A comparative analysis of forest cover and catchment water yield relationships in northern China

Abstract

a b s t r a c tDuring the past few decades, China has implemented several large-scale forestation programs that have increased forest cover from 16.0% in the 1980s to 20.4% in 2009. In northern China, water is the most sensitive and limiting ecological factor. Understanding the dynamic interactions between forest ecosystems and water in different regions is essential for maximizing forest ecosystem services. We examined forest cover and runoff relationships in northern China using published data from a variety of sources. In the Loess Plateau region, forest cover is not correlated with annual precipitation (r = 0.08, p > 0.05) at micro (<50 km 2 ) and meso scales (50-1000 km 2 ), while they are positively correlated at macro (>1000 km 2 ) scale (r = 0.77, p < 0.05). Moreover, forest cover is negatively correlated with the runoff coefficient (r = À0.64, p < 0.05). In Northwest China, natural forest distribution is highly correlated with annual precipitation (r = 0.48, p < 0.05) but not with the runoff coefficient (r = À0.09, p > 0.05). In Northeast China, we found a positive relationship between forest cover and the runoff coefficient (r = 0.77, p < 0.05), but the correlation between forest cover and precipitation was not significant (r = 0.28, p > 0.05). The multiple stepwise regression analysis indicated that runoff was influenced by altitude, annual precipitation, forest cover, and PET (potential evapotranspiration) in Northeast China. We concluded that geographic differences could mask the true role of forests in the partitioning of rainfall into runoff and evapotranspiration (ET) in a catchment. In determining the forest-water relationship, one must consider climatic controls on ET in addition to forest cover. Forests could potentially enhance the complementary relationship between ET and PET. Therefore, a greater amount of ET in forested areas may decrease the PET on a regional scale.

Global pattern for the effect of climate and land cover on water yield

“…In humid regions (P/PET41) where PET plays a dominant role in water yield or evapotranspiration, a decrease in PET will likely cause a significant increase in water yield. This is consistent with the findings that afforestation can increase water yield in large watersheds of humid regions 11,12 because afforestation cools local land surface temperature 39 and thus decreases PET.…”

“…Several reviews of these experiences involving more than 250 PWEs from around the globe have reported that, although forest changes significantly affect the water yield [3][4][5] , the magnitude of any change varies greatly from one watershed to another 6,7 . Some studies, especially in large watersheds, found that forest changes have limited effects 8 , no effects 9,10 or even positive effects 11,12 on water yield. These highly variable and apparently inconsistent results have led to debates in both research and resource management communities, especially when another catastrophic flood or drought occurs somewhere in the world 13 .…”

Responses of soil moisture in different land cover types to rainfall events in a re-vegetation catchment area of the Loess Plateau, China

“…Re-vegetation can result in the increase of vegetation cover (Xin et al, 2008), improvement of soil nutrient levels (Zhou et al, 2008) and recovery of soil physical properties (Vallauri et al, 2002). However, re-vegetation also aggravated water scarcity (Wang et al, 2011a), which was one of the most prominent issues related to sustainable development. Addressing the trade-offs among water availability, grain production and carbon sequestration is the basis for ensuring the sustainable provision of ecosystem services in the Loess Plateau and requires a detailed understanding of the eco-hydrological processes involved.…”

Effect of climatic change and afforestation on water yield in the Rocky Mountain Area of North China

“…Sun et al (2006) suggests that the average water yield reduction may vary from about 50 mm/yr (50%) in the semi-arid Loess Plateau region in northern China to about 300 mm/yr (30%) in the tropical southern region. Wang et al (2011a) using a variety of published data showed there is a positive relationship between forest cover and the runoff coefficient (r = 0.77, p < 0.05) in Northeast China. However, contradictory reports on the impact of forest on water yield also exist.…”