Monitoring rain and flood events in Chaco Xerophhytic forest by SMOS and AMSR-E

R.RAHMOUNE, C.VITTUCCI, P.FERRAZZOLI, L.GUERRIERO; V. BARRAZA, F. GRINGS, H. KARSZENBAUM

Arles

Workshop; SMOS SCIENCE WORKSHOP; 2011

The European Space Agency (ESA)

The objective of this work is to investigate the capability of SMOS and AMSR-E in monitoring events occurred in Chaco Xerophytic forest, including Bermejo sub-basin. The selected area is a part of the large La Plata Basin (LPB), covering parts of Argentina, Brazil, Bolivia, Paraguay, and Uruguay. Within LPB, a main issue is to monitor and predict the impact of global change and land use change (deforestation and replacement by intensive soy crop production) on regional weather, climate,hydrology and agriculture. More recently, extreme hydrological events, such as flood and drought, are strongly affecting different regions within this basin. Since the coverage of hydrometric and meteorological stations is limited, satellite missions constitute a fundamental data contributor. This area is being addressed in a ESA SMOS Exploitation project and in a SACDAquarius NASA-CONAE project. The main goals of these projects are related with soil moisture retrieval within different vegetated areas (forest, wetlands, agriculture), with the aim of generating precedent soil condition data for prediction models. The particular region selected by us spans the North-East of Argentina (24S-26S Lat, 60W-62W Lon). In general, it is covered by the continuous and deciduous Chaco forest, which is xerophytic, that is adapted to leave in an arid environment. The biomass is moderate, typically ranging between 70?110 t/ha. The area is crossed by Bermejo river, along which the forest is mixed with grasslands and shrub-lands. This river is subject to frequent flooding events, creating severe problems to local communities. A monitoring project has been started, based on a network of stations measuring precipitation and water level (http://www.corebe.org.ar). Within this region, signatures collected by both SMOS and AMSR-E in 2010 have been processed and analyzed. For selected boxes, multitemporal trends of emissivity and polarization ratio have been obtained at L band, 42° (by SMOS) and at C and X band, 55° (by AMSR-E). In presence of important flood and rain events, relevant maps of emissivity and polarization ratio have been produced.In general, floods produce variations of microwave signatures which are localized in the pixels along Bermejo river, and last some weeks. Conversely, the effects of heavy rainfalls are observed over wider areas, but last only few days, due to rapid drying. A multifrequency investigation indicates that rain and flood events are clearly detectable at all the three frequencies (L, C and X) for mixed pixels along the river, while the sensitivity of L band is clearly better within the homogeneous forest. Tests of the forward model and the retrieval algorithm of SMOS are in progress. The forward model generally reproduces both the absolute values and the variations of the brightness temperature. Retrieved values of soil moisture follow the trends of ECMWF estimates, although lower values are predicted during drying phases. This aspect is under investigation.