Biophysical Climate Effects of Afforestation and Vegetation Greening in China from 1982 to 2011

Abstract:

Large-area afforestation and reforestation projects have been performed in China since the 1980s. It has been reported that these programmes are one of the main causes of regional carbon uptake. Besides, these increased forest areas, in combined with increased leaf area index—so called ‘vegetation greening’, are also expected to biophysically influence the near-surface temperature and regional hydrological cycle through reduced land surface albedo, increased evapotranspiration (ET) and surface roughness (reduced aerodynamic resistance). In this presentation, we will show the benefits of combining the remote sensing observations and inventory-based data for detecting the spatiotemporal changes of forest dynamics in China over the past three decades. Using a global climate model with a higher spatial resolution zoomed grid over China, we found that 30-year vegetation dynamics have the largest impact on surface air temperature in spring (that is, from March to May), with the greening-induced ET enhancement causing a general cooling of -0.04 ^oC decade^-1 (~25% of the simulated spring warming) averaged across the country. In southern China where the largest increase of forest area has been found, the potential cooling effects of increased ET were offset by the warming effects of lower albedo. Meanwhile, we found that the widespread increase in ET has not caused a consistent decline in soil moisture or drier surface hydrological environment. Driven by the vegetation feedback, the model simulated that an increased precipitation, although statistically insignificant, supplied enough water to offset the potential ET-induced water deficit in North and Southeast China. Despite these regional biophysical impacts, the vegetation-induced spring cooling in China may also exert remote temperature effects in northern high latitudes, accounting for ~58% of simulated spring warming over the Russian Arctic and ~61% of simulated spring cooling over the Canadian Arctic. Our studies systematically assess the consequences of 30-year forest dynamics in China on surface energy balance and water cycling both regionally and globally under current plantation policy and the changing climate system. This should contribute to the strengthened understanding in terms of deploying forests as the natural climate solutions.