Trend changes in global greening and browning: contribution of short‐term trends to longer‐term change

Abstract

Field observations and time series of vegetation greenness data from satellites provide evidence of changes in terrestrial vegetation activity over the past decades for several regions in the world. Changes in vegetation greenness over time may consist of an alternating sequence of greening and/or browning periods. This study examined this effect using detection of trend changes in normalized difference vegetation index (NDVI) satellite data between 1982 and 2008. Time series of 648 fortnightly images were analyzed using a trend breaks analysis (BFAST) procedure. Both abrupt and gradual changes were detected in large parts of the world, especially in (semi-arid) shrubland and grassland biomes where abrupt greening was often followed by gradual browning. Many abrupt changes were found around large-scale natural influences like the Mt Pinatubo eruption in 1991 and the strong 1997/98 El Niñ o event.The net global figure -considered over the full length of the time series -showed greening since the 1980s. This is in line with previous studies, but the change rates for individual short-term segments were found to be up to five times higher. Temporal analysis indicated that the area with browning trends increased over time while the area with greening trends decreased. The Southern Hemisphere showed the strongest evidence of browning. Here, periods of gradual browning were generally longer than periods of gradual greening. Net greening was detected in all biomes, most conspicuously in croplands and least conspicuously in needleleaf forests. For 15% of the global land area, trends were found to change between greening and browning within the analysis period. This demonstrates the importance of accounting for trend changes when analyzing long-term NDVI time series.

A conceptual model for assessing rainfall and vegetation trends in sub‐Saharan Africa from satellite data

“…Pricope et al (2013) found a consistently declining NDVI over the period 1999-2011 in northern and eastern Ethiopia, along the Somali coast and in central Kenya, where this pattern extended into central Tanzania. A similar pattern of vegetation deterioration was identified in the East African Horn by our study and by de Jong et al (2012). Here, a positive trend in vegetation greenness was also found across central parts of southern Africa, which is in accordance with Harris et al (2014).…”

Recent trends in sea surface temperature off Mexico

“…The number and position of the breakpoints are estimated from the seasonally adjusted data (Yt -Ŝt) with the method proposed by Bai and Perron (2003), which minimizes the Bayesian information criterion (BIC) to determine the optimal number of breaks and iteratively minimizes the residual sum of squares to estimate the optimum break position. Verbesselt et al (2010) give a full description and validation of the method, which has been applied as a normalized difference vegetation index (NDVI; Verbesselt et al, 2010Verbesselt et al, , 2012de Jong et al, 2012). We tested the method suitability for monthly temperature values.…”

Spatiotemporal changes of vegetation on the Tibetan Plateau and relationship to climatic variables during multiyear periods from 1982–2012

“…Ecological restoration projects during the last decade have promoted the vegetation cover in Three-River Source Regions, which is located in central part of the TP ). Linear regression is simple, robust, and the results are easy to interpret (Fensholt et al 2009;Peng et al 2012b) but the overall linear trend is a simplification of the actual temporal patterns of vegetation growth change during the entire study period (de Jong et al 2011(de Jong et al , 2012Piao et al 2011). For example, spring NDVI on the TP exhibits combined greening and browning trends, which are averaged out by a simple linear trend analysis during whole period.…”

“…The combination of these changes has greatly impacted vegetation growth (Ding et al 2010;Mao et al 2007;Mohammat et al 2013;Peng et al 2012b;Xu et al , 2012Yang et al 2005;Yang and Piao 2006;Zhang et al 2010). Linear trend analysis over a long series of years may obscure significant changes appearing within shorter time intervals (de Jong et al 2012). Comparative analysis of results from multi-periods, changes in vegetation NDVI over the most recent years, and dynamics of NDVI trends are poorly studied.…”