Increase In Vegetation Greenness Research Articles

Identification of environmental anomaly hot spots in West Africa from time series of NDVI and rainfall

Studies of the impact of human activity on vegetation dynamics of the Sahelian belt of Africa have been recently re-invigorated by new scientific findings that highlighted the primary role of climate in the drought crises of the 1970s–1980s. Time series of satellite observations revealed a re-greening of the Sahelian belt that indicates no noteworthy human effect on vegetation dynamics at sub continental scale from the 1980s to late 1990s. However, several regional/local crises related to natural resources occurred in the last decades despite the re-greening thus underlying that more detailed studies are needed. In this study we used time-series (1998–2010) of SPOT–VGT NDVI and FEWS–RFE rainfall estimates to analyse vegetation – rainfall correlation and to map areas of local environmental anomalies where significant vegetation variations (increase/decrease) are not fully explained by seasonal changes of rainfall. Some of these anomalous zones (hot spots) were further analysed with higher resolution images Landsat TM/ETM+ to evaluate the reliability of the identified anomalous behaviour and to provide an interpretation of some example hot spots. The frequency distribution of the hot spots among the land cover classes of the GlobCover map shows that increase in vegetation greenness is mainly located in the more humid southern part and close to inland water bodies where it is likely to be related to the expansion/intensification of irrigated agricultural activities. On the contrary, a decrease in vegetation greenness occurs mainly in the northern part (12°–15°N) in correspondence with herbaceous vegetation covers where pastoral and cropping practices are often critical due to low and very unpredictable rainfall. The results of this study show that even if a general positive re-greening due to increased rainfall is evident for the entire Sahel, some local anomalous hot spots exist and can be explained by human factors such as population growth whose level reaches the ecosystem carrying capacity as well as population displacement leading to vegetation recovery.

Tracking the effect of climate change on ecosystem functioning using protected areas: Africa as a case study

Protected areas represent important core ‘units’ for in situ conservation. However, the current static system is at risk from the effects of global environmental change. This is especially true in Africa, a biodiversity-rich continent expected to be hit hard by climate change. Focusing on African protected areas that experience limited human impact (International Union for Conservation of Nature (IUCN) categories I and II), we tested three hypotheses regarding the impact of climate change on the dynamics of net primary productivity (NPP). We expected a lower annual NPP and higher seasonality in NPP in Eastern and Southern Africa; changes in NPP dynamics to coincide with changes in precipitation; no correlation between changes in NPP dynamics and human development. To test these expectations, we used the Normalised Difference Vegetation Index (NDVI) as an index of NPP. Results show that, between 1982 and 2008, an increased vegetation greenness was observed in 27% of the protected areas monitored (mostly in Western Africa), and an increased seasonality in 9% of them (mostly in Eastern and Southern Africa). Our results lend support to current expectations regarding the impacts of climate change, and demonstrate how protected areas of IUCN categories I and II could be used to track the effect of climate change on ecosystem functioning in Africa, and possibly elsewhere. The study highlights the need for a dynamic approach to conservation, where the relevance and efficiency of management actions need to be regularly evaluated. It also demonstrates that satellite-based approaches offer a cheap, verifiable way to quickly identify protected areas of concern at a global scale, supporting managers in their effort to design and apply adaptive management strategies.

The potential of vegetation feedback to alleviate climate aridity over the United States associated with a 2×CO2 climate condition

This study examines the potential impact of vegetation feedback on changes in summer climate aridity over the contiguous United States (US) due to the doubling of atmospheric CO2 concentration using a set of 100-year-long climate simulations made by a global climate model interactively coupled with a dynamic vegetation model. The Thornthwaite moisture index (Im), which quantifies climate aridity on the basis of atmospheric water supply (i.e., precipitation) and atmospheric water demand (i.e., potential evapotranspiration, PET), is used to measure climate aridity. Warmer atmosphere and drier surface resulting from increased CO2 concentration increase climate aridity over most of the contiguous US. This phenomenon is due to larger increments in PET than in precipitation, regardless of the presence or absence of vegetation feedback. Compared to simulations without active dynamic vegetation feedback, the presence of vegetation feedback significantly alleviates the increase in aridity. This vegetation-feedback effect is most noticeable in the subhumid regions such as southern, midwestern and northwestern US, primarily by the increasing vegetation greenness. In these regions, the greening in response to warmer temperatures enhances moisture transfer from soil to atmosphere by evapotranspiration (ET). The increased ET and subsequent moistening over land areas result in weaker surface warming (1–2 K) and PET (3–10 mm month−1), and greater precipitation (4–10 mm month−1). Collectively, they result in moderate increases in Im. Our results suggest that moistening by enhanced vegetation feedback may prevent aridification under climatic warming especially in areas vulnerable to climate change, with consequent implications for mitigation strategies.

Dry land tree management for improved household livelihoods: Farmer managed natural regeneration in Niger

Farmer Managed Natural Regeneration (FMNR), a set of practices farmers use to foster the growth of indigenous trees on agricultural land, has drawn substantial attention as a contributing factor to a trend of increasing vegetation greenness in the Republic of Niger. This paper identifies drivers of FMNR adoption and assesses its impacts on rural households in the Region of Maradi, Niger, an area covering 42,000 square kilometers. The results show that 26% of households practice a form of FMNR involving both pruning and protecting woody vegetation. Adoption is strongly linked to soil type, market access, and the education level of the head of household. FMNR raises household income and increases crop diversity, household migration rates, and the density and diversity of trees on farmland. It is estimated that FMNR raises the annual gross income of the region by between 17 and 21 million USD and has contributed an additional 900,000 to 1,000,000 trees to the local environment. These findings support the value of continued promotion of FMNR as an inexpensive means of enhancing rural livelihoods and an attractive alternative to reforestation efforts relying on tree planting.

Impact of vegetation feedback on the temperature and its diurnal range over the Northern Hemisphere during summer in a 2 × CO2 climate

This study examines the potential impact of vegetation feedback on the changes in the diurnal temperature range (DTR) due to the doubling of atmospheric CO2 concentrations during summer over the Northern Hemisphere using a global climate model equipped with a dynamic vegetation model. Results show that CO2 doubling induces significant increases in the daily mean temperature and decreases in DTR regardless of the presence of the vegetation feedback effect. In the presence of vegetation feedback, increase in vegetation productivity related to warm and humid climate lead to (1) an increase in vegetation greenness in the mid-latitude and (2) a greening and the expansion of grasslands and boreal forests into the tundra region in the high latitudes. The greening via vegetation feedback induces contrasting effects on the temperature fields between the mid- and high-latitude regions. In the mid-latitudes, the greening further limits the increase in T max more than T min, resulting in further decreases in DTR because the greening amplifies evapotranspiration and thus cools daytime temperature. The greening in high-latitudes, however, it reinforces the warming by increasing T max more than T min to result in a further increase in DTR from the values obtained without vegetation feedback. This effect on T max and DTR in the high latitude is mainly attributed to the reduction in surface albedo and the subsequent increase in the absorbed insolation. Present study indicates that vegetation feedback can alter the response of the temperature field to increases in CO2 mainly by affecting the T max and that its effect varies with the regional climate characteristics as a function of latitudes.

Reduction of spring warming over East Asia associated with vegetation feedback

Over East Asia, surface air temperature displays a significant increasing trend particularly in early months of the year for the period of 1982–2000. Warming per decade is strongest in late winter, 1.5°C in February and 1.1°C in March, but is significantly reduced in spring, 0.4°C in April and 0.1°C in May. During the analysis period, the reduced temperature increase from late winter to spring is found to be in contrast with the increased vegetation greenness derived from the satellite‐measured leaf area index over the domain. We examined this inverse relationship using two climate model experiments— coupled with and without a dynamic vegetation model. In both experiments, strong warming in winter is relatively well reproduced, but weak warming in spring is observed only in the coupled experiment. Analysis of the surface energy budget indicates that weaker spring warming results from an evaporative cooling effect due to the increased vegetation greenness. Over East Asia, the vegetation‐evaporation feedback, therefore, may produce seasonal asymmetry in the warming trend.

Investigation of Vegetation Dynamics using Long-Term Normalized Difference Vegetation Index Time-Series

Problem statement: The Normalized Difference Vegetation Index (NDVI) is the most extensively used satellite-derived index of vegetat ion health and density. Since climate is one of the most important factors affecting vegetation conditi on, satellite-derived vegetation indexes have been often used to evaluate climatic and environmental c hanges at regional and global scale. The proposed study attempted to investigate the temporal vegetat ion dynamics in the whole Africa using historical NDVI time-series. Approach: For this aim, 15 day maximum value NDVI composites at 8 km spatial resolution produced from the NASA Global Inventory Mapping and Monitoring System (GIMMS) had been used. They were derived from data collected da ily by NOAA AVHRR satellites. The AVHRR NDVI GIMMS dataset was freely available and gives global coverage over an extensive time period. First of all, the selected NDVI base data had been geometrically pre-processed and organized into a historical database implemented in order to grant t heir spatial integration. Starting from this archiv e, monthly and yearly NDVI historical time-series, ext ended from 1982-2006, had been then developed and analysed on a pixel basis. Several routines had e been developed in IDL (Interactive Data Language programming tool) with the purpose of applying suit able statistical analysis techniques to the histori cal information in the database in order to identify th e long-term trend components of generated NDVI time-series and extract vegetation dynamics. Specif ic tests had been then considered in order to defin e the validity of results. Results: The existence of clear regional trends of NDVI, bot h decreasing and increasing had been showed, which helped to highlight areas subject, respectively to reduction or increase in vegetation greenness. Conclusion: As the relationship between the NDVI and vegetatio n productivity was well established, these estimated long-term trend components may be also, with much more caution, related to historical and ongoing lan d degradation or improvement processes.

Increase in vegetation greenness and decrease in springtime warming over east Asia

This study investigates the impact of increased vegetation greening on the springtime temperature over east Asia for 1982–2000. An analysis of station‐based temperature records and satellite‐measure normalized difference vegetation index (NDVI) indicates that slight warming (<0.4°C 10‐yr−1) occurred over regions that experienced large increase in NDVI (≥0.08 10‐yr−1). On the contrary, strong warming (≥0.8°C 10‐yr−1) occurred over regions that exhibited minor changes in NDVI (<0.04 10‐yr−1). For the most part, this inverse NDVI–temperature relationship observed with the daily maximum temperature. Thus, it is suggested that the decrease in warming was mostly attributable to the increase in evapotranspiration associated with increased vegetation greening. Earlier vegetation growth may have further strengthened the effect of this vegetation–evaporation on spring temperature.

Trends in the surface vegetation dynamics of the national parks of Spain as observed by satellite sensors

AbstractQuestions: What are the current dynamics, as observed by synoptic sensors, of surface vegetation in Spanish protected areas? Are these areas and their vegetation types uniformly affected by the increase in vegetation greenness detected throughout Europe?Location: Iberian National Parks of Spain.Methods: We used the normalized difference vegetation index (NDVI) from global inventory modeling and mapping studies (GIMMS) advanced very high resolution radiometer (AVHRR) dataset to monitor surface vegetation. NDVI is a surrogate for the photosynthetically active radiation absorbed by vegetation (fAPAR). This functional attribute has a short‐time response to disturbances, is connected to ecosystem services and can be monitored through remote sensing. First, we provide a baseline description of the NDVI dynamics in the parks and analysed its temporal trends (1981–2003). Then, we evaluated the relationships of the seasonal dynamics and interannual trends with the climate conditions, vegetation types and conservation histories of the parks.Results: The parks showed two patterns of NDVI dynamics corresponding to Mediterranean and Eurosiberian regions. Most parks showed areas with positive NDVI trends that tended to have higher proportions of Mediterranean coniferous and mixed forests, oro‐Mediterranean scrublands, heathlands, maquis and garrigues. Negative trends were scarce and associated with marshes and Alpine coniferous forests. The lack of a common response in all parks was related to their different environmental conditions, management, and conservation histories. Conclusions: National parks are changing in the short term but not uniformly. This study represents a basis for the incorporation of functional attributes of ecosystems in the management and monitoring of protected areas in the face of global change.

Recent trends in vegetation dynamics in the African Sahel and their relationship to climate

Contrary to assertions of widespread irreversible desertification in the African Sahel, a recent increase in seasonal greenness over large areas of the Sahel has been observed, which has been interpreted as a recovery from the great Sahelian droughts. This research investigates temporal and spatial patterns of vegetation greenness and rainfall variability in the African Sahel and their interrelationships based on analyses of Normalized Difference Vegetation Index (NDVI) time series for the period 1982–2003 and gridded satellite rainfall estimates. While rainfall emerges as the dominant causative factor for the increase in vegetation greenness, there is evidence of another causative factor, hypothetically a human-induced change superimposed on the climate trend.

A recent greening of the Sahel—trends, patterns and potential causes

For the last four decades there has been sustained scientific interest in contemporary environmental change in the Sahel (the southern fringe of the Sahara). It suffered several devastating droughts and famines between the late 1960s and early 1990s. Speculation about the climatology of these droughts is unresolved, as is speculation about the effects of land clearance on rainfall and about land degradation in this zone. However, recent findings suggest a consistent trend of increasing vegetation greenness in much of the region. Increasing rainfall over the last few years is certainly one reason, but does not fully explain the change. Other factors, such as land use change and migration, may also contribute. This study investigates the nature of a secular vegetation trend across the Sahel and discusses several potential causative factors.

Greening of arctic Alaska, 1981–2001

Here we analyzed a time series of 21‐yr satellite data for three bioclimate subzones in northern Alaska and confirmed a long‐term trend of increase in vegetation greenness for the Alaskan tundra that has been detected globally for the northern latitudes. There was a 16.9% (±5.6%) increase in peak vegetation greenness across the region that corresponded to simultaneous increases in temperatures. We also examined the changes for four specific vegetation types using an 11‐yr finer resolution (1‐km) satellite data and found that the temporal changes in peak and time‐integrated greenness were greatest in areas of moist nonacidic tundra. These changes in greenness between 1981 and 2001 correspond approximately to a 171 g/m2 (±81 g/m2) increases in aboveground plant biomass for Alaskan tundra. This remotely sensed interpretation is conducted in the absence of long‐term biomass records in the region.

Frequency analysis of natural vegetation distribution using NDVI/AVHRR data from 1981 to 2000 for North America: Correlations with SOI

We develop new methods to study and monitor changes in the distribution of vegetation in North America. The Normalized Difference Vegetation Index (NDVI), which is a level 3 data product from channel 1 and 2 of NOAA/AVHRR Pathfinder, is used for the study. Frequency analysis for uniformly divided NDVI ranges is used to study interannual trends in vegetation distribution. The study is done for each region specified by vegetation type and some geological considerations, and covers the entire area of North America. The period of the study covers 1981 to 2000. Correlation coefficients are found for different vegetation greenness levels and Southern Oscillation Indices (SOIs). Correlations between vegetation distribution and climatic phenomena such as ENSO occurrences are suggested. Long-term increase in vegetation greenness on decadal time scales for some regions in North America is suggested. The work is of significance to interannual variability of natural vegetation and its connection to known physical phenomena such as ENSO and droughts.