Abstract
Climate change and large-scale afforestation characterize the conditions in the Upper Dongjiang River Basin (UDRB), which is one of the most important headwater basins in southern China. It is important to understand whether, and to what extent, the observed runoff change can be attributed to forest and/or climate change. Using process- and relation-based methods, we found precipitation in spring (March–May) decreased notably, while precipitation in summer (June–August) showed an increase from the reference period (1961–1990) to the afforestation period (1991–2010). In comparison, annual averaged potential evapotranspiration did not change much. Both of the methods indicated forest had a positive effect while climate change exerted a negative impact on annual averaged runoff in the UDRB. As a result, the observed annual averaged runoff only showed a little decrease from the reference period to the afforestation period. The climate change impact on monthly averaged runoff basically followed the pattern of precipitation change. Except in July and August, climate change exerted negative or little impact on runoff in most of other months. In comparison, the forest effects on monthly averaged runoff change showed a totally different pattern. Except in May and June, forest exerted positive impact on runoff in other months. As a result, the observed monthly averaged runoff in May and June experienced notable reduction, while those in other months experienced increase or no change. The UDRB provides evidence that additional forest cover would not injure but even increase runoff, especially dry season runoff. The study has important implications for sustainable water management and afforestation in this subtropical region and for similar river basins.
Highlights
In forest-dominated watersheds, forest and climate change have been commonly recognized as two major drivers affecting the hydrologic cycle (Wei and Zhang 2010, Zhang et al 2011, Li et al 2012, Creed et al 2014, Ellison et al 2017, Bai et al 2020)
The climate change impact on monthly averaged runoff basically followed the pattern of precipitation change
The estimated contribution of climate change to monthly averaged runoff basically followed the pattern of precipitation change
Summary
In forest-dominated watersheds, forest and climate change have been commonly recognized as two major drivers affecting the hydrologic cycle (Wei and Zhang 2010, Zhang et al 2011, Li et al 2012, Creed et al 2014, Ellison et al 2017, Bai et al 2020). Some studies, especially in large watersheds, found that afforestation or reforestation have limited effects (Buttle and Metcalfe 2000), no effects (Antonio et al 2008), or even positive effects on water resources (Zhou et al 2010, Wang et al 2011) This issue is becoming increasingly complicated under climate change because shifts in precipitation and temperature can exert a profound impact on the hydrologic cycle and spatio-temporal pattern of water resources (Cuo et al 2009, Kang et al 2014, Shi et al 2015, Li et al 2016, Sorribas et al 2016, Zhang et al 2018), while increasing carbon dioxide concentration influences the water and energy balances in land–atmosphere interaction through its effects on plant physiology (Gedney et al 2006, Betts et al 2007, Mao et al 2015, Fowler et al 2019). Separating their contributions to hydrologic cycle, especially the runoff process, is essential for understanding and managing interactions between forest and climate change to ensure long-term water availability and ecosystem functions (Liu et al 2014; Kang et al 2016, Li et al 2020a)
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