

In order to be able to study the capability of the LSM to simulate the evolution of drought conditions, we have selected a 12 year period that covers a transition from wet to dry conditions. This period has been selected based on the behaviour of the Spain02 gridded dataset of precipitation.

Then, we have worked on the extension of SAFRAN to the whole of Spain, in order to be able to perform the high resolution 10 year long analysis on the area of study. SAFRAN is an atmospheric analysis system, which is based on optimal interpolation over climatically homogeneous zones (areas where spatial gradients of meteorological variables are not very relevant) and is able to reliably take vertical variations into account. In order to define the "climatically homogeneous zones" we have chosen to use a basin-based delimitation, instead of the AEMET alert zones, as we did in previous studies, as it facilitates the extension to Portugal, keeping a similar performance.

Finally, we will perform land-surface simulations with SURFEX. We will work with the ISBA-3L scheme, which is part of the SURFEX framework. We have tested it in the NE of Spain, comparing the simulated soil wetness to different remote sensing products, including SMOS, ASCAT and a high resolution soil moisture product derived from SMOS
using DISPATCH (Merlin et al. 2013). The comparisons show that the behaviour of SURFEX is close to the remote sensing products in those areas where we know that the inversion algorithms used by the remote sensing products work well, this is, flat areas which are not close to the sea.

In the future we will continue improving the SAFRAN dataset and we will work on the validation of the LSM. Furthermore, we are looking to couple the SURFEX LSM to a routing scheme, in order to calculate river flows. Due to the high degree human influence in the Spanish basins, we will choose a routing scheme that is able to, at least, simulate the effect of dams. In the future we may also work on the inclusion of irrigation into the LSM.