Increase In Precipitation Rate Research Articles

Lower Tropospheric Processes: A Control on the Global Mean Precipitation Rate

AbstractThe spread in global mean precipitation among climate models is explored in two ensembles using the complementary perspectives of surface evaporation and energy budgets. Models with higher global mean precipitation have stronger oceanic evaporation, driven by drier near‐surface air. The drier surface conditions occur alongside increases in near‐surface temperature and moisture at 925 hPa, which point to stronger boundary layer mixing. Correlations suggest that the degree of lower tropospheric mixing explains 18%–49% of the intermodel precipitation variance. To test this hypothesis, the degree of mixing is indirectly varied in a single‐model experiment by adjusting the relative humidity threshold that controls low‐cloud fraction. Indeed, increasing lower tropospheric mixing results in more global mean precipitation. Energetically, increased precipitation rates are associated with more downwelling longwave radiation to the surface and weaker sensible heat fluxes. These results highlight how lower‐tropospheric processes must be better constrained to reduce the precipitation discrepancy among climate models.

Evaluation the Effectiveness Implementation of the Weather Modification Technology for Mitigating Peatland Fires

The objective of this article is to evaluate the effectiveness implementation of the weather modification technology (WMT) for mitigating peatland fire disasters in Riau Province, Indonesia. The implementation of this WMT in Indonesia has been relatively new and challenging as this cutting-edge technology may increase the precipitation rates and therefore, it may reduce the risk of peat fire hazards in the huge massive areas. The Riau province has experienced serious peatland fire disasters from the period of 2014 to 2016. The evaluation of WMT in this article was focused on four regions within Riau encompassing Indragiri Hilir regency, Meranti Island, Pelalawan, and Siak. The Tropical Rainfall Measuring Mission (TRMM) satellite data were used to calculate the precipitation rates. The method applied to evaluating the effectiveness of WMT was the Target Only Method (TOM). This method calculated the precipitation rates during the WMT period, which is compared to the historical precipitation data in a similar period. The total duration of a 3-year WMT implementation was 380 days, and the results were considered successful as an increase of precipitation rate (PCH) = 2.09 > 1.00. Hence, there was an increase in the average of precipitation rate during WMT period of 2014-2016 in Riau.

Clumped isotope constraints on changes in latest Pleistocene hydroclimate in the northwestern Great Basin: Lake Surprise, California

AbstractDuring the Last Glacial Maximum (LGM) and subsequent deglaciation, the Great Basin in the southwestern United States was covered by numerous extensive closed-basin lakes, in stark contrast with the predominately arid climate observed today. This transition from lakes in the Late Pleistocene to modern aridity implies large changes in the regional water balance. Whether these changes were driven by increased precipitation rates due to changes in atmospheric dynamics, decreased evaporation rates resulting from temperature depression and summer insolation changes, or some combination of the two remains uncertain. The factors contributing to these large-scale changes in hydroclimate are critical to resolve, given that this region is poised to undergo future anthropogenic-forced climate changes with large uncertainties in model simulations for the 21st century. Furthermore, there are ambiguous constraints on the magnitude and even the sign of changes in key hydroclimate variables between the Last Glacial Maximum and the present day in both proxy reconstructions and climate model analyses of the region. Here we report thermodynamically derived estimates of changes in temperature, precipitation, and evaporation rates, as well as the isotopic composition of lake water, using clumped isotope data from an ancient lake in the northwestern Great Basin, Lake Surprise (California). Compared to modern climate, mean annual air temperature at Lake Surprise was 4.7 °C lower during the Last Glacial Maximum, with decreased evaporation rates and similar precipitation rates to modern. During the mid-deglacial period, the growth of Lake Surprise implied that the lake hydrologic budget briefly departed from steady state. Our reconstructions indicate that this growth took place rapidly, while the subsequent lake regression took place over several thousand years. Using models for precipitation and evaporation constrained from clumped isotope results, we determine that the disappearance of Lake Surprise coincided with a moderate increase in lake temperature, along with increasing evaporation rates outpacing increasing precipitation rates. Concomitant analysis of proxy data and climate model simulations for the Last Glacial Maximum are used to provide a robust means to understand past climate change, and by extension, predict how current hydroclimates may respond to expected future climate forcings. We suggest that an expansion of this analysis to more basins across a larger spatial scale could provide valuable insight into proposed climate forcings, and aid in climate model process depiction. Ultimately, our analysis highlights the importance of temperature-driven evaporation as a mechanism for lake growth and retreat in this region.

Experimental and theoretical modelling of kinetic and equilibrium Ba isotope fractionation during calcite and aragonite precipitation

Barium isotope fractionation during calcite and aragonite inorganic precipitation was studied in mixed flow reactors as a function of precipitation rate at 25 °C and pH = 6.3 ± 0.1. The measured Ba isotope fractionation that occurs between calcite and the forming fluid in the investigated range of calcite growth rates (10-8.0 ≤ Rp(calcite) ≤ 10−7.3 mol/m2/s) is insignificant. Barium isotope fractionation between aragonite and the fluid decreases with increasing precipitation rate from Δ137/134Baaragonite-fluid = +0.25 ± 0.06‰ for Rp(aragonite) ≤ 10−8.7 mol/m2/s to −0.10 ± 0.08‰ for Rp(aragonite) = 10−7.6 mol/m2/s, thus reflecting preferential incorporation of either heavy or light Ba isotopes in aragonite at slow and fast growth rates, respectively. The dependence of Ba isotope fractionation on aragonite growth rate is well described by the surface reaction kinetic model developed by DePaolo (2011) when the values +0.27‰ and −2.0 ± 0.2‰ are used for the equilibrium and kinetic Ba isotope fractionation factor, respectively. The enrichment of aragonite in the heavier Ba isotopes is consistent with the equilibrium fractionation factor of +0.34‰, calculated here between Ba-substituted aragonite and Ba2+ (aq), from first-principles calculations. This positive fractionation is related to a shorter average BaO bond length in the aragonite structure while the coordination number does not change much (i.e. 9). The lack of isotope fractionation between the Ba aquo ions and the 6-coordinated Ba in calcite likely suggests that the coordination reduction required for the incorporation in the lattice of Ba adsorbed at calcite growing sites proceeds without isotope fractionation with the fluid. Otherwise the precipitated calcite should have been enriched in heavy isotopes by ∼0.17‰, as predicted by first-principles calculations. These results are the first experimental measurements of Ba isotope fractionation during inorganic calcite and aragonite mineral formation and set the basis for understanding the mechanisms controlling Ba isotope composition in CaCO3 minerals that is an essential perquisite for application of this isotopic system in natural samples.

Ambient Factors Controlling the Wintertime Precipitation Distribution across Mountain Ranges in the Interior Western United States. Part II: Changes in Orographic Precipitation Distribution in a Pseudo–Global Warming Simulation

AbstractTwo high-resolution (4 km) regional climate simulations over a 10-yr period are conducted to study the changes in wintertime precipitation distribution across mountain ranges in the interior western United States (IWUS) in a warming climate. One simulation represents the current climate, and another represents an ~2050 climate using a pseudo–global warming approach. The climate perturbations are derived from the ensemble mean of 15 global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). These simulations provide an estimate of average changes in wintertime orographic precipitation enhancement and finescale distribution across mountain ranges. The variability in these changes among CMIP5 models is quantified using statistical downscaling relations between orographic precipitation distribution and upstream conditions, developed in Part I. The CMIP5 guidance indicates a robust warming signal (~2 K) over the IWUS by ~2050 but minor changes in relative humidity and cloud-base height. The IWUS simulations reveal a widespread increase in precipitation on account of higher precipitation rates during winter storms in this warmer climate. This precipitation increase is most significant over the mountains rather than on the surrounding plains. The increase in precipitation rate is largely due to an increase in low-level cross-mountain moisture transport. The application of the statistical relations indicates that individual CMIP5 models disagree about the magnitude and distribution of orographic precipitation change in the IWUS, although most agree with the ensemble-mean-predicted orographic precipitation increase.

The Geometry of Rimed Aggregate Snowflakes: A Modeling Study

AbstractComputer simulations of the aggregation and riming of ice crystals are performed to investigate the geometry of rimed aggregate snowflakes. Due to the universality of the geometry of aggregates, the conversion to a graupel‐like particle is self‐similar and independent from specific properties of the aggregate, when formulated in properly normalized variables. Hence, the particle habit of the primary crystals, the size of the aggregate or the density of the rime mass, does not lead to a structural change in the transition to graupel. Therefore, this transition can be parameterized by a similarity approach using simulations of many individual rimed aggregates. These parameterizations can replace the classic fill‐in model used in many cloud models. The parameterizations are applied and tested in a one‐dimensional Lagrangian superparticle model to simulate the growth of aggregates in a liquid layer. We find that the similarity model for the geometry of rimed snowflakes leads to a more rapid growth by riming and, hence, an increased precipitation rate compared to the fill‐in model. The main reason for this is that the increase of the maximum dimension during the early stages of riming is properly taken into account by the similarity model, whereas it is neglected by the fill‐in model.

Rural solid waste-characteristics and leachate pollution assessment for different precipitation levels, China.

Open dumping adversely affects the environment and remains the most widely used method for waste disposal in many developing rural areas in China. Information regarding the impact of rural solid waste (RSW) on the environment remains limited. The objectives of this study are to investigate the characteristics of RSW and the impact of different precipitation rates, and to evaluate the contamination potential of RSW using a leachate pollution index (LPI). The study showed that leachate concentration was significantly influenced by precipitation rates at the initial precipitation stages. Precipitation rates of 42.00mm/day appeared to have the largest dilution effects. In contrast, the concentrations of leachate at rainfall rates of 24.00mm/day and soaking were steady, and no similar trends were observed. The highest amounts of pollutants in leachate were the result of soaking. In the first week of our experiment, the LPI value for each rural area waste sample rapidly increased with rising precipitation rates from soaking to 42.00mm/day. However, no significant change in LPI was observed thereafter (after 5weeks) even with increasing precipitation rates. The values of chemical oxygen demand, biochemical oxygen demand, total nitrogen, and NH3-N in the leachate after 10weeks were 4.00, 7.34, 1.87, and 2.21 times higher, respectively, than those of the prescribed leachate quality standards in China. The results of our study suggest the following course of action for the three dump sites investigated: in Banqiao, given the size of the population and the size of the waste amount, landfill might be a suitable way for disposing of RSW. In Machen, building a standardized waste collection site would be an economical solution for reducing potential pollution risks. In Jiuduhe, increasing the transportation rate of solid waste might be an effective solution. The results of this study can help to improve the understanding of leachate pollution in Chinese rural areas.

Climatic determinants impacting the distribution of greenness in China: regional differentiation and spatial variability.

This study investigated climatic determinants for regional greenness in China and spatially variable correlations between climatic determinants and vegetation in specific regions using the geographical detector and geographically weighted regression (GWR) methodologies. The analyses were based on normalized difference vegetation index (NDVI) and interpolations of climatic determinants from 652 Chinese meteorological stations. The study period (1982-2013) was divided into two stages (T1-T2) before and after the inflection year identified by the accumulative anomaly of NDVI. Three typical regions (R1-R3) were then selected according to the same NDVI variation trend as China in the two periods. Precipitation was the dominant climatic factor of NDVI in China, and the effect of temperature on greenness increased with warming from T1 to T2. In a relatively arid region (R1), the effect of precipitation in T2 was further strengthened compared to T1. Meanwhile, the effect of minimum temperature in T2 also increased compared with T1 in a relatively humid region (R2), becoming the major climatic determinant. In addition to the regional differentiation, spatial variability was investigated by comparing normalized coefficients of GWR for climatic determinants; this showed significant spatial heterogeneity within each region. Temperature impact areas also existed within precipitation-dominated regions (R1 and R3), where areas of precipitation impact expanded from T1 to T2. Furthermore, regression coefficients between NDVI dynamics and climate variability revealed relationships between regional differentiation and spatial variability. For example, the increasing precipitation rate could mediate the adverse impacts on greenness caused by the higher warming rate in relatively arid regions (R1).

Ontario Winter Lake-effect Systems (OWLeS): Bulk Characteristics and Kinematic Evolution of Misovortices in Long-Lake-Axis-Parallel Snowbands

Abstract During the Ontario Winter Lake-effect Systems (OWLeS) field campaign, 12 long-lake-axis-parallel (LLAP) snowband events were sampled. Misovortices occurred in 11 of these events, with characteristic diameters of ~800 m, differential velocities of ~11 m s−1, and spacing between vortices of ~3 km. A detailed observational analysis of one such snowband provided further insight on the processes governing misovortex genesis and evolution, adding to the growing body of knowledge of these intense snowband features. On 15–16 December 2013, a misovortex-producing snowband was exceptionally well sampled by ground-based OWLeS instrumentation, which allowed for integrated finescale dual-Doppler and surface thermodynamic analyses. Similar to other studies, horizontal shearing instability (HSI), coupled with stretching, was shown to be the primary genesis mechanism. The HSI location was influenced by snowband-generated boundaries and location of the Arctic front relative to the band. Surface temperature observations, available for the first time, indicated that the misovortices formed along a baroclinic zone. Enhanced mixing, higher radar reflectivity, and increased precipitation rate accompanied the vortices. As the snowband came ashore, OWLeS participants indicated an increase in snowfall and white out conditions with the passage of the snowband. A sharp, small-scale pressure drop, coupled with winds of ~16 m s−1, marked the passage of a misovortex and may be typical of snowband misovortices.

Study of the effect of temperature on microbially induced carbonate precipitation

Temperature is a key factor that contributes to microbially induced calcium carbonate precipitation. At low temperatures, low enzyme activity results in a lack of calcium precipitation. In this study, Sporosarcina pasteurii and Bacillus megaterium were compared. Firstly, the optical density curves and enzyme activity curves of both bacteria were obtained during 48-h culture. Then, optical density, enzyme activity, and productive rates for calcium carbonate were measured to analyze the influence of temperature. Finally, the effect of urea concentration on carbonate precipitation was studied by changing the urea concentration that was added during inoculation. The obtained results showed that at high temperature, the growth rate of B. megaterium was close to that of S. pasteurii, while the opposite result was found at low temperature. The urease activities of B. megaterium were similar at different temperature conditions. At high temperature, B. megaterium showed lower enzyme activity, while at low temperature, it surpassed that of S. pasteurii. The same results were found for enzyme activity and for the precipitation rates of calcium carbonate. The addition of urea to the medium increased precipitation rates, and higher urea concentrations increased the obtained precipitation rates. With 20 g/L urea, the precipitation rate of B. megaterium at 15 °C matched that without urea addition at 30 °C. Therefore, adding urea to the medium at the time of inoculation can effectively overcome the low calcium precipitation at low temperature and enable subsequent low-temperature engineering applications.

Impact of aerosol number concentration on precipitation under different precipitation rates

Mainly by modifying the number concentration and size of cloud droplets, the dynamic and thermodynamic effects of aerosols are important in the formation of precipitation, but so far different and occasionally opposite responses of precipitation to aerosol concentration have been noted. By conducting two numerical experiments with different aerosol concentrations, the impact of aerosol number concentration on precipitation under different precipitation rates is examined. To this end, the Weather Research and Forecasting (WRF) model with a two‐moment aerosol‐aware bulk microphysical scheme was applied. Results indicate that mainly through redistribution of precipitation both spatially and temporarily, more hygroscopic aerosols in the atmosphere could potentially reduce light precipitation events, but increase heavy precipitation events. In regions with a high precipitation rate (> 1 mm/hr), an ample influx of water vapour exists. Thus, cloud droplets have no need to compete for water vapour in order to grow, which results in an enhancement of precipitation under the polluted atmosphere. On the other hand, less efficient autoconversion processes and/or increased cloud‐top evaporation may contribute to the decrease in light (< 0.6 mm/hr) to moderate (0.6–1 mm/hr) precipitation under the polluted atmosphere. A delay in the onset of precipitation is identified in the polluted experiment, which leads to a significant increase in precipitation rate, primarily due to more freezing of cloud droplets and extra release of latent heat of freezing, which invigorates cloud developments, while intensification of secondary clouds by aerosols might have also partly contributed.

Multiple rock-slope failures from Mannen in Romsdal Valley, western Norway, revealed from Quaternary geological mapping and 10Be exposure dating

Oversteepened valley walls in western Norway have high recurrences of Holocene rock-slope failure activity causing significant risk to communities and infrastructure. Deposits from six to nine catastrophic rock-slope failure (CRSF) events are preserved at the base of the Mannen rock-slope instability in the Romsdal Valley, western Norway. The timing of these CRSF events was determined by terrestrial cosmogenic nuclide dating and relative chronology due to mapping Quaternary deposits. The stratigraphical chronology indicates that three of the CRSF events occurred between 12 and 10 ka, during regional deglaciation. Congruent with previous investigations, these events are attributed to the debuttressing effect experienced by steep slopes following deglaciation, during a period of paraglacial relaxation. The remaining three to six CRSF events cluster at 4.9 ± 0.6 ka (based on 10 cosmogenic 10Be samples from boulders). CRSF events during this later period are ascribed to climatic changes at the end of the Holocene thermal optimum, including increased precipitation rates, high air temperatures and the associated degradation of permafrost in rock-slope faces. Geomorphological mapping and sedimentological analyses further permit the contextualisation of these deposits within the overall sequence of post-glacial fjord-valley infilling. In the light of contemporary climate change, the relationship between CRSF frequency, precipitation, air temperature and permafrost degradation may be of interest to others working or operating in comparable settings.

Numerical modelling of landscape and sediment flux response to precipitation rate change

Abstract. Laboratory-scale experiments of erosion have demonstrated that landscapes have a natural (or intrinsic) response time to a change in precipitation rate. In the last few decades there has been growth in the development of numerical models that attempt to capture landscape evolution over long timescales. However, there is still an uncertainty regarding the validity of the basic assumptions of mass transport that are made in deriving these models. In this contribution we therefore return to a principal assumption of sediment transport within the mass balance for surface processes; we explore the sensitivity of the classic end-member landscape evolution models and the sediment fluxes they produce to a change in precipitation rates. One end-member model takes the mathematical form of a kinetic wave equation and is known as the stream power model, in which sediment is assumed to be transported immediately out of the model domain. The second end-member model is the transport model and it takes the form of a diffusion equation, assuming that the sediment flux is a function of the water flux and slope. We find that both of these end-member models have a response time that has a proportionality to the precipitation rate that follows a negative power law. However, for the stream power model the exponent on the water flux term must be less than one, and for the transport model the exponent must be greater than one, in order to match the observed concavity of natural systems. This difference in exponent means that the transport model generally responds more rapidly to an increase in precipitation rates, on the order of 105 years for post-perturbation sediment fluxes to return to within 50 % of their initial values, for theoretical landscapes with a scale of 100×100 km. Additionally from the same starting conditions, the amplitude of the sediment flux perturbation in the transport model is greater, with much larger sensitivity to catchment size. An important finding is that both models respond more quickly to a wetting event than a drying event, and we argue that this asymmetry in response time has significant implications for depositional stratigraphies. Finally, we evaluate the extent to which these constraints on response times and sediment fluxes from simple models help us understand the geological record of landscape response to rapid environmental changes in the past, such as the Paleocene–Eocene thermal maximum (PETM). In the Spanish Pyrenees, for instance, a relatively rapid (10 to 50 kyr) duration of the deposition of gravel is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest that the rapid response observed is more easily explained through a diffusive transport model because (1) the model has a faster response time, which is consistent with the documented stratigraphic data, (2) there is a high-amplitude spike in sediment flux, and (3) the assumption of instantaneous transport is difficult to justify for the transport of large grain sizes as an alluvial bedload. Consequently, while these end-member models do not reproduce all the complexity of processes seen in real landscapes, we argue that variations in long-term erosional dynamics within source catchments can fundamentally control when, how, and where sedimentary archives can record past environmental change.

Tropical continental downdraft characteristics: mesoscale systems versus unorganized convection

Abstract. Downdrafts and cold pool characteristics for strong mesoscale convective systems (MCSs) and isolated, unorganized deep precipitating convection are analyzed using multi-instrument data from the DOE Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign. Increases in column water vapor (CWV) are observed leading convection, with higher CWV preceding MCSs than for isolated cells. For both MCSs and isolated cells, increases in wind speed, decreases in surface moisture and temperature, and increases in relative humidity occur coincidentally with system passages. Composites of vertical velocity data and radar reflectivity from a radar wind profiler show that the downdrafts associated with the sharpest decreases in surface equivalent potential temperature (θe) have a probability of occurrence that increases with decreasing height below the freezing level. Both MCSs and unorganized convection show similar mean downdraft magnitudes and probabilities with height. Mixing computations suggest that, on average, air originating at heights greater than 3 km must undergo substantial mixing, particularly in the case of isolated cells, to match the observed cold pool θe, implying a low typical origin level. Precipitation conditionally averaged on decreases in surface equivalent potential temperature (Δθe) exhibits a strong relationship because the most negative Δθe values are associated with a high probability of precipitation. The more physically motivated conditional average of Δθe on precipitation shows that decreases in θe level off with increasing precipitation rate, bounded by the maximum difference between surface θe and its minimum in the profile aloft. Robustness of these statistics observed across scales and regions suggests their potential use as model diagnostic tools for the improvement of downdraft parameterizations in climate models.

Increasing precipitation rate from sodium aluminate solution by adding active seed and ammonia

Remarkably increasing precipitation rate of sodium aluminate solution was studied by adding active seed and ammonia. The fine active gibbsite seed with irregular edge, large specific area and high oil adsorption capacity was prepared by sodium bicarbonate solution and sodium aluminate. The seeded precipitation rate reached up to 65% by adding <20 g L−1 active seeds into the sodium aluminate solution. Moreover, 75% precipitation rate was obtained due to the coupling contribution from the active seed and ammonia. Ammonia added in the initial precipitation stage improved precipitation rate, whereas minimal change in precipitation rate occurred by adding ammonia in latter period of precipitation. High precipitation rate also led to precipitation of fine gibbsite. In addition, increasing ammonia amount benefitted the formation of Al(OH)4− and slightly reduced the amount of Al2O(OH)62−. Electrical conductivity in solution was decreased by adding ammonia. This is quite probably attributed to the increase in ionic pairs of Na+Al(OH)4− and subsequently precipitation of gibbsite from Al(OH)4−.

Anthropogenic hydrological cycle disturbance at a regional scale: State-wide evapotranspiration trends (1979–2015) across Nebraska, USA

Trends in monthly evapotranspiration (ET) rates across Nebraska, the most intensely irrigated state within the US, were calculated by the calibration-free version of the nonlinear complementary relationship of evaporation over the 1979–2015 period utilizing North American Regional Reanalysis (NARR) net radiation, 10-m wind velocity, as well as Parameter Regression Independent Slope Model (PRISM) air- and dew-point temperature data. State-averaged modeled ET rates rose by 5.5 mm decade−1 due to the presence of wide-spread large-scale irrigation projects in accordance with a 2.4 mm decade−1 increase in PRISM precipitation (P) and a simultaneous −2.8 mm decade−1 drop in United States Geological Survey’s state-averaged annual streamflow rates, raising the state-wide ET to P ratio from 0.89 to 0.91 over the modeled time-period. ET rates over irrigated crops increased by 7 mm decade−1 despite a −4.4 mm decade−1 drop in precipitation rates. A similar increase in ET rates (6 mm decade−1) required 8.1 mm decade−1 increase in precipitation rates across the non-irrigated Sand Hills of Nebraska. Published NARR ET rates are unable to pick up this unusual regional trend. Since an increase in precipitation rates should normally decrease the ET ratio, as predicted by the Budyko curve, this study yields evidence on how dramatically sustained large-scale irrigation can alter the regional hydrologic cycle not only through a) trivially depleting streamflow rates and/or lowering groundwater table levels; b) suppressing precipitation locally (while enhancing it a long distance downwind), but also; c) reversing the trajectory of the regional ET ratio under generally increasing trends of precipitation.

Bridging Glaciological and Hydrological Trends in the Pamir Mountains, Central Asia

With respect to meteorological changes and glacier evolution, the southern Pamir Mountains are a transition zone between the Pamirs, Hindu Kush and Karakoram, which are water towers of Central Asia. In this study, we compare runoff and climate trends in multiple time periods with glacial changes reported in the literature. Recent glacier evolution in the Southern Pamirs and its contribution to river runoff are studied in detail. Uncertainties of estimating glacier retreat contribution to runoff are addressed. Runoff trends in the Pamir-Hindu Kush-Karakoram region appear to be a strong proxy for glacier evolution because they exhibit the same spatial pattern as glacial change. There is an anomaly in the North-West Pamirs and Northern Karakoram, showing decreasing runoff trends. In the opposite way, there is a glacier and hydrological change experienced in the Southern Pamirs and Hindu Kush. The prevailing hypothesis for the Karakoram Anomaly, decreasing summer temperatures along with increasing precipitation rates, seems to be valid for the North-Western Pamirs, as well. In the Southern Pamirs, temperature trends have been rising since 1950. Here, the unique water cycle of exclusively winter precipitation does not protect glaciers from accelerated retreat. Snow cover is preset to melt within the seasonal water cycle, due to much lower precipitation amounts falling on glaciers. Therefore, a probable increase in westerly precipitation in both regions causes glacier mass gain in the Northern Pamirs and rising river flows in the Southern Pamirs.

Sources of trace elements in wet deposition in Pamukkale, Denizli, western Turkey

ABSTRACTForty-two rainwater samples were collected during December 2011 and November 2012 in Pamukkale, Denizli, Turkey to investigate the characteristics of trace elements in wet deposition. The samples were analyzed by inductively coupled plasma optical emission spectrometry. Zn, Al, and Fe concentrations contributed 50.4% to the total element concentration. The trace element concentrations in rainwater samples showed seasonal variations, with high and low values in spring and summer, respectively. The daily total trace element concentrations of rainwater samples decreased exponentially with increasing precipitation rates. The wet deposition fluxes of trace elements were more affected by precipitation heights than concentrations. Enrichment factor analysis showed that Cr, Ni, Mn, Cd, Zn, Pb, Cu, Li, Sr, Co, and Ba indicate anthropogenic enrichment, while Al, Fe, and Ti were considered to be of crustal origin. As a result of principal component analysis, a three-component system of precipitation consisted of a mixed component (crustal and anthropogenic), a local pollution component, and an anthropogenic component, which explains 86.5% of the total variance. A significant fraction of the measured anthropogenic pollutants was transported to the sampling area from source regions in the North Atlantic Ocean, northern Europe, and the Balkans based on back-trajectory analysis. The acidic rain events, high concentrations, and fluxes of trace elements obtained in this study show that wet deposition in Pamukkale may be crucial for impacts on the local travertine. Trace elements that reach travertine by wet deposition may be viewed as a risk because of the anthropogenic origins of air pollutants.

Vegetation and climate during the Last Glacial high stand (ca. 28–22 ka BP) of the Sea of Galilee, northern Israel

Abstract Despite ongoing discussions on hydroclimatic conditions in the southern Levant during the Last Glacial, detailed knowledge about the Levantine paleovegetation, which is an important indicator for the paleoclimate, is limited. To investigate the paleovegetation in northern Israel, we analyzed the pollen assemblage of a sediment core that was drilled at the Ohalo II archaeological site on the southwestern shore of the Sea of Galilee (Lake Kinneret). We refined the lithology and the age-depth model with the help of five new radiocarbon dates. The core comprises a continuous sediment profile of mainly laminated authigenic calcites and detrital material that deposited between ca. 28,000 and 22,500 years before present, when the Sea of Galilee rose above the modern lake level stand and temporarily merged with Lake Lisan, the precursor of the Dead Sea. The well-dated and high-resolution pollen record suggests that steppe vegetation with grasses, other herbs, and dwarf shrubs predominated in northern Israel during the investigated period. In contrast to the Holocene, there was no continuous vegetation belt of the Mediterranean biome in the vicinity of the Sea of Galilee. Mediterranean elements such as deciduous oaks only occurred in limited amounts and were probably patchily distributed. These results disagree with previous pollen-based hypotheses from the region that assumed the spread of Mediterranean forest during glacial periods. While the pollen data may indicate semiarid conditions in northern Israel and give no evidence of increased effective moisture, previous hydroclimatic studies suggested increased precipitation rates that are consistent with high lake levels (Sea of Galilee/Lake Lisan). Thus, we discuss factors influencing the pollen assemblage and the plant cover.

The Resolution Dependence of Contiguous U.S. Precipitation Extremes in Response to CO2 Forcing

Abstract Precipitation extremes have a widespread impact on societies and ecosystems; it is therefore important to understand current and future patterns of extreme precipitation. Here, a set of new global coupled climate models with varying atmospheric resolution has been used to investigate the ability of these models to reproduce observed patterns of precipitation extremes and to investigate changes in these extremes in response to increased atmospheric CO2 concentrations. The atmospheric resolution was increased from 2° × 2° grid cells (typical resolution in the CMIP5 archive) to 0.25° × 0.25° (tropical cyclone permitting). Analysis has been confined to the contiguous United States (CONUS). It is shown that, for these models, integrating at higher atmospheric resolution improves all aspects of simulated extreme precipitation: spatial patterns, intensities, and seasonal timing. In response to 2 × CO2 concentrations, all models show a mean intensification of precipitation rates during extreme events of approximately 3%–4% K−1. However, projected regional patterns of changes in extremes are dependent on model resolution. For example, the highest-resolution models show increased precipitation rates during extreme events in the hurricane season in the U.S. Southeast; this increase is not found in the low-resolution model. These results emphasize that, for the study of extreme precipitation there is a minimum model resolution that is needed to capture the weather phenomena generating the extremes. Finally, the observed record and historical model experiments were used to investigate changes in the recent past. In part because of large intrinsic variability, no evidence was found for changes in extreme precipitation attributable to climate change in the available observed record.