Trends In Vegetation Greenness Research Articles

The long-term trends (1982–2006) in vegetation greenness of the alpine ecosystem in the Qinghai-Tibetan Plateau

The increased rate of annual temperature in the Qinghai-Tibetan Plateau exceeded all other areas of the same latitude in recent decades. The influence of the warming climate on the alpine ecosystem of the plateau was distinct. An analysis of alpine vegetation under changes in climatic conditions was conducted in this study. This was done through an examination of vegetation greenness and its relationship with climate variability using the Advanced Very High Resolution Radiometer satellite imagery and climate datasets. Vegetation in the plateau experienced a positive trend in greenness, with 18.0 % of the vegetated areas exhibiting significantly positive trends, which were primarily located in the eastern and southwestern parts of the plateau. In grasslands, 25.8 % of meadows and 14.1 % of steppes exhibited significant upward trends. In contrast, the broadleaf forests experienced a trend of degradation. Temperature, particularly summer temperature, was the primary factor promoting the vegetation growth in the plateau. The wetter and warmer climate in the east contributed to the favorable conditions for vegetation. The alpine meadow was mostly sensitive to temperature, while the steppes were sensitive to both temperature and precipitation. Although a warming climate was expected to be beneficial to vegetation growth in the alpine region, the rising temperature coupled with reduced precipitation in the south did not favor vegetation growth due to low humidity and poor soil moisture conditions.

Consistent response of vegetation dynamics to recent climate change in tropical mountain regions

Global climate change has emerged as a major driver of ecosystem change. Here, we present evidence for globally consistent responses in vegetation dynamics to recent climate change in the world's mountain ecosystems located in the pan-tropical belt (30°N-30°S). We analyzed decadal-scale trends and seasonal cycles of vegetation greenness using monthly time series of satellite greenness (Normalized Difference Vegetation Index) and climate data for the period 1982-2006 for 47 mountain protected areas in five biodiversity hotspots. The time series of annual maximum NDVI for each of five continental regions shows mild greening trends followed by reversal to stronger browning trends around the mid-1990s. During the same period we found increasing trends in temperature but only marginal change in precipitation. The amplitude of the annual greenness cycle increased with time, and was strongly associated with the observed increase in temperature amplitude. We applied dynamic models with time-dependent regression parameters to study the time evolution of NDVI-climate relationships. We found that the relationship between vegetation greenness and temperature weakened over time or was negative. Such loss of positive temperature sensitivity has been documented in other regions as a response to temperature-induced moisture stress. We also used dynamic models to extract the trends in vegetation greenness that remain after accounting for the effects of temperature and precipitation. We found residual browning and greening trends in all regions, which indicate that factors other than temperature and precipitation also influence vegetation dynamics. Browning rates became progressively weaker with increase in elevation as indicated by quantile regression models. Tropical mountain vegetation is considered sensitive to climatic changes, so these consistent vegetation responses across widespread regions indicate persistent global-scale effects of climate warming and associated moisture stresses.

Satellite-based analysis of recent trends in the ecohydrology of a semi-arid region

Abstract. We present a regional framework for an integrated and spatiotemporally distributed assessment of human-induced trends in the hydrology and the associated ecological health of a semi-arid basin where both human activities (i.e. agriculture) and natural ecosystems are highly groundwater dependent. To achieve this, we analysed the recent trends (from year 2000 to 2010) in precipitation, evapotranspiration (actual and potential) and vegetation greenness (i.e. NDVI) using a combination of satellite and ground-based observations. The trend assessment was applied for the semi-arid Konya Basin (Turkey), one of the largest endorheic basins in the world. The results revealed a consistent increasing trend of both yearly evapotranspiration (totally 63 MCM yr−1 from croplands) and mean NDVI (about 0.004 NDVI yr−1 in irrigated croplands), especially concentrating in the plain part of the basin, while no significant trends were observed for the precipitation and potential evapotranspiration variables. On the contrary, a consistent decreasing trend of both yearly evapotranspiration (totally −2.1 MCM yr−1) and mean NDVI (−0.001 NDVI yr−1) was observed in the wetlands, which also cannot be explained by trends in precipitation and potential evapotranspiration. The emerging picture suggest that the greening trend of the vegetation and increasing of evapotranspiration in the plain are related to land cover changes (i.e. conversion into irrigated croplands) and to the intensification of the supplementary irrigation for agriculture, which in turn caused drying out of some wetlands and the natural vegetation which mostly depend on the groundwater, the main source of irrigation water as well. Our study presented an example of the utility of spatially and temporally continuous RS data in assessing the regional trends in hydrological and ecological variables and their interactions in a spatially distributed manner in a semi-arid region, which can also be adapted to other regions. Such spatiotemporally distributed analysis at the basin level is particularly important considering that most of the water management interventions also take place at this scale.

Recent Declines in Warming and Vegetation Greening Trends over Pan-Arctic Tundra

Vegetation productivity trends for the Arctic tundra are updated for the 1982–2011 period and examined in the context of land surface temperatures and coastal sea ice. Understanding mechanistic links between vegetation and climate parameters contributes to model advancements that are necessary for improving climate projections. This study employs remote sensing data: Global Inventory Modeling and Mapping Studies (GIMMS) Maximum Normalized Difference Vegetation Index (MaxNDVI), Special Sensor Microwave Imager (SSM/I) sea-ice concentrations, and Advanced Very High Resolution Radiometer (AVHRR) radiometric surface temperatures. Spring sea ice is declining everywhere except in the Bering Sea, while summer open water area is increasing throughout the Arctic. Summer Warmth Index (SWI—sum of degree months above freezing) trends from 1982 to 2011 are positive around Beringia but are negative over Eurasia from the Barents to the Laptev Seas and in parts of northern Canada. Eastern North America continues to show increased summer warmth and a corresponding steady increase in MaxNDVI. Positive MaxNDVI trends from 1982 to 2011 are generally weaker compared to trends from 1982–2008. So to better understand the changing trends, break points in the time series were quantified using the Breakfit algorithm. The most notable break points identify declines in SWI since 2003 in Eurasia and 1998 in Western North America. The Time Integrated NDVI (TI-NDVI, sum of the biweekly growing season values of MaxNDVI) has declined since 2005 in Eurasia, consistent with SWI declines. Summer (June–August) sea level pressure (slp) averages from 1999–2011 were compared to those from 1982–1998 to reveal higher slp over Greenland and the western Arctic and generally lower pressure over the continental Arctic in the recent period. This suggests that the large-scale circulation is likely a key contributor to the cooler temperatures over Eurasia through increased summer cloud cover and warming in Eastern North America from more cloud-free skies.

Greenness in semi-arid areas across the globe 1981–2007 — an Earth Observing Satellite based analysis of trends and drivers

Semi-arid areas, defined as those areas of the world where water is an important limitation for plant growth, have become the subject of increased interest due to the impacts of current global changes and sustainability of human lifestyles. While many ground-based reports of declining vegetation productivity have been published over the last decades, a number of recent publications have shown a nuanced and, for some regions, positive picture. With this background, the paper provides an analysis of trends in vegetation greenness of semi-arid areas using AVHRR GIMMS from 1981 to 2007. The vegetation index dataset is used as a proxy for vegetation productivity and trends are analyzed for characterization of changes in semi-arid vegetation greenness. Calculated vegetation trends are analyzed with gridded data on potential climatic constraints to plant growth to explore possible causes of the observed changes. An analysis of changes in the seasonal variation of vegetation greenness and climatic drivers is conducted for selected regions to further understand the causes of observed inter-annual vegetation changes in semi-arid areas across the globe. It is concluded that semi-arid areas, across the globe, on average experience an increase in greenness (0.015 NDVI units over the period of analysis). Further it is observed that increases in greenness are found both in semi-arid areas where precipitation is the dominating limiting factor for plant production (0.019 NDVI units) and in semi-arid areas where air temperature is the primarily growth constraint (0.013 NDVI units). Finally, in the analysis of changes in the intra-annual variation of greenness it is found that seemingly similar increases in greenness over the study period may have widely different explanations. This implies that current generalizations, claiming that land degradation is ongoing in semi-arid areas worldwide, are not supported by the satellite based analysis of vegetation greenness.

Changes in satellite‐derived vegetation growth trend in temperate and boreal Eurasia from 1982 to 2006

AbstractMonitoring changes in vegetation growth has been the subject of considerable research during the past several decades, because of the important role of vegetation in regulating the terrestrial carbon cycle and the climate system. In this study, we combined datasets of satellite‐derived Normalized Difference Vegetation Index (NDVI) and climatic factors to analyze spatio‐temporal patterns of changes in vegetation growth and their linkage with changes in temperature and precipitation in temperate and boreal regions of Eurasia (> 23.5°N) from 1982 to 2006. At the continental scale, although a statistically significant positive trend of average growing season NDVI is observed (0.5 × 10−3 year−1, P = 0.03) during the entire study period, there are two distinct periods with opposite trends in growing season NDVI. Growing season NDVI has first significantly increased from 1982 to 1997 (1.8 × 10−3 year−1, P < 0.001), and then decreased from 1997 to 2006 (−1.3 × 10−3 year−1, P = 0.055). This reversal in the growing season NDVI trends over Eurasia are largely contributed by spring and summer NDVI changes. Both spring and summer NDVI significantly increased from 1982 to 1997 (2.1 × 10−3 year−1, P = 0.01; 1.6 × 10−3 year−1P < 0.001, respectively), but then decreased from 1997 to 2006, particularly summer NDVI which may be related to the remarkable decrease in summer precipitation (−2.7 mm yr−1, P = 0.009). Further spatial analyses supports the idea that the vegetation greening trend in spring and summer that occurred during the earlier study period 1982–1997 was either stalled or reversed during the following study period 1997–2006. But the turning point of vegetation NDVI is found to vary across different regions.

Water availability as the driver of vegetation dynamics in the African Sahel from 1982 to 2007

In this paper we explore soil moisture as a principal determinant of Sahelian vegetation dynamics for the period 1982–2007 and compare it to the findings obtained with commonly used rainfall as the main driver. We used remotely sensed Normalized Vegetation Diference Index (NDVI) as proxy for the vegetation greenness response to water availability (rainfall and soil moisture). The association between the variables was determined for two different temporal foci: either all-season data (including the long dry period) or only the months of the growing season (JASO) were included into the analyses. Finally, NDVI residual time series, originating from regressing NDVI on rainfall were searched for significant long-term trends in vegetation greenness induced by other factors than water availability. The results show a west–east gradient of increasing moisture throughout the Sahel for the 26-year period, but not for NDVI. Large areas in the western Sahel, in particular in large parts of Senegal, underwent a strong greening (NDVI + 0.09 and more) whereas no significant increase in rainfall or soil moisture was detected in that region. Quite the contrary was observed in Sudan, where significantly more rain fell from 1982 to 2007 but NDVI decreased with − 0.03 and more. The study revealed that when using all-season data to correlate NDVI with water availability higher correlations are obtained as compared to restricting the analyses to JASO. For rainfall and soil moisture maximum r-values of 0.95 and 0.92, respectively, were achieved when using all-season data and 0.87 and 0.86, respectively, for the JASO analysis.

Comparison of phenology trends by land cover class: a case study in the Great Basin, USA

AbstractDirect impacts of human land use and indirect impacts of anthropogenic climate change may alter land cover and associated ecosystem function, affecting ecological goods and services. Considerable work has been done to identify long‐term global trends in vegetation greenness, which is associated with primary productivity, using remote sensing. Trend analysis of satellite observations is subject to error, and ecosystem change can be confused with interannual variability. However, the relative trends of land cover classes may hold clues about differential ecosystem response to environmental forcing. Our aim was to identify phenological variability and 10‐year trends for the major land cover classes in the Great Basin. This case study involved two steps: a regional, phenology‐based land cover classification and an identification of phenological variability and 10‐year trends stratified by land cover class. The analysis used a 10‐year time series of Advanced Very High Resolution Radiometer satellite data to assess regional scale land cover variability and identify change. The phenology‐based regional classification was more detailed and accurate than national or global products. Phenological variability over the 10‐year period was high, with substantial shifts in timing of start of season of up to 9 weeks. The mean long‐term trends of montane land cover classes were significantly different from valley land cover classes due to a poor response of montane shrubland and pinyon‐juniper woodland to the early 1990s drought. The differential response during the 1990s suggests that valley ecosystems may be more resilient and montane ecosystems more susceptible to prolonged drought. This type of regional‐scale land cover analysis is necessary to characterize current patterns of land cover phenology, distinguish between anthropogenically driven land cover change and interannual variability, and identify ecosystems potentially susceptible to regional and global change.

Recent history of trends in vegetation greenness and large-scale ecosystem disturbances in Eurasia

Recent history of trends in vegetation greenness and large-scale ecosystem disturbances in Eurasia

Links and broken chains: evidence of human-caused changes in land cover in remotely sensed images

Abstract Land use intensification on shrinking forage resources characterizes many livestock producing communities. Remotely sensed images can show land cover change, but how household decision making is reflected in images had not been synthesized. For eight areas in the US, Africa, and Mongolia (>340,000 km 2 ), we ranked constraints in decision making, and quantified vegetation greenness trends from 1981 to 2004 and land cover change using 1990 and 2000 Landsat images. Constraints in decision making varied across the sites, but ecological settings ranked highest. Five sites showed increasing greenness (2.4–8.0% increase per decade; P ≤ 0.01); the African sites showed no change or declining greenness (−2.5%; P = 0.048). Land cover change in the US sites was modest, with most sites suitable for cultivation already converted by 1990. Cover change was minor in Mongolia, despite profound changes in government and economy. The Kenyan site showed the largest change in land cover. We hypothesize a humped relationship, where households in undeveloped regions lack the resources to convert land cover. Developed regions have reached some stasis in land use. Developing regions with high human population growth and residents with access to machinery show the greatest land cover change.

Recent history of trends in vegetation greenness and large-scale ecosystem disturbances in Eurasia

Recent patterns of land cover and vegetation dynamics on the Euasian continent have been linked to changes in the global carbon cycle. Our study was conducted to evaluate patterns in a 19-yr record of global satellite observations of terrestrial vegetation from the Advanced Very High Resolution Radiometer (AVHRR) as a means to characterize major trends in both vegetation egreenness and ecosystem disturbance. The fraction absorbed of photosynthetically active radiation (FPAR) by vegetation canopies worldwide has been computed from the AVHRR at a monthly time interval from 1982 to 2000 and gridded at a spatial resolution of 8 km globally. Unlike previous studies of the AVHRR multiyear time-series of vegetation dynamics, the 8-km spatial resolution makes it possible to compare disturbance events and greenness trends at the same level of spatial detail. Positive trends in FPAR were detected throughout a major greenbelt of central-eastern Europe starting in the mid-1980s. This Eurasian greenbelt extended in a wide swath over the Urals, into the vicinity of Lake Baykal south of the central Siberian plateau, mainly along a latitude belt from 55°.N to 65°N. There was also significantly positive greening in relatively large areas of Great Britain, Italy, Greece, Turkey, the Caucasus and southern India. Nonetheless, a strong downward trend in the FPAR time-series over most of Eurasia was observed by the end of the 1990s. Throughout the 19-yr time period, Eurasia was also impacted by many notable droughts and other disturbance events that could have substantially offset decadal carbon gains attributed to satellite-observed greening. Large-scale ecosystems disturbance events were identified in the FPAR time-series by locating anomalously low values (FPAR-LO) that lasted longer than 12 consecutive months at any 8-km pixel. We find verifiable evidence of numerous disturbance types across Eurasia, including regional patterns of severe droughts, forest fires and insect outbreaks.

Assessing land cover change resulting from large surface mining development

A remote sensing based land cover change assessment methodology is presented and applied to a case study of the Oil Sands Mining Development in Athabasca, Alta., Canada. The primary impact was assessed using an information extraction method applied to two LANDSAT scenes. The analysis based on derived land cover maps shows a decrease of natural vegetation in the study area (715,094ha) for 2001 approximately −8.64% relative to 1992. Secondary assessment based on a key resources indicator (KRI), calculated using normalized difference vegetation index (NDVI measurements acquired by NOAA–AVHRR satellites), air temperature and global radiation was performed for a time period from 1990 to 2002. KRI trend analysis indicates a slightly decreasing trend in vegetation greenness in close proximity to the mining development. A good agreement between the time series of inter-annual variations in NDVI and air temperature is observed increasing the confidence of NDVI as an indicator for assessing vegetation productivity and its sensitivity to changes in local conditions.

Vegetation index trends for the African Sahel 1982–1999

Pathfinder AVHRR NDVI data have been analyzed for the African Sahel to study recent trends in vegetation greenness. A strong increase in seasonal NDVI was observed over large areas in the Sahel during the period 1982–1999. The increase is interpreted as a vegetation recovery from the drought periods of the 1980's. Although strong shifts in satellite overpass times have led to shifting solar zenith angles (SZA) over the time period, only minimal influence of SZA's on the Pathfinder NDVI was found in our data. A preliminary analysis of rainfall data indicates increasing rainfall during the period. The observed trends may have important implications to the Sahel including changes to the water cycle, energy exchange and carbon storage.