Abstract
Over the past several decades, rocky desertification has led to severe ecological problems in karst areas in South China. After a rocky desertification treatment project was completed, the vegetation coverage changed greatly and, consequently, increased the ecology water consumption (approximately equal to the actual evapotranspiration) of the regional vegetation. Thus, it intensified the regional water stresses. This study explored the changes in the actual evapotranspiration (ETa) response to the vegetation coverage changes in the rocky desertification areas in South China based on the precipitation (P), potential evapotranspiration (ETp) and NDVI (the normalized difference vegetation index) datasets. The revised Bagrov model was used to simulate the actual evapotranspiration changes with the supposed increasing NDVI. The results indicated that the average NDVI value was lower when the rocky desertification was more severe. The ETa, evapotranspiration efficiency (ETa/ETp) and potential humidity (P/ETp) generally increased with the increasing NDVI. The sensitivity of the ETa response to vegetation coverage changes varied due to different precipitation conditions and different rocky desertification severities. The ETa was more sensitive under drought conditions. When a drought occurred, the ETa exhibited an average increase of 40~60 mm with the NDVI increasing of 0.1 in the rocky desertification areas. Among the 5 different severity categories of rocky desertification, the ETa values’ responses to NDVI changes were less sensitive in the severe rocky desertification areas but more sensitive in the extremely and potential rocky desertification areas. For example, with the NDVI increasing of 0.025, 0.05, 0.075, and 0.1, the corresponding ETa changes increased by an average of 2.64 mm, 10.62 mm, 19.19 mm, and 27.58 mm, respectively, in severe rocky desertification areas but by 4.94 mm, 14.99 mm, 26.80, and 37.13 mm, respectively, in extremely severe rocky desertification areas. Understanding the vegetation ecological water consumption response to the vegetation coverage changes is essential for the vegetation restoration and water stresses mitigation in rocky desertification areas.
Highlights
In the karst areas of South China, intensive vegetation degradation and severe rocky desertification have threatened the local ecological security [1]
Our study focused on the ETa response to NDVI changes in the different severity categories of the rocky desertification areas
The main conclusions of our study were as follows: The evapotranspiration efficiency (ETa/ETp) and potential humidity (P/ETp) values were greatly influenced by the precipitation and NDVI changes and were more sensitive in the lower precipitation conditions
Summary
In the karst areas of South China, intensive vegetation degradation and severe rocky desertification have threatened the local ecological security [1]. Vegetation restoration is crucial for improving the regional eco-environmental quality [2]. After 2008, the rocky desertification treatment project was conducted by the government and greatly improved the local ecological environment, and large changes in the vegetation coverage occurred in this region [3]. Water has been a key factor limiting the eco-restoration and construction of the vegetation [4, 5]. As the vegetation coverage increased, the vegetation ecological water consumption was likely to rise [6, 7]. The increase in vegetation coverage intensified the water stresses in this region [12]. Understanding the vegetation ecological water consumption response to the vegetation coverage changes is essential for rational ecological construction and ecological sustainable development in rocky desertification areas
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