Quantifying the effects of climate and environmental changes on evapotranspiration variability in the Sahel

• Published in: Journal of hydrology (Amsterdam) Vol. 642; p. 131874
• Main Authors: Nkiaka, Elias, Bryant, Robert G., Dembélé, Moctar, Yonaba, Roland, Imuwahen Priscilla, Aigbedion, Karambiri, Harouna
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-10-2024
• Subjects: Analytical methods; Elasticity concept; Great green wall initiative; Least square and double logarithm elasticity models; NDVI; Partial correlation coefficient; Analytical methods; Great green wall initiative; Elasticity concept; Partial correlation coefficient; Least square and double logarithm elasticity models; NDVI
• ISSN: 0022-1694
• DOI: 10.1016/j.jhydrol.2024.131874

•Significant increasing trends in annual ET in most parts of the Sahelian belt.•Precipitation, humidity, and vapour pressure (climatic factors), and soil moisture and NDVI (environmental factors) are the most important variables controlling increase in ET.•Vapour pressure has the highest positive elasticity score (2.58) while net radiation has the highest negative elasticity score (−9.58) on ET.•The study covers the whole Sahelian belt from west to east making it to stand out from previous studies in the region that cover mostly the western Sahel.
Whilst considerable research has been carried out to understand the effects of reforestation on evapotranspiration (ET), such studies are generally absent in the Sahel even though the region is currently undergoing extensive reforestation to halt desertification and land degradation. The objective of this study is to identify and quantify the dominant climatic and environmental factors influencing ET variability in the Sahel. However, achieving this goal in the Sahel is hindered by a lack of in situ monitoring data. To overcome this challenge, this study adopts geospatial datasets along with analytical methods to assess the climatic and environmental factors affecting ET in 45 watersheds in the Sahel over a period of four decades (1982–2021). Analyses show significant increasing trends in annual ET in more than 90% of the watersheds. Precipitation and mean temperature show significant increasing trends in all watersheds while windspeed, vapour pressure, solar radiation, specific humidity, and atmospheric evaporative demand show mixed results with both increasing and decreasing trends in different watersheds. Environmental variables including soil moisture, and vegetation cover measured using the normalised difference vegetative index (NDVI) also show consistent increasing trends in all watersheds. Statistical analyses further show that climatic and environmental factors contribute about 80% of ET variance. The relative contribution of climatic variables on ET variance is 75.11% while that of environmental variables is 24.71%. This suggests that climatic factors have a higher influence on ET variability than environmental factors. Analyses using the double logarithm elasticity model show that vapour pressure has the highest positive elasticity coefficient (2.58) on ET while net radiation has the highest negative elasticity coefficient (−9.58). This is the first study to cover the whole Sahelian belt from west to east and the results may be crucial for adopting climate-smart reforestation policies, enhance regional water management and improve our knowledge of vegetation-hydrology-climate interactions in the Sahel.