Célia M. Gouveia

Response of vegetation to drought time-scales across global land biomes

We evaluated the response of the Earth land biomes to drought by correlating a drought index with three global indicators of vegetation activity and growth: vegetation indices from satellite imagery, tree-ring growth series, and Aboveground Net Primary Production (ANPP) records. Arid and humid biomes are both affected by drought, and we suggest that the persistence of the water deficit (i.e., the drought time-scale) could be playing a key role in determining the sensitivity of land biomes to drought. We found that arid biomes respond to drought at short time-scales; that is, there is a rapid vegetation reaction as soon as water deficits below normal conditions occur. This may be due to the fact that plant species of arid regions have mechanisms allowing them to rapidly adapt to changing water availability. Humid biomes also respond to drought at short time-scales, but in this case the physiological mechanisms likely differ from those operating in arid biomes, as plants usually have a poor adaptability to water shortage. On the contrary, semiarid and subhumid biomes respond to drought at long time-scales, probably because plants are able to withstand water deficits, but they lack the rapid response of arid biomes to drought. These results are consistent among three vegetation parameters analyzed and across different land biomes, showing that the response of vegetation to drought depends on characteristic drought time-scales for each biome. Understanding the dominant time-scales at which drought most influences vegetation might help assessing the resistance and resilience of vegetation and improving our knowledge of vegetation vulnerability to climate change.

The 2009/10 drought in China: possible causes and impacts on vegetation

AbstractSeveral provinces of China experienced an intense drought episode during 2009 and 2010. The drought was particularly severe in southwestern and northern China, where the accumulated precipitation from May 2009 to April 2010 was about 25% less than normal. The decline of accumulated precipitation over northern China was mostly noticeable during the summer season of 2009 and it was comparable to recent dry episodes. The southwestern China drought resulted from a sequence of dry months from summer 2009 to winter 2010, corresponding to the driest event since at least 1951. The suppression of rainfall in summer over both regions was in agreement with a weakened broad-scale South Asian summer monsoon, possibly influenced by an El Nino developing phase, whereas the extremely negative phases of the Arctic Oscillation during the winter of 2010 may have contributed to the persistence of the drought in southwestern China. The assessment of the associated impacts indicates that water reservoirs were severely ...

European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling

Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO–EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models.

Large-Scale Atmospheric Circulation Driving Extreme Climate Events in the Mediterranean and its Related Impacts

It is widely accepted that the Mediterranean basin represents one of the most prominent hot spots of climate change and is a particularly vulnerable region in the world. Recent trends toward a hotter and drier climate appear to be related to changes in atmospheric circulation patterns, particularly over the western Mediterranean. The combined effects of precipitation decrease and surface-temperature increase in the Mediterranean will most probably lead to important changes in the region’s water cycle. In fact, the present tendency toward a drier climate with a higher frequency of drought events agrees with climate change scenarios that point to increasing probabilities of drought episodes and severe heat waves (HWs). Here, we provide a multidisciplinary review of the state-of-the-knowledge science of these two natural hazards in the Mediterranean. This chapter covers a wide range of atmospheric circulation phenomena with a direct impact on climate and socioeconomic activities in the twentieth century and with relatively high probabilities of changing significantly throughout the twenty-first century (e.g., water resources, renewable energy, agriculture, and vegetation dynamics) and also natural hazards (e.g., droughts, HWs, and sea surges and flooding in Venice).

The record precipitation and flood event in Iberia in December 1876: description and synoptic analysis

The first week of December 1876 was marked by extreme weather conditions that affected the south-western sector of the Iberian Peninsula, leading to an all-time record flow in two large international rivers. As a direct consequence, several Portuguese and Spanish towns and villages located in the banks of both rivers suffered serious flood damage on 7 December 1876. These unusual floods were amplified by the preceding particularly autumn wet months, with October 1876 presenting extremely high precipitation anomalies for all western Iberia stations. Two recently digitised stations in Portugal (Lisbon and Evora), present a peak value on 5 December 1876. Furthermore, the values of precipitation registered between 28 November and 7 December were so remarkable that, the episode of 1876 still corresponds to the maximum average daily precipitation values for temporal scales between 2 and 10 days. Using several different data sources, such as historical newspapers of that time, meteorological data recently digitised from several stations in Portugal and Spain and the recently available 20th Century Reanalysis, we provide a detailed analysis on the socio-economic impacts, precipitation values and the atmospheric circulation conditions associated with this event. The atmospheric circulation during these months was assessed at the monthly, daily and sub-daily scales. All months considered present an intense negative NAO index value, with November 1876 corresponding to the lowest NAO value on record since 1865. We have also computed a multivariable analysis of surface and upper air fields in order to provide some enlightening into the evolution of the synoptic conditions in the week prior to the floods. These events resulted from the continuous pouring of precipitation registered between 28 November and 7 December, due to the consecutive passage of Atlantic low-pressure systems fuelled by the presence of an atmospheric-river tropical moisture flow over central Atlantic Ocean.

Different growth sensitivity to climate of the conifer Juniperus thurifera on both sides of the Mediterranean Sea.

Mediterranean plants cope with cold wet winters and dry hot summers, with a drought gradient from northwest to southeast. Limiting climatic conditions have become more pronounced in the last decades due to the warming trend and rainfall decrease. Juniperus thurifera L., a long-lived conifer tree endemic to the western Mediterranean region, has a disjunct distribution in Europe and Africa, making it a suitable species to study sensitivity to climate in both sides of the Mediterranean Basin. Tree-ring width chronologies were built for three J. thurifera stands at Spain (Europe) and three in Morocco (Africa) and correlated with monthly temperature and precipitation. The temporal stability of climate-growth relationships was assessed using moving correlations; the drought effect on growth was calculated using the monthly standardized precipitation-evapotranspiration index (SPEI) at different temporal scales. In the wettest stands, increasing spring temperature and summer precipitation enhanced growth, while in the driest stands, growth was enhanced by higher spring precipitation and lower summer temperature. The climate-growth correlations shifted during the twentieth century, especially since the 1970s. Particularly noticeable is the recent negative correlation with previous autumn and winter precipitation in the wettest stands of J. thurifera, probably related with an effect of cloud cover or flooding on carbon storage depletion for next year growth. The driest stands were affected by drought at long time scales, while the wettest stands respond to drought at short time scales. This reveals a different strategy to cope with drought conditions, with populations from drier sites able to cope with short periods of water deficit.

Effects of Recent Minimum Temperature and Water Deficit Increases on Pinus pinaster Radial Growth and Wood Density in Southern Portugal

Western Iberia has recently shown increasing frequency of drought conditions coupled with heatwave events, leading to exacerbated limiting climatic conditions for plant growth. It is not clear to what extent wood growth and density of agroforestry species have suffered from such changes or recent extreme climate events. To address this question, tree-ring width and density chronologies were built for a Pinus pinaster stand in southern Portugal and correlated with climate variables, including the minimum, mean and maximum temperatures and the number of cold days. Monthly and maximum daily precipitations were also analyzed as well as dry spells. The drought effect was assessed using the standardized precipitation-evapotranspiration (SPEI) multi-scalar drought index, between 1 to 24-months. The climate-growth/density relationships were evaluated for the period 1958-2011. We show that both wood radial growth and density highly benefit from the strong decay of cold days and the increase of minimum temperature. Yet the benefits are hindered by long-term water deficit, which results in different levels of impact on wood radial growth and density. Despite of the intensification of long-term water deficit, tree-ring width appears to benefit from the minimum temperature increase, whereas the effects of long-term droughts significantly prevail on tree-ring density. Our results further highlight the dependency of the species on deep water sources after the juvenile stage. The impact of climate changes on long-term droughts and their repercussion on the shallow groundwater table and P. pinaster’s vulnerability are also discussed. This work provides relevant information for forest management in the semi-arid area of the Alentejo region of Portugal. It should ease the elaboration of mitigation strategies to assure P. pinaster’s production capacity and quality in response to more arid conditions in the near future in the region.

Analyses of human exposure to urban air quality in a children population

PM levels of less than 2.5 μm and 10 μm and their effect on children health are studied and it is proposed a ventilation system to avoid outdoor air pollution inlet. Results reveal a positive correlation between indoor and outdoor PM concentrations, the importance of indoor sources and outdoor activity, and building permeability relevance. PM size confirms to be also important in matter of deposition velocity, building penetration and health effects. Some relation between CO and attended urgent cases in the city hospital was found. The effect of seasonality is also noticed in children health problems and PM concentration.

Influence of Climate Variability on Wheat Production in Portugal

In this work we describe the temporal evolution of wheat production and yield in Portugal and the spatial context of this production in Alentejo region (Southern Portugal). Then we have identified the geographical extent of this area and related with wheat yield, using remote sensing data. For this purpose, we have used the normalized difference vegetation index (NDVI), retrieved between 1982 and 1999 from the AVHRR instrument. The year-to-year variations in Portuguese vegetation greenness were estimated and related to national wheat yield. A significant correlation was found over Alentejo region and a validation using Corine2000 land cover map has confirmed the correspondence with arable land code pixels. Finally, we evaluate the relevance of the North Atlantic Oscillation (NAO) pattern in terms of wheat yield. A significant influence of the NAO, associated to spatial patterns of variation of different climatic fields, namely precipitation and radiation, on wheat yield in Alentejo region was found. The most significant monthly correlations were obtained for the two important stages in vegetative cycle, namely: February/March and April to June (NAO/Yield, Precipitation/Yield and\break Radiation/Yield).

The Impacts of the NAO on the Vegetation Activity in Iberia

The present study analyses the relation between North Atlantic Oscillation (NAO) and satellite-based measures of vegetation dynamics (as obtained using Normalized Difference Vegetation Index, NDVI), carbon absorption by living plants (obtained by Net Primary Production, NPP estimates) over Iberian Peninsula and wheat yield in Portugal. There is a strong evidence that positive (negative) values of winter NAO induce low (high) vegetation activity in the following spring and summer seasons. Consequently, significant correlations patterns between NAO and NPP were also obtained, identifying a negative impact in spring and summer over southern Iberia. These features are mainly associated with the impact of NAO on winter precipitation, together with the strong dependence of the spring and summer vegetation activity on water availability during the previous winter. The different role played by NAO along the vegetative cycle of wheat yield in Portugal is also assessed and results obtained suggest using spring NDVI together with NAO in April and June to build up a simple model of wheat yield in Portugal. Results reveal to be satisfactory and are expect to be useful to estimate crop production and to perform agricultural monitoring.