Increase In Effective Precipitation Research Articles

Impacts of climate change on water footprint components of rainfed and irrigated wheat in a semi-arid environment.

Climate change is one of the biggest environmental challenges that significantly impact water resources and the quantity and quality of agricultural products. Assessment of these impacts during the historical period and under future climate is essential for achieving a sustainable agricultural system in the face of climate change threats and water scarcity. In this research, we evaluated the yield and water footprint of rainfed and irrigated wheat during the historical period (1986-2015) and two future periods (2016 to 2055) in a semi-arid environment in Fars province, Iran. The future climate data was selected from the CanESM2 model outputs (bias-corrected and downscaled using the SDSM model) under the RCP4.5 scenario, and the yield projection was made using the AquaCrop model. Our result showed that for both irrigated and rainfed wheat, the yield significantly increases in southern parts of the study area in future climates, primarily because of an increase in effective precipitation. Other regions will experience a marginal yield decrease or no yield changes (in the case of irrigated wheat). Our assessments of the water footprint of wheat production showed a significant reduction in green and blue water footprints in the southern regions. In other regions, various patterns emerged for irrigated and rainfed wheat, but an overall increase was observed. The southern regions of the study area will be more suitable for wheat production owing to the higher yield and lower water footprint.

Environmental and Biophysical Effects of the Bowen Ratio over Typical Farmland Ecosystems in the Loess Plateau

The Bowen ratio (β) comprehensively reflects physical characteristics of the land-surface climate. In this study, eddy covariance systems installed at Dingxi and Qingyang were used to conduct energy distribution measurements and observations characteristic of semi-arid and semi-humid farmland ecosystems on the China Loess Plateau. We studied mechanisms by which eco-environmental factors influence β. Additionally, we investigated responses of physiological and ecological factors to water and heat exchange under seasonally dry and wet conditions within each farmland ecosystem. Our results showed that sensible heat flux in the semi-arid farmland was the main consumer of available energy. In the semi-humid area, latent heat flux in summer had the dominant role in energy distribution (mean β 0.71). The β in the semi-arid region was 1.5 times higher than that in the semi-humid region during the growing season. β increased with an increase in the vapor pressure deficit (VPD) and ground–air temperature difference (Ts − Ta), and decreased significantly with an increase in effective precipitation and soil moisture. The change in β with environmental factors was more clear-cut in semi-arid areas than in semi-humid areas. The Priestley–Taylor coefficient (α) and β satisfied a power function law in the growing season. There was a strong correlation between them, with the coefficients of determination for semi-humid and semi-arid areas being 0.62 and 0.72, respectively. β decreased with an increase in the normalized difference vegetative index (NDVI), with this phenomenon being more obvious in the semi-humid zone (R2 = 0.40). β responded more rapidly to NDVI in the semi-arid area than in the semi-humid area. There was a negative exponential relationship between canopy stomatal conductance (Gs) and β, which displayed a stronger declining trend with the increase in Gs in the semi-arid area than in the semi-humid area. This study provides an important reference for the determination of land-surface characteristics of semi-arid and semi-humid farmland ecosystems on the Loess Plateau and for improving parameterization of land-surface processes.

N-Alkanes and compound carbon isotope records from Lake Yiheshariwusu in the Hulun Buir sandy land, northeastern China

The Hulun Buir sandy land in northern China is located at the northern limit region of the East Asian summer monsoon (EASM) and is therefore sensitive to the extension of the front of the rainfall belt. Here we report an n-alkane and compound-specific carbon isotope record from the Holocene sediments of Lake Yiheshariwusu in the middle of the Hulun Buir sandy land. The sediments contain a suite of n-alkanes with a strong odd over even carbon number predominance, with the maximum contribution from nC31, which is a typical distribution in grassland regions. The low temperatures in this cold region greatly limit the growth of C4 plants and thus the long-chain n-alkanes in lake sediments are mainly derived from leaf wax lipids of C3 plants growing within the sandy land. In this C3-vegetation-dominated region, the δ13C27–33 value (weighted carbon isotope values of nC27– nC33) are regulated mainly by the physiological and biochemical responses of plants to water stress and are therefore interpreted as a proxy of effective precipitation or humidity. The δ13C27–33 time series shows a trend of gradually decreasing values that suggests an increase in effective precipitation since 8.5 ka (1 ka = 1000 cal yr BP). Relative droughts occurred during the intervals of 6.3–5.5, 4.1–3.6 ka, and during the last 200 years. In addition, the δ13C27–33 time series and comparable paleoenvironmental records from neighboring sites suggest opposite trends of summer monsoon rainfall between northeastern and southeastern China. We suggest that a coupled process between low and high latitudes (the western Pacific Subtropical High and the Okhotsk High) may have played a fundamental role in regulating the shift of the frontal rainfall belt and monsoon rainfall distribution in eastern China during the Holocene.

Predictable hydrological and ecological responses to Holocene North Atlantic variability

Climate variations in the North Atlantic region can substantially impact surrounding continents. Notably, the Younger Dryas chronozone was named for the ecosystem effects of abrupt changes in the region at circa (ca.) 12.9-11.7 ka (millennia before 1950 AD). Holocene variations since then, however, have been hard to diagnose, and the responsiveness of terrestrial ecosystems continues to be debated. Here, we show that Holocene climate variations had spatial patterns consistent with changes in Atlantic overturning and repeatedly steepened the temperature gradient between Nova Scotia and Greenland since >8 ka. The multicentury changes correlated with hydrologic and vegetation changes in the northeast United States, including when an enhanced temperature gradient coincided with subregional droughts indicated by water-level changes at multiple coastal lakes at 4.9-4.6, 4.2-3.9, 2.8-2.1, and 1.3-1.2 ka. We assessed the variability and its effects by replicating signals across sites, using converging evidence from multiple methods, and applying forward models of the systems involved. We evaluated forest responses in the northeast United States and found that they tracked the regional climate shifts including the smallest magnitude (∼5% or 50 mm) changes in effective precipitation. Although a long-term increase in effective precipitation of >45% (>400 mm) could have prevented ecological communities from equilibrating to the continuously changing conditions, our comparisons confirm stable vegetation-climate relationships and support the use of fossil pollen records for quantitative paleoclimate reconstruction. Overall, the network of records indicates that centennial climate variability has repeatedly affected the North Atlantic region with predictable consequences.

Global peatland initiation driven by regionally asynchronous warming

Widespread establishment of peatlands since the Last Glacial Maximum represents the activation of a globally important carbon sink, but the drivers of peat initiation are unclear. The role of climate in peat initiation is particularly poorly understood. We used a general circulation model to simulate local changes in climate during the initiation of 1,097 peatlands around the world. We find that peat initiation in deglaciated landscapes in both hemispheres was driven primarily by warming growing seasons, likely through enhanced plant productivity, rather than by any increase in effective precipitation. In Western Siberia, which remained ice-free throughout the last glacial period, the initiation of the world's largest peatland complex was globally unique in that it was triggered by an increase in effective precipitation that inhibited soil respiration and allowed wetland plant communities to establish. Peat initiation in the tropics was only weakly related to climate change, and appears to have been driven primarily by nonclimatic mechanisms such as waterlogging due to tectonic subsidence. Our findings shed light on the genesis and Holocene climate space of one of the world's most carbon-dense ecosystem types, with implications for understanding trajectories of ecological change under changing future climates.

Correlation of satellite image time-series for the detection and monitoring of slow-moving landslides

Slow-moving landslides are widespread in many landscapes with significant impacts on the topographic relief, sediment transfer and human settlements. Their area-wide mapping and monitoring in mountainous terrain, however, is still challenging. The growing archives of optical remote sensing images offer great potential for the operational detection and monitoring of surface motion in such areas. This study proposes a multiple pairwise image correlation (MPIC) technique to obtain a series of redundant horizontal displacement fields, and different multi-temporal indicators for a more accurate detection and quantification of surface displacement. The technique is developed and tested on a series of monoscopic and stereoscopic Pléiades satellite images at a test site in the South French Alps. Empirical tests confirm that MPIC significantly increased detection accuracy (F−measure=0.85) and that the measurement error can be reduced by averaging velocities from all pair combinations covering a given time-step (i.e. when stereo-pairs are available for at least one date). The derived inventory and displacement fields of 169 slow-moving landslides show a positive relationship between the landslide size and velocities, as well as a seasonal acceleration of the largest landslides in response to an increase in effective precipitation. The processing technique can be adapted to better exploit increasingly available time-series from a variety of optical satellites for the detection and monitoring of landslide displacement.

Holocene freshwater wetland and mangrove dynamics in the eastern Kimberley, Australia

ABSTRACTIn 1990, the freshwater wetlands and mangroves near Wyndham, north‐west Australia, were Ramsar‐listed due to their ecological importance. To understand wetland formation and stability over time, two sediment cores from the King River and one from the Parry Lagoons wetlands were analysed using sedimentological and palynological techniques. During postglacial sea‐level rise, mangroves extended across all sites and were supported by enhanced freshwater input. Between 7.4 and 6.3k cal a BP the mangrove forest contracted, probably driven by sea‐level stabilization, and hypersaline mudflats, reflecting the onset of drier climatic conditions, developed along the King River. After 6.3k cal a BP mangrove diversity declined, probably linked to peak dryness around 4k cal a BP. The Parry Lagoons wetlands are at least approx. 600 years old and their development is probably related to an increase in effective precipitation since approx. 1k cal a BP. The region's mangroves could be considered relatively stable under changing climate as they are still present today, although reduced in biodiversity and areal extent. The early phases of development of the Parry Lagoons freshwater systems cannot be resolved but given the character of these wetlands, freshwater input appears to be the vital driver of ecosystem functioning.

Paleoclimate evolution since 27. 7kaBP reflected by grain size variation of a sediment core from Lake Xingkai,northeastern Asia

结合孢粉分析,对兴凯湖-根长269cm的沉积岩芯研究表明:沉积物粒度分布特征可以较好地反映区域气候变化,即粗粉砂和砂增多对应于降水减少的低湖面时期,细粉砂增多对应于降水增加的高湖面时期,而粘土增加则对应于气候干燥的静水沉积环境。约27740-25540cal aBP时期,沉积物颗粒较粗,湖区处于低湖面的冷干气候;而随后25540-23650 cal aBP时期,中粉砂增加,粘土较少,分选性较好,湖区处于冷湿气候环境23650-19940cal aBP阶段,湖面封冻期长,沉积物粘土较多,湖区气候冷干,对应于末次盛冰期。19940-14510cal aBP阶段,细粉砂增加,比前期降水增多,温度也有所升高。14510-10800cal aBP时期,本地区进入晚冰期,沉积物粒径波动频繁,依次出现较高含量的细粉砂-粗粉砂-粘土阶段,反映了暖湿到干燥的气候变化,对应于北欧的Bölling/Older Dryas/Alleröd/Younger Dryas气候波动期。10800-1050cal aBP,总体上沉积物粒径变化不大,中粗粉砂含量基本保持低值,细粉砂逐渐增加,粘土逐渐减少,显示深水稳定沉积环境,降水逐渐增多,处于全新世暖湿期;其中8330-7000cal aBP阶段,粗颗粒迅速增加较多,对应于8.2 cal kaBP冷事件。约1050cal aBP以来,沉积物中值粒径大幅度增加,湖面水位下降幅度较大,气候变凉干,也反映了人类活动增强造成水土流失加剧。;Lake Xingkai,a boumlary lake between China and Russia, is the largest freshwater lake in Northeast Asia. The pale climate variation since 27.7kaBP was reconstmcted based on a 269cm-long sediment core in Lake Xingkai. The chronology wasmeasured by ²¹⁰Pb and ¹³⁷Cs activities and AMS¹⁴C dating. Grain size distribution of the lake sediment was inferred to he a proxyfor past precipitation, compared to pollen analysis. The high percentage of coarse sill and hi Md values reflect a low lake level,and increase in fine silt indicating plentiful precipitation and the high clay content correspond to cold dry climate. the results showthat: It was in cold-dry between 27740 and 25540 cal aBP, when lake level was low, as indicated by high Md values and coarsesilt contents of the lake sediments. During 25540 and 23650 cal aBP, the sediments was characterized by low clay content, mark-ing a significant increase in effective precipitation in cold wet climate. The Last Glacial Maximum between 23650 and 19940cal aBP was marked by high content of clay because of the frozen lake surface, corresponding to especially cold-dry. From 19940to 14510 cal aBP, precipitation increased when fine silt content increased. The Ilucluating characteristics of the sediments grainsize indicated that precipitation increased first and decreased finally during 14510 and 10800 cal aBP, corresponding to Bolling/OI-der Dryas/Allerod/Younger Dryas periods. From 10800 to 1050 cal aBP, lake level rose evidently suggested by higher content offine silt when the precipitation was relatively abundant in Holocene, in which 90-78m section shows that the sand and coarse siltcontent increased sharply, indicating that the lake level experienced a rapidly decline because of cold-dry climate around the 8. 2kaBP. Since 1105 cal aBP, the portion of sand and coarse silt increased markedly, reflecting low lake level under a cool-dry climate,oompanied with remarkable increase in soil erosion and terrestrial material into lake possibly related with local human activities.

A Late Holocene Vegetation and Environment Record from Byenup Lagoon, South-western Australia

South-western Australia has a Mediterranean-type climate and its infertile soils support a highly diverse angiosperm flora. Little is known of the vegetation history of this region, and this means that little can be said of the roles of environmental stability, climate change, or human impact on the maintenance or development of the high biodiversity of the region. This study presents a pollen and fossil charcoal record from two peat profiles from a freshwater lagoon region near Lake Muir, east of Manjimup, in south-western Australia. The record shows a glimpse of an early Holocene where a mix of Casuarina and eucalypts with an understorey of heath and some open herbaceous vegetation, including chenopods, occurred. Fire was not an important factor at this time. The main record begins from about 4800 BP, and shows a vegetation mix of Corymbia calophylla and Eucalyptus marginata, with the latter becoming dominant by about 3500 BP. Corymbia calophylla again becomes prominent in the last few centuries. A heathy understorey is present throughout the last 4800 years, but was apparently less dense during phases when C. calophylla was more prominent. Melaleuca woodland has been the main vegetation type around the wetland areas and areas of inundation since the mid-Holocene. Major fire periods at Byenup, around 4200 BP and between about 3000 and 2000 BP, did not result in major vegetation changes. An analysis of cation content in the sediments suggests that weathering and erosion rates have been relatively stable throughout the record, but an increase in phosphorus and possibly organic matter in the surface layers suggests that agricultural practices have led to changes in the chemistry of sediments. It is hypothesised that an increase in effective precipitation about 4800 BP led to the initiation of the continuous part of the sediment record at Byenup. This increase most likely resulted from a more effective westerly wind stream. Changes since this time are more likely a result of changing fire regime and the interaction of species, rather than climate shifts.

The palaeoecology of a treed bog in western boreal Canada: a study based on microfossils, macrofossils and physico-chemical properties

The developmental histories of a wetland and the surrounding upland vegetation in the southern boreal region of western Canada are traced through microfossil, macrofossil, physico-chemical and radiometric analyses of a 425 cm deep core consisting of sandy gyttja and peat. Microfossil analysis includes algal, fungal and zoological ‘Types’ which are illustrated and described, with notes on their occurrence as observed in several peat sequences of western boreal Canada. Local wetland development started in the central area of a 65 ha closed depression at c. 5000 BP, due to a rise in the groundwater table related to a gradual increase in effective precipitation in the region. Initial stages were characterised by Typha-dominated marsh communities that suggest marked seasonal fluctuations in local water levels. The accumulation of organic matter could not keep pace with the ever-rising groundwater table, and a shallow eutrophic pond with aquatic macrophytes developed locally. The body of open water was surrounded by marsh vegetation that was gradually being displaced towards the margins of the depression. At 4330 BP moist conditions became prevalent throughout the growing season. A brown-moss dominated treed rich fen replaced the shore marsh community and gradually began to encroach on the small pond. The basin completely terrestrialised at 3260 BP. Autogenic processes caused by peat accumulation resulted in a transition towards a Sphagnum-dominated treed poor fen. At 2790 BP a treed bog became established, firstly dominated by Sphagnum angustifolium and S. magellanicum indicating moist local conditions. After 1870 BP S. fuscum became dominant, indicating drier conditions locally. The upland vegetation just before local wetland formation was characterised by Picea in relatively wet depressions and by Populus in drier areas. Some grassland patches were present, most probably on the more southerly exposed slopes of the hills. Picea was locally displaced by wetland vegetation at c. 5000 BP, whereas deciduous forest and some grassland stands continued to dominate the surrounding hills. The coniferous taxa Pinus and Picea began to invade the uplands after 4330 BP, contemporaneously with the development of the local peatland. This marks the time at which the modern southern boreal ecosystem dominated by peatlands in lowlands and mixed wood forest in uplands became established in the area.

A comparison of postglacial arcellacean (“Thecamoebian”) and pollen succession in Atlantic Canada, illustrating the potential of arcellaceans for paleoclimatic reconstruction

Cores dating back to deglaciation were taken from three lakes in Atlantic Canada and analyzed for arcellaceans and pollen. Paleotemperatures and paleo-precipitation were calculated from the pollen data using transfer functions. A sudden warming is recorded by the pollen around 10,000 years B.P., followed by a general warming to the mid Holocene Hypsithermal, then by a decrease in temperature and increase in effective precipitation to the present. The three lakes, two in western Newfoundland and one in eastern Nova Scotia, contain similar late glacial (13-10 ka), early Holocene (10-8 ka), mid Holocene (8-4 ka), and late Holocene (4-0 ka) arcellacean assemblages. Immediately following retreat of the ice sheets,Centropyxis aculeata, Centropyxis constricta, Difflugia oblonga, Difflugia urceolata, andDifflugia coronawere common. The latter part of the late glacial is characterized by sparse assemblages dominated byC. aculeata.The arcellacean record thus suggests a climatic reversal in Atlantic Canada between 11,500 and 10,000 years B.P., analogous to the Younger Dryas, although this is not recorded by the pollen. Species diversity increased sharply at the beginning of the Holocene, andD. oblongais the dominant taxon in early Holocene sediments.Difflugia oblongaremained common through the mid Holocene, but percentages ofC. aculeatawere very low, andPontigulasia compressaandDifflugia bacilliferapeaked in abundance during the Hypsithermal. The late Holocene is characterized by a resurgence inC. aculeataat the expense of other taxa. The increase inHeleopera sphagniandNebella collarissince 5,000 years B.P. at the two sites in southwestern Newfoundland reflects paludification in response to increased precipitation since the Hypsithermal. Because the changes in arcellacean assemblages are regionally synchronous in all three lakes and coincide with climatically driven vegetational successions indicated by the pollen record, arcellaceans appear to respond to climatic change, and thus may be useful paleoecological and paleolimnological indicators. With their quicker generation time, these protists may be better suited than pollen to recording short-lived phenomena, like the mid-Holocene Hypsithermal and the Younger Dryas reversal.

Pollen evidence from tropical Australia for the onset of an ENSO-dominated climate at c. 4000 BP

The Holocene climatic history of tropical northern Australia is re-examined using the recently published pollen record from Groote Eylandt to corroborate and refine previous climatic inter pretations. We identify a four-stage Holocene comprising: (1) a continuous increase in effective precipitation (EP) from the beginning of the Holocene to about 5000 BP; (2) a mid-Holocene EP maximum from about 5000 to about 4000 BP; (3) a marked decline in EP somewhere between 4000-3500 Bp; and (4) an EP recovery in the last <2000 years. The mid-Holocene EP maximum is 1000 years later than Holocene EP maxima from temperate Southern Australia and suggests that the records are decoupled at this time. We focus on pollen evidence of environmental change at c. 4000 BP, which marks a break between a continuously ameliorating (increasing EP) climate but with small mean variation in the earlier Holocene and a steady (no directional trend) but highly variable later Holocene. We believe that this break represents the first evidence from the monsoonal lowlands of northern Australia for the onset of 'modern' ENSO-dominated ocean-atmosphere interactions in the Holocene. A simple conceptual model of trans-Pacific teleconnections is presented to explain this onset and as an hypothesis for testing.

A 12 000‐Year Record of Forest History form Cahaba Pond, St. Clair County, Alabama

A 650—cm sediment sequence from Cahaba Pond, St. Clair County, Alabama spans the past 12 000 yr and has yielded a pollen and plant—macrofossil record indicating major changes in forest composition during the Holocene interglacial. Both pollen and plant macrofossils from sediments of this 0.2—ha pond primarily reflect changes in local and extralocal forests within the surrounding watershed. Four distinct pollen assemblage zones were recognized: a Fagus—Ostrya zone from 12 000 to 10 200 BP, a Pinus—Magnolia zone from 10 200 to 10 000 BP, a Quercus—Carya zone from 10 000 to 8400 BP, and a Nyssa—Pinus zone from 84 BP to the present. Forests of the early Holocene (12 000 to 10 000 BP) were mesic and predominantly composed of broadleaved deciduous trees, dominated by beech (Fagus grandifolia) and with substantial representation of hornbeam (Ostrya/Carpinus), oak (Quercus), hickory (Carya), elm (Ulmus), and ash (Fraxinus). Atlantic white cedar (Chamaecyparis thyoides), today a coastal species, extended inland to St. Clair County during the early Holocene. Eastern white pine (Pinus strobus), hemlock (Tsuga), striped maple (Acer pensylvanicum), and mountain maple (Acer spicatum), today rare or absent in Alabama, extended southward of their present ranges into central Alabama 10 000 yr ago. Outliers of mixed, mesic hardwood communities in the southern Ridge and Valley and Piedmont provinces may be relicts that date from the early Holocene, a time with high species richness and equable climate. After 10 000 BP, forests became more xeric, with oaks and hickories predominant. Cahaba Pond, formerly dominated by submersed aquatics such as Najas gracillima, became shallower, and floating—leaved and emergent aquatics became abundant. A decrease in effective precipitation is inferred for the time period between 10 0000 and 8400 BP. After 8400 BP, black gum (Nyssa sylvatica), southern pines (Diploxylon Pinus), red maple (Acer rubrum), sweetgum (Liquidambar styraciflua), buttonbush (Cephalanthus occidentalis), and other elements of the modern flora became established locally. Water levels in the pond became higher, and sedimentation rate diminished, as observed in other pond sites in the region. An increase in effective precipitation in the late Holocene reflects the establishment of the modern atmospheric circulation patterns, including increased frequency of hurricanes developing in the Gulf of Mexico and the equatorial Atlantic Ocean.

A POLLEN DIAGRAM FROM QUINCAN CRATER, NORTH‐EAST QUEENSLAND, AUSTRALIA

SummaryPollen analytical results from the organic sediments of Quincan Crater broadly confirm the sequence of vegetation changes indicated in a previous study at Lake Euramoo. Only the later stage of the transition from sclerophyll vegetation to ‘warm temperate’ rain forest, culminating about 6000 B.P., is represented at Quincan, but indicates that the change was most probably due to an increase in effective precipitation. Afterwards rain forest remained the principal vegetation type for 3000 or 4000 years but changed from the initial ‘warm temperate’ to a ‘subtropical’ kind probably as a result of an increase in temperature and possibly also of precipitation. At about 2000 B.P. the ‘subtropical’ rain forest assumed a ‘drier’ facies and there was a partial readvance of the sclerophyll vegetation.