Changes and response mechanisms of leaf area index and evapotranspiration in the typical natural landscapes of the Loess Plateau in northern Shaanxi of China under the human intervention

Abstract

Exploring the relationship between human activity, vegetation leaf area index (LAI), and land surface evapotranspiration (ET) on the Loess Plateau in northern Shaanxi is crucial for maintaining regional ecosystem functions and optimally allocating water resources. This study investigated the driving mechanism of LAI on ET under the intervention of the human activity intensity (HAIS) by analyzing seasonal and interannual variability characteristics and processes using remote sensing data of land use, LAI, and ET in typical natural landscapes (forest, grassland, and desert) in northern Shaanxi from 2000 to 2020. The primary findings were: (1) In the previous two decades, grassland HAIS was the largest, mainly distributed in central districts and counties, and gradually decreasing. The LAI and ET were ranked as follows: forest > grassland > desert, with an interannually increasing tendency, and the yearly mean LAI and ET of forest reached 2.18 and 16.47 mm, respectively. (2) The LAI and ET of the three typical natural landscapes changed substantially during the growing season (April-October) of vegetation, which increased and then decreased, reaching a maximum in June-August. The LAI and ET displayed noticeable numerical clustering among the months, with higher and concentrated values in June-August and lower values in April, May, and October. (3) Forest and grassland HAIS negatively affected LAI, and detrimentally regulated ET by primarily influencing LAI4-LAI7 (LAI from April to July). Desert HAIS had a significant positive link with the LAI and primarily regulated ET by positively influencing LAI6-LAI10. Compared to forest and grassland, the coregulatory effect of LAI on ET in the desert lagged relatively in the month. Our study recommends accelerating the conversion of the desert to forest and grassland on the Loess Plateau in northern Shaanxi for stabilizing landscape ecosystem function and the reciprocal feedback between vegetation and water resources faster.