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In addition, the study demonstrated that remotely-sensed vegetation indices such as the seasonal variation in the density of green vegetation are particularly suitable to monitor regional variation in soil salinity. Besides primary salinization due to arrested drainage and landscape stagnation, anthropogenic activities increased secondary salinization, especially in the agricultural areas with shallow groundwater tables and irrigated croplands. Subsurface salinity (i.e., measured at 100 cm depth) showed clear regional patterns in natural soil salinity that are related to the annual water budget and topography. Soil electrical conductivity (EC) was used as an indicator of salinity, and supplementary information on salt crusts was derived from Google Earth imagery. It is based on extensive dataset of 492 surface and 142 subsurface samples taken along east-west transects across the Dry Chaco. This study is a regional assessment of soil salinity and salinization processes in the central Argentinean Dry Chaco. Local studies have shown that deforestation leads to changes in the soil-water balance, and can expedite groundwater rise and mobilization of water-soluble salts to the surface affecting plant growth and crop productivity. The potential impact of these newly established agricultural lands on the surrounding environment is of great concern. The Dry Chaco is a semi-arid ecoregion in South America that hosts one of the largest dry forests in the world, but expansion of dryland agriculture and cattle ranching led to gradual conversion of native vegetation to anthropogenic land cover. Our results suggest that the different hydrological responses of various LSMs to vegetation changes may need further attention to gain benefits from vegetation data assimilation. However, the revised soil parameters generally reduced the bias between simulated surface soil moisture and pixel-scale in situ observations and the bias between simulated Tb and regional Soil Moisture Ocean Salinity (SMOS) observations. A time-series comparison of the simulations to independent satellite-based estimates of evapotranspiration and brightness temperature (Tb) showed that no LSM setup significantly outperformed another for the entire region and that not all LSM simulations improved with updated parameter values.
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Furthermore, the different LSM structures redistributed water differently in response to these parameter updates.
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A relative comparison in terms of water budget components and “efficiency space” for various baseline and revised experiments showed that large regional and long-term differences in the simulated water budget partitioning relate to different LSM structures, whereas smaller local differences resulted from updated soil, vegetation and land cover parameters. The default LIS parameters were revised with (i) improved soil parameters, (ii) satellite-based interannually varying vegetation indices (leaf area index and green vegetation fraction) instead of climatological vegetation indices, and (iii) yearly land cover information instead of static land cover. Most large-scale LSMs may lack the ability to correctly represent the ongoing deforestation processes in this region, because most LSMs use climatological vegetation indices and static land cover information. The impact of this revision was tested over the South American Dry Chaco, an ecoregion characterized by deforestation and forest degradation since the 1980s. In this study, we tested the impact of a revised set of soil, vegetation and land cover parameters on the performance of three different state-of-the-art land surface models (LSMs) within the NASA Land Information System (LIS).