{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T00:47:59Z","timestamp":1782780479244,"version":"3.54.5"},"reference-count":62,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2013,2,4]],"date-time":"2013-02-04T00:00:00Z","timestamp":1359936000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>The \u2018rain use efficiency\u2019 (RUE) may be defined as the ratio of above-ground net primary productivity (ANPP) to annual precipitation, and it is claimed to be a conservative property of the vegetation cover in drylands, if the vegetation cover is not subject to  non-precipitation related land degradation. Consequently, RUE may be regarded as means of normalizing ANPP for the impact of annual precipitation, and as an indicator of  non-precipitation related land degradation. Large scale and long term identification and monitoring of land degradation in drylands, such as the Sahel, can only be achieved by use of Earth Observation (EO) data. This paper demonstrates that the use of the standard  EO-based proxy for ANPP, summed normalized difference vegetation index (NDVI) (National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) Global Inventory Modeling and Mapping Studies 3rd generation (GIMMS3g)) over the year (\u03a3NDVI), and the blended EO\/rain gauge based  data-set for annual precipitation (Climate Prediction Center Merged Analysis of Precipitation, CMAP) results in RUE-estimates which are highly correlated with precipitation, rendering RUE useless as a means of normalizing for the impact of annual precipitation on ANPP. By replacing \u03a3NDVI by a \u2018small NDVI integral\u2019, covering only the rainy season and counting only the increase of NDVI relative to some reference level, this problem is solved. Using this approach, RUE is calculated for the period 1982\u20132010. The result is that positive RUE-trends dominate in most of the Sahel, indicating that  non-precipitation related land degradation is not a widespread phenomenon. Furthermore, it is argued that two preconditions need to be fulfilled in order to obtain meaningful results from the RUE temporal trend analysis: First, there must be a significant positive linear correlation between annual precipitation and the ANPP proxy applied. Second, there must be a near-zero correlation between RUE and annual precipitation. Thirty-seven percent of the pixels in Sahel satisfy these requirements and the paper points to a range of different reasons why this may be the case.<\/jats:p>","DOI":"10.3390\/rs5020664","type":"journal-article","created":{"date-parts":[[2013,2,4]],"date-time":"2013-02-04T11:10:35Z","timestamp":1359976235000},"page":"664-686","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":185,"title":["Assessing Land Degradation\/Recovery in the African Sahel from Long-Term Earth Observation Based Primary Productivity and Precipitation Relationships"],"prefix":"10.3390","volume":"5","author":[{"given":"Rasmus","family":"Fensholt","sequence":"first","affiliation":[{"name":"Department of Geosciences and Natural Resource Management, University of Copenhagen, \u00d8ster Voldgade 10, DK-1350 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kjeld","family":"Rasmussen","sequence":"additional","affiliation":[{"name":"Department of Geosciences and Natural Resource Management, University of Copenhagen, \u00d8ster Voldgade 10, DK-1350 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Per","family":"Kaspersen","sequence":"additional","affiliation":[{"name":"DTU Climate Centre, Systems Analysis Division, Ris\u00f8 DTU, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Silvia","family":"Huber","sequence":"additional","affiliation":[{"name":"Geographic Resource Analysis & Science A\/S, Department of Geography and Geology, University of Copenhagen, \u00d8ster Voldgade 10, DK-1350 Copenhagen K, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Stephanie","family":"Horion","sequence":"additional","affiliation":[{"name":"Department of Geosciences and Natural Resource Management, University of Copenhagen, \u00d8ster Voldgade 10, DK-1350 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Else","family":"Swinnen","sequence":"additional","affiliation":[{"name":"Remote Sensing and Earth Observation Processes, Global Vegetation Research Group, VITO, Boeretang 200, B-2400 MOL, Belgium"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2013,2,4]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"137","DOI":"10.1016\/S0921-8181(00)00040-0","article-title":"The nature of rainfall variability over Africa on time scales of decades to millenia","volume":"26","author":"Nicholson","year":"2000","journal-title":"Global Planet. 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