We analyzed potential land degradation processes in semiarid regions worldwide using long time series of remote sensing images and the Normalized Difference Vegetation Index (NDVI) for the period 1981 to 2011. The objectives of the study were to identify semiarid regions showing a marked decrease in potential vegetation activity, indicative of the occurrence of land degradation processes, and to assess the possible influence of the observed drought trends quantified using the Standardized Precipitation Evapotranspiration Index (SPEI). We found that the NDVI values recorded during the period of maximum vegetation activity (NDVI_max) predominantly showed a positive evolution in the majority of the semiarid regions assessed, but NDVI_max was highly correlated with drought variability, and the trends of drought events influenced trends in NDVI_max at the global scale. The semiarid regions that showed most increase in NDVI_max (the Sahel, northern Australia, South Africa) were characterized by a clear positive trend in the SPEI values, indicative of conditions of greater humidity and lesser drought conditions. While changes in drought severity may be an important driver of NDVI trends and land degradation processes in semiarid regions worldwide, drought did not apparently explain some of the observed changes in NDVI_max. This reflects the complexity of vegetation activity processes in the world’s semiarid regions, and the difficulty of defining a universal response to drought in these regions, where a number of factors (natural and anthropogenic) may also affect on land degradation.

This study detects climate trends and variability from precipitation and temperature observations in Ecuador and assesses their links to the El Niño Southern Oscillation (ENSO) for the period 1966–2011, using the El Niño 1+2 and El Niño 3.4 indices. Excluding the Amazonian region (for which there is a lack of data), two main regions were distinguishable in terms of variability and trends among climate variables, especially for precipitation. In general, there was no trend in precipitation for the coastal region, and a very close relationship between the magnitude and seasonal distribution of precipitation and the El Niño 1+2 variability was found. In contrast, for the mountainous region (the Andes), there was an increase of precipitation during the study period, and a signal of El Niño 3.4 influence was detected. Temperatures were spatially homogeneous and showed an intense warming trend, except for maximum temperatures in the coastal region. The El Niño 1+2 influence on temperature was large from January to July. The results provide evidence of the close control exerted by the ENSO, especially in the coast of Ecuador, as well as for the occurrence of significant warming across the country independent of the ENSO phenomenon.