Mean Maximum Summer Temperature Research Articles

Temperature and relative humidity trends in the northernmost region of South Africa, 1950–2016

The northernmost Limpopo Province is located in one of the warmest regions of South Africa, where the agricultural sector is prone to heat stress. The aim of this study was to explore air temperature and relative humidity trends for the region, which have implications for agricultural adaptation and management (amongst other sectors). In particular, we investigated seasonal, annual and decadal scale air temperature and relative humidity changes for the period 1950–2016. Positive temperature trends were recorded for this period, averaging +0.02 °C/year, with the strongest changes observed in mean maximum summer temperatures (+0.03 °C/year). Interannual temperature variability also increased over time, especially for the period 2010–2016, which presents probability densities of <50% for minimum temperatures. Positive relative humidity trends (+0.06%/year) were also recorded for the period 1980–2016, but proved to be the least predictable weather parameter, with probability densities of <0.5% across seasons for the study period. Considering the substantial interannual variability in temperature and relative humidity, there is clear increased risk for the agricultural sector, particularly for small-scale farmers who generally have limited capacity to adapt. Climate science focusing on the southern African region should continue to establish the impact of climate change and variability on specific small-scale farming systems and enterprises, with recommendations for strategic adaptation based on up-to-date evidence.Significance: Heat indices have increased, and variability in temperature and relative humidity has substantially increased over recent decades. Changes in air temperature and relative humidity have direct and/or indirect negative effects on sectors such as agriculture, leading to reduced productivity. The small-scale farming sector, which contributes significantly to national food security in developing countries, is the production system most exposed and vulnerable to observed changes/extremes in temperature and relative humidity. There is an urgent need to build capacity of small-scale farmers for appropriate adaptation to observed changes in climate based on up-to-date evidence.

A seven-fold rise in the probability of exceeding the observed hottest summer in India in a 2 °C warmer world

Heatwaves and extreme temperatures during summer (April–May) in India have profound implications on public health, mortality, water availability, and productivity of labourers. However, how the frequency of the hottest summers in observed record (1951–2015) will change under the warming climate in India is not well explored. Using observations from the India Meteorological Department, we show that mean maximum summer temperature has increased significantly in three (arid, monsoon, and savannah) out of five major climatic regions of India during 1951–2015. We identify the hottest summer in the observed record in the five climatic regions in India. The arid, cold, and temperate regions experienced the hottest summer in 2010 while monsoon and Savannah regions witnessed the hottest summer in 1979 and 1973, respectively. Based on simulations from the Climate of 20th Century Plus (C20C+) Detection and Attribution project, we show that the regional hottest summer of 2010 can be attributed to the anthropogenic warming. We then use simulations of a large (2000 year) ensemble of the EC-Earth model to estimate the exceedance probability of the observed hottest summer in the present climate, 2 °C and 3 °C warming worlds in India. The exceedance probability of the observed hottest summers shows a rise of more than seven and twenty-fold in the 2 °C and 3 °C warming world, respectively, compared to the present climate. The projected increases in the frequency of the hot summers and associated heatwave days will pose great societal challenges in the future in India.

+A 5680-year tree-ring temperature record for southern South America

It is widely documented that the Earth’s surface temperatures have increased in recent decades. However, temperature increment patterns are not uniform around the globe, showing different or even contrasting trends. Here we present a mean maximum summer temperature record, based on tree-ring widths, over the past 5682 years (3672BC – 2009AD) for southern South America (SSA), covering from mid-Holocene to the present. This is the longest such record for the Southern Hemisphere (SH), and expands available annual proxy climate records for this region in more than 2060 years. Our record explains 49% of the temperature variation, and documents two major warm periods between 3140–2800BC and 70BC – 150AD, which coincide with the lack of evidence of glacier advances in SSA. Recent decades in the reconstruction (1959–2009) show a warming trend that is not exceptional in the context of the last five millennia. The long-term relationship between our temperature reconstruction and a reconstructed total solar irradiance record, with coinciding cycles at 293, 372, 432–434, 512 and 746 years, indicate a persistent influence of solar forcing on centennial climate variability in SSA. At interannual to interdecadal scales, reconstructed temperature is mainly related to the internal climate variability of the Pacific Ocean, including El Niño Southern Oscillation (ENSO) and longer oscillations. Our study reveals the need to characterize regional-scale climate variability and its drivers, which in the context of global-scale processes such as anthropogenic warming, interact to modulate local climate affecting humans and ecosystems.

Heat tolerance in garden roses

Roses generally experience a decrease in flower productivity and size in response to summer temperatures greater than 30°C that is common throughout the southern states of the USA. In College Station, Texas, the August mean and mean maximum summer temperatures can be 32 and 40°C, respectively. Under these extreme heat stress conditions, a large rose germplasm collection was evaluated for flowering intensity that takes into account both flower number and flower size. Of the 234 accessions evaluated, most showed moderate flowering during August and about 6% consistently had over 50% flower intensity in August. Experiments done in the growth chamber with potted roses containing young flower buds indicated that a 3-h heat shock (44°C) treatment resulted in decreased flower size and increased flower abscission. Consequently, this approach was used to assess the heat tolerance of 18 rose cultivars in this collection. The results indicated that field ratings of heat tolerance based on flower productivity were negatively correlated to flower abscission and leaf necrosis (r=-0.55* and r=-0.64**) and not correlated with leaf MTS (cell membrane thermostability) of the potted rose plants subjected to the heat shock treatment.

River reaches with impaired riparian tree cover and channel morphology have reduced thermal resilience

AbstractThis study evaluated the effects of riparian tree cover and channel morphology on the thermal regimes of 3 adjacent rivers in different years. Riparian tree cover was found to exert a strong modifying influence on stream temperature, with reduced mean maximum summer temperature at sites having greater tree cover. The effect of tree cover changed among years, such that greater cover was required to maintain a given water temperature regime in the warmer summer of 2013 than in 2014 or 2015. Water temperature was also related to mean depth in some years; shallower sites, typically associated with artificial channel widening, showed greater temperature extremes. These results suggest that the thermal resilience of modified streams can be improved by restoration of riparian tree cover and restored channel morphology. This finding is relevant to climate change proofing of temperate river channels, where cold‐water fauna are important elements of the biotic community.

Improved statistical downscaling models based on canonical correlation analysis, for generating temperature scenarios over Greece

This study attempts to improve upon statistical downscaling (Sd) models based on the classical approach which uses canonical correlation analysis, in order to generate temperature scenarios over Greece. Considering the long-term trends of the predictor variables (1,000–500 hPa thickness field geopotential heights—using NCEP data) and the predictand variables (observed mean maximum summer temperatures over Greece), a new Sd model is constructed. Regression models using generalized least square estimators are developed in order to eliminate the trends within the time series. The advantages of the suggested method compared to the classical method are quantified in terms of a number of distinct performance criteria, e.g., Mean squared error which is the basic criterion of the estimated downscaled values relative to the observed. Finally, the suggested Sd models are used to evaluate the effects of a future climate scenario (IPCC-SRES: A2) on mean maximum summer temperatures over Greece. The results from the climate projection indicate a temperature increase for the period 2070–2100 which is smaller than the corresponding increase from the classical approach.

Genetic Evidence for Restricted Dispersal along Continuous Altitudinal Gradients in a Climate Change-Sensitive Mammal: The American Pika

When faced with rapidly changing environments, wildlife species are left to adapt, disperse or disappear. Consequently, there is value in investigating the connectivity of populations of species inhabiting different environments in order to evaluate dispersal as a potential strategy for persistence in the face of climate change. Here, we begin to investigate the processes that shape genetic variation within American pika populations from the northern periphery of their range, the central Coast Mountains of British Columbia, Canada. At these latitudes, pikas inhabit sharp elevation gradients ranging from sea level to 1500 m, providing an excellent system for studying the effects of local environmental conditions on pika population genetic structure and gene flow. We found low levels of neutral genetic variation compared to previous studies from more southerly latitudes, consistent with the relatively recent post-glacial colonization of the study location. Moreover, significant levels of inbreeding and marked genetic structure were detected within and among sites. Although low levels of recent gene flow were revealed among elevations within a transect, potentially admixed individuals and first generation migrants were identified using discriminant analysis of principal components between populations separated by less than five kilometers at the same elevations. There was no evidence for historical population decline, yet there was signal for recent demographic contractions, possibly resulting from environmental stochasticity. Correlative analyses revealed an association between patterns of genetic variation and annual heat-to-moisture ratio, mean annual precipitation, precipitation as snow and mean maximum summer temperature. Changes in climatic regimes forecasted for the region may thus potentially increase the rate of population extirpation by further reducing dispersal between sites. Consequently, American pika may have to rely on local adaptations or phenotypic plasticity in order to survive predicted climate changes, although additional studies are required to investigate the evolutionary potential of this climate change sensitive species.

Effectiveness of Using Summer Thermal Indices to Classify and Protect Brook Trout Streams in Northern Ontario

Abstract We tested five thermal indices for their ability to differentiate streams containing brook trout Salvelinus fontinalis from streams not containing brook trout in forested watersheds of the Precambrian Shield, northern Ontario, with the goal of identifying and protecting riparian areas of thermally sensitive trout streams during timber harvesting. Logistic regression was used to predict brook trout presence and absence, with maximum summer temperature, mean summer temperature, mean sampling temperature, mean maximum summer temperature, and thermal stability as independent variables. Brook trout streams were cooler and thermally more stable than non-brook-trout streams, but temperatures overlapped considerably between the two types of stream. Correct classification of streams ranged from 60.3% for summer temperature stability to 67.1% for maximum summer and mean sampling temperatures. The models yielded correct predictions more often for brook trout absence (∼80%) than for brook trout presence (≤50...

Geographic variation in size and shape in the southern brown bandicoot, Isoodon obesulus (Peramelidae : Marsupialia), in Western Australia

Geographic variation in body size and shape was examined among populations of the southern brown bandicoot, Isoodon obesulus, in the south-west of Western Australia, with a view to determining the possible presence of adaptive divergence. Analysis of variance and canonical variate analysis were employed to examine the variation in body weight, head length, pes length and ear length among six locations. Significant sexual dimorphism was detected for these morphological variables, with males being larger than females. Significant geographic variation in overall body size and shape was found for both males and females. Correlations between body size and shape and each of five environmental variables (mean annual rainfall, mean maximum summer temperature, mean minimum winter temperature, relative humidity and latitude) were tested. Neither body size nor shape was correlated with any of the five variables, but both were related to habitat structure, with larger bandicoots being found in open forest habitats, while smaller bandicoots were found among swamp reeds. If the above variation has a genetic basis, these differences between locations may represent adaptive divergence and thus be of importance when formulating a conservation strategy for this species.

Breeding Ecology of the Western Long-billed Corella, Cacatua pastinator pastinator

The breeding ecology of a small population of the western long-billed corella, Cacatua p. pastinator, was investigated for 6 years in the central wheatbelt of Western Australia. Pair-bonds tended to be long-lasting; however, the divorce rate for birds breeding for the first time was 25% with an overall rate of 15%. Females formed stable pair-bonds by age 2, and bred for the first time between 3 and 5 years old; males started breeding when 5 years old. Clutches (range from one to four, mode three) were started in early August; 78% are started in the last 3 weeks of the month. Mean clutch size, brood size and number fledged were 2.7 , 1.9 and 1.6 respectively; there were no significant differences in these parameters among the six years of the study. Hatching was asynchronous and was followed by the death of the young nestlings when they were significantly smaller (77%) than their older siblings. Nestlings fledged when they were about 60 days old; neither their mass or degree of wing growth influenced fledging age. Mean mass of fledglings from broods of three was significantly greater than that of broods of two or one. Productivity was assessed by the numbers of young fledging, surviving the post-fledging period, and reaching independence. Neither mass nor condition at fledging influenced any of these measures; productivity in all three increased with clutch size. Rainfall and temperature had no influence on the numbers fledged, but the number reaching independence was significantly and positively correlated with the mean maximum summer temperature. The results are discussed in relation to the results from studies of other species of cockatoos living in the wheatbelt of Western Australia.

Trout Biomass and Habitat Relationships in Southern Ontario Streams

We examined relationships between the biomass of trout (species of Salvelinus and Salmo) and physical and biological habitat variables in streams to identify habitat factors that might limit trout biomass. Thirty sites were chosen to span a wide array of habitat types. At each site we measured a large number of habitat variables representing instream cover, substrate, stream morphology and velocity, stream temperature and food availability. Two habitat quality index models developed by Binns and Eiserman for Wyoming streams accounted for only 6.7 and 9.2% of the variation in trout biomass at Ontario stream sites. Different factors must limit trout biomass in Wyoming streams than in Ontario streams. Regression and discriminant function analyses indicated that trout biomass in southern Ontario is correlated with microcommunity biomass (measured as ATP of the suspended solids, and representing bacteria, fungi, and algae), percent pool area, mean maximum summer temperature, biomass of small benthic invertebrates, presence of piscivorous fish, and a variable representing pools and overhead cover. Microcommunity biomass was the most important habitat variable in these analyses and it was significantly correlated with basin yield. We hypothesize that microcommunity biomass is a surrogate measure of localized groundwater inflow, which, in turn, has a beneficial effect on the microhabitat of trout eggs and underyearlings.