Transition zones between dry and humid climates are highly sensitive areas where small changes in the spatial and temporal distribution of rainfall may have vast consequences on vegetation development. Rainfall regimes are expected to change worldwide and predictions include variations in total annual precipitation and timing of rain events. In this context, evaluating the relationship between vegetation activity and rainfall variability along transition zones is particularly relevant. In this study, 54 years (1961–2013) of gridded monthly rainfall data (Climatic Research Unit Time‐Series Version 3.22 [CRU TS3.22]) were used to analyse annual and inter‐annual rainfall variability. Land surface phenology (LSP) metrics (2000–2013) were derived from MODIS 16‐day composites Normalized Difference Vegetation Index (NDVI) data (MOD13Q1 product) and relationship between rainfall variability and LSP metrics was assessed. Annual rainfall showed a strong seasonality in the northeast of the study area that diminishes towards the southwest. Inter‐annual rainfall variability, which showed a significant 8‐year cycle periodicity after 1980, was stronger in the southwest of the region. For most of the study area, summer rainfall (November–January) showed significant negative correlation with August–October Southern Oscillation Index (SOI) average, although this connection was not reflected in annual precipitation totals. Regarding vegetation response to rainfall variability, two main areas were identified where differences in LSP metrics between wet and dry years were larger than the average. The first one was a zone within the humid to semi‐arid transition belt, where NDVI maximum, NDVI amplitude and NDVI integral showed higher values during wet years. The second one was the central north area, which showed higher NDVI amplitude values during dry years. In the study area, water availability is a sensitive issue for natural ecosystems, agriculture and cattle‐raising. These results provide a better understanding of the relationship between rainfall variability and vegetation changes, which is useful information for the development of future management policies.

Soil salinization is considered an environmental threat as high salt content hinders plant growth. Soil salinity is usually associated with climate aridity at a regional scale, while topography, subsurface hydrology, and land use combine with climate to produce salinization patterns at landscape scale. In this study, the first such assessment for the study area, we investigated the relationship between climate, groundwater level (GWL) changes, and soil salinity. For comparison, two adjacent vegetation units used as marginal grazing lands were selected: thickets of Allenrolfea patagonica (Ap thicket), located at the base of a scarp, and bushes of Cyclolepis genistoides (Cg bush), located away from the topographic discontinuity. Electrical conductivity (ECrs) maps derived from LANDSAT‐8/OLI were used to analyze salinity patterns. The results showed that GWL rose in coincidence with precipitation events and fell during dryer and warmer periods. GWL was always closer to the surface in the Ap thicket, and level changes were more likely to occur there. ECrs showed a seasonal pattern with significantly higher (p < 0.05) values in the Ap thicket during summer. Within the Cg bush, relatively higher ECrs appeared around a permanent water trough. Within this zone, ECrs values during summer were significantly higher (p < 0.05). Coupled evaluation of GWL dynamics and soil salinization patterns showed that GWL changes interact with land use practices to produce local‐scale patterns of salinization. Topography played an important role in controlling soil surface properties through its influence on groundwater dynamics and small topographic changes produced largely different conditions for vegetation growth.

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