Warm-dry Climate Research Articles

Precipitation stable isotope variability and subcloud evaporation processes in a semi‐arid region

AbstractThe stable isotopic (2H/1H and 18O/16O) composition of precipitation has been used for a variety of hydrological and paleoclimate studies, a starting point for which is the behaviour of stable isotopes in modern precipitation. To this end, daily precipitation samples were collected over a 7‐year period (2008–2014) at a semi‐arid site located at the Macquarie Marshes, New South Wales (Australia). The samples were analysed for stable isotope composition, and factors affecting the isotopic variability were investigated. The best correlation between δ18O of precipitation was with local surface relative humidity.The reduced major axis precipitation weighted local meteoric water line was δ2H = 7.20 δ18O + 9.1. The lower slope and intercept (when compared with the Global Meteoric Water Line) are typical for a warm dry climate, where subcloud evaporation of raindrops is experienced. A previously published model to estimate the degree of subcloud evaporation and the subsequent isotopic modification of raindrops was enhanced to include the vertical temperature and humidity profile. The modelled results for raindrops of 1.0 mm radius showed that on average, the measured D‐excess (=δ2H − 8 δ18O) was 19.8‰ lower than that at the base of the cloud, and 18% of the moisture was evaporated before ground level (smaller effects were modelled for larger raindrops). After estimating the isotopic signature at the base of the cloud, a number of data points still plotted below the global meteoric water line, suggesting that some of the moisture was sourced from previously evaporated water.Back trajectory analysis estimated that 38% of the moisture was sourced over land. Precipitation samples for which a larger proportion of the moisture was sourced over land were 18O and 2H‐enriched in comparison to samples for which the majority of the moisture was sourced over the ocean.The most common weather systems resulting in precipitation were inland trough systems; however, only East Coast Lows contributed to a significant difference in the isotopic values. Copyright © 2016 Australian Nuclear Science and Technology Organisation. Hydrological Processes. © 2016 John Wiley & Sons, Ltd.

Caracterización seminal de individuos ovinos criollos colombianos de pelo en el departamento de Sucre

El objetivo de este trabajo fue caracterizar el semen de individuos ovinos criollos colombianos de pelo en la granja de la Universidad de Sucre. El estudio se llevó a cabo en la granja “El Perico” de la Universidad de Sucre, a 50 msnm, clima cálido seco y con formación vegetal de bosque seco tropical. Se utilizaron cuatro ovinos criollos adultos, no emparentados, los cuales fueron colectados cuatro veces a intervalos de cinco días, mediante la técnica de electroeyaculación y se evaluaron las características seminales macroscópicas y microscópicas. Se encontró que el color predominante es el blanco mate (66,7%) seguido del blanco brillante (33,3%) (p<0.05), el aspecto seminal es cremoso (60%), el volumen seminal promedio es 1,41±0,11ml, la movilidad individual es 74,09±2%, la movilidad masal es del 3,77±0,12 y la concentración espermática promedio de 711,89x106±133,86x106esp/ml. Se encontró que el 76,64±1,99% de los espermatozoides tenían una morfología normal y el 80,47±1,28% de los espermas presentaron una membrana plasmática funcional. La evaluación seminal permitió demostrar que el semen de los ovinos criollos, presentan características similares a las reportadas en razas foráneas, aunque con mayores volúmenes y mejor porcentaje de integridad de membrana. Se concluye que el semen de los ovinos criollos colombianos de pelo, presenta características de calidad similares a otras razas, lo que le permite ser usado en programas mejoramiento genético.

Influence of droughts on Nothofagus pumilio forest decline across northern Patagonia, Argentina

AbstractUnderstanding the influence of climatic variations on forest decline is a major challenge for scientists investigating global changes. Although reductions in tree growth have previously been associated with forest decline, comprehensive efforts to understand these relationships are rare. Based on ring‐width variations, we determine the influence of climatic fluctuations on the onset and temporal evolution of Nothofagus pumilio forest decline in the Patagonian Andes. Basal area increment (BAI) data from 294 Nothofagus trees at 11 stands in a 500‐km latitudinal transect along the forest–steppe ecotone were used to identify the dominant patterns of regional growth. Three Regional dominant patterns, showing common variations in BAI, were derived. Two BAI patterns show high rates of growth from early to mid‐20th century, followed by sustained negative trends over the last 3–6 decades, whereas the third pattern is characterized by a positive trend since the 1960s. Tipping points in growth trends of the first two patterns are associated with two extreme dry–warm climate events in spring–summer of 1942–1943/1943–1944/1944–1945 and 1978–1979. Both severe droughts were preceded by up to 10 yr of wet periods that promoted above‐average tree growth. We concluded that severe droughts occurring after wet periods trigger the decline of large, dominant N. pumilio trees with high rates of growth. The coincidence between major changes in regional growth with two of the most severe droughts in the instrumental records shows that climatic variations over northern Patagonia synchronize the beginning of forest decline at a regional scale. As these dry–mesic N. pumilio sites will face more severe droughts in the 21st century, as suggested by future climate scenarios, the areas affected by forest decline would increase substantially.

Interannual variability of average minimum temperatures derived from tree rings in the mid-Qinling Mountains, China, for the past 138years.

In this study, spruce tree rings from the southern slope of mid-Qinling Mountains were adopted to investigate the characteristics of average minimum temperatures during the past 138years. Analysis showed that the interannual variability in radial growth of trees was positively correlated with the interannual variability of average minimum temperatures from previous December to current September (VTM DS) in the study area during 1955-2010 AD. Based on the correlation analysis, the VTM DS were reconstructed for 1876-2013AD with an explained variance of 42.5% for the calibration period. Among the 22 dramatic changing years, extreme changes occurred more times when it was cooling, while the warming was comparatively gentle. Both the 10-year filtering of VTM DS series and the frequency of occurrences for those dramatic changing years showed a relatively stationary variation after the early 1950s. Over the last five decades, the accumulated VTM DS series showed an obvious warming trend, and the increase of the minimum temperature had contributed to the regional warming. The comparison of VTM DS and the dryness/wetness indices generally reflected cold-wet and warm-dry climate conditions in the study area. Significant positive correlations between the reconstructed VTM DS and the gridded minimum temperature indicated a regional representative of the temperature reconstruction, and positive correlations between VTM DS and sea surface temperature (SST) of the Indian Ocean and western Pacific regions suggested a possible linkage between the VTM DS variations and the Asian summer monsoon. Synchronous fluctuations in three tree-ring study series and connections of VTM DS with Arctic oscillation (AO) and El Niño-Southern Oscillation (ENSO) activities suggested that the minimum temperature variations in the TTH area responded sensitively to large-scale climate fluctuations and were the results of atmosphere-ocean interactions.

Definition of homogeneous fertility areas through factorial and geostatistical analysis

In a flat lot of 4 ha, with dry warm climate and Mollisols were determined the bulk density, pH and content of sand, silt, clay, organic matter, Ca, Mg, K and P, in the first 150mm of soil, doing a sampling in a semi-regular grid with cell size of 25 x 25m.A factorial analysis was reduced the number of variables to two (factors). The contents of clay, Ca and Mg shaped the first factor, and the second the pH and the contents of organic matter and phosphorus. To each factor and their variables was made an analysis of semivariance and the respective map of its spatial distribution using interpolation with block kriging.In the map of factor 1 homogeneous areas were better defined, and there was a greater spatial correlation between this map and those of their variables. The factor 2 variables presented a spatial structure in patches that not corresponded with the factor structure, making its zoning produced not adequate to establish a possible programme of fertility management with techniques of precision agriculture. The zoning which gives the factor 1 should be used for this purpose.

Dynamic Response of Satellite-Derived Vegetation Growth to Climate Change in the Three North Shelter Forest Region in China

Since the late 1970s, the Chinese government has initiated ecological restoration programs in the Three North Shelter Forest System Project (TNSFSP) area. Whether accelerated climate change will help or hinder these efforts is still poorly understood. Using the updated and extended AVHRR NDVI3g dataset from 1982 to 2011 and corresponding climatic data, we investigated vegetation variations in response to climate change. The results showed that the overall state of vegetation in the study region has improved over the past three decades. Vegetation cover significantly decreased in 23.1% and significantly increased in 21.8% of the study area. An increase in all three main vegetation types (forest, grassland, and cropland) was observed, but the trend was only statistically significant in cropland. In addition, bare and sparsely vegetated areas, mainly located in the western part of the study area, have significantly expanded since the early 2000s. A moisture condition analysis indicated that the study area experienced significant climate variations, with warm-wet conditions in the western region and warm-dry conditions in the eastern region. Correlation analysis showed that variations in the Normalized Difference Vegetation Index (NDVI) were positively correlated with precipitation and negatively correlated with temperature. Ultimately, climate change influenced vegetation growth by controlling the availability of soil moisture. Further investigation suggested that the positive impacts of precipitation on NDVI have weakened in the study region, whereas the negative impacts from temperature have been enhanced in the eastern study area. However, over recent years, the negative temperature impacts have been converted to positive impacts in the western region. Considering the variations in the relationship between NDVI and climatic variables, the warm–dry climate in the eastern region is likely harmful to vegetation growth, whereas the warm–wet conditions in the western region may promote vegetation growth.

Preliminary design method for naturally ventilated buildings using target air change rate and natural ventilation potential maps in the United States

Natural ventilation design is one of the most effective strategies for designing green buildings. The cost-effectiveness of this strategy should be considered to balance its benefits with its higher initial costs. In addition, it is becoming increasingly important to discuss the potential energy savings. For this purpose, quantitative evaluations are valued during the early stages of building planning and design because a building's shape can have large impacts on the performance of natural ventilation. However, few studies have fully examined the criteria for this type of evaluation. In this paper, a target air change rate is proposed as a desired criterion. The target air change rate is defined as the point where the gradient of the increase in the cooling effect from natural ventilation reaches a maximum. Above this point the rate of improvement in building comfort is more modest. In addition, this paper provides maps of indices for the United States. The maps help architects obtain a clear understanding of their design directions, e.g., a carefully designed natural ventilation strategy is highly recommended for building projects in warm-dry climates, where the internal gains are moderate, and for building projects in cold climates, where the internal gains are very high.

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Two natural rubber (Hevea brasiliensis) most popular and widely planted clones RRIM 600 and RRII 105 in the traditional region of India, were evaluated for immature growth performance in warm dry climate of Bastar region in chattisgarh state. The state is a non-tradional rubber growing region and the crop experiences severe drought in the summer months. Prolonged high temperature, low rainfall and soil moisture are the major environmental constraints affecting the performance of clones in the region. Growth performance, effect of seasonal changes on the growth in terms of girth and morphological characters of the clones was assessed. Both the clones observed satisfactory growth in the region. RRIM 600 showed over all superiority and better adaptability in the region. The mean annual girth increment of clones was 6.2 cm. highest girth contribution for both clones was recorded in the wet season, while the lowest was observed during the summer. RRIM 600 also showed more vigorous morphological growth in terms of stem height and canopy structure. Clones attain a tappable girth after the nine years of field planting in the region. Various growth parameter, overall clones performance and adaptability in the region has been discussed. The present study may provide information on the feasibility of rubber cultivation and performance of clones under adverse climate with further support in the identification of suitable best clones for such nontraditional regions.

Comparative estuarine and marine migration ecology of Atlantic salmon and steelhead: blue highways and open plains

This synthesis focuses on the estuarine and ocean ecology of Atlantic salmon (Salmo salar) and steelhead (Oncorhynchus mykiss) across their southern ranges in North America. General life history and ecology share many common traits including iteroparity, duration of freshwater (0–3 years) and marine (2–5 years) rearing, ocean emigration at relatively large sizes and strong surface orientation compared to other salmonids. Despite parallels in life history and anthropogenic pressures, several differences emerged for these species. First, steelhead have greater life history diversity and a broader geographic distribution. Generally, estuary habitats serve as short-term migration corridors for both species. However, some steelhead populations used lagoon habitat in south-coast watersheds. While both species are epipelagic, Atlantic salmon exhibit more vertical migration. Atlantic salmon tend to follow migratory highways—relatively narrow bands along the coastal shelf, then crossing the Atlantic to feed inshore and in fjords of West Greenland. Conversely, steelhead exit the coastal shelf quickly, dispersing across the Pacific, and rarely use coastal environments. Despite inhabiting rivers in warm dry Mediterranean climates, the extended range and stability of southern steelhead distribution is likely buffered by cool upwelled waters of the California Current. Whereas Atlantic salmon populations are restricted by warmer Northwest Atlantic circulation patterns lacking cool upwelling with greater susceptibility to warming associated with climate change. Determining the rate of marine habitat changes in the Atlantic and Pacific Oceans is important to the conservation of these species, including subtleties of temporal and spatial habitat use, and adaptability to ocean ecosystems under climate change.

Influence of Absorptance in the Building Envelope of Affordable Housing in Warm Dry Climates

In Mexico, as in many other countries, the energy crisis has permeated throughout many sectors, particularly the construction sector. Mexico has started to develop and implement actions for the efficient use of energy in order to reduce its consumption. The field of building construction has been particularly active in studying ways to optimize the use of energy, especially regarding energy use indoors. One of the main goals of architectural design is to create the proper indoor conditions so individuals can carry out their daily activities in a comfortable area. Interior space must be designed and calculated to provide a comfortable temperature, appropriate lighting, sound control and ventilation for individuals to carry out their daily activities, but must also address the energy required to provide all these characteristics. In warm dry climates, air-conditioning is responsible for a significant amount of the energy consumed in buildings. Proper building design is necessary in order to reduce energy consumption in this sector.This paper shows the results of simulations with the Energy Plus software to compare the thermal performance of a low-cost housing located in a warm dry climate, Hermosillo, Sonora, with similar construction systems in the envelope. Furthermore, an analysis of the effect of the color exterior finish, represented as a gradual change in the absorptance to solar radiation. The simulation is performed for two conditions of use of low-cost housing, the first condition considers the room without air conditioning and the second considers the air conditioned room. To simulate analyzed housing with air conditioning, is used an air conditioner from the database Energy Plus, corresponding to a Mini-split system compact unit zone cooling with a COP (Coefficient of performance) of 1.83.

Cooling Average Potential of Evaporative Cooling System in Dry Warm Climate

The high summer temperatures, high solar radiation and common inadequate thermal design of buildings obliges the occupants to recur to the use cooling equipment such as evaporative air-conditioning to achieve acceptable levels of habitability. Evaporative cooling systems require considerable electric energy and a significant constant clean water supply during operation. Therefore, this paper presents the results of a field study aims to quantify in this kind of weather, the potential cooling means having the following strategies: indirect evaporative cooling and shading devices; indirect evaporative cooling, shading devices and thermal mass; indirect evaporative cooling, solar protection, thermal mass and nocturnal radiative cooling; indirect evaporative cooling, thermal insulation and nocturnal radiative cooling; and finally indirect evaporative cooling, thermal insulation, thermal mass and nocturnal radiative cooling. The method consisted of measuring the reduction in air temperature is achieved with each of these cooling strategies, applied in three research modules of same construction features, orientation and dimensions during the summer 2012.Then quantified the cooling average potential by the method proposed by Dr. Eduardo Gonzalez (1989). Finally registration was the water consumption with each of these strategies and estimated required consumption by direct evaporative cooling to achieve the same cooling potential. The results obtained indicate that the IEC/TI/NRC had cooling potential of 822.89 Wh/m2day, followed IEC/SP with 764.19 Wh/m2day and finally IEC/SP+TM 568.60 Wh/m2day.

Energy Saving in a Dry Climate and Vertical Housing

Aspects such as mass development of horizontal housing with inappropriate designs for a region with warm and dry climate, the incessant investment in electrical energy, the continuous growth of cities towards the outskirts, and the downward trend in population density give rise to excessive energy consumption. This paper presents a study on the horizontal growth in the city of Hermosillo, Sonora, Mexico where the climate is warm and dry and the use of air conditioning is essential. In Hermosillo, 40 dwellings develop per hectare, which lack bioclimatic strategies and need to be supplied with electrical energy, street lighting, and urban infrastructure. In other cities such as in central Europe, up to 300 dwellings are developed per hectare and in South America, 150 dwellings per hectare. In these major cities, vertical housing is developed, which restrains territory growth. Based on this study, it can be demonstrated that sustainable vertical housing for warm dry climates such as the one in the State of Sonora can provide significant saving on electricity consumption and urban infrastructure in comparison to the mass development of horizontal housing with no bioclimatic techniques. This saving can be a determinant in the development of sustainable vertical housing.

Holocene temperature fluctuations in the northern Tibetan Plateau

Arid Central Asia (ACA) lies on a major climatic boundary between the mid-latitude westerlies and the northwestern limit of the Asian summer monsoon, yet only a few high-quality reconstructions exist for its climate history. Here we calibrate a new organic geochemical proxy for lake temperature, and present a 45-yr-resolution temperature record from Hurleg Lake at the eastern margin of the ACA in the northern Tibetan Plateau. Combination with other proxy data from the same samples reveals a distinct warm–dry climate association throughout the record, which contrasts with the warm–wet association found in the Asian monsoon region. This indicates that the climatic boundary between the westerly and the monsoon regimes has remained roughly in the same place throughout the Holocene, at least near our study site. Six millennial-scale cold events are found within the past 9000yr, which approximately coincide with previously documented events of northern high-latitude cooling and tropical drought. This suggests a connection between the North Atlantic and tropical monsoon climate systems, via the westerly circulation. Finally, we also observe an increase in regional climate variability after the mid-Holocene, which we relate to changes in vegetation (forest) cover in the monsoon region through a land-surface albedo feedback.

Biomarkers as paleoclimate proxies in peatlands in coastal high plains in Asturias, N Spain

This study represents an attempt to correlate wet and dry episodes as defined by biomarker parameters in peat profiles of Asturias (North Spain). The peats developed in a coastal location on high plains at heights ranging between 115 and 256m above sea level. The peat profiles which cover different Holocene intervals exhibit growth rates ranging from 0.05 to 0.56mm/yr and so provide records of different resolution.Biomarkers have revealed the widespread occurrence of nonadecan-2-one (K19), a characteristic of Cantabrian peatlands, different periods of dominance by higher plants and bacterial triterpenoids and an alternance of humid and dry periods as reflected in the n-alkane ratios. A change from a more arboreous vegetation before 4000cal.yr BP in the relatively dry warm climate of the Middle Holocene to a Sphagnum-herbaceous dominant vegetation typical of cooler wetter conditions is observed. The wet episode between 2200 and 3000cal.yr BP has a widespread occurrence in the studied profiles, whereas other dry–wet episodes are only recorded in some peat deposits and may be associated with local conditions.

Mechanism of palygorskite formation in the Red Clay Formation on the Chinese Loess Plateau, northwest China

The morphological characteristics and microstructures of the authigenic palygorskite occurring with smectite and carbonate minerals in the Late Miocene Red Clay Formation, on the Chinese Loess Plateau, have been investigated with the powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). The XRD results indicate that the red clay sediments contain quartz, feldspar, calcite, dolomite, illite, kaolinite, chlorite, palygorskite, and smectite, and SEM analyses show that palygorskite is a common component. Delicate palygorskite fibers radiate from the margins of platy smectite, suggesting a pedogenic origin during the weathering of pre-existing smectite, a process that involved intense dissolution of the smectite and an adjustment in its structure. Moreover, palygorskite occurs as coatings, pore-fillings, and pore-bridging cements among dolomite rhombs, suggesting that the fibrous palygorskite was formed by a direct dolomite precipitation from pore fluids, mostly after dolomite crystallization. There is evidence to show that these two mechanisms took place synchronously in the Red Clay Formation, and that the two processes are related. Under alkaline conditions, with high-pH (~8.0) fluids rich in magnesium, magnesium ions occupy the interlayer positions in the smectite, and this results in a misfit between the Mg octahedral sheet and the smectite layer, thereby allowing interaction between the magnesium ions and smectite layers and a reorganization of the structure to form palygorskite. Then, with this kind of palygorskite as a crystal nucleus, more palygorskite grows through a direct chemical deposition process. According to previous studies, the red clay sediments experienced a steady dry–warm climate with periods of high rainfall and evaporation. The warm climate would have increased the rate of weathering of minerals, and subsequently enhanced the ions content and pH in the soil solutions during dry periods. This soil environment is favorable for smectite transformation and palygorskite deposition. This study has improved our understanding of the environmental and paleoclimatic changes during the time that palygorskite formed in the arid soils of the Chinese Loess Plateau.

Climate-controlled landscape evolution in the Western Transverse Ranges, California: Insights from Quaternary geochronology of the Saugus Formation and strath terrace flights

The Las Posas and Ojai Valleys, located in the actively deforming Western Transverse Ranges of California, contain well-preserved flights of strath terraces and Quaternary strata (i.e., Saugus Formation) that when numerically dated elucidate the tectonic, geomorphic, and fluvial histories that sculpted the landscape since ca. 140 ka. This study includes 14 new optically stimulated luminescence and 16 new terrestrial cosmogenic nuclide ages from the late Pleistocene to Holocene that record two regional aggradation events and four intervals of strath terrace formation. Geochronologic data indicate that terrestrial Saugus strata in the Las Posas Valley (Camarillo Member) prograded over marine deposits at ca. 125 and 80 ka and are as young as 60–25 ka, which is an order of magnitude younger than the youngest Saugus strata elsewhere in Southern California. These results highlight the need for precise dating of Saugus strata where identified and utilized to assess rates of tectonic deformation. Based on its compositional character, thickness, stratigraphic relations, and inferred ages, the Camarillo member of the Saugus Formation is correlated with sediments of the Mugu aquifer identified in subcrop throughout the Ventura Basin and thus provides a new regional chronostratigraphic subsurface datum. The aggradation of these sediments and similar deposits in the study area between 13 and 4 ka is subsequent to the transition from humid to semiarid climate correlating to the end of the ultimate and penultimate glacial maximums. Aggradation is inferred to have resulted from increased sediment supply in response transient vegetative conditions and consequent hillslope destabilization. Similar to aggradational events, strath terrace cover sediments ages correlate to dry warm climate intervals, indicating straths in Southern California were cut at ca. 110–100 ka, 50–35 ka, 26–20 ka, and 15–4 ka. These results support recent mathematical and experimental models of strath formation, where increased sediment flux and decreased water discharge enhances lateral erosion rates and inhibits vertical incision. Subsequent incision and strath terrace formation is inferred to occur during intervening wet climate intervals. The correlation of strath terrace ages and aggradational events with environmental changes that are linked to global climate indicates that climate rather than tectonics exhibits first-order control of depositional, denudational, and incisional processes in the Western Transverse Ranges. Moreover, these results provide a chronostratigraphic framework that allows these landforms to be regionally correlated and used to assess rates of active tectonics where geochronologic data are unavailable.

Adaptive Thermal Comfort for Occupants of Low-Cost Dwellings in a Hot Dry Climate

Adaptive models are based on the observation that there are some actions that people can and actually do take to achieve thermal comfort. Studies regarding thermal comfort conditions in economical dwellings were carried out simultaneously in seven Mexican cities, corresponding to warm dry and warm humid climates. In this article, case studies of low-cost dwellings in the city of Hermosillo (in northwest Mexico), are presented and analyzed. Field surveys were carried out to obtain information about the physical characteristics of the dwellings and their occupants, as well as the indoor thermal environment. Neutral temperature was obtained from the applied survey. The high neutral temperature reveals the effect of inhabitants' adaptation mechanism to extreme climates. Occupant comfort votes as a function of indoor air temperatures were analyzed, and different characteristics such as age, size and gender were evaluated separately. The results show the variability of the neutral temperature and the tolerance to temperature changes, depending on the population's specific characteristics. In many cases where the population does not have access to artificial acclimatization devices, the neutral temperature values for specific climates and people can inform architects when choosing the most suitable thermal strategies for building design.

A Survey of the Arthropod Pests and Plant Parasitic Nematodes Associated with Commercial Figs,Ficus carica(Moraceae), in South Africa

Edible figs originate from Arabia Felix, present-day Yemen (Eisen 1901) and have been cultivated in the Lower Jordan valley since 11 400-11 200 B.C. (Kislev et al. 2006). Genetic distinction of fig cultivars in Italian isles and natural populations occurring in the Mediterranean basin (Khadari et al. 2005), indicate introduction from the east Arabian Peninsula (Kislev et al. 2006). Eisen (1901) suggested that this introduction to Europe occurred around 800 B.C. by the Phoenicians and Greeks. Under Roman rule they spread to the rest of Europe, but only slowly towards the east, with the first documented edible figs appearing in China by A.D. 1550. At first the fig was considered a luxury for the rich, but it soon became a traded commodity, forming an integral part of the human diet. The ideal climate of Portugal for fig production secured the development of a superior industry there. With the explorations of the Spanish and Portuguese, figs were subsequently established in almost all countries they visited. Today figs are grown all over the world, but they especially favour a warm-temperate Mediterranean-type climate. Figs require sufficient moisture during the active growth period, but a warm dry climate when fruit are ripening (P. Botma, pers. comm.). The winter rainfall areas of South Africa, such as the Swartland and Klein Karoo in the Western Cape are therefore ideal for fig cultivation whereas fruit quality is negatively affected by higher fungal contamination in summer rainfall areas (M. Wohlfarter, pers. obs.).

An ice-core record of vegetation and climate changes in the central Tibetan Plateau during the last 550 years

We present a 550-year ice-core pollen record with a 5-year resolution from the Puruogangri ice field in the central Tibetan Plateau. Analysis of the relationship between pollen record and instrumental observations suggests that the sum of the steppe and meadow pollen taxa is a good indicator of summer (June-August) temperature, whereas the ratios of Cyperaceae/(Gramineae+Artemisia) [Cy/(G+A)] as well as M/S (meadow to steppe percentages) are indicative of humidity changes in this region. Together with delta (18)O and glacial accumulation records, the response of vegetation to climate change over the past 500 years was revealed. Desert vegetation dominated during 1450-1640 AD, a time period characterized by cold-wet climate, while steppe vegetation expanded during 1640-1915 when warm-dry climate prevailed. Afterwards, during a cold and humid period, desert vegetation expanded again. Since 1980-2002, due to the increase of summer temperatures, steppe and meadow vegetation predominates, while areas with desert vegetation are reduced. This proxy series is the first high-resolution ice-core pollen record spanning the last 550 years for the central Tibetan Plateau.

Determinación Experimental y Contraste Numérico de la Resistencia Térmica de un Muro de Bloques de Concreto Hueco

This paper presents design and construction of an experimental test to determine the thermal resistance of a hollow concrete blocks wall, according to the international standard known as guarded hot plate. The construction procedure and implementation of the device are described, reproducing operations conditions for buildings located in warm dry climate, and the thermal resistance was experimentally and numerically determined. The results were found by applying controlled temperature differences on both sides of the wall between heating and cooling temperature zones, in steady state conditions. Experimental and numerical results show variations in the value of thermal resistance, ranging from 0.15 to 0.19 °C m2/W. Values of the thermal resistance were fitted to an empirical expression as function of the temperature difference between the walls and the average temperature of the wall.