Increase In Precipitation Amount Research Articles

Foliage development and resource allocation determine the growth responses of silver birch (Betula pendula) to elevated environmental humidity.

Scenarios for future climate predict an increase in precipitation amounts and frequency of rain events, resulting in higher air humidity and soil moisture at high latitudes, including in northern Europe. We analysed the effects of artificially elevated environmental humidity (air relative humidity and soil moisture) on leaf gas exchange, water relations, growth and phenology of silver birch (Betula pendula) trees growing at the Free Air Humidity Manipulation (FAHM) experimental site situated in the hemiboreal vegetation zone, in eastern Estonia, with no occurring water deficit to the trees. The environmental humidity manipulation did not significantly affect the water relations traits but did affect some leaf gas exchange parameters, growth and phenology of the trees. Elevated air humidity (H) did not influence photosynthetic capacity and stomatal conductance, while the trees exhibited higher stomatal sensitivity to leaf-to-air vapour pressure difference compared to the trees at ambient conditions (C) or at an elevated soil moisture (I). H trees demonstrated reduced height growth and foliage biomass, increased allocation to stem radial growth, and prolonged leaf retention in autumn compared to the C trees. Increased air humidity supports longer leaf retention and growth period, but this does not translate into increased growth parameters at the tree level. The changes in tree growth in response to increasing atmospheric humidity could plausibly be explained by (1) retardation of foliage development and (2) changes in resource allocation, causing a shift in the ratio of photosynthetic to non-photosynthetic tissues in favour of the latter. Under high atmospheric evaporative demand, higher stomatal sensitivity in H trees induces faster stomatal closure, which may result in carbon starvation. A future rise in atmospheric humidity at high latitudes may lead to reduced tree growth and forest productivity, in contrast to the predicted future of forests.

Effects of Gd on hot tearing susceptibility of as-cast Mg96.94-Zn1-Y(2−x)-Gdx-Zr0.06 alloys reinforced with LPSO phase

In the present work, the effects of Gd on hot tearing susceptibility (HTS) of as-cast Mg96.94-Zn1-Y(2−x)-Gdx-Zr0.06 (x = 0, 0.5, 1, 1.5, 2 at%) alloys reinforced with long-period stacking ordered (LPSO) phase was studied. The HTS of the alloys was predicted and confirmed by differential thermal analysis system and hot tearing test system, respectively. Based on the cooling curves, shrinkage stress curves and microstructure evolution observed by SEM, TEM and EBSD, the hot tearing mechanism of the alloys was explored. The results showed that the HTS of Mg96.94-Zn1-Y(2−x)-Gdx-Zr0.06 alloys significantly decreased with the increasing of Gd content. When Gd content was 0.5 and then increased to 1 at%, the decrease in HTS of the alloys was attributed to the combined effects of grain refinement and increased secondary phase amount. When Gd content increased to 1.5 and then to 2 at%, the grain size of the alloys increased instead, and the HTS continued to decrease. This was attributed to the increase of pinning effect of LPSO phase and the increase of residual liquid feeding capacity caused by the increase of precipitation amount of the secondary phase. The combined effects of the two made up for the negative effects of grain coarsening. In Mg96.94-Zn1-Gd2-Zr0.06 alloy, the amount of LPSO phase was the most, and the pinning effect on grain boundaries was the strongest. The intergranular bridges composed of LPSO phase hindered the initiation and propagation of hot tearing, thus, the alloy had the lowest HTS.

Climate-soil interactions improve the stability of grassland ecosystem by driving alpine plant diversity

The grassland ecosystem plays an important role in maintaining ecological security. This study intends to better understand the effects of climate-soil interaction on the alpine grassland ecosystem and to further deepen the understanding of plant diversity and its influencing factors in the alpine meadow, alpine steppe, and desert steppe of the Qilian Mountains of China. Therefore, the soil nutrient contents such as soil organic carbon, nitrogen, available phosphorus, ammonium nitrogen, and nitrate-nitrogen were measured from the uppermost 0–40 cm soil layer. In addition, the regional vegetation characteristics were also investigated and plant diversity index values were determined. The three grassland types showed obvious variations in soil nutrient content and plant diversity index values. Alpine meadow and alpine steppe showed the highest plant diversity and soil nutrients, evident by greater soil organic carbon and nitrogen contents compared to the desert steppe. With the increase in precipitation amounts, the plant height and number of typical plants increased, but no significant impact of elevation was found. Plant diversity was positively correlated with annual precipitation and soil organic carbon, which were the primary factors determining plant diversity in the Qilian Mountains. Compared to other grassland types, alpine meadows showed the most complex network, indicating the greatest ecological stability and strong resistance to environmental changes. These findings revealed a close link between the species diversity, soil nutrients, and major climatic factors in the Qilian Mountains, which are critical for predicting plant diversity in the context of climate change.

Performance evaluation, error decomposition and Tree-based Machine Learning error correction of GPM IMERG and TRMM 3B42 products in the Three Gorges Reservoir Area

Satellite precipitation products (SPPs) have excellent development prospects in hydrometeorology research for their high spatial-temporal resolution. Understanding the performance of SPPs is essential before their application in estimating multiple processes. This paper evaluated the accuracy and error composition of GPM IMERG Final-run V06 and TRMM 3B42V7 in the Three Gorges Reservoir Area (TGRA) based on the China Gauge-based Daily Precipitation Analysis dataset (CGDPA) during 2001–2019. Afterwards, the precipitation correction by merging satellite and gauge observation precipitation was conducted with three Tree-based Machine Learning models, Decision Tree (DT), Adaptive Boosting Decision Trees (Adaboost), and Random Forest (RF). The results show that: (1) Two SPPs can well reflect the spatial pattern and in-year variation of precipitation in the TGRA. However, they are limited in estimating precipitation amount for seriously underestimated the light rain or overestimated torrential rain. Under the influence of climate and variety terrains, the SPPs accuracy in the middle-elevation relief mountains of downstream is significantly higher than that in the low-elevation relief mountains of upstream. Moreover, that on the monthly and annual scales are higher than on the daily scale. Comparing two SPPs, the area proportions of IMERG-F better than 3B42V7 are 64.0%, 86.0%, and 81.6% on daily, monthly and annual scales, respectively. (2) Both the systematic error components of two SPPs raise with the increase of precipitation amount, and the error spatial pattern of 3B42V7 is more affected by precipitation. The random error component of light rain and daily precipitation is higher than other grades and scales. Despite this, the random error component decreases significantly when daily precipitation is accumulated. (3) The three primary factors affecting error correction of SPPs are precipitation amount, longitude, and DEM in TGRA. Among the three Tree-based methods, the RF showed the best error correction effect, and it can significantly improve the monthly and annual precipitation accuracy and better reproduce probability density function (PDF). Cumulative precipitation can reduce the random error component of daily precipitation and have high correction accuracy when cumulative time exceeds 5-days.

Using a Paired Chironomid δ18O and Aquatic Leaf Wax δ2H Approach to Reconstruct Seasonality on Western Greenland During the Holocene

AbstractThe Arctic hydrological cycle is predicted to intensify as the Arctic warms, due to increased poleward moisture transport during summer and increased evaporation from seas once ice‐covered during winter. Records of past Arctic precipitation seasonality are important because they provide a context for these ongoing changes. In some Arctic lakes, stable isotopes of oxygen and hydrogen (δ18O and δ2H, respectively) vary seasonally, due to seasonal changes in precipitation δ18O and δ2H. We reconstruct precipitation seasonality from Lake N3, a well‐dated lake sediment archive in Disko Bugt, western Greenland, by generating Holocene records of two proxies that are produced at different times of the year, and therefore record different lake water seasonal isotopic compositions. Aquatic plants synthesize waxes throughout the summer, and their δ2H reflects winter‐biased precipitation δ2H at Lake N3, whereas chironomids synthesize their head capsules between late summer and winter, and their δ18O reflects summer‐biased precipitation δ18O at Lake N3. During the middle Holocene at Lake N3, aquatic plant leaf wax was strongly 2H‐depleted, while chironomid chitin was 18O‐enriched. We guide interpretations of these records using sensitivity tests of a lake water and energy balance model, where we change precipitation amount and isotope seasonality inputs. The sensitivity tests suggest that the contrasting trends between proxies were likely caused by an increase in precipitation amount during all seasons and an increase in precipitation isotope seasonality, in addition to proxy‐specific mechanisms, highlighting the importance of understanding lake‐ and proxy‐specific systematics when interpreting records from sediment archives.

Enhanced Wet Deposition of Water‐Soluble Organic Nitrogen During the Harvest Season: Influence of Biomass Burning and In‐Cloud Scavenging

AbstractGlobally water‐soluble organic nitrogen (WSON) accounts for about one third of water‐soluble total nitrogen in atmospheric deposition, yet the key factors influencing WSON deposition remain uncertain. In the present study, precipitation and aerosol samples were collected during 2016–2018 at a forest site in the Pearl River Delta, south China. Rainwater WSON concentrations were found to elevate significantly during fall, and wet deposition of WSON during fall could account for about 50% of its annual total wet deposition. The wet deposition and rainwater concentrations of K+ and levoglucosan, which are tracers for biomass burning emissions, also increased substantially during fall. The average WSON/water‐soluble total nitrogen ratio in precipitations (0.48) was over two times higher than that in aerosols (0.20) during fall, while during other seasons, the ratios in precipitations (0.17) and in aerosols (0.19) were comparable. Moreover, concentrations of WSON in rainwater, unlike that of inorganic N, did not decrease significantly with the increase of precipitation amount during fall. These results suggested that enhanced biomass burning during fall (harvest season) might be an important source of in‐cloud WSON, and in‐cloud scavenging, instead of below‐cloud washout, likely contributed remarkably to the wet deposition of WSON.

Projected changes to wind loads coinciding with rainfall for building design in Canada based on an ensemble of Canadian regional climate model simulations

Strong wind coinciding with rainfall is an important weather phenomenon in many science and engineering fields. This study investigates changes in hourly extreme driving rain wind pressure (DRWP)—a climatic variable used in building design in Canada—for future periods of specified global mean temperature change using an ensemble of a Canadian regional climate model (CanRCM4) driven by the Canadian Earth system model (CanESM2) under the Representative Concentration Pathway 8.5 scenario. Evaluation of the model shows that the CanRCM4 ensemble reproduces hourly extreme wind speeds and rainfall (> 1.8 mm/h) occurrence frequency and the associated design (5-year return level) DRWP across Canada well when compared with 130 meteorological stations. Significant increases in future design DRWP are projected over western, eastern, and northern Canada, with the areal extent and relative magnitude of the increases scaling approximately linearly with the amount of global warming. Increases in future rainfall occurrence frequency are driven by the combined effect of increases in precipitation amount and changes in precipitation type from solid to liquid due to increases in air temperature; these are identified as the main factors leading to increases in future design DRWP. Future risk ratios of the design DRWP are highly dependent on those of the rainfall occurrence, which shows large increases over the three regions, while they are partly affected by the increases in future extreme wind speeds over western and northeastern Canada. Increases in DRWP can be an emerging risk for existing buildings, particularly in western, eastern, and northern Canada, and a consideration for managing and designing buildings across Canada.

Implementation of a novel seeding material (NaCl/TiO2) for precipitation enhancement in WRF: Description of the model and spatiotemporal window tests

Precipitation enhancement might play a key role in combating constantly increasing frequency of occurrence of draughts in many areas around the globe. This article is a numerical study of the performances of two precipitation enhancers using seven different spatiotemporal windows. The investigated artificial aerosols are the pure NaCl—being a well-researched seeding material—and the core/shell NaCl/TiO2 (abbreviated as CSNT)—being a novel seeding material very recently developed. The activation properties of CSNT are for the first time incorporated into the Weather Research and Forecasting (WRF) model. The performances of two seeding materials, as well as their benchmark against the control case without seeding are investigated in terms of the accumulated surface precipitation and cloud microphysics processes. This study shows multiple advantages of the new seeding agent in terms of both the total accumulated surface precipitation and the increased precipitation area. The best location for release of CSNT in terms of the highest increase of precipitation amount is when both cyclonic and anticyclonic cells are seeded. The largest increase of precipitation area is found when the seeding takes place in front of the cloud and below the cloud base. In this case, the seeded cloud with CSNT releases precipitation over approximately 2 times larger area that the unseeded cloud. The conducted numerical experiments showed that the introduction of CSNT into the cloud environment significantly increases the number concentration of cloud droplets and ice.

Projection and uncertainty of precipitation extremes in the CMIP5 multimodel ensembles over nine major basins in China

This study presented an analysis of projection and uncertainty of precipitation extremes over 9 river basins in China based on the outputs of 18 global climate models (GCMs) with 3 Representative Concentration Pathways (RCPs) from the Coupled Model Inter-comparison Project Phase 5 (CMIP5). The temporal and spatial changes in precipitation extremes for the period 2020–2100 were analyzed using the climate indices defined by the Expert Team on Climate Detection and Indices (ETCCDI). Uncertainty of GCMs and RCPs in the projections of precipitation extremes was quantified using the variance-based sensitivity analysis method. The model simulations generally predict a consistent intensification of precipitation extremes during the 21st century with respect to different RCPs scenarios: the higher emission scenarios (e.g., RCP8.5), the larger intensity and frequency of precipitation extremes. The projected changes in precipitation extremes exhibit a large spatial variation across China. The high-latitude and high elevation regions of China (e.g., Continental and Southwest basins) are projected to respond more strongly to the increase in precipitation amount and intensity (e.g., RCPTOT, RX1day and RX5day), while southeastern and southern China (e.g., Southeast and Pearl River basins) tend to be more sensitive to the increase in the frequency of precipitation extreme (e.g., R10mm and R20mm). Consecutive dry days (CDD) is projected to decrease in northern China (e.g., Continental basin) but increase in southern China (e.g., Southeast, Pearl River, and Yangtze River basins). Uncertainty analysis shows that variation of GCMs contributes >90% uncertainty of precipitation extremes projections for the whole China, with larger uncertainty range under the higher emission scenarios (e.g., RCP8.5). The uncertainty from RCPs is generally limited (contribution <10%) in comparison with GCMs, and slightly increases with the long-term projections of precipitation extremes.

Seed yield and oil quality as affected by Camelina cultivar and planting date

ABSTRACTCamelina [Camelina sativa (L.) Crantz] has been identified as a potential oilseed crop for fallow replacement in cropping systems in the semiarid US Great Plains. However, camelina production is limited to the northern Great Plains region. We investigated the effects of three planting dates [mid-March, early-April, and mid-April] and three cultivars (Blaine Creek, Pronghorn, and Shoshone) on spring camelina seed yield and oil quality under non-irrigated conditions in western Kansas. Results showed planting in April increased seed yield by 34% compared with mid-March planting date. Blaine Creek produced greatest seed yield among the cultivars. Planting in mid-March increased oil, polyunsaturated fatty acids (PUFA), and linolenic acid concentrations compared with April planting dates. Saturated fatty acid (SFA) concentration increased with an April planting date. Heat stress in the growing season reduced seed yield, oil, PUFA, linoleic, and linolenic acid concentrations. However, increase in precipitation amounts improved seed yield, oil, PUFA, and linolenic acid concentrations. Our findings showed early- to mid-April is the best-planting window for optimum spring camelina stands and seed yield in this environment.

Precipitation amount and frequency affect seedling emergence and growth of Reaumuria soongarica in northwestern China

Climate change is shifting the amount and frequency of precipitation in many regions, which is expected to affect seedling recruitment across ecosystems. However, the combined effects of precipitation amount and frequency on seedling recruitment remain largely unknown. An understanding of the effects of precipitation amount and frequency and their interaction on seedling emergence and growth of typical desert plants is vital for managing populations of desert plants. We conducted two experiments to study the effects of variation in precipitation on Reaumuria soongarica (Pall.) Maxim. First, greenhouse experiments were conducted to examine the effects of three precipitation amount treatments (ambient, +30%, and –30%) and two precipitation frequency treatments (ambient and –50%) on seedling emergence. Second, the morphological responses of R. soongarica to changes in precipitation amount and frequency were tested in a controlled field experiment. Stage-specific changes in growth were monitored by sampling in different growth seasons. Our results showed that precipitation amount significantly affected germination, seedling emergence, and growth of R. soongarica, and there was a larger effect with decreased precipitation frequency compared with ambient. Germination and seedling emergence increased as precipitation increased under the same frequency of precipitation. The highest emergence percentage was obtained with a 30% increase in precipitation amount and a 50% reduction in precipitation frequency. Compared with ambient precipitation, a 30% increase in precipitation amount increased above- and below-ground biomass accumulation of R. soongarica during the growth season. A decrease of 30% in precipitation amount also resulted in an increase in below-ground biomass and root/shoot ratio in the early stages of the growth season, however, above- and below-ground biomass showed the opposite results at the end of the growth season, with larger effects on above-ground than below-ground biomass under decreased precipitation frequency. When precipitation frequency decreased by 50%, values of all growth traits increased for a given amount of precipitation. We concluded that precipitation frequency may be as important as precipitation amount to seedling emergence and growth of R. soongarica, and that understanding the effects of precipitation variability on seedling recruitment requires the integration of both precipitation amount and frequency. In particular, the combination of a 30% increase in precipitation amount and 50% reduction in precipitation frequency increased the emergence and growth of seedlings, suggesting that alteration of amount and frequency of precipitation caused by climate change may have significant effects on seedling recruitment of R. soongarica.

Spatio-temporal analysis of present and future precipitation responses over South Germany

Abstract Assessment of future precipitation responses is crucial for various sectors which include tourism, agriculture, and energy yield. The study is focused on South Germany and aims to analyse the future spatio-temporal responses of annual and seasonal precipitation. Future precipitation data were derived and analysed from a number of regional climate models (RCMs), while climate simulations were performed for the future periods 2021–2050 and 2071–2100, under the A1B and B1 Intergovernmental Panel on Climate Change (IPCC) emission scenarios. Spatial interpolation and distribution of precipitation was performed using the ordinary Kriging method within ArcGIS 10.2.1. The results indicated that precipitation in South Germany is expected to increase for both applied scenarios by 10–12%. Seasonal analysis indicated that with the exception of the summer season (JJA), where precipitation by the end of the century is expected to face an 8–16% reduction, in general it will show an increase in the upcoming years. Spatial analysis indicated that areas located on the highlands will face significant reductions that will reach up to 20%. Conversely, areas located in the lowlands will have increased precipitation. The increase in precipitation amount can have a direct positive impact on the sustainable development of tourism, agriculture, energy yield and water resources in South Germany.

Grassland species respond differently to altered precipitation amount and pattern

An increase in precipitation amount with prolonged inter-rainfall intervals is predicted to occur in the Inner Mongolia grassland in the future. However, how the native species respond to such alterations remains poorly understood. We collected the seeds of eight species from a natural community and raised their seedlings by pot culture. The responses of these species to manipulated precipitation amount and inter-rainfall intervals were examined by rainout shelters. The biomass production in seven out of eight species was enhanced by increased precipitation amount. However, the impacts of prolonged inter-rainfall interval differed substantially among species, with one being promoted, two suppressed and five not affected. For most species, biomass allocations among vegetative organs were neither affect by precipitation amount nor by inter-rainfall intervals. In contrast, the impacts on species’ reproductive allocation were highly species-dependent. Soil moisture, soil temperature and soil inorganic nitrogen played important roles in affecting species’ biomass production but the pathways, directions (positive or negative) and magnitudes were species-dependent. Given that these eight species jointly represent about 80% of community biomass production, the impact of altered precipitation pattern on grassland ecosystems may be more difficult to predict than that of altered amount.

Distribution of isotopes and chemicals in precipitation in Shule River Basin, northwestern China: an implication for water cycle and groundwater recharge

The distribution of stable isotopes and ions in precipitation in the Shule River Basin, northwestern China, were investigated to understand the regional water cycle and precipitation input to groundwater recharge. The study found that the mean annual concentrations of Ca2+, Na+, SO4 2–, Cl–, Mg2+, NO3 –, and K+ in the basin were lower than those in other arid areas of northwestern China. The average concentrations of ions in the lower reaches of the Shule River were higher than those in the upper reaches. The results showed that the main ionic concentrations decreased with the increase of precipitation amount, indicating that heavy precipitation cannot only wash crustal aerosols out of the atmosphere, but also create a dilution effect. Cl– and Na+ in precipitation had a strong and positive correlation, suggesting a common origin for the two ions. However, the excess of Na+, combined with non-marine SO4 2– and NO3 –, indicated that some ions were contributed by terrestrial origins. In the extremely arid regions of northwestern China, the evaporation process obviously changes the original relationship between δ2H and δ18O in precipitation, and leads to dexcess values <8‰. δ18O and temperature were significantly correlated, suggested that temperature strongly affected the characteristics of isotopes in the study area. The δ18O value indicates a dominant effect of westerly air masses and southwest monsoon in warm months, and the integrated influence of westerly and Siberian-Mongolian polar air masses in cold months. The d-excess values were generally lower in warm months than those in cold months, indicating that post-condensation processes played a significant role in the water cycle. The results provide reliable precipitation input information that can be used in future groundwater recharge calculations in the study area.

Fuel moisture sensitivity to temperature and precipitation: climate change implications

The objective of this paper is to examine the sensitivity of fuel moisture to changes in temperature and precipitation and explore the implications under a future climate. We use the Canadian Forest Fire Weather Index System components to represent the moisture content of fine surface fuels (Fine Fuel Moisture Code, FFMC), upper forest floor (duff) layers (Duff Moisture Code, DMC) and deep organic soils (Drought Code, DC). We obtained weather data from 12 stations across Canada for the fire season during the 1971–2000 period and with these data we created a set of modified weather streams from the original data by varying the daily temperatures by 0 to +5 °C in increments of 1 °C and the daily precipitation from −40 to 40 % in increments of 10 %. The fuel moistures were calculated for all the temperature and precipitation combinations. When temperature increases we find that for every degree of warming, precipitation has to increase by more than 15 % for FFMC, about 10 % for DMC and about 5 % for DC to compensate for the drying caused by warmer temperatures. Also, we find in terms of the number of days equal to or above an FFMC of 91, a critical value for fire spread, that no increase in precipitation amount alone could compensate for a temperature increase of 1 °C. Results from three General Circulation Models (GCMs) and three emission scenarios suggest that this sensitivity to temperature increases will result in a future with drier fuels and a higher frequency of extreme fire weather days.

Seasonal reversal of the influence of El Niño–Southern Oscillation on very large wildfire occurrence in the interior northwestern United States

AbstractSatellite‐mapped fire perimeters and the multivariate El Niño–Southern Oscillation index were used to examine the impact of concurrent El Niño–Southern Oscillation (ENSO) phase on very large fire (VLF) occurrences over the intermountain northwestern United States (U.S.) from 1984 to 2012. While the warm phase of ENSO promotes drier and warmer than normal conditions across the region during winter and spring that favor widespread fire activity the following summer, a reduction in VLFs was found during the warm phase of ENSO during summer concurrent with the fire season. This paradox is primarily tied to an anomalous upper level trough over the western U.S. and positive anomalies in integrated water vapor that extend over the northwestern U.S. during summers when the warm phase of ENSO is present. Collectively, these features result in widespread increases in precipitation amount during the summer and a curtailment of periods of critically low‐fuel moistures that can carry wildfire.

A climate change projection for summer hydrologic conditions in a semiarid watershed of central Arizona

Potential climate change impacts on summer precipitation and subsequent hydrologic responses in the southwestern U.S. are poorly constrained at present due to a lack of studies accounting for high resolution processes. In this investigation, we apply a distributed hydrologic model to the Beaver Creek watershed of central Arizona to explore its utility for climate change assessments. Manual model calibration and model validation were performed using radar-based precipitation data during three summers and compared to two alternative meteorological products to illustrate the sensitivity of the streamflow response. Using the calibrated and validated model, we investigated the watershed response during historical (1990–2000) and future (2031–2040) summer projections derived from a single realization of a mesoscale model forced with boundary conditions from a general circulation model under a high emissions scenario. Results indicate spatially-averaged changes across the two projections: an increase in air temperature of 1.2 °C, a 2.4-fold increase in precipitation amount and a 3-fold increase in variability, and a 3.1-fold increase in streamflow amount and a 5.1-fold increase in variability. Nevertheless, relatively minor changes were obtained in spatially-averaged evapotranspiration. To explain this, we used the simulated hydroclimatological mechanisms to identify that higher precipitation limits radiation through cloud cover leading to lower evapotranspiration in regions with orographic effects. This challenges conventional wisdom on evapotranspiration trends and suggest that a more nuanced approach is needed to communicate hydrologic vulnerability to stakeholders and decision-makers in this semiarid region.

Late Quaternary glacier sensitivity to temperature and precipitation distribution in the Southern Alps of New Zealand

Glaciers respond to climate variations and leave geomorphic evidence that represents an important terrestrial paleoclimate record. However, the accuracy of paleoclimate reconstructions from glacial geology is limited by the challenge of representing mountain meteorology in numerical models. Precipitation is usually treated in a simple manner and yet represents difficult-to-characterize variables such as amount, distribution, and phase. Furthermore, precipitation distributions during a glacial probably differed from present-day interglacial patterns. We applied two models to investigate glacier sensitivity to temperature and precipitation in the eastern Southern Alps of New Zealand. A 2-D model was used to quantify variations in the length of the reconstructed glaciers resulting from plausible precipitation distributions compared to variations in length resulting from change in mean annual air temperature and precipitation amount. A 1-D model was used to quantify variations in length resulting from interannual climate variability. Assuming that present-day interglacial values represent precipitation distributions during the last glacial, a range of plausible present-day precipitation distributions resulted in uncertainty in the Last Glacial Maximum length of the Pukaki Glacier of 17.1 km (24%) and the Rakaia Glacier of 9.3 km (25%), corresponding to a 0.5°C difference in temperature. Smaller changes in glacier length resulted from a 50% decrease in precipitation amount from present-day values (−14% and −18%) and from a 50% increase in precipitation amount (5% and 9%). Our results demonstrate that precipitation distribution can produce considerable variation in simulated glacier extents and that reconstructions of paleoglaciers should include this uncertainty.

Differences between two climatological periods (2001–2010 vs. 1971–2000) and trend analysis of temperature and precipitation in Central Brazil

In the framework of the IWAS/Agua-DF project, this study focuses on changes in mean surface air temperature and accumulated precipitation in Central Brazil over the past 40 years. It has two main objectives: (1) comparison between two climatological periods (2001–2010 and 1971–2000) and (2) trend analysis of climate variables. Time series of meteorological and rain gauge stations from Central Brazil have been organized in a databank, which contains tools for homogeneity tests. From that, 4 temperature and 55 precipitation time series were sufficient homogeneous, while 1 temperature and 5 precipitation time series were identified as inhomogeneous. Reliable spatial distribution was produced using proper interpolation method. Trends and significance levels were calculated by Rapp’s estimator of slope and Mann–Kendall test, respectively. The most important results of the comparisons and trend analysis in the last four decades are: (1) marked increase in annual and seasonal mean surface air temperature, (2) evident decreases of accumulated rainfall in winter and autumn, and (3) apparent increase of precipitation amounts in the rainy season.

Vegetation and Soil 15N Natural Abundance in Alpine Grasslands on the Tibetan Plateau: Patterns and Implications

The natural abundance of nitrogen (N) stable isotopes (δ15N) has the potential to enhance our understanding of the ecosystem N cycle at large spatial scales. However, vegetation and soil δ15N patterns along climatic and edaphic gradients have not yet been fully understood, particularly for high-altitude ecosystems. Here we determined vegetation and soil δ15N in alpine grasslands on the Tibetan Plateau by conducting four consecutive regional surveys during 2001–2004, and then examined their relationships with both climatic and edaphic variables. Our results showed that both vegetation and soil N in Tibetan alpine grasslands were more 15N-enriched than global averages. Vegetation δ15N did not exhibit any significant trend along the temperature gradient, but decreased significantly with an increase in precipitation amount. In contrast, soil δ15N did not vary with either mean annual temperature or precipitation. Our results also indicated that soil δ15N exhibited a slight increase with clay content, but decreased with soil carbon:nitrogen ratio. A general linear model analysis revealed that variations in vegetation δ15N were dominantly determined by climatic variables, whereas soil δ15N was related to edaphic variables. These results provide clues for potential climatic and edaphic regulations on ecosystem N cycle in these high-altitude regions.