Suitability of modelled and remotely sensed essential climate variables for monitoring Euro-Mediterranean droughts

Abstract

Abstract. Two new remotely sensed Leaf Area Index (LAI) and Surface Soil Moisture (SSM) satellite products are compared with two sets of simulations of the ORCHIDEE and ISBA-A-gs land surface models to investigate how recent droughts affected vegetation over the Euro-Mediterranean area. We analyze the interannual variability over the period 1991–2008. The leaf onset and the Length of the vegetation Growing Period (LGP) are derived from the satellite-derived LAI and from the modelled LAI. The LGP values produced by the photosynthesis-driven phenology model of ISBA-A-gs are closer to the satellite-derived LAI LGP than those produced by ORCHIDEE. In the latter, the phenology is based on a growing degree-day model for leaf onset, and on both climatic conditions and leaf life span for senescence. Further, the interannual variability of LAI is better captured by ISBA-A-gs than by ORCHIDEE. The summer 2003 drought case study shows a relatively good agreement of the modelled LAI anomalies with the observations, but the two models underestimate plant regrowth in the autumn. A better representation of the root-zone soil moisture profile could improve the simulations of both models. The satellite-derived SSM is compared with SSM simulations of ISBA-A-gs, only, as ORCHIDEE has no explicit representation of SSM. Overall, the ISBA-A-gs simulations of SSM agree well with the satellite-derived SSM and are used to detect regions where the satellite product could be improved. Finally, a correspondence is found between the interannual variability of detrended SSM and LAI. The predictability of LAI is less pronounced using remote sensing observations than using simulated variables. However, consistent results are found in July for the croplands of Ukraine and southern Russia.