Changes in satellite‐derived spring vegetation green‐up date and its linkage to climate in China from 1982 to 2010: a multimethod analysis

Abstract

The change in spring phenology is recognized to exert a major influence on carbon balance dynamics in temperate ecosystems. Over the past several decades, several studies focused on shifts in spring phenology; however, large uncertainties still exist, and one understudied source could be the method implemented in retrieving satellite-derived spring phenology. To account for this potential uncertainty, we conducted a multimethod investigation to quantify changes in vegetation green-up date from 1982 to 2010 over temperate China, and to characterize climatic controls on spring phenology. Over temperate China, the five methods estimated that the vegetation green-up onset date advanced, on average, at a rate of 1.3 ± 0.6 days per decade (ranging from 0.4 to 1.9 days per decade) over the last 29 years. Moreover, the sign of the trends in vegetation green-up date derived from the five methods were broadly consistent spatially and for different vegetation types, but with large differences in the magnitude of the trend. The large intermethod variance was notably observed in arid and semiarid vegetation types. Our results also showed that change in vegetation green-up date is more closely correlated with temperature than with precipitation. However, the temperature sensitivity of spring vegetation green-up date became higher as precipitation increased, implying that precipitation is an important regulator of the response of vegetation spring phenology to change in temperature. This intricate linkage between spring phenology and precipitation must be taken into account in current phenological models which are mostly driven by temperature.

Notable shifting in the responses of vegetation activity to climate change in China

“…Climate warming has greatly affected vegetation growth in China over the past three decades (Zhou et al, 2001;McMahon et al, 2010;Mao et al, 2012;Cong et al, 2013;Xu et al, 2014). According to this study, the positive relationship between temperature and NDVI became negative over the course of the study period, although this result was not statistically significant.…”

Analysis of CO<sub>2</sub> mole fraction data: first evidence of large-scale changes in CO<sub>2</sub> uptake at high northern latitudes

“…The warming-induced earlier onset of springtime carbon uptake is also supported by observed increases in vegetation greenness described by NDVI inferred from space-borne sensors (Gong and Shi, 2003;Mao et al, 2012;Cong et al, 2013). Increases in autumn NDVI have also been observed and while this is indicative of increased photosynthetic activity it is not necessarily inconsistent with the observed early onset of net carbon release.…”

Trends in Spring Phenology of Western European Deciduous Forests

“…Many studies use data from AVHRR sensor to study leaf/surface phenology, for example [19,27,28], probably because of a longer time series spanning over three decades thus providing a long record of vegetation conditions ideal to study the long-term effect of climate variability on vegetation phenology. However, for highly fragmented ecosystems/landscapes, i.e., in Western Europe, vegetation type-specific studies are generally challenging to undertake when using data from AVHRR sensor because the pixel is always likely to be composed of more than one landcover type.…”

“…In some parts of USA, temporal trends (negative and positive) were only found in the satellite derived SOS ensemble metrics from two methods (HANTS and Midpoint pixel ) that produced relatively more accurate SOS metrics, but no trend was found in the ground observations [19]. Of recent, temporal trends were detected over China in the satellite SOS estimates [27,28], but no results were reported in regard to ground observations. However, a study focusing on leaf unfolding dates of broadleaf deciduous forest in Northern China found significant spatial and temporal correlations between ground observations and satellite SOS estimates [29], but temporal trend analysis on SOS was not done.…”

“…A global analysis of vegetation phenology shows that satellite-based phenological estimates provide realistic estimates of the several phenological events (e.g., SOS) [33], however in a global context the validation of satellite-based phenological estimates was based only on spatially limited network of phenological stations, and temporal phenological shifts were also not quantified. Lack of ground observations to validate the phenological changes detected from satellite-derived metrics will continue to cast uncertainty on the phenological changes detected from satellite data, and the use of multimethods to retrieve phenological metrics [19,28] is not likely to remove this uncertainty. Without in situ observations, it remains difficult to show that the phenological changes detected from satellite data are real changes, especially when it is not known if the method (e.g., Midpoint pixel ) being employed to extract phenological metrics is capable of producing metrics with phenological changes commensurate with that in in situ observations (e.g.…”