Interannual Temperature Variability Research Articles

The Summer Heat Balance of the Oregon Inner Shelf Over Two Decades: Mean and Interannual Variability

AbstractSummer temperature and velocity measurements from 14 years in 15 m of water over the inner shelf off Oregon were used to investigate interannual temperature variability and the capacity of the across‐shelf heat flux to buffer net surface warming. There was no observable trend in summer mean temperatures, and the standard deviation of interannual variability (0.5°C) was less than the standard deviation in daily temperatures each summer (1.6°C, on average). Yet net surface heat flux provided a nearly constant source of heat each year, with a standard deviation less than 15 of the interannual mean. The summer mean across‐shelf upwelling circulation advected warmer water offshore near the surface, cooling the inner shelf and buffering the surface warming. In most years (11 out of 14), this two‐dimensional heat budget roughly closed with a residual less than 20 of the leading term. Even in years when the heat budget did not balance, the observed temperature change was negligible, indicating that an additional source of cooling was needed to close the budget. A comparison of the residual to the interannual variability in fields such as along‐shelf wind stress, stratification, and along‐shelf currents found no significant correlation, and further investigation into the intraseasonal dynamics is recommended to explain the results. An improved understanding of the processes that contribute to warming or cooling of the coastal ocean has the potential to improve predictions of the impact of year‐to‐year changes in local winds and circulation, such as from marine heat waves or climate change, on coastal temperatures.

Interannual variability and trends in sea surface temperature, sea surface wind, and sea level anomaly in the South China Sea

ABSTRACTIn this study, we analysed the interannual variability of sea surface temperature (SST), sea surface wind (SSW), and sea level anomaly (SLA) in the South China Sea (SCS) during 1985–2016 using monthly reanalysis and satellite datasets. An empirical orthogonal function (EOF) analysis was performed to evaluate the interannual variability of each variable. The warming rate of SST was 0.18 ± 0.26°C decade−1 in the SCS. The first EOF of SST was characterized by basin-wide warming, with the highest anomalies in the northern deep basin. The first temporal coefficient of SST was negatively correlated with the Niño 3.4 index, with a lag of 6 mo. The mean rising rate of SLA was 7.6 cm decade−1, with the greatest trend in the coastal water of Vietnam, which exhibited a similar spatial pattern with the first EOF of SLA. The temporal coefficient of SLA was negatively correlated with that of SST, with a lag of 5 mo. The trend of SSW was around 0.8 m s−1 decade−1 over the SCS. The first EOF of SSW was characterized by an anticyclonic pattern. The temporal coefficient was correlated with that of SST, with a lead of 2 mo. Wavelet coherence was used to investigate the cross-correlation relationship between SST and other variables. SST and SLA had a strong negative correlation in the 8–16-mo (1–1.5 yr) band. The high positive wavelet coherencies between SST and SSW and Niño 3.4 were mainly in the 32–64 mo (3–5 yr) band in the SCS.

Characteristics of Climate Change in Northern Xinjiang in 1961–2017, China

Xinjiang is located in the core China’s ‘Belt and Road’ development, and northern Xinjiang is an important region for economic development. In recent years, due to the strong influence of global climate change and human disturbance, regional climate instability and ecological-economic-social system sensitivity have grown. In this paper, seasonal, interannual, interdecadal, spatial, abrupt, and periodic variations of temperature and precipitation in northern Xinjiang were analyzed using daily surface air temperature and precipitation data from 49 meteorological stations during 1961–2017. At the same time, the driving factors of climate change are discussed. Methods included linear regression, cumulative anomaly, the Mann-Kendall test, and Morlet wavelet analysis. The results indicated that during the study period, annual mean temperature and annual precipitation increased significantly at rates of 0.35°C/10 yr and 13.25 mm/10 yr, respectively, with abrupt changes occurring in 1994 and 1986. Annual mean temperature and annual precipitation in all four seasons showed increasing trends, with the maximum increases in winter of 0.42°C/10 yr and 3.95 mm/10 yr, respectively. The general climate in northern Xinjiang showed a trend towards increasingly warm and humid. In terms of spatial distribution, the temperature and precipitation in high mountainous areas increased the most, while basins areas increased only slightly. Periodic change analysis showed that annual mean temperature and annual precipitation experienced two climatic shifts from cold to warm and dry to wet, respectively. Population change, economic development and land use change are important factors affecting climate change, and more research should be done in this field.

Comparison of Lysimeter-Derived Crop Coefficients for Legacy and Modern Drought-Tolerant Maize Hybrids in the Texas High Plains

HighlightsDaily maximum crop coefficient (Kc) values were similar for legacy hybrids and a modern drought-tolerant (DT) hybrid.Later planting dates for a DT hybrid resulted in average season lengths ~25 days shorter than those of legacy hybrids.Results illustrated the effects of environment, planting date, interannual variation in temperature, and the importance of climate-specific Kc functions.DT hybrids may be more effective at reproductive growth during periods of heat stress in semi-arid environments, although additional data are needed to support this conclusion.Abstract. Corn (Zea mays L.) is a major irrigated crop grown in the Southern High Plains including the Texas Panhandle. Irrigation from the Ogallala Aquifer is required to sustain profitable corn production in the region by supplementing inadequate and erratic rainfall. Effective irrigation scheduling works to extend limited groundwater resources by avoiding water losses associated with runoff and/or percolation below the root zone. The use of crop coefficient (Kc) and reference evapotranspiration (ETo) values to estimate daily crop water use (ETc) remains an effective scheduling tool that can complement other irrigation scheduling approaches. Both Food and Agriculture Organization (FAO-56) piecewise and curvilinear Kc values for corn are found in the literature. However, advances in corn genetics have led to questions about the applicability of Kc values developed using legacy corn hybrids to irrigation of modern drought-tolerant (DT) hybrids. Lysimeter-derived Kc values for legacy corn hybrids grown in large weighing lysimeter fields at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, were compared with those derived from a modern DT corn hybrid recently grown in the same fields. Results indicated that although midseason daily Kc values were similar for all hybrids, average season length was ~25 days shorter for the modern DT hybrid, characterized by a shortened initial growth period followed by more rapid increase of Kc during the development period. However, plots of Kc over thermal time illustrated that the differences in season length were likely attributable to later planting dates associated with the DT corn hybrids. Average seasonal water use was 730 and 811 mm for the legacy and modern DT hybrids, respectively (three years each), with corresponding average yields of 1.2 and 1.4 kg ha-1. Results suggest that published Kc and Kcb values developed with legacy corn hybrids remain largely applicable to modern DT corn hybrids when used with accurate estimates of effective canopy-based growth stages and climate-specific Kc functions. Keywords: Crop coefficients, Drought-tolerant, Evapotranspiration, Maize, Weighing lysimeters.

Targeted model evaluations for climate services: A case study on heat waves in Bangladesh

Though not a sufficient condition, the ability to reproduce key elements of climate variability over the historical record should be a minimum requirement for placing any confidence in a model’s climate forecasts or projections of climate change. When projections are used to guide practical adaptation, model evaluations should focus on the weather and climate events of interest to decision-makers, their physical drivers in the climate system and their variability on decision-relevant timescales. This paper argues for a greater emphasis on such targeted model evaluations to enable useful climate services. We illustrate this approach through a case study on heat waves in Bangladesh, but draw wider conclusions that are applicable to climate services development more broadly.The simulation of heat waves in Bangladesh is evaluated in several climate models, focusing on timescales relevant to the long-term viability of a heat action plan: the average, interannual variability and seasonality of temperature and heat-wave frequency. Where the physical drivers of variability are broadly captured, a considered interpretation of the models could provide insights into future heat-wave behaviour. However, substantial biases are found in the statistics and in some physical drivers of heat, raising questions about the suitability of some of the models for determining certain aspects of future risk. Specifically, simple bias corrections cannot be used to make inferences about possible future changes in various weather statistics such as timing of heat waves during the year. Results emphasize the potential pitfalls of performing only perfunctory climatological evaluations and highlight areas for model improvement in the simulation of South Asian climate variability.

Evaluation of CMIP6 AMIP climate simulations with the ACCESS-AM2 model

The most recent version of the ACCESS-AM2 atmosphere-only climate model is introduced with results from the CMIP6 Atmospheric Model Intercomparison Project (AMIP) experiments configured with two land-surface models: CABLE and JULES. AMIP simulations are required as part of the CMIP6 core experiments. They are forced by prescribed time-varying observed sea surface temperature and sea-ice variations as well as variations in natural and anthropogenic external forcings. We evaluate the performance of the two configurations using three historical realisations for each. Model biases are estimated both globally and for the Australian region. The model shows close agreement with observed interannual variations of global-mean temperature across the latitude range 65°N–65°S. This is also true for the land-only temperature for 65°N–65°S, and a more stringent test of the model is driven by specified observed sea surface temperatures. Patterns of mean precipitation are simulated reasonably well, although there are biases in the amount and distribution of precipitation, typical of longstanding problems in representing this aspect of the climate. Selected features of the atmospheric circulation are discussed, including air temperatures and wind speeds. For the Australian region, in addition to examining the climatological patterns of temperature and precipitation, important drivers of climate variability are reviewed: El Niño-Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode. In general, the correlation patterns for precipitation simulated by ACCESS-AM2 are somewhat weaker than in observations, although the ensemble means show better agreement than individual ensemble members. Overall, the two different land-surface schemes perform similarly. ACCESS-AM2 has reduced root mean square errors for both temperature and precipitation of around 15–20% at the global scale compared to the older CMIP5 versions of the model: ACCESS 1.0 and ACCESS 1.3.

Analysis of Meteorological Elements and Climate Change in Poyang Lake Basin

In our study, five stations of Poyang Lake were selected: Nanchang, Boyang, Jingde, Lushan and Jing’an. The three observational values of temperature, precipitation and evaporation in these five stations from 1988 to 2017 were analyzed. Through average, extreme value, linear regression and cumulative anomaly analysis, the interannual temperature variation trend of the five stations is consistent and is expected to continue to rise over the next 20 years; precipitation shows different changes in different periods; evaporation is decreasing year by year. This study is of great significance to the maintenance of ecological function and security of Poyang Lake.

Interannual Variation of Upper Stratospheric Ozone in the Northern Midlatitudes in Early Winter Caused by Planetary Waves

AbstractOzone mixing ratios in the upper stratosphere, observed with a millimeter‐wave radiometer at Rikubetsu (43.46°N, 143.77°E), Japan, from November 1999 to February 2017 showed both interannual and seasonal variation, which was characterized by a winter maximum and a summer minimum. During the study period, the summer minima were nearly constant whereas the winter maxima varied interannually and also displayed short‐term variability. The observed ozone mixing ratios at 1 hPa were anticorrelated with temperature at 1 hPa from MERRA‐2 data. The slope of the relationship between the logarithm of ozone concentration and the reciprocal of temperature differed between winter data and both summer and annual data. Therefore, we inferred that both chemistry and dynamics affect short‐term variation of ozone mixing ratios in winter. We then examined the contribution of the polar vortex to interannual variations in ozone and temperature at 1 hPa. When the polar vortex was strong, wave number‐1 planetary waves at high latitude propagated toward the midlatitudes instead of vertically. The vertical component of the wave number‐1 Eliassen‐Palm flux along 43°N at 1 hPa was strongly correlated with zonal mean zonal wind along 60°N at 50 hPa. When the zonal mean westerly wind was strong in December, upper stratospheric (~1 hPa) temperatures over Rikubetsu and over a point on the opposite side of the globe (by longitude) were significantly lower and higher, respectively, than the climatological temperature. Thus, planetary wave propagation related to zonal mean westerly wind strength induced early winter interannual variation in upper stratospheric ozone in the midlatitudes.

Estimating the influence of thermal inertia and feedbacks in the atmosphere–ocean system on the variability of global surface temperature

The present climate is characterized not only by the trend due to the increase in the concentrations of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability, calculated via the computational results from the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program, show significant inter-model differences. In particular, inter-model distinctions in decadal anomalies of the global and hemispheric temperatures reach four times the value. However, unlike the inter-model differences in climate sensitivity, the reasons for a wide range of estimates of climate variability are still unclear. Based on the two-component energy-balance stochastic model, the paper analyzes the inter-annual and inter-decadal variability of the mean global surface temperature (GST) to feedback and the thermal inertia of the atmosphere-ocean system, assuming that the external forcing is random fluctu-ations of the radiation balance at the top of the atmosphere. Using the obtained ab-solute and relative sensitivity functions, the influence of thermal inertia and feed-backs in the climate system on the inter-annual and inter-decimal variability (variance) of the GST and its spectrum is estimated.

Occurrence of ‘blue’ and ‘frost’ rings reveal frost sensitivity of eastern Baltic provenances of Scots pine

Assisted gene flow is advised as one of the most effective means to sustain the productivity of forests under warming climate via application of the provenances (genotypes) capable to utilize longer vegetation season. Nevertheless in the temperate and boreal zones, the extension of vegetation period also subjects trees to effects of frosts, which can have severe economic impact under warming climate. In this study, wood anatomical anomalies related to late frosts in spring (‘frost’ rings) and early frosts in late summer (‘blue’ rings) for the eastern Baltic provenances of Scots pine (Pinus sylvestris L.) with a contrasting field performance were analysed retrospectively. Three trials with the age of 40 year in Latvia were sampled. The frost-related wood anomalies were identified using microscopy methods. Generalized mixed effects models were used to assess the effect of provenance on the probability of frost damage, accounting for the design of the trials, as well as for the inter-annual variability. The overall mean probability of frost-related wood anomalies was low (ca. 0.025), yet it increased with continentality of the trials, showing limited relation to the inter-annual variability of minimum temperatures. The probability of anomalies decreased with age. Provenance had a significant effect on the occurrence of ‘frost’ and ‘blue’ rings, implying genetically determined frost sensitivity, while the genotype (provenance) by environment (trial) interaction indicated high phenotypic plasticity of the trees. The probability of anomalies appeared related to the field performance of the provenances. The low-performing provenances (Dippoldiswalde and Eibenstock, which originated from the Orr Mountains) were most sensitive to frost, while the top-performing ones (Rytel and, particularly, Güstrow, which originated from coastal areas) showed only a few anomalies, indicating the linkage between frost sensitivity and growth. The local provenance, which showed an average field performance, also showed intermediate sensitivity to early frosts, thus supporting a necessity for the assisted gene flow in the eastern Baltic region.

Interannual Variability of Mixed Layer Dynamics in the Ecuadorian Ocean

AbstractTime series spanning 22 years of monthly conductivity‐temperature‐depth profiles are used to examine upper water column temperature interannual variability near the Ecuador coastline. The sampling program began in 1992 (and continues) by Ecuador's National Institute of Oceanography of the Navy and National Fisheries Institute. The five coastal stations are located 8 NM away from the coast and extend from 2°S to 1°N. The anomaly data show marked interannual variations with distinct characteristics associated with El Niño Southern Oscillation (ENSO) indices. Heat content and the 20°C isotherm depth are both largest during El Niño periods and weakest during La Niña periods. The first mode empirical orthogonal function (EOF) decomposition of the anomaly coastal station data represents bulk variations of the thermocline depth and has temporal variability coupled to Niño 3.4 and 1+2 indices. Coastal observations are compared with observations obtained from the offshore TAO/Triton buoys located along 95°W from 2°S to 2°N. The EOF decomposition of TAO buoy time series shows similar spatial EOF structure. The first EOF amplitude time series from coastal and TAO station decomposition is correlated, showing that the dominant variability of the upper water column near the coast is coupled to variations along the equator and seaward of the Galápagos. Coupling between ENSO indices and ERA‐1 zonal wind stress from the central Pacific (Niño 4) with observed coastal temperature structure shows that effects of El Niño forcing are strongly influencing the Ecuadorian Sea eastward of the Galápagos Islands.

The east–west division of changing precipitation in Nepal

AbstractChanges to precipitation patterns and extremes over the Nepalese Himalayas were examined using a high‐resolution, station‐based daily dataset, Asian Precipitation‐Highly Resolved Observational Data Integration Towards Evaluation (0.05° × 0.05° APHRODITE) from 1951 to 2007. The annual statistics of extreme precipitation across Nepal show a significant increase since the end of the 20th century. However, seasonal mean precipitation shows a remarkable decrease in western Nepal, particularly since 1980, forming an east–west division in the precipitation change. This decreasing trend of precipitation led to a reduction to the dry‐season stream flow of Karnali River, the major river in western Nepal. At the same time, the increasing extreme precipitation produced greater threat of flash flood in Nepal. This east–west division of the precipitation trend agrees with the second leading mode of the mean precipitation variability, which was traced to the interannual variability of the Indian Ocean sea surface temperature that showed a slowdown of warming. Similar to the APHRODITE trends, precipitation simulated by the fifth phase of the Coupled Model Intercomparison Project (CMIP5) models depicted the decreasing historical trend in western Nepal, but future projections reverse that trend towards an all‐Nepal increase. CMIP5 future climate projections depict continual warming in the Indian Ocean, potentially reversing the historical decreasing trends of precipitation in western Nepal.

The Role of Soil Moisture Feedbacks in Future Summer Temperature Change over East Asia

AbstractThe increased mean temperature and temperature variability under global warming can have many adverse impacts on human and natural systems. However, how soil moisture‐atmosphere interaction can affect future climate change over East Asia remains largely unclear. We use long‐term regional climate simulations with the Community Climate System Model‐Weather Research and Forecasting (CCSM‐WRF) model system to investigate the role of soil moisture feedbacks in future summer surface air temperature change over East Asia. Results show that summer surface air temperature and precipitation are projected to increase over most of East Asia by the end of 21st century under the Representative Concentration Pathway 8.5 (RCP8.5) scenario. Soil moisture feedbacks lead to an increased summer mean temperature of 0.15°C averaged over East Asia, with key regions appearing over the northern part of Tibetan Plateau, Sichuan Basin, and the middle and lower reaches of the Yangtze River Basin during 2071‐2100 under the RCP8.5 scenario. And regionally averaged interannual temperature variability induced by soil moisture feedbacks is substantially enhanced as a whole. Regarding the spatial distribution, soil moisture feedbacks on interannual temperature variability are projected to strengthen notably over the northern part of Tibetan Plateau, the Hexi Corridor, and Sichuan Basin and weaken over the south Tibetan Plateau, southeast China, and the areas surrounding the Lake Baikal. The stronger responses of surface heat and the atmospheric boundary layer to dry anomalies than wet anomalies lead to an obvious dry‐wet asymmetry of soil moisture feedbacks on summer surface air temperature over the key areas of East Asia.

Estimating the Influence of Thermal Inertia and Feedbacks in the Atmosphere–Ocean System on the Variability of the Global Surface Air Temperature

The modern climate of our planet is characterized not only by a trend caused by an increase in the concentration of greenhouse gases in the atmosphere, but also by fluctuations covering a wide range of frequencies and scales. The global climate variability based on the modeling results of the Coupled Model Intercomparison Project Phase 5 of the World Climate Research Program is characterized by significant differences between models. In particular, for the decadal-scale anomalies of the global and hemispheric temperatures, the standard deviation differences between models are as high as fourfold. However, in contrast to the differences in climate sensitivity between models, the causes of a wide range of the estimates of climate variability are still not entirely understood. The research in this paper is based on two-component energy-balance stochastic model. We analyze the sensitivity of interannual and interdecade variability of the mean global surface temperature (GST) to the feedback and thermal inertia of the atmosphere–ocean system under the assumption that the main external forcing factor is random fluctuations of the radiation balance at the upper boundary of the atmosphere. We estimate the influence of thermal inertia and feedback in the climate system on the interannual and interdecade variability (variance) of the GST and the spectrum of its fluctuations using the absolute and relative sensitivity functions derived in the research.

On what scales can GOSAT flux inversions constrain anomalies in terrestrial ecosystems?

Abstract. Interannual variations in temperature and precipitation impact the carbon balance of terrestrial ecosystems, leaving an imprint in atmospheric CO2. Quantifying the impact of climate anomalies on the net ecosystem exchange (NEE) of terrestrial ecosystems can provide a constraint to evaluate terrestrial biosphere models against and may provide an emergent constraint on the response of terrestrial ecosystems to climate change. We investigate the spatial scales over which interannual variability in NEE can be constrained using atmospheric CO2 observations from the Greenhouse Gases Observing Satellite (GOSAT). NEE anomalies are calculated by performing a series of inversion analyses using the GEOS-Chem adjoint model to assimilate GOSAT observations. Monthly NEE anomalies are compared to “proxies”, variables that are associated with anomalies in the terrestrial carbon cycle, and to upscaled NEE estimates from FLUXCOM. Statistically significant correlations (P<0.05) are obtained between posterior NEE anomalies and anomalies in soil temperature and FLUXCOM NEE on continental and larger scales in the tropics, as well as in the northern extratropics on subcontinental scales during the summer (R2≥0.49), suggesting that GOSAT measurements provide a constraint on NEE interannual variability (IAV) on these spatial scales. Furthermore, we show that GOSAT flux inversions are generally better correlated with the environmental proxies and FLUXCOM NEE than NEE anomalies produced by a set of terrestrial biosphere models (TBMs), suggesting that GOSAT flux inversions could be used to evaluate TBM NEE fluxes.

Ocean climate variability off Newfoundland and Labrador over 1979–2010: A modelling approach

A coupled ice-ocean model with a horizontal resolution of 7 km is developed for the Newfoundland and Labrador Shelves to examine climate trend and variability of ocean and ice conditions over 1979–2010. Daily surface atmospheric forcing is applied and monthly open boundary conditions are prescribed. The model has reasonable skill in simulating interannual and decadal variability and long-term (1979–2010) trend for temperature, salinity, transport and ice over the Newfoundland and Labrador Shelves. At a long-term monitoring station both the model and observation show substantial interannual variability in the surface temperature and salinity, a warming trend in the surface temperature, and no trend in the surface salinity. The model sea ice extent south of 55°N shows significant interannual and decadal variability and a declining trend consistent with observations. Both model and altimetric observation show a declining trend in the transport of the shelf-edge Labrador Current from 1993 to 2010. The total Labrador Current volume transport is correlated with the North Atlantic Oscillation with time lags of 0–3 years, with the inshore branch having a positive trend while the shelf-edge branch having no trend. The inshore Labrador Current shows an increase of the freshwater transport associated with an increase of the volume transport due to large-scale baroclinic forcing, with the interannual and decadal variability of the freshwater transport dominated by the volume transport; while the shelf-edge transport shows a decrease of the freshwater transport associated with an increase of salinity, with the interannual and decadal variability of the freshwater transport dominated by salinity.

Evaluation of multi‐RCM high‐resolution hindcast over the CORDEX East Asia Phase II region: Mean, annual cycle and interannual variations

AbstractBased on the Coordinated Regional Downscaling Experiment‐East Asia second phase (CORDEX‐EA‐II) with higher resolution, model results driven by ERA‐Interim reanalysis using WRF, RegCM4 and CCLM are evaluated against the observational datasets including CN05.1, CRU and GPCP during the period of 1989–2009. The results show that the RCMs have the capability to simulate the annual and seasonal mean surface air temperature and precipitation, however, some biases are produced. The biases are highly dependent on the geophysical locations and the RCMs applied, and CCLM agrees better with the observed precipitation over ocean. CCLM also outperforms the other two RCMs in simulating the interannual variations of temperature and precipitation in most sub‐regions, which can be attributed to its better presentation of the interannual variation of large scale circulation. Generally, all the three RCMs can well reproduce the seasonal cycles of the surface air temperature in most sub‐regions, however, only in the northern regions of China can the RCMs well reproduce the seasonal cycles of precipitation.

Seasonal and synoptic climatic drivers of tree growth in the Bighorn Mountains, WY, USA (1654–1983 CE)

In the United States’ (US) Northern Rockies, synoptic pressure systems and atmospheric circulation drive interannual variation in seasonal temperature and precipitation. The radial growth of high-elevation trees in this semi-arid region captures this temperature and precipitation variability and provides long time series to contextualize instrumental-era variability in synoptic-scale climate patterns. Such variability in climate patterns can trigger extreme climate events, such as droughts, floods, and forest fires, which have a damaging impact on human and natural systems. We developed 11 tree-ring width (TRW) chronologies from multiple species and sites to investigate the seasonal climatic drivers of tree growth in the Bighorn Mountains, WY. A principal component analysis of the chronologies identified 54% of shared common variance (1894–2014). Tree growth (expressed by PC1) was driven by multiple seasonal climate variables: previous October and current July temperatures, as well as previous December and current April precipitation, had a positive influence on growth, whereas growth was limited by July precipitation. These seasonal growth-climate relationships corresponded to circulation patterns at higher atmospheric levels over the Bighorn Mountains. Tree growth was enhanced when the winter jet stream was in a northward position, which led to warmer winters, and when the spring jet stream was further south, which led to wetter springs. The second principal component, explaining 19% of the variance, clustered sites by elevation and was strongly related to summer temperature. We leverage this summer temperature signal in our TRW chronologies by combining it with an existing maximum latewood density (MXD) chronology in a nested approach. This allowed us to reconstruct Bighorn Mountains summer (June, July, and August) temperature (BMST) back to 1654, thus extending the instrumental temperature record by 250 years. Our BMST reconstruction explains 39–53% of the variance in regional summer temperature variability. The 1830s were the relatively coolest decade and the 1930s were the warmest decade over the reconstructed period (1654–1983 CE) – which excludes the most recent 3 decades. Our results contextualize recent drivers and trends of climate variability in the US Northern Rockies, which contributes to the information that managers of human and natural systems need in order to prepare for potential future variability.

Evaluation of the CORDEX regional climate models performance in simulating climate conditions of two catchments in Upper Blue Nile Basin

This study was targeted at evaluating the performance of six Regional Climate Models (RCMs) used in Coordinated Regional Climate Downscaling Experiment (CORDEX). The evaluation is on the bases of how well the RCMs simulate the seasonal mean climatology, interannual variability and annual cycles of rainfall, maximum and minimum temperature over two catchments in western Ethiopia during the period 1990–2008. Observed data obtained from the Ethiopian National Meteorological Agency was used for performance evaluation of the RCMs outputs. All Regional Climate Models (RCMs) have simulated seasonal mean annual cycles of precipitation with a significant bias shown on individual models; however, the ensemble mean exhibited better the magnitude and seasonal rainfall. Despite the highest biases of RCMs in the wet season, the annual cycle showed the prominent features of precipitation in the two catchments. In many aspects, CRCM5 and RACMO22 T simulate rainfall over most stations better than the other models. The highest biases are associated with the highest error in simulating maximum and minimum temperature with the highest biases in high elevation areas. The rainfall interannual variability is less evident in Finchaa with short rainy season experiencing a larger degree of interannual variability. The differences in performance of the Regional Climate Models in the two catchments show that all the available models are not equally good for particular locations and topographies. In this regard, the right regional climate models have to be used for any climate change impact study for local-scale climate projections.

Phenology of the tree community in a seasonal forest in southern Brazil

Seasonal variations in environmental factors, such as precipitation, influence plant phenology and the relative importance of each factor, differ according to the ecosystem in question. In this study, we evaluated the phenology of 60 tree species in a seasonal semi-deciduous forest located at the southern border of the tropical zone (23°26′35ʺS and 51°15′30ʺW) during 3 years. We aimed to investigate the relationship of leaf fall, leaf flushing, budding, flowering, immature and mature fruit phenophases with precipitation, temperature and photoperiod. We also analyzed whether the phenological patterns of tree community were seasonal and similar between consecutive years. Although the climate of the region is classified as Cfa, there are two distinct season: a hot humid summer and a cold drier winter. Leaf fall occurred predominantly in the dry season, with leaf flushing and flowering at the end of the dry and early wet season. The mature fruits were observed throughout the year. For the six phenophases analyzed, the percentage of species did not differ among the three study years. The tree community presented, in general, weakly seasonal phenological patterns, mainly in response to variations in temperature and photoperiod. The mature fruits showed seasonal patterns when the species were grouped by dispersal syndrome. This predictability suggests that small inter-annual variations in precipitation and temperature are not relevant for the studied tree species’ phenology.