Watershed Evapotranspiration Increased due to Changes in Vegetation Composition and Structure Under a Subtropical Climate¹

Abstract

Natural forests in southern China have been severely logged due to high human demand for timber, food, and fuels during the past century, but are recovering in the past decade. The objective of this study was to investigate how vegetation cover changes in composition and structure affected the water budgets of a 9.6-km 2 Dakeng watershed located in a humid subtropical mountainous region in southern China. We analyzed 27 years (i.e., 1967-1993) of streamflow and climate data and associated vegetation cover change in the watershed. Land use ⁄ land cover census and Normalized Difference of Vegetation Index (NDVI) data derived from remote sensing were used to construct historic land cover change patterns. We found that over the period of record, annual streamflow (Q) and runoff ⁄ precipitation ratio did not change significantly, nor did the climatic variables, including air temperature, Hamon's potential evapotranspiration (ET), pan evaporation, sunshine hours, and radiation. However, annual ET estimated as the differences between P and Q showed a statistically significant increasing trend. Overall, the NDVI of the watershed had a significant increasing trend in the peak spring growing season. This study concluded that watershed ecosystem ET increased as the vegetation cover shifted from low stock forests to shrub and grasslands that had higher ET rates. A conceptual model was developed for the study watershed to describe the vegetation cover-streamflow relationships during a 50-year time frame. This paper highlighted the importance of eco-physiologically based studies in understanding transitory, nonstationary effects of deforestation or forestation on watershed water balances.

Effect of reforestation on annual water yield in a large watershed in northeast China

“…Annual water yield was estimated as the difference between measured precipitation and actual ET. We assumed no change in soil water storage during the study period as Sun et al (2008) and Li et al (2014) did. Our result agrees with the general conclusions reached for small watersheds that there were detectable changes in annual water yield when at least 20 % of the forest cover was re-established (Bosch and Hewlett 1982;Moore and Scott 2005).…”

Detection of global runoff changes: results from observations and CMIP5 experiments

“…This conclusion is also supported by Sterling et al (2013) in the case of taking into account the irrigation. On the other hand, Liu et al (2008) and Sun et al (2008) indicate that deforestation over China, associated with irrigation, leads to increased evapotranspiration over the 20th century. Other studies, over individual river basins, suggested that the sign of land use induced change was unclear (e.g.…”

Increased Vegetation Greenness Aggravates Water Conflicts during Lasting and Intensifying Drought in the Poyang Lake Watershed, China

“…It has been successfully applied in many countries such as the U.S. and Mexico [27,30]. Compared to other process-based ecosystem models, the WaSSI model has two advantages: (1) it can simulate the water cycle in a changing climate, and (2) the input data for this model can be acquired more easily than those of other models [27].…”