Present-day Precipitation Research Articles

Nature of extreme precipitation over Ukraine in the 21st century

The article examines the state of precipitation over the territory of Ukraine over recent decades. Through the example of central months of the seasons differences in monthly and average daily precipitation amounts for the period of 2000-2014 are shown. Within the most territory of Ukraine summer precipitation is almost twice as high as spring and autumn one. During all seasons the greatest amount of precipitation is observed in the Carpathian region. Distribution of average long-term precipitation values over the rest of the territory coincides in spring, summer and autumn: the highest precipitation values are observed in the western and north-western parts and decrease to the south-east.
 The article studies a yearly precipitation rate at low-land and mountain meteorological stations. It proposes to separate criteria of precipitation extremality depending on the regions. All extreme daily precipitation can be divided into the following categories: > 20-30 mm / day, > 30-50 mm / day, > 50 mm / day. Each category of extreme precipitation has its a certain economic risk, but the third class can cause not only economic risks, but also risks associated with human life and activities. The distinct feature of the present-day precipitation consists in redistribution of precipitation in the middle of the months, when a daily precipitation rate increases together with intervals between heavy rains.
 In order to analyze the changes of precipitation regime, the approach of dividing the rates of monthly precipitation amount by the rates of extreme and non-extreme precipitation is proposed. A comparative analysis of daily precipitation in different seasons and over different climatic periods was also carried out. The article studies the proportion of daily precipitation of up to 15 mm and the one exceeding 15 mm forming a part of monthly rates of precipitation over the territory of Ukraine. In January, rainfalls exceeding 15 mm make up from 5-10 % of the total amount of monthly precipitation, except the Carpathian region and the southwestern regions of Ukraine where those exceed 20-25 %. In spring, the amount of rainfalls increases and its percentage of the monthly precipitation amount is around 20 % over most of the regions. Until summer, the amount of rainfalls increases and in July its percentage is 50-70 %. Until autumn, the amount of those starts decreasing, however, the percentage of rainfalls is almost twice as high as in spring, and for most of the regions it is about 30-40 %. Such breakdown of the monthly precipitation rates into two components allows determination during a period in question of precipitation amounts we have each month.
 The maximum daily precipitation amounts serve as an important indicator of the precipitation regime which shows the potential danger from extreme precipitation. For different regions the threshold values of the upper limit of rainfalls taken as a maximum daily value for the period of 2000-2014 differ. In winter and spring time, the limit of rainfalls amount per day usually hits 20-30 mm for the most territory of the country. At the same time there are certain areas where the limit values of the daily rainfalls rate reach 40-50 mm. The most significant rainfalls are observed in summer. Despite the fact that the territory of such rainfalls is quite patchy, nevertheless, those areas where precipitation rate over one day may reach 70 mm are the most vulnerable and have high risks for human life and activities. In autumn, the threshold values are 30-40 mm.
 The breakdown of the rates of monthly precipitation amount into extreme and non-extreme ones allows determination in future of whether the precipitation regime changes because of extreme or non-extreme values. Also, in the long run, a comparative analysis of the rates of showers and weak rainfalls in the late 20th and early 21st centuries can be carried out and a tendency of precipitation regime seasonal change over the next decade can be obtained which will help us to identify vulnerable regions suffering from extreme precipitation rates.

Inverse relationship between present-day tropical precipitation and its sensitivity to greenhouse warming

Future changes in rainfall have serious impacts on human adaptation to climate change, but quantification of these changes is subject to large uncertainties in climate model projections. To narrow these uncertainties, significant efforts have been made to understand the intermodel differences in future rainfall changes. Here, we show a strong inverse relationship between present-day precipitation and its future change to possibly calibrate future precipitation change by removing the present-day bias in climate models. The results of the models with less tropical (40° S–40° N) present-day precipitation are closely linked to the dryness over the equatorial central-eastern Pacific, and project weaker regional precipitation increase due to the anthropogenic greenhouse forcing 1–6 with stronger zonal Walker circulation. This induces Indo-western Pacific warming through Bjerknes feedback, which reduces relative humidity by the enhanced atmospheric boundary-layer mixing in the future projection. This increases the air–sea humidity difference to enhance tropical evaporation and the resultant precipitation. Our estimation of the sensitivity of the tropical precipitation per 1 K warming, after removing a common bias in the present-day simulation, is about 50% greater than the original future multi-model projection. A present-day bias identified in climate projections means that future tropical rainfall may be underestimated. This bias can be addressed by constraining projections with observations.

Palaeoclimate, glacier and treeline reconstruction based on geomorphic evidences in the Mongun-Taiga massif (south-eastern Russian Altai) during the Late Pleistocene and Holocene

Little is known about the extent of glaciers and dynamics of the landscape in south-eastern Russian Altai. The effects of climate-induced fluctuations of the glaciers and the upper treeline of the Mongun-Taiga mountain massif were, therefore, reconstructed on the basis of in-situ, multiannual observations, geomorphic mapping, radiocarbon and surface exposure dating, relative dating (such as Schmidt-hammer and weathering rind) techniques and palaeoclimate-modelling.During the maximal advance of the glaciers, their area was 26-times larger than now and the equilibrium line of altitude (ELA) was about 800 m lower. Assuming that the maximum glacier extent took place during MIS 4, then the average summer temperatures were 2.7 °C cooler than today and the amount of precipitation 2.1 times higher. Buried wood trunks by a glacier gave ages between 60 and 28 cal ka BP and were found 600–700 m higher than the present upper treeline. This evidences a distinctly elevated treeline during MIS 3a and c. With a correction for tectonics we reconstructed the summer warming to have been between 2.1 and 3.0 °C. During MIS 3c, the glaciated area was reduced to less than 0.5 km2 with an increase of the ELA of 310–470 m higher than today. Due to higher precipitation, the glaciated area during MIS 3a was close to the current ELA. Exposure dating (10Be) would indicate that the maximum glacier extension was 24 ka BP, but the results are questionable. From a geomorphic point of view, the maximum extent can more likely be ascribed to the MIS4 stage. We estimate a cooling of summer temperature of – 3.8 to – 4.2 °C and a decrease in precipitation of 37–46% compared to the present-day situation. Samples of wood having an age of 10.6–6.2 cal ka BP were found about 350 m higher than the present treeline. It seems that the summer temperature was 2.0–2.5 °C higher and annual precipitation was double that of the present-day. For that period, the reconstructed glaciation area was 1 km2 less than today. Three neoglacial glacier advances were detected. The glaciers covered about double the area during the Little Ice Age (LIA), summer cooling was 1.3 °C with 70% of the present-day precipitation. The reconstructed amplitude of climatic changes and the shift of the altitudinal zones show that the landscape has reacted sensitively to environmental changes and that dramatic changes may occur in the near future.

Super-Clausius–Clapeyron Scaling of Extreme Hourly Convective Precipitation and Its Relation to Large-Scale Atmospheric Conditions

AbstractPresent-day precipitation–temperature scaling relations indicate that hourly precipitation extremes may have a response to warming exceeding the Clausius–Clapeyron (CC) relation; for the Netherlands the dependency on surface dewpoint temperature follows 2 times the CC relation (2CC). The authors’ hypothesis—as supported by a simple physical argument presented here—is that this 2CC behavior arises from the physics of convective clouds. To further investigate this, the large-scale atmospheric conditions accompanying summertime afternoon precipitation events are analyzed using surface observations combined with a regional reanalysis. Events are precipitation measurements clustered in time and space. The hourly peak intensities of these events again reveal a 2CC scaling with the surface dewpoint temperature. The temperature excess of moist updrafts initialized at the surface and the maximum cloud depth are clear functions of surface dewpoint, confirming the key role of surface humidity on convective activity. Almost no differences in relative humidity and the dry temperature lapse rate were found across the dewpoint temperature range, supporting the theory that 2CC scaling is mainly due to the response of convection to increases in near-surface humidity, while other atmospheric conditions remain similar. Additionally, hourly precipitation extremes are on average accompanied by substantial large-scale upward motions and therefore large-scale moisture convergence, which appears to accelerate with surface dewpoint. Consequently, most hourly extremes occur in precipitation events with considerable spatial extent. Importantly, this event size appears to increase rapidly at the highest dewpoint temperature range, suggesting potentially strong impacts of climatic warming.

Present-day constraint for tropical Pacific precipitation changes due to global warming in CMIP5 models

The sensitivity of the precipitation responses to greenhouse warming can depend on the present-day climate. In this study, a robust linkage between the present-day precipitation climatology and precipitation change owing to global warming is examined in inter-model space. A model with drier climatology in the present-day simulation tends to simulate an increase in climatological precipitation owing to global warming. Moreover, the horizontal gradient of the present-day precipitation climatology plays an important role in determining the precipitation changes. On the basis of these robust relationships, future precipitation changes are calibrated by removing the impact of the present-day precipitation bias in the climate models. To validate this result, the perfect model approach is adapted, which treats a particular model’s precipitation change as an observed change. The results suggest that the precipitation change pattern can be generally improved by applying the present statistical approach.

Regolith production and chemical weathering of granitic rocks in central Chile

We have evaluated the long-term chemical and physical weathering mass balance of an anomalously thick saprolite profile (>30m thickness) developed in granitic rocks near Curacaví, Coastal Range of central Chile. The results of geochemical mass balance calculations for the regolith profile point to a moderate depletion for Na and Sr due to the plagioclase dissolution and precipitation of kaolinite. Furthermore, silicon shows a predominantly constant behaviour along the profile that is indicative of incongruent weathering of plagioclase, strongly suggesting that quartz dissolution conditions are not reached. In addition, low depletion of K, Mg, Ca, Rb, and Ba in the saprolite indicates a low degree of K-feldspar, biotite and hornblende weathering. Denudation rates calculated using cosmogenic 10Be data range from 20 to 70m/Ma. If the saprolite thickness has reached a steady-state condition, the reported denudation rates lead to mineral residence times in the upper part of the saprolite profile of about 0.5 to 1.8Ma. With such duration a higher weathering degree than observed at Curacaví would be expected. This apparent contradiction might be explained if all of the weatherable plagioclase has been dissolved under the present-day precipitation and temperature conditions of the Curacavi region. Therefore, we propose that the Curacaví profile could be in local equilibrium with respect to the weatherable fraction of plagioclase. A local equilibrium regime may be reached when the overall degree of depletion is small in a weathering profile. Uniform elemental distribution and low weathering degree in the thick weathering profile at Curacaví defy the traditional notion of weathering regimes and reveal the importance of exploratory studies in order to better understand weathering process in Mediterranean and semi-arid climate regions.

Last Glacial Maximum precipitation pattern in the Alps inferred from glacier modelling

Abstract. During the Last Glacial Maximum (LGM), glaciers in the Alps reached a maximum extent, and broad sections of the foreland were covered by ice. In this study, we simulated the alpine ice cap using a glacier flow model to constrain the prevailing precipitation pattern with a geomorphological reconstruction of ice extent. For this purpose we forced the model using different temperature cooling and precipitation reduction factors. The use of the present-day precipitation pattern led to a systematic overestimation of the ice cover on the northern part of the Alps relative to the southern part. To reproduce the LGM ice cap, a more severe decrease in precipitation in the north than in the south was required. This result supports a southwesterly advection of atmospheric moisture to the Alps, sustained by a southward shift of the North Atlantic storm track during the LGM.

The transfer of seasonal isotopic variability between precipitation and drip water at eight caves in the monsoon regions of China

This study presents new stable isotope data for precipitation (δ18Op) and drip water (δ18Od) from eight cave sites in the monsoon regions of China (MRC), with monthly to bi-monthly sampling intervals from May-2011 to April-2014, to investigate the regional-scale climate forcing on δ18Op and how the isotopic signals are transmitted to various drip sites.The monthly δ18Op values show negative correlation with surface air temperature at all the cave sites except Shihua Cave, which is opposite to that expected from the temperature effect. In addition, although the monthly δ18Op values are negatively correlated with precipitation at all the cave sites, only three sites are significant at the 95% level. These indicate that, due to the various vapor sources, a large portion of variability in δ18Op in the MRC cannot be explained simply by either temperature or precipitation alone.All the thirty-four drip sites are classified into three types based on the δ18Od variability. About 82% of them are static drips with little discernable variation in δ18Od through the whole study period, but the drip rates of these drips are not necessary constant. Their discharge modes are site-specific and the oxygen isotopic composition of the stalagmites growing from them may record the average of multi-year climatic signals, which are modulated by the seasonality of recharge and potential effects of evaporation, and in some cases infiltration from large rainfall events. About 12% of the thirty-four drip sites are seasonal drips, although the amplitude of δ18Od is narrower than that of δ18Op, the monthly response of δ18Od to coeval precipitation is not completely damped, and some of them follow the seasonal trend of δ18Op very well. These drips may be mainly recharged by present-day precipitation, mixing with some stored water. Thus, the stalagmites growing under them may record portions of the seasonal climatic signals embedded in δ18Op. About 6% of the thirty-four drip sites are medium-variability drips, with constant and relatively low δ18Od values in the wet season, but with variable and relatively high δ18Od values in the dry season, reflecting flow switching in the karst or evaporation inside the cave.

Hydrochemical characteristic and interaction process of surface and groundwater in mid-lower reach of Hanjiang River, China

Hanjiang River, the largest tributary of Yangtze, faces environmental pressures from South-to-North Water Transfer project and anthropogenic influences. In order to reveal the chemical characteristics of river and contribution of groundwater to the river along mid-lower reaches of Hanjiang River, field works have been conducted in wet and dry seasons. The major ion compositions are characterized by the dominance of Ca2+, and HCO3 − in surface water and groundwater. As a result, calcite weathering is a dominant process for surface water and groundwater. Additionally, dolomite weathering also contributes to hydrochemical evolution in the groundwater of the basin. Stable isotopes (δ18O, δD) show that both surface and groundwater most probably originate from present-day precipitation. Isotopic of both surface water and groundwater can provide greater confidence in identifying the weathering and extent of interaction processes. It was found that river water was mainly recharged by tributaries in wet season while recharged by groundwater in dry season. Dissolved solute flux from tributaries and groundwater to the river was estimated by water balance budget model and environmental tracer mass balance approach. Tributaries and groundwater contribute to mid-lower reach of Hanjiang River in wet season and dry season, respectively. From section H1 to H9, there were 455.4 kg/s of total dissolved solute (TDS) transferred from tributaries to the main channel and 99.8 kg/s of TDS fluxed from groundwater to river water in dry season.

Origin and evolution of geothermal fluids from Las Tres Vírgenes and Cerro Prieto fields, Mexico – Co-genetic volcanic activity and paleoclimatic constraints

Major and trace elements, noble gases, and stable (δD, δ18O) and cosmogenic (3H, 14C) isotopes were measured from geothermal fluids in two adjacent geothermal areas in NW-Mexico, Las Tres Vírgenes (LTV) and Cerro Prieto (CP). The goal is to trace the origin of reservoir fluids and to place paleoclimate and structural-volcanic constraints in the region. Measured 3He/4He (R) ratios normalized to the atmospheric value (Ra = 1.386 × 10−6) vary between 2.73 and 4.77 and are compatible with mixing between a mantle component varying between 42 and 77% of mantle helium and a crustal, radiogenic He component with contributions varying between 23% and 58%. Apparent U–Th/4He ages for CP fluids (0.7–7 Ma) suggest the presence of a sustained 4He flux from a granitic basement or from mixing with connate brines, deposited during the Colorado River delta formation (1.5–3 Ma). Radiogenic in situ4He production age modeling at LTV, combined with the presence of radiogenic carbon (1.89 ± 0.11 pmC – 35.61 ± 0.28 pmC) and the absence of tritium strongly suggest the Quaternary infiltration of meteoric water into the LTV geothermal reservoir, ranging between 4 and 31 ka BP. The present geochemical heterogeneity of LTV fluids can be reconstructed by mixing Late Pleistocene – Early Holocene meteoric water (58–75%) with a fossil seawater component (25–42%), as evidenced by Br/Cl and stable isotope trends. CP geothermal water is composed of infiltrated Colorado River water with a minor impact by halite dissolution, whereas a vapor-dominated sample is composed of Colorado River water and vapor from deeper levels. δD values for the LTV meteoric end-member, which are 20‰–44‰ depleted with respect to present-day precipitation, as well as calculated annual paleotemperatures 6.9–13.6 °C lower than present average temperatures in Baja California point to the presence of humid and cooler climatic conditions in the Baja California peninsula during the final stage of the Last Glacial Pluvial period. Quaternary recharge of the LTV geothermal reservoir is related to elevated precipitation rates during cooler-humid climate intervals in the Late Pleistocene and Early Holocene. The probable replacement of connate water or pore fluids by infiltrating surface water might have been triggered by enhanced fracture and fault permeability through contemporaneous tectonic–volcanic activity in the Las Tres Vírgenes region. Fast hydrothermal alteration processes caused a secondary, positive δ18O-shift from 4‰ to 6‰ for LTV and from 2‰ to 4‰ for CP geothermal fluids since the Late Glacial infiltration.

An assessment of the mean annual precipitation needed to sustain Lake Sambhar in Rajasthan, India, during mid-Holocene time

An application of a simple hydrological model to likely climatic conditions of Lake Sambhar provides tighter bounds on the range of increased precipitation seen during the early- to mid-Holocene than those inferred from paleoclimatic proxies. To examine past lake levels, we developed a simple lake model, based on hydrological principles of a watershed balance between precipitation, evaporation, and runoff from the watershed to calculate daily depth and volume. Calculations reveal that early- to mid-Holocene rainfall was most likely in a range of 40–65% greater than present levels, resulting in lake depths of ~6–8 m. This estimate incorporates all major sources of uncertainty into the lake model, but it is likely that the value of mid-Holocene precipitation lies in the lower part of the 40–65% range. Additionally, a 40–65% greater precipitation could have led to greater interannual variability in lake levels, which may account for the lack of clear shorelines. We find, however, that it is unlikely that Lake Sambhar filled to its maximum depth of 21 m above the present-day lakebed during this period due both to the much greater precipitation than today required to maintain a lake of such depth (greater than double present-day precipitation) and to the lack of current evidence (no shorelines and little vegetation). We also find that differences between mid-Holocene and present-day winter insolation alone have virtually no effect on average annual lake depths.

Simulation of present-day precipitation over India using a regional climate model

The objective of the present paper is to examine the capability of the regional climate model version 3 (RegCM3) to simulate the annual as well as seasonal precipitation variability over the Indian subcontinent. RegCM3 has been run at 40 km horizontal resolution for the period of 1982–2006 continuously and model results were compared to the observed precipitation datasets of India Meteorological Department (IMD) and CPC Merged Analysis of Precipitation (CMAP). Model evaluation has been done using different statistical methods like mean bias error (MBE), root mean square error, mean percentage error (MPE) and studied the spatial pattern of annual and seasonal variability and trend. Daily precipitation data at 1° × 1° grids of IMD have been used to study observed climatological means (both annual and seasonal), regression trends, interannual and intraseasonal variability over India from 1951 to 2007. The spatial distribution of annual precipitation shows a decreasing trend over west coast of India, central India, hilly region of India and an increasing trend is found over the northwest India, peninsular India and northeast India. The temporal distribution of daily precipitation shows highest rainfall of 18 mm/day in mid July (in composite flood cases only) and 12 mm/day during August (in composite drought cases only). The RegCM3 simulated annual and seasonal precipitation variability is close to the observed IMD and CMAP over all India (AI). During winter and pre-monsoon season, the model has overestimated the mean precipitation while underestimated in summer and post-monsoon season. Overall, annual precipitation showed the deficiency of −22.44 % compared to IMD and −1.41 % compared to CMAP over India. To understand the possible cause of annual and seasonal precipitation biases over India and its six homogeneous regions, the vertical difference (model mines National Centre for Environmental Prediction; NCEP) fields of water vapor mixing ratio (WVMR) and air temperature from surface to top level (1σ–18σ level) have been studied in detail. The model produced more moisture at the lower level during winter (JF) and pre-monsoon (MAM) season and reduced WVMR at the same levels during summer (JJAS) and post (OND) monsoon over India. High moisture content at the lower level simulated in the model can explain the increased precipitation during JF and MAM season and vice versa during JJAS and OND. Similar results were found over the homogeneous regions of India. This analysis indicates that the RegCM3 has more transport of vertical WVMR from surface to mid layer of the troposphere compared to NCEP.

Assessment of precipitation climatology in an ensemble of CORDEX-East Asia regional climate simulations

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 64:141-158 (2015) - DOI: https://doi.org/10.3354/cr01302 Assessment of precipitation climatology in an ensemble of CORDEX-East Asia regional climate simulations Bo Huang*, Stefan Polanski, Ulrich Cubasch Institute of Meteorology, Freie Universität Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany *Corresponding author: huangb@zedat.fu-berlin.de ABSTRACT: An ensemble of regional climate simulations from the Coordinated Regional Downscaling Experiment in East Asia (CORDEX-East Asia) was analysed to evaluate the ability of 5 regional climate models (RCMs) and their ensemble mean in reproducing the key features of present-day precipitation (1989-2008). We emphasised (1) an extreme rainfall event, (2) seasonal climatology, (3) annual cycles and inter-annual variability and (4) the monsoon characteristics. We highlighted 4 sub-monsoon regions, viz. South Asian Summer Monsoon (SAS), the East Asian Summer Monsoon (EAS), the Western North Pacific Tropical Monsoon (WNP) and the Australian-Maritime Continent Monsoon (AUSMC). We found that the RCMs showed a reasonable performance to capture the extreme rainfall event in 1998. The RCMs simulated the seasonal mean, annual cycle and inter-annual variability acceptably. However, individual models exhibited significant biases in some sub-regions and seasons. Moreover, most of the RCMs significantly improved their performance in capturing precipitation climatology and monsoon characteristics over the Korean Peninsula, the Korea Strait and southern Japan. Based upon this performance study, we conclude that the present set of RCMs from CORDEX can be used to provide useful information on climate projections over East Asia. KEY WORDS: CORDEX-East Asia · Regional climate model · Ensemble simulations · Precipitation climatology · Monsoon characteristics Full text in pdf format PreviousNextCite this article as: Huang B, Polanski S, Cubasch U (2015) Assessment of precipitation climatology in an ensemble of CORDEX-East Asia regional climate simulations. Clim Res 64:141-158. https://doi.org/10.3354/cr01302 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 64, No. 2. Online publication date: July 29, 2015 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2015 Inter-Research.

Evaluation for Moroccan dynamically downscaled precipitation from GCM CHAM5 and its regional hydrologic response

Abstract Study region Morocco (excluding Western Sahara). Study focus This study evaluated Moroccan precipitation, dynamically downscaled (0.18-degree) from three runs of the studied GCM ECHAM5/MPI-OM, under the present-day (1971–2000/20C3M) and future (2036–2065/A1B) climate scenarios. The spatial and quantitative properties of the downscaled precipitation were evaluated by a verified, fine-resolution reference. The effectiveness of the hydrologic responses, driven by the downscaled precipitation, was further evaluated for the study region over the upstream watershed of Oum er Rbia River located in Central Morocco. New hydrological insights for the region The raw downscaling runs reasonably featured the spatial properties but quantitatively misrepresented the mean and extreme intensities of present-day precipitation. Two proposed bias correction approaches, namely stationary Quantile-Mapping (QM) and non-stationary Equidistant CDF Matching model (EDCDFm), successfully reduced the system biases existing in the raw downscaling runs. However, both raw and corrected runs projected great diversity in terms of the quantity of future precipitation. Hydrologic simulations performed by a well-calibrated Variable Infiltration Capacity model successfully reproduced the present-day streamflow. The driven flows were identified highly correlated with the effectiveness of the downscaled precipitation. The future flows were projected to be markedly diverse, mainly due to the varied precipitation projections. Two of the three flow simulation runs projected slight to severe drying scenarios, while another projected an opposite trend for the evaluated future period.

Environmental heterogeneity predicts species richness of freshwater mollusks in sub-Saharan Africa

Species diversity and how it is structured on a continental scale is influenced by stochastic, ecological, and evolutionary driving forces, but hypotheses on determining factors have been mainly examined for terrestrial and marine organisms. The extant diversity of African freshwater mollusks is in general well assessed to facilitate conservation strategies and because of the medical importance of several taxa as intermediate hosts for tropical parasites. This historical accumulation of knowledge has, however, not resulted in substantial macroecological studies on the spatial distribution of freshwater mollusks. Here, we use continental distribution data and a recently developed method of random and cohesive allocation of species distribution ranges to test the relative importance of various factors in shaping species richness of Bivalvia and Gastropoda. We show that the mid-domain effect, that is, a hump-shaped richness gradient in a geographically bounded system despite the absence of environmental gradients, plays a minor role in determining species richness of freshwater mollusks in sub-Saharan Africa. The western branch of the East African Rift System was included as dispersal barrier in richness models, but these simulation results did not fit observed diversity patterns significantly better than models where this effect was not included, which suggests that the rift has played a more complex role in generating diversity patterns. Present-day precipitation and temperature explain richness patterns better than Eemian climatic condition. Therefore, the availability of water and energy for primary productivity during the past does not influence current species richness patterns much, and observed diversity patterns appear to be in equilibrium with contemporary climate. The availability of surface waters was the best predictor of bivalve and gastropod richness. Our data indicate that habitat diversity causes the observed species–area relationship, and hence, that environmental heterogeneity is a principal driver of freshwater mollusk richness on a continental scale.

Evaluation of regional climate model temperature and precipitation outputs over Scandinavia

Present-day precipitation and temperature simulations from regional climate models (RCMs) are compared with 2 re-analysis datasets, a hindcast dataset and observations over Scan- dinavia. The selected RCM data consist of 25 runs from the ENSEMBLES project, the re-analysis datasets are ERA-40 and ERA-Interim from ECMWF, the hindcast is NORA10 from MET Norway, and observations consist of E-OBS gridded data as well as data from meteorological stations. We studied the interannual variability and mean annual temperature and precipitation cycle for 1981 to 2000 and for 2001 to 2012 for 5 locations in Norway and Sweden: Oslo, Bergen, Trondheim, Tromso and Ostersund. The results show rather large differences between models and observa- tions, demonstrating the need for bias adjustment of results from climate models. A model ranking is provided to indicate which model gives the best representation of present climate over Scandi- navia. The performance measure used is the root-mean-square deviation of mean and standard deviation of monthly values at the 5 selected locations. The regional models RACMO2 and RCA show the smallest deviations from observed climate. Among the top-ranking model runs, most were driven by the global model ECHAM5 and some by a version of HadCM3. These 2 GCMs are also present among the worst-performing GCM-RCM combinations, indicating that selection of RCMs is crucial. For robust projections, an ensemble mean is still needed.

Carbon and oxygen stable isotope compositions of late Pleistocene mammal teeth from dolines of Ajoie (Northwestern Switzerland)

Fossils of megaherbivores from eight late Pleistocene 14C- and OSL-dated doline infillings of Ajoie (NW Switzerland) were discovered along the Transjurane highway in the Swiss Jura. Carbon and oxygen analyses of enamel were performed on forty-six teeth of large mammals (Equus germanicus, Mammuthus primigenius, Coelodonta antiquitatis, and Bison priscus), coming from one doline in Boncourt (~80ka, marine oxygen isotope stage MIS5a) and seven in Courtedoux (51–27ka, late MIS3), in order to reconstruct the paleoclimatic and paleoenvironmental conditions of the region. Similar enamel δ13C values for both periods, ranging from −14.5 to −9.2‰, indicate that the megaherbivores lived in a C3 plant-dominated environment. Enamel δ18OPO4 values range from 10.9 to 16.3‰ with a mean of 13.5±1.0‰ (n=46). Mean air temperatures (MATs) were inferred using species-specific δ18OPO4–δ18OH2O-calibrations for modern mammals and a present-day precipitation δ18OH2O-MAT relation for Switzerland. Similar average MATs of 6.6±3.6°C for the deposits dated to ~80ka and 6.5±3.3°C for those dated to the interval 51–27ka were estimated. This suggests that these mammals in the Ajoie area lived in mild periods of the late Pleistocene with MATs only about 2.5°C lower than modern-day temperatures.

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.

Multi-tracer investigation of groundwater in El Eulma Basin (northwestern Algeria), North Africa

The hydrogeochemical and isotopic compositions of groundwaters of the Mio-Plio-Quaternary (MPQ) aquifer of the El Eulma area, Northeast Algeria were examined to determine the main factors controlling groundwater chemistry and salinity as well as its hydrogeochemical evolution. Groundwater occurs in different water-bearing formations belonging to Quaternary, Neogene, Upper Cretaceous and Jurassic age. Different geochemical interpretation methods were used to identify the geochemical characteristics. Groundwater of the MPQ aquifer has the highest salinity values (564.5 ≤ total dissolved solids ≤ 2,333 mg/L) in the study area due to the impact of saltwater of Chotts and/or Sebkha “Bazar” and agricultural activities. Plotting data in a Piper diagram showed that Cl and SO4 are the dominant anions, whereas Na is the most dominant cation, although sometimes replaced by Ca and/or Mg in the groundwaters. Dissolution of carbonate and sulphate minerals in the aquifer matrices and recharge areas as well as cation exchange is shown to modify the concentration of ions in groundwater. Groundwater-mineral equilibria showed the prevailing dissolution-precipitation reactions in the groundwater. The groundwaters are depleted in 2H and 18O and display an isotopic signature close to that of meteoric water with d-excess values indicating present-day precipitation over the region and reflect the contribution of vapour masses from Mediterranean Sea and Atlantic origin. The isotopic features suggest that most of the groundwaters at the study area result from mixing between recent recharge and an older component recharged under climatic conditions cooler than at present.

Quantitative reconstruction of precipitation changes on the NE Tibetan Plateau since the Last Glacial Maximum – extending the concept of pollen source area to pollen-based climate reconstructions from large lakes

Abstract. Pollen records from large lakes have been used for quantitative palaeoclimate reconstruction, but the influences that lake size (as a result of species-specific variations in pollen dispersal patterns that smaller pollen grains are more easily transported to lake centre) and taphonomy have on these climatic signals have not previously been systematically investigated. We introduce the concept of pollen source area to pollen-based climate calibration using the north-eastern Tibetan Plateau as our study area. We present a pollen data set collected from large lakes in the arid to semi-arid region of central Asia. The influences that lake size and the inferred pollen source areas have on pollen compositions have been investigated through comparisons with pollen assemblages in neighbouring lakes of various sizes. Modern pollen samples collected from different parts of Lake Donggi Cona (in the north-eastern part of the Tibetan Plateau) reveal variations in pollen assemblages within this large lake, which are interpreted in terms of the species-specific dispersal and depositional patterns for different types of pollen, and in terms of fluvial input components. We have estimated the pollen source area for each lake individually and used this information to infer modern climate data with which to then develop a modern calibration data set, using both the multivariate regression tree (MRT) and weighted-averaging partial least squares (WA-PLS) approaches. Fossil pollen data from Lake Donggi Cona have been used to reconstruct the climate history of the north-eastern part of the Tibetan Plateau since the Last Glacial Maximum (LGM). The mean annual precipitation was quantitatively reconstructed using WA-PLS: extremely dry conditions are found to have dominated the LGM, with annual precipitation of around 100 mm, which is only 32% of present-day precipitation. A gradually increasing trend in moisture conditions during the Late Glacial is terminated by an abrupt reversion to a dry phase that lasts for about 1000 yr and coincides with "Heinrich event 1" in the North Atlantic region. Subsequent periods corresponding to the Bølling/Allerød interstadial, with annual precipitation (Pann) of about 350 mm, and the Younger Dryas event (about 270 mm Pann) are followed by moist conditions in the early Holocene, with annual precipitation of up to 400 mm. A drier trend after 9 cal. ka BP is followed by a second wet phase in the middle Holocene, lasting until 4.5 cal. ka BP. Relatively steady conditions with only slight fluctuations then dominate the late Holocene, resulting in the present climatic conditions. The climate changes since the LGM have been primarily driven by deglaciation and fluctuations in the intensity of the Asian summer monsoon that resulted from changes in the Northern Hemisphere summer solar insolation, as well as from changes in the North Atlantic climate through variations in the circulation patterns and intensity of the westerlies.