 The paper defines rain use efficiency, RUE, as the ratio of above-ground net primary productivity, ANPP, to annual precipitation, and claims that it is a conservative property of vegetation cover in drylands if non-precipitation-related land degradation does not occur. RUE can be used to normalize ANPP for the impact of annual precipitation and as an indicator of non-precipitation related land degradation. The paper uses Earth observation, EOF, data, specifically summed normalized difference vegetation index, NDVA, from NOAA Advanced Very High Resolution Radiometer, AVHRA, Global Inventory Modeling and Mapping Studies 3rd Generation, GEMMS-3G, to estimate RUE. However, the results show that RUE is not useful as a means of normalizing for the impact of annual precipitation on ANPP because it is highly correlated with precipitation. The paper suggests replacing sigma NDVI with that small NDVI integral, covering only the rainy season and counting only the increase of NDVI relative to some reference level, which solves the problem. Using this approach, RUE is calculated for the period 1982 to 2010. The paper argues that two preconditions need to be fulfilled in order to obtain meaningful results from the RUE Temporal Trend Analysis, a significant positive linear correlation between annual precipitation and the ANPP proxy applied, and a near zero correlation between RUE and annual precipitation. 37% of the pixels in Sahel satisfy these requirements. The paper points to different reasons why this may be the case. This article was authored by L. Swinnin, Stephanie Horian, Precasperson, and others. We are article.tv, links in the description below.