Significance tests for covariate-dependent trends in inhomogeneous spatio-temporal point processes

Modeling and inference for spatial and spatio-temporal point processes is an issue that has been broadly investigated in the last years. Application fields such as forestry, epidemiology and ecology have been the main engine driving such raised interest. The inclusion of spatially varying covariates in the models for the intensity function is becoming of particular interest, but little attention has been paid to testing the significance of such covariates. Testing the significance of covariates is important if one seeks to explain which covariates have an effect in the spatial or spatio-temporal distribution of the point pattern observed. We thus provide practical procedures to build statistical tests of significance for covariates that have an effect on the intensity function of a point pattern. Our approximation focuses on the conditional intensity function, by considering nonparametric kernel-based estimators. We calculate thinning probabilities under the conditions of absence and presence of a covariate and compare them through divergence measures. Based on Monte Carlo experiments, we approximate the statistical properties of our tests under a variety of practical scenarios. An application on testing the significance of a covariate in a spatio-temporal data set on wildfires is also developed.     

Objective probabilities about future climate are a matter of opinion

In this paper, the unfeasibility of producing “objective” probabilistic climate change scenarios is discussed. Realizing that the knowledge of “true” probabilities of the different scenarios and temperature changes is unachievable, the objective must be to find the probabilities that are the most consistent with what our state of knowledge and expert judgment are. Therefore, subjective information plays, and should play, a crucial role. A new methodology, based on the Principle of Maximum Entropy, is proposed for constructing probabilistic climate change scenarios when only partial information is available. The objective is to produce relevant information for decision-making according to different agents’ judgment and subjective beliefs. These estimates have desirable properties such as: they are the least biased estimate possible on the available information; maximize the uncertainty (entropy) subject to the partial information that is given; The maximum entropy distribution assigns a positive probability to every event that is not excluded by the given information; no possibility is ignored. The probabilities obtained in this manner are the best predictions possible with the state of knowledge and subjective information that is available. This methodology allows distinguishing between reckless and cautious positions regarding the climate change threat.     

Possible climatic impacts of tropical deforestation

Large-scale conversion of tropical forests into pastures or annual crops will likely lead to changes in the local microclimate of those regions. Larger diurnal fluctuations of surface temperature and humidity deficit, increased surface runoff during rainy periods and decreased runoff during the dry season, and decreased soil moistrue are to be expected.It is likely that evapotranspiration will be reduced because of less available radiative energy at the canopy level since grass presents a higher albedo than forests, also because of the reduced availability of soil moisture at the rooting zone primarily during the dry season. Recent results from general circulation model (GCM) simulations of Amazonian deforestation seem to suggest that the equilibrium climate for a grassy vegetation in Amazonia would be one in which regional precipitation would be significantly reduced.Global climate changes probably will occur if there is a marked change in rainfall patterns in tropical forest regions as a result of deforestation. Besides that, biomass burning of tropical forests is likely adding CO₂ into the atmosphere, thus contributing to the enhanced greenhouse warming.     

Extreme climatic events in the Amazon basin

During 2009 the Amazon basin was hit by a heavy flooding with a magnitude and duration few times observed in several decades. Torrential rain in northern and eastern Amazonia during the austral summer of 2008–2009 swelled the Amazon River and its tributaries. By July 2009, water levels of the Rio Negro, a major Amazon tributary, reached at Manaus harbor a new record, the highest mark of the last 107?years. During the 2008–2009 hydrological year, the rainy season on northern and northwestern Amazonia started prematurely, and was followed by a longer-than-normal rainy season. An anomalously southward migration of the ITCZ during May–June 2009, due to the warmer than normal surface waters in the tropical South Atlantic, was responsible for abundant rainfall in large regions of eastern Amazonia and Northeast Brazil from May to July 2009. We also compared the flood of 2009 with other major events recorded in 1989 and 1999. The hydrological consequences of this pattern were earlier than normal floods in Amazon northern tributaries, which peak discharges at their confluences with the main stem almost coincided with the peaks of southern tributaries. Since the time displacement of the contribution to the main stem of northern and southern Amazon tributaries is fundamental for damping flood waves in the main stem, the simultaneous combinations of peak discharges of tributaries resulted in an extreme flood.     

Evolution and modulation of tropical heating from the last glacial maximum through the twenty-first century

Twentieth century observations show that during the last 50?years the sea-surface temperature (SST) of the tropical oceans has increased by ~0.5°C and the area of SST >26.5 and 28°C (arbitrarily referred to as the oceanic warm pool: OWP) by 15 and 50% respectively in association with an increase in green house gas concentrations, with non-understood natural variability or a combination of both. Based on CMIP3 projections the OWP is projected to double during twenty-first century in a moderate CO₂ forcing scenario (IPCC A1B scenario). However, during the observational period the area of positive atmospheric heating (referred to as the dynamic warm pool, DWP), has remained constant. The threshold SST (T _H ), which demarks the region of net heating and cooling, has increased from 26.6°C in the 1950s to 27.1°C in the last decade and it is projected to increase to ~28.5°C by 2100. Based on climate model simulations, the area of the DWP is projected to remain constant during the twenty-first century. Analysis of the paleoclimate model intercomparison project (PMIP I and II) simulations for the Last Glacial maximum and the Mid-Holocene periods show a very similar behaviour, with a larger OWP in periods of elevated tropical SST, and an almost constant DWP associated with a varying T _H . The constancy of the DWP area, despite shifts in the background SST, is shown to be the result of a near exact matching between increases in the integrated convective heating within the DWP and the integrated radiative cooling outside the DWP as SST changes. Although the area of the DWP remains constant, the total tropical atmospheric heating is a strong function of the SST. For example the net heating has increased by about 10% from 1950 to 2000 and it is projected to increase by a further 20% by 2100. Such changes must be compensated by a more vigorous atmospheric circulation, with growth in convective heating within the warm pool, and an increase of subsiding air and stability outside the convective warm pool and an increase of vertical shear at the DWP boundaries. This finding is contrary to some conclusions from other studies but in accord with others. We discuss the similarities and differences at length.     

The droughts of 1997 and 2005 in Amazonia: floodplain hydrology and its potential ecological and human impacts

It is well known that most of the severe droughts in Amazonia, such as that of 1997, are El Niño-related. However, in 2005, the Amazon was affected by a severe drought that was not El Niño-related, as most of the rainfall anomalies that have happened in southwestern Amazonia are driven by sea surface temperature anomalies in the tropical North Atlantic. Earlier studies have analyzed both droughts in terms of their meteorological causes and impacts in terra firme (non-flooded) forests. This study compares the hydrological effects of both droughts on the Amazonian floodplain and discusses their potential ecological and human impacts based on an extensive literature review. The results revealed that the effects of the 2005 drought were exacerbated because rainfall was lower and evaporation rates were higher at the peak of the dry season compared to the 1997 drought. This induced a more acute depletion of water levels in floodplain lakes and was most likely associated with higher fish mortality rates. Based on the fact that the stem growth of many floodplain species is related to the length of the non-flooded period, it is hypothesized that the 1997 drought had more positive effects on floodplain forest growth than the 2005 drought. The fishing community of Silves in central Amazonia considered both droughts to have been equally severe. However, the 2005 drought was widely broadcasted by the press; therefore, the governmental mitigation efforts were more comprehensive. It is suggested that the availability of new communication technology and greater public awareness regarding environmental issues, combined with the new legal framework for assessing the severity of calamities in Brazil, are among the primary factors that explain the difference in societal response between the two droughts.     

Climate change adaptation of coffee production in space and time

Savannas constitute the most fire-prone vegetation type on earth and are a significant source of greenhouse gas emissions. Most savanna fires are lit by people for a variety of livelihood applications. ‘Savanna burning’ is an accountable activity under the Kyoto Protocol, but only Australia, as a developed economy, accounts for emissions from this source in its national accounts. Over the past decade considerable effort has been given to developing savanna burning projects in northern Australia, combining customary indigenous (Aboriginal) approaches to landscape-scale fire management with development of scientifically robust emissions accounting methodologies. Formal acceptance by the Australian Government of that methodology, and its inclusion in Australia’s developing emissions trading scheme, paves the way for Aboriginal people to commercially benefit from savanna burning projects. The paper first describes this Australian experience, and then explores options for implementing community-based savanna burning emissions reduction projects in other continental savanna settings, specifically in Namibia and Venezuela. These latter examples illustrate that savanna fire management approaches potentially have broader application for contributing to livelihood opportunities in other fire-prone savanna regions.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Daily Meteorological Observations in Cádiz – San Fernando. Analysis of the Documentary Sources and the Instrumental Data Content (1786–1996)

Meteorological observations in the city of Cádiz are acknowledged as having been made from the middle of the 18th century onwards although they were only recorded and preserved in documentary form from 1789 onwards. Data readings were taken at the new Naval Observatory in San Fernando, ten kilometres from Cádiz, from 1797 onwards. Continuous series for temperature and atmospheric pressure at a daily resolution have been compiled and constructed from 1817 until 1996. The data series is composed of thrice daily observations made at Cádiz (1821–1880) by local observers and hourly data from Naval Observatory at San Fernando (1870–1996).