Wet Episodes Research Articles

Changes in atmospheric circulation patterns associated with high and low rainfall regimes in the Hawaiian Islands region on multiple time scales

We examine a suite of climate variables in the North Pacific associated with different temporal scales of dry and wet episodes in the Hawaiian Islands. The goal is to ascertain whether varying the length in the occurrence of such events from seasonal to multi-decadal results from different ocean–atmosphere circulation patterns over the North Pacific region. We find that as the dryness period lengthens, the spatial scale of the anomalies widens, but the characteristics of the anomalous circulation fields exhibit elements evident at each time scale. At the longest (multi-decadal) time scales during the wet season (November–April), the major anomalous circulation features associated with above (below) average rainfall in Hawai'i are a strengthening (weakening) of the North Pacific mid-latitude westerlies associated with a strengthened (weakened) Aleutian Low system, a slight weakening (strengthening) of the northeast trade winds, with anomalous northerly (southerly) component to the south of the Islands, together with diminished (enhanced) precipitation across most of the tropical North Pacific.During the summer dry season (May–October) a characteristic pattern that is evident at different time scales during drier than normal periods is a strengthening of the trade winds to the south of the Islands, with sinking motion extending from the latitude of Hawai'i eastward to Central America. Conversely, wet summers are associated with generally weaker trades to the south with a tendency for anomalous southwesterly component. We also consider possible changes in the relationship of Hawaiian rainfall to changes in the Pacific-Decadal Oscillation (PDO) but conclude that the record is too short to establish the significance of any changes in an overall negative correlation.

Modeling annual discharge of six Mexico’s northern rivers (doi:10.4136/ambi-agua.705)

The overall goal of this report was to understand river discharge variability to improve conventional water management practices of Mexico’s northern subtropical rivers. This report addresses whether: a) river discharge tendencies, patterns and cycles can be detected with proxy and instrumental records; and b) annual discharge can be forecasted by stochastic models. Eleven gauging stations of six major rivers; three lowland rivers discharging into the Pacific Ocean (Rios Santa Cruz, Acaponeta, and San Pedro); five upland rivers draining into the Pacific Ocean (Rio San Pedro: Pena del Aguila, Refugio Salcido, San Felipe, Vicente Guerrero and Saltito), one river flowing across the interior Basin (Rio Nazas: Salome Acosta) and two more rivers discharging into the Northern Gulf of Mexico (Rio San Juan: El Cuchillo and Rio Ramos: Pablillos) were statistically analyzed. Instrumental recorded daily discharge data (1940-1999) and reconstructed time series data (1860-1940) using dendrochronological analysis delivered annual discharge data to be modeled using autoregressive integrated moving average, ARIMA models. Spectral density analysis, autocorrelation functions and the standardized annual discharge data evaluated annual discharge frequency cycles. Results showed ARIMA models with two autoregressive and one moving average coefficient adequately project river discharge for all gauging stations with four of them showing significant declining patterns since 1860. ARIMA models in combination with autocorrelation and spectral density techniques as well as standardized departures, in agreement with present (2002-2010) observations, forecast a wet episode that may last between 9 and 12 years thereafter entering again into a dry episode. Three dry-wet spell cycles with different time scales (1-2 years; 4-7 years; 9-12 years) could be discerned from these analyses that are consistent for all three northern Mexico’s river clusters that emerged from a multivariate analysis test.

Previous Land Use Alters the Effect of Climate Change and Facilitation on Expanding Woodlands of Spanish Juniper

In Mediterranean–continental regions, changes in land use are leading to the expansion of valuable habitats like endemic Juniperus thurifera woodlands, but the impact of reduced rainfall, due to climate change, on this expansion remains uncertain. We assessed the early performance of J. thurifera in different global change scenarios with and without facilitation. Saplings were transplanted in three ecosystems types with different previous land use (woodlands, former agricultural fields, and former livestock pastures), microhabitats (open vs. understory of adult trees) and were subjected to two watering regimens. We characterized the abiotic environment and measured survival, growth and two ecophysiological parameters. Former livestock pastures were the least favorable ecosystem, where the nursing effect was greatest. Former agricultural fields had the highest survival, but were more sensitive than woodlands to water scarcity. Reduced rainfall decreased photochemical efficiency, particularly in the least favorable scenarios, but did not affect survival. Water use efficiency enhanced growth under the canopy, but not in the open, whereas photochemical efficiency enhanced growth and survival more in the open. Facilitation was critical for effective recruitment in the harshest scenarios: former livestock pastures and reduced rainfall. Comparison with previous studies suggests that establishment depends on infrequent wet episodes. In Mediterranean ecosystems, changes in land use and climate change are leading to woodland expansion due to the modulating effect of facilitation of the oncoming adverse drier conditions. Nevertheless, the positive effect of facilitation and the negative impact of aridity on tree recruitment are strongly influenced by previous land-use history.

Climatic fluctuations during the LIA and post-LIA in the Kumaun Lesser Himalaya, India: Evidence from a 400 y old stalagmite record

This paper presents the first stable isotope (δ18O and δ13C) data of a ∼400 years (1590–2006 AD) long annual to decadal-resolution speleothem record collected from the Indian Lesser Himalaya. The data show a variation from −2.7 to −5.9‰ in δ18O and −5.3 to −8.8‰ in δ13C. The isotopic analyses indicate that the climate during this period can be divided into two stages: a wet phase during the Little Ice Age (LIA) (1590–1850 AD) and comparatively dry phase during the post-LIA after 1850 AD. However, the record also documents the minor dry events during the LIA and a wet episode after the LIA. Within the age uncertainty, the dry spells during the LIA are linked with the historical drought events in the Indian subcontinent and similar latitudes. The isotopic record is consistent with a number of previous studies in the areas influenced by the Westerlies but appears to be conflicting to the regions, dominated by the Indian Summer Monsoon (ISM). This may be due to the possible changes in the strength of Westerlies in the study area and added by negative anomaly of North Atlantic Oscillation (NAO) during the LIA.

Rainfall Response in Northeast Brazil from Ocean Climate Variability during the Second Half of the Twentieth Century

Abstract The authors investigated the rainfall variability response in northern Northeast Brazil (NNEB) from El Niño/La Niña (EN/LN) events and from the meridional sea surface temperature gradient (MGRAD) over the tropical Atlantic during the period 1948–97. The diagnostic analysis was stratified according to four climatic series of scenarios associated with EN, LN, and positive and negative MGRAD. During ENs, which were more numerous and more intense after the 1970s, the MGRAD was generally not noticeable, and the drought impact in NNEB was mainly due to the warm Pacific influence. Conversely, during LNs, the MGRAD signal was important, but there was an inverse relationship between the third and the fourth quarters of the twentieth century. Thus, before the 1970s the LNs were associated with positive MGRAD, which led to an inverse influence inducing minor changes in seasonal rainfall in NNEB. After the 1970s the LNs were linked to negative MGRAD, which induced a cumulative wet influence in NNEB. The positive MGRADs were generally associated with ENs, which reinforced the drought impact in NNEB. The well-marked negative MGRADs, which all occurred after the beginning of the 1970s, were generally linked with large LNs that induced very consistent wet episodes in NNEB. Interestingly, the two low-frequency variations in the tropical oceans observed during the second half of the twentieth century (i.e., from a few to several strong ENs and from none to numerous strong negative MGRADs) occurred concomitantly with symmetric long-term changes in the Pacific decadal oscillation (PDO) and the North Atlantic Oscillation (NAO). This symmetrical long-term climate behavior during the second half of the twentieth century could have lead to an inverse influence on the climate over the north Northeast Brazil, in agreement with a quasi-null long-term trend of the rainfall observed in that region all along this period. Such symmetrical behavior seems to have been unique during the last 150 years.

Rainfall, spring discharge and past human occupancy in the Eastern Mediterranean

In ancient times human activities were tightly related and sensitive to rainfall amounts and seasonal distribution. East Mediterranean settlements were concentrated around numerous small to large springs, such as the Judean Mountains area. The goals of this study were to determine (a) the sensitivity of total discharge, recession curve, and response time of such springs to annual precipitation patterns, and (b) how spring hydrology responds to series of drought or wet years and to transitions from drought to normal and/or wet episodes (and vice versa). These goals were achieved by setting a finite-element hydro-geological flow model for selected perched springs that characterize the numerous springs throughout the carbonate karst terrain in the Judean Mountains. In addition, we estimated the effect of proposed regional past climate changes on the springs; in so doing, we transfer climate change to community size, livelihood and economic strength that were highly dependent on agricultural productivity. The results of the hydro-geological model revealed that these mountainous communities had the potential to prosper during historically wetter episodes and were probably adapted to short-term variability in annual rainfall. However, moderate to extreme droughts lasting only a few years could have led to a partial or even total abandonment of the springs as focal sites of intensive agricultural production. Spring drying eliminated the primary cause for the location of settlement. This occurred simultaneously in numerous settlements around the mountains of the southern Levant and therefore, must have caused dramatic economic and societal changes in the entire region, perhaps even resonating afar.

Spatial and temporal connections in groundwater contribution to evaporation

Abstract. In climate models, lateral terrestrial water fluxes are usually neglected. We estimated the contribution of vertical and lateral groundwater fluxes to the land surface water budget at a subcontinental scale, by modeling convergence of groundwater and surfacewater fluxes. We present a hydrological model of the entire Danube Basin at 5 km resolution, and use it to show the importance of groundwater for the surface climate. Results show that the contribution of groundwater to evaporation is significant, and can locally be higher than 30 % in summer. We demonstrate through the same model that this contribution also has important temporal characteristics. A wet episode can influence groundwater contribution to summer evaporation for several years afterwards. This indicates that modeling groundwater flow has the potential to augment the multi-year memory of climate models. We also show that the groundwater contribution to evaporation is local by presenting the groundwater travel times and the magnitude of groundwater convergence. Throughout the Danube Basin the lateral fluxes of groundwater are negligible when modeling at this scale and resolution. This suggests that groundwater can be adequately added in land surface models by including a lower closed groundwater reservoir of sufficient size with two-way interaction with surface water and the overlying soil layers.

Key role of the Atlantic Multidecadal Oscillation in 20th century drought and wet periods over the Great Plains

[1] The Great Plains of North America are susceptible to multi-year droughts, such as the 1930s ‘Dust Bowl’. The droughts have been linked to SST variability in the Pacific and Atlantic basins. This observationally rooted analysis shows the SST influence in multi-year droughts and wet episodes over the Great Plains to be significantly more extensive than previously indicated. The remarkable statistical reconstruction of the major hydroclimate episodes attests to the extent of the SST influence in nature, and facilitated evaluation of the basin contributions. We find the Atlantic SSTs to be especially influential in forcing multi-year droughts; often, more than the Pacific ones. The Atlantic Multidecadal Oscillation (AMO), in particular, contributed the most in two of the four reconstructed episodes (Dust Bowl Spring, 1980s fall wetness), accounting for almost half the precipitation signal in each case. The AMO influence on continental precipitation was provided circulation context from analysis of NOAA's 20th Century Atmospheric Reanalysis. A hypothesis for how the AMO atmospheric circulation anomalies are generated from AMO SSTs is proposed to advance discussion of the influence pathways of the mid-to-high latitude SST anomalies. Our analysis suggests that the La Nina–US Drought paradigm, operative on interannual time scales, has been conferred excessive relevance on decadal time scales in the recent literature.

Freshwater fish δ18O indicates a Messinian change of the precipitation regime in Central Africa

Tracking terrestrial environmental change throughout the Neogene is a challenge, notably in areas such as Central Africa where the few available data consist of a few vertebrate fossil assemblages. Here we aim to quantify the evolution of the δ 18 O of the main water body between four Neogene wet episodes in the Chad basin, ranging from the Late Miocene to the early Pliocene. The δ 18 O of the open water body was inferred from oxygen isotope measurements of phosphate in the apatite of open water fish tooth enamel. The more open the fish habitat, the lower the δ 18 O, as revealed by the teeth of the large tiger fish ( Hydrocynus ) sampled in the four available Chadian vertebrate fossiliferous areas, i.e., Toros-Menalla (anthracotherid unit), Kossom Bougoudi, Kolle, and Koro Toro, all located in the Djurab Desert (Chad) and dated at 7.04 ± 0.18 Ma, 5.26 ± 0.23 Ma, 3.96 ± 0.48 Ma, and 3.58 ± 0.27 Ma, respectively. The δ 18 O values increased by ∼2‰ between the two sites having ages that bracket the Messinian time period, and there was a slight increase of ∼0.6‰ difference between the three Pliocene sites. These results reflect unambiguously change in the water cycle in Central Africa during the late Neogene, interpreted as a constant drying trend between the four successive wet episodes registered in the Djurab and a shift during the Messinian.

Relationship between daily atmospheric circulation types and winter dry/wet spells in western Iran

AbstractAiming at better understanding the causes and processes leading to meteorological dry and wet episodes in western Iran, the present study investigates the space and time variability of winter dry/wet events and their associated large‐scale atmospheric driving circulations. Using monthly precipitation data of 140 weather stations for 1965–2000, meteorological dry/wet spells are assessed through the 1‐month Standardized Precipitation Index (SPI). By applying the Principal Component Analysis (PCA) with Varimax rotation to the SPI field, three sub‐regions of independent climatic variability are identified. Large‐scale daily atmospheric circulation patterns are then classified into twelve circulation types (CTs) by applying PCA to the 500 hPa geopotential height fields coupled with the non‐iterative K‐means clustering technique, in which extreme rotated principal component scores, in their positive and negative phases, are considered as potential groups and their centroids are computed by averaging all days that fulfil the extreme score criterion. The linkage between daily CTs and winter dry/wet spells in the region is investigated by correlating the frequencies of occurrence of each CT with the time series of dry/wet events, derived from both the rotated principal component scores of SPI and the SPI series at three representative stations of the identified sub‐regions. Severe/extreme events have also been considered. A performance index is applied to test the relationship between CTs and dry/wet events. Results show statistically significant correlations between the frequencies of occurrence of the identified CTs and of dry/wet spells at the three representative stations, suggesting that particular CTs are potential predictors for the winter dry/wet events in western Iran. Copyright © 2011 Royal Meteorological Society

A framework for Late Quaternary lake-level fluctuations in Lake Karakul, eastern Pamir, focusing on lake–glacier landform interaction

This paper presents a framework for Late Quaternary lake-level fluctuation in the closed-basin lake “Lake Karakul” (eastern Pamir) on the basis of the stereoscopic observation of remote sensing data, field mapping and relative dating. The palaeoshorelines (approximately 60 in number) observed around the Lake Karakul can be classified into four groups: H Shorelines, M Shorelines, L Shorelines and LL Shorelines (in the descending order of height). The highest level of each of the above palaeoshoreline groups is 205 m, 85 m, 35 m and 10 m above the present lake level (3915 m asl). From the glacial landform developments and related valley-fill sedimentation patterns around the threshold of the present basin closure, the lake-level fluctuation defined by these palaeoshoreline groups was found to be a consequence of the water balance change within the closed basin. With respect to the timing of the palaeolake highstands, the relationship between lacustrine terraces and terminal moraines suggests the synchroneity of the highest stand of each palaeolake with the corresponding maximum glacier advance. The tentative chronology of the lake-level fluctuation was established from the synthesis of the style of geomorphic development and related glaciation, relative dating on moraine gravels, and the correlations to established glacial histories in and around the Pamir. The periods of the palaeolake highstands indicated by H, M, L and LL shorelines seem to be correlated with the antepenultimate glacial (MIS 8), penultimate glacial (MIS 6), early last glacial (MIS 4) and the late last glacial (MIS 2) periods, respectively. Based on this chronology, each of the 60 palaeoshorelines are expected to show stable lake surfaces during lake regressive stages toward the terminations from the glacial maxima of MIS 8, 6, 4 and 2. Given that the distinct landforms of each palaeoshoreline group were formed in association with the predominant stagnation or small re-transgression of the palaeolake, the short-term cooling and/or wetter episodes, which turned positive lake hydrologic balances from negative ones, were superimposed on the major palaeoclimate changes during the glacial termination periods.

ENSO and solar activity signals from oxygen isotopes in diatom silica during late glacial-Holocene transition in Central Andes (18°S)

The late glacial-Holocene transition from the Lago Chungara sedimentary record in northern Chilean Altiplano (18°S) is made up of laminated sediments composed of light-white and dark-green pluriannual couplets of diatomaceous ooze. Light-white sediment laminae accumulated during short-term extraordinary diatom blooms whereas dark-green sediment laminae represent the baseline limnological conditions during several years of deposition. Diatom oxygen isotope ratios (δ18Odiatom) from 40 consecutive dark-green laminae, ranging from 11,990 to 11,450 cal year BP, show that a series of decadal-to-centennial dry–wet oscillations occurred. Dry periods are marked by relatively high isotope values whereas wet episodes are indicated by lower values. This interpretation agrees with the reconstructions of terrigenous inputs and regional effective moisture availability carried out in the lake but there is a systematic temporal disagreement between them owing to the non-linear response of the lacustrine ecosystem to environmental forcings. Furthermore, the δ18Odiatom record tracks effective moisture changes at a centennial scale. Three major phases have been established (11,990–11,800, 11,800–11,550, and 11,550–11,450 cal year BP). Each phase is defined by an increasing isotope trend followed by a sudden depletion. In addition, several wet and dry events at a decadal scale are superimposed onto these major trends. Spectral analyses of the δ18Odiatom values suggest that cycles and events could have been triggered by both El Nino-Southern Oscillation (ENSO) and solar activity. Significant ENSO frequencies of 7–9 years and 15–17 years, and periodicities of the solar activity cycles such as 11 years (Schwabe), 23 years (Hale) and 35 years (Bruckner) have been recognised in the oxygen isotope time series. Time–frequency analysis shows that although solar and ENSO forcing were present at the onset of the Holocene, they were more intense during the late glacial period. The early Holocene might have been mainly governed by La Nina-like conditions that correspond to wet conditions over the Andean Altiplano.

Dating Human Occupation on Diatom-Phytolith-Rich Sediment: Case Studies of Mustang Spring and Lubbock Lake, Texas, USA

The Great Plains of North America have a rich archaeological record that spans the period from Late Glacial to Historic times, a period that also witnessed significant changes in climate and ecology. Chronometric dating of archaeological sites in many areas of the Great Plains, however, is often problematic, largely because charcoal and wood—the preferred materials for radiocarbon dating—are scarce in this grassland environment with few trees. Two reference archaeological sites are studied here: Mustang Spring and Lubbock Lake, Texas, USA. We carry out a geochronological approach based on a cross-study of carbon-derived data: combustion yield, δ13C, 14C age differences between high temperature and low temperature released carbon, and the 14C age itself. A study that incorporates multiple approaches is required to solve issues induced by the sedimentological context, which is rich in both freshwater diatoms and phytoliths from quite different origins. Analysis of carbon-derived data allows us to draw a succession model of dry and wet episodes and to associate it with a chronological framework. In this way, we can assert that, for the Mustang Spring site, several human occupations existed from ∼11 kyr BP to ∼8.7 kyr BP along the 110-cm-long series with an interruption of ∼150 yr that is associated with a palustrine environment between the Plainview and Firstview occupations.

Variations of monsoonal precipitation over the last 16,000 years in the eastern Nanling Mountains, South China

A 350-cm-long sediment core was recovered from Dahu Swamp in the eastern Nanling Mountains in south China for paleoclimatic investigation. Twelve 14C dates determined on organic-rich bulk samples establish a chronological sequence for this core and yield a bottom age of ~16,000 cal years BP. Multiproxies including dry bulk density, magnetic susceptibility, organic carbon isotope, median grain size, silt-size fraction and total organic matter content were used to study variations of precipitation in relation to the East Asian monsoon. The core sediments are characterized by shifts between the lacustrine sediments and marshy sediments, implying hydrological variations between expansion and shrinkage of the water body in the swamp, and suggesting relatively wetter and drier conditions, respectively. Two relatively wetter episodes lasting from ~15,000 to 14,000 cal years BP and from ~13,500 to 12,800 cal years BP were revealed, possibly corresponding to the Bolling and the Allerod warming events, and three relatively drier phases occurred between ~16,000 and 15,000 cal years BP, between ~14,000 and 13,500 cal years BP and between ~12,800 and 11,500 cal years BP. The three events synchronize with the Oldest Dryas, the Older Dryas and the Younger Dryas cooling events, respectively. A distinctly humid period lasted from ~10,000 to 6,000 cal years BP in the early- and mid- Holocene was interpreted as the Holocene Optimum period. Several short dry events were revealed, including the most pronounced one at ~8,100 cal years BP that coincides with the “8,200 year” cooling event. Multiproxies indicate an evidently dry climate prevailing in the mid-Holocene (from ~6,000 to 3,000 cal years BP), reflecting a weakening of the East Asian summer monsoon. The general trend of Holocene climate shows agreement with the 25°N summer solar insolation, suggesting that the orbitally induced insolation have played a key role in the Holocene climate in south China.

The Western Libya Montes Valley System on Mars: Evidence for episodic and multi-genetic erosion events during the Martian history

A valley network in the Western Libya Montes region extending from 80°E to 83.4°E and 1.2°S to 3.9°N exhibits significant detail about water release processes and duration of erosional activities. The valley system originates at the southeastern offshoot of Syrtis Major and drains down to Isidis Planitia over a distance of about 300 km. Midstream, the valley network splits into a shorter eastern and a longer western part. For most of its length, the valley exhibits an interior channel which allows constraining discharges ranging from 15,000 m 3/s to 430,000 m 3/s and yielding sediment volumes up to 250 tons/s. Based on stratigraphic relations, the valley system evolved during a period of about 2.8 billion years with major wet episodes in the Noachian (< 4.1 Ga), the Hesperian (3.6 to 3.0 Ga) and the Amazonian (2.8 to 1.4 Ga). While precipitation dominated the fluvial activity during the Noachian era, as indicated by dendritic drainage pattern, the close correlation of lava deposits and valley source regions suggests that volcanic processes, such as ground ice melting and/or hydrothermal water release, might have played a major role during the Hesperian and Amazonian fluvial activities. In addition, multiple volcanic events in the Hesperian and Amazonian ages show that Syrtis Major was active, at least locally, until 1.4 Ga ago. Discharge estimates demonstrate a significant increase from precipitation-induced to volcanic-triggered water release. Fluvial erosion rates, discharges, sediment transport rates, and the lack of any widespread chemical alteration products, such as sulphates and phyllosilicates that are indicative for large long-lasting standing bodies of water, suggest relatively short valley formation times of only a few thousands of years. Compared with the total age of the valley system, short episodic water release events separated by long dry and inactive periods of some hundreds of millions of years, at least in the Hesperian and Amazonian, seem to be more realistic rather than a continuous flow. The youngest channel segment dates back to less than 1.4 Ga. This indicates the presence of surface runoff at that time, which required atmospheric conditions that support water to be stable on the surface even late in Martian history. In summary, the Western Libya Montes Valley System demonstrates episodic and multi-genetic erosion events over most of the Martian history, with a clear change in the erosion style from precipitation to volcanic-triggered water release during the early Hesperian.

Pentad Evolution of the 1988 Drought and 1993 Flood over the Great Plains: An NARR Perspective on the Atmospheric and Terrestrial Water Balance

Abstract The evolution of the atmospheric and land surface states during extreme hydroclimate episodes over North America is investigated using the North American Regional Reanalysis (NARR), which additionally, and successfully, assimilates precipitation. The pentad-resolution portrayals of the atmospheric and terrestrial water balance over the U.S. Great Plains during the 1988 summer drought and the July 1993 floods are analyzed to provide insight into the operative mechanisms including regional circulation (e.g., the Great Plains low-level jet, or GPLLJ) and hydroclimate (e.g., precipitation, evaporation, soil moisture recharge, runoff). The submonthly (but supersynoptic time scale) fluctuations of the GPLLJ are found to be very influential, through related moisture transport and kinematic convergence (e.g., ∂υ/∂y), with the jet anomalies in the southern plains leading the northern precipitation and related moisture flux convergence, accounting for two-thirds of the dry and wet episode precipitation amplitude. The soil moisture influence on hydroclimate evolution is assessed to be marginal as evaporation anomalies are found to lag precipitation ones, a lead–lag not discernible at monthly resolution. The pentad analysis thus corroborates the authors’ earlier findings on the importance of transported moisture over local evaporation in Great Plains’ summer hydroclimate variability. The regional water budgets—atmospheric and terrestrial—are found to be substantially unbalanced, with the terrestrial imbalance being unacceptably large. Pentad analysis shows the atmospheric imbalance to arise from the sluggishness of the NARR evaporation, including its overestimation in wet periods. The larger terrestrial imbalance, on the other hand, has its origins in the striking unresponsiveness of the NARR’s runoff, which is underestimated in wet episodes. Finally, the influence of ENSO and North Atlantic Oscillation (NAO) variability on the GPLLJ is quantified during the wet episode, in view of the importance of moisture transports. It is shown that a significant portion (∼25%) of the GPLLJ anomaly (and downstream precipitation) is attributable to NAO and ENSO’s influence, and that this combined influence prolongs the wet episode beyond the period of the instigating GPLLJ.

Historical fire and multidecadal drought as context for piñon–juniper woodland restoration in western Colorado

Fire is known to structure tree populations, but the role of broad-scale climate variability is less clear. For example, the influence of climatic "teleconnections" (the relationship between oceanic-atmospheric fluctuations and anomalous weather patterns across broad scales) on forest age structure is relatively unexplored. We sampled semiarid piñon-juniper (Pinus edulis-Juniperus osteosperma) woodlands in western Colorado, U.S.A., to test the hypothesis that woodland age structures are shaped by climate, including links to oceanic-atmospheric fluctuations, and by past fires and livestock grazing. Low-severity surface fire was lacking, as fire scars were absent, and did not influence woodland densities, but stand-replacing fires served as long-rotation (>400-600 years), stand-initiating events. Old-growth stands (>300 years old) were found in 75% of plots, consistent with a long fire rotation. Juniper and piñon age structures suggest contrasting responses during the past several centuries to dry and wet episodes linked to the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO). Juniper density increased slightly during periods of drought, positive (warm) AMO (after approximately 10-year lag), and negative (cool) PDO. In contrast, piñon populations may still be recovering from a long, drought-filled period (AD 1620-1820), with pulses of recovery favored during cool AMO, warm PDO, and above-average moisture periods. Analysis of 20th-century tree establishment and instrumental climate data corroborate the long-term relationships between age structure and climate. After Euro-American settlement (AD 1881), livestock grazing reduced understory grasses and forbs, reducing competition with tree seedlings and facilitating climate-induced increases in piñons. Thus tree populations in these woodlands are in flux, affected by drought and wet periods linked to oceanic-atmospheric variability, Euro-American livestock grazing, and long-rotation, high-severity fires. Reductions in livestock grazing levels may aid ecological restoration efforts. However, given long-term fluctuations in tree density and composition, and expected further drought, thinning or burning to reduce tree populations may be misdirected.

Combination Therapy With Desmopressin and an Anticholinergic Medication for Nonresponders to Desmopressin for Monosymptomatic Nocturnal Enuresis: A Randomized, Double-Blind, Placebo-Controlled Trial

Desmopressin is an approved medical therapy for the treatment of monosymptomatic primary nocturnal enuresis. In cases of limited response to desmopressin, we have added anticholinergic therapy to desmopressin (combination therapy). To evaluate this treatment strategy, we examined the efficacy of combination therapy for primary nocturnal enuresis in desmopressin-nonresponders. Only patients with primary nocturnal enuresis refractory to the maximal dosage of desmopressin were enrolled. Children with lower urinary tract symptoms or bowel dysfunction were excluded, on the basis of a 3-day, 24-hour, frequency-volume chart and elimination record. Children continued to take desmopressin and were assigned randomly, in a double-blind manner, to receive either extended-release anticholinergic medication or placebo. Patients were reassessed after 1 month of therapy, with a 1-week nocturnal record. Forty-one desmopressin-nonresponders were enrolled, and 7 patients were excluded because of noncompliance. The treatment groups were equally matched with respect to age, gender, functional bladder capacity, and number of wet nights per week. After 1 month of treatment, there was a significant reduction in the mean number of wet nights in the combination therapy group, compared with the placebo group. With a generalized estimating equation approach, there was a significant 66% decrease in the risk of a wet episode, compared with the placebo group. This study represents the first prospective, placebo-controlled trial examining the effect of desmopressin in combination with long-acting, anticholinergic, bladder-relaxing therapy for monosymptomatic primary nocturnal enuresis.

A humid corridor across the Sahara for the migration of early modern humans out of Africa 120,000 years ago.

It is widely accepted that modern humans originated in sub-Saharan Africa approximately 150-200 thousand years ago (ka), but their route of dispersal across the currently hyperarid Sahara remains controversial. Given that the first modern humans north of the Sahara are found in the Levant approximately 120-90 ka, northward dispersal likely occurred during a humid episode in the Sahara within Marine Isotope Stage (MIS) 5e (130-117 ka). The obvious dispersal route, the Nile, may be ruled out by notable differences between archaeological finds in the Nile Valley and the Levant at the critical time. Further west, space-born radar images reveal networks of-now buried-fossil river channels that extend across the desert to the Mediterranean coast, which represent alternative dispersal corridors. These corridors would explain scattered findings at desert oases of Middle Stone Age Aterian lithic industries with bifacial and tanged points that can be linked with industries further to the east and as far north as the Mediterranean coast. Here we present geochemical data that demonstrate that water in these fossil systems derived from the south during wet episodes in general, and penetrated all of the way to the Mediterranean during MIS 5e in particular. This proves the existence of an uninterrupted freshwater corridor across a currently hyperarid region of the Sahara at a key time for early modern human migrations to the north and out of Africa.

Mercury mobility in mine waste from Hg-mining areas in Almería, Andalusia (Se Spain)

Mining wastes and calcines from two abandoned mining areas (Valle del Azogue and Bayarque in Almería) have been characterized. In the mining wastes, the dominant mercury phases are cinnabar and elemental mercury in the matrix. In the calcines, however, the dominant mercury phase is elemental mercury bounded to the matrix. Water-leaching experiments were conducted on low-grade stockpiles and calcines in order to simulate the mobilization of mercury by runoff under environmental conditions. The laboratory column-leaching experiments show a possible mobilization of mercury from Hg 0 dissolution, colloid transport and a possible dissolution of calomel and other soluble phases in the mine wastes from the Valle del Azogue and Bayarque mines. Equilibrium speciation modeling of Hg, conducted using the numerical code MINTEQ, showed that the theoretical dominant mercury species in the calcine and mining wastes samples are Hg(OH) 2, HgCl 2, HgClOH and Hg 0. In some leachates obtained from the Valle del Azogue mining wastes (sample A06), the high Hg concentrations may indicate the possible dissolution of mineral phases such as calomel and other soluble phases, which are subsaturated. The environmental results indicate a great environmental mobility of mercury, especially during wet episodes associated with intense precipitation events, when there are significative amounts of secondary soluble minerals.