Simulation of site-scale water fluxes in desert and natural oasis ecosystems of the arid region in Northwest China     

Mingjuan Xie  Geping Luo  Olaf Hellwich  Amaury Frankl  Wenqiang Zhang  Chunbo Chen  Chen Zhang  Philippe De Maeyer 《水文研究》2021,35(12):e14444

The study of water fluxes is important to better understand hydrological cycles in arid regions. Data-driven machine learning models have been recently applied to water flux simulation. Previous studies have built site-scale simulation models of water fluxes for individual sites separately, requiring a large amount of data from each site and significant computation time. For arid areas, there is no consensus as to the optimal model and variable selection method to simulate water fluxes. Using data from seven flux observation sites in the arid region of Northwest China, this study compared the performance of random forest (RF), support vector machine (SVM), back propagation neural network (BPNN), and multiple linear regression (MLR) models in simulating water fluxes. Additionally, the study investigated inter-annual and seasonal variation in water fluxes and the dominant drivers of this variation at different sites. A universal simulation model for water flux was built using the RF approach and key variables as determined by MLR, incorporating data from all sites. Model performance of the SVM algorithm (R² = 0.25–0.90) was slightly worse than that of the RF algorithm (R² = 0.41–0.91); the BPNN algorithm performed poorly in most cases (R² = 0.15–0.88). Similarly, the MLR results were limited and unreliable (R² = 0.00–0.66). Using the universal RF model, annual water fluxes were found to be much higher than the precipitation received at each site, and natural oases showed higher fluxes than desert ecosystems. Water fluxes were highest during the growing season (May–September) and lowest during the non-growing season (October–April). Furthermore, the dominant drivers of water flux variation were various among different sites, but the normalized difference vegetation index (NDVI), soil moisture and soil temperature were important at most sites. This study provides useful insights for simulating water fluxes in desert and oasis ecosystems, understanding patterns of variation and the underlying mechanisms. Besides, these results can make a contribution as the decision-making basis to the water management in desert and oasis ecosystems.  相似文献   

Latitudinal patterns of export production recorded in surface sediments of the Chilean Patagonian fjords (41–55°S) as a response to water column productivity     

Claudia Aracena  Carina B. Lange  José Luis Iriarte  Lorena Rebolledo  Silvio Pantoja 《Continental Shelf Research》2011,31(3-4):340-355

The Chilean Patagonian fjords region (41–56°S) is characterized by highly complex geomorphology and hydrographic conditions, and strong seasonal and latitudinal patterns in precipitation, freshwater discharge, glacier coverage, and light regime; all of these directly affect biological production in the water column. In this study, we compiled published and new information on water column properties (primary production, nutrients) and surface sediment characteristics (biogenic opal, organic carbon, molar C/N, bulk sedimentary δ¹³C_org) from the Chilean Patagonian fjords between 41°S and 55°S, describing herein the latitudinal pattern of water column productivity and its imprint in the underlying sediments. Based on information collected at 188 water column and 118 sediment sampling sites, we grouped the Chilean fjords into four main zones: Inner Sea of Chiloé (41° to ～44°S), Northern Patagonia (44° to ～47°S), Central Patagonia (48–51°S), and Southern Patagonia (Magellan Strait region between 52° and 55°S). Primary production in the Chilean Patagonian fjords was the highest in spring–summer, reflecting the seasonal pattern of water column productivity. A clear north–south latitudinal pattern in primary production was observed, with the highest average spring and summer estimates in the Inner Sea of Chiloé (2427 and 5860 mg C m^?2 d^?1) and Northern Patagonia (1667 and 2616 mg C m^?2 d^?1). This pattern was closely related to the higher availability of nutrients, greater solar radiation, and extended photoperiod during the productive season in these two zones. The lowest spring value was found in Caleta Tortel, Central Patagonia (91 mg C m^?2 d^?1), a site heavily influenced by glacier meltwater and river discharge loaded with glacial sediments. Biogenic opal, an important constituent of the Chilean fjord surface sediments (Si_OPAL ～1–13%), reproduced the general north–south pattern of primary production and was directly related to water column silicic acid concentrations. Surface sediments were also rich in organic carbon content and the highest values corresponded to locations far away from glacier influence, sites within fjords, and/or semi-enclosed and protected basins, reflecting both autochthonous (water column productivity) and allochthonous sources (contribution of terrestrial organic matter from fluvial input to the fjords). A gradient was observed from the more oceanic sites to the fjord heads (west–east) in terms of bulk sedimentary δ¹³C_org and C/N ratios; the more depleted (δ¹³C_org ?26‰) and higher C/N (23) values corresponded to areas close to rivers and glaciers. A comparison of the Chilean Patagonian fjords with other fjord systems in the world revealed high variability in primary production for all fjord systems as well as similar surface sediment geochemistry due to the mixing of marine and terrestrial organic carbon.  相似文献   

Do earthquake storms repeat in the Apennines of Italy?     

Claudio Chiarabba  Pasquale De Gori  Alessandro Amato 《地学学报》2011,23(5):300-306

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Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south-eastern Amazonia     

José Tasso Felix Guimarães  Prafulla Kumar Sahoo  Mariana Maha Jana Costa De Figueiredo  Karen da Silva Lopes  Markus Gastauer  Silvio Junio Ramos  Cecilio Frois Caldeira  Pedro Walfir M. Souza-Filho  Luiza Santos Reis  Marcio Sousa Da Silva  Paulo Rogenes Pontes  Renato Oliveira Da Silva Junior  Tarcísio Magevski Rodrigues 《第四纪科学杂志》2021,36(2):255-272

This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.  相似文献   

On Turbulent Fluxes During Strong Winter Bora Wind Events     

Nevio Babić  Željko Večenaj  Hrvoje Kozmar  Kristian Horvath  Stephan F. J. De Wekker  Branko Grisogono 《Boundary-Layer Meteorology》2016,158(2):331-350

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Will economic growth and fossil fuel scarcity help or hinder climate stabilization?     

Elmar Kriegler  Ioanna Mouratiadou  Gunnar Luderer  Nico Bauer  Robert J. Brecha  Katherine Calvin  Enrica De Cian  Jae Edmonds  Kejun Jiang  Massimo Tavoni  Ottmar Edenhofer 《Climatic change》2016,136(1):7-22

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Hybrid mafic dykes from Delwara Shear Zone,Mt. Abu,NW India     

Manoj K. Pandit  Ramona Dotzler  Helga De Wall 《Journal of the Geological Society of India》2016,87(1):35-42

Mafic dykes intrude the composite Mt. Abu granite batholith as a minor and the last phase of magmatism. The dykes are sub-vertical, variable in width and visibly compact, however, features of alteration and shearing can be seen. The dykes occurring within the recently identified and described, Delwara Shear Zone (DWSZ), from the western margin of the Mt. Abu batholith are intensely to moderately sheared and intricately mixed with the host granitoids. The mafic dykes occurring within the shear zone bear evidence of assimilating the host granitoids during their ascent, seen as relicts, streaks and sub-rounded K-feldspar clasts in mafic dykes. The hybridization has resulted in unusual geochemical signatures of the mafic dykes such as higher silica levels, erratic and high incompatible trace element abundances and lack of any systematic trends. Mixing line calculations on the mafic dyke samples reveal between 30 to 60% felsic input into the mafic dykes. Mafic dykes outside the shear zone in the Mt. Abu are meter scale in width and generally free of felsic inclusions owing to small volumes of mafic melts. Large volume of mafic melts are required for assimilating up to 60% felsic component which has been identified as approximately 100 m wide zone within the DWSZ. Shearing has played an important role in providing the channel ways and for sustained high temperatures to allow such hybridization.  相似文献   

Investigation of dominant modes of monsoon ISO in the northwest and eastern Himalayan region     

Sandipan Mukherjee  Srabanti Ballav  Sandeep Soni  Kireet Kumar  Utpal Kumar De 《Theoretical and Applied Climatology》2016,125(3-4):489-498

This study investigates the altitudinal variation of dominant modes of summer monsoon intra-seasonal oscillation (ISO) over the Northwest (NWH) and Eastern Himalayan (EH) region using (i) spatially scattered 133 number of station rainfall observations and (ii) latitudinal transect-wise (LT) rainfall variation, obtained from an observed interpolated gridded rainfall data for the period 1995–2004. The altitudinal variation of dominant modes of monsoon ISO were investigated by exploring the strong and weak phases of the principal components of 10–90 days bandpass rainfall data of June to September with respect to location specific station height. Investigation of frequency of days for light and moderate rainfall along with the occurrence of total seasonal rainy days has revealed existence of a rainfall maximum around 2100 m height for the NWH region. Similarly, the total seasonal rainy days of EH region was found to have maxima between 1100 and 1400 m height. Analyses of the spatially scattered station rainfall observation for the NWH region showed that the strong periods of ISO modes exist around 747.9 (±131.7) m and 2227.2 (±100.2) m heights. Over the EH region, the dominant modes of the monsoon ISO were found to be centred around 1200 m. Significant alterations of strong and weak phases of monsoon ISO as a response to altitudinal variation in the mountain surface were observed when latitudinal transect-wise variation of monsoon ISO modes were investigated.  相似文献   

A GCM investigation of dust aerosol impact on the regional climate of North Africa and South/East Asia     

Y. Gu  Y. Xue  F. De Sales  K. N. Liou 《Climate Dynamics》2016,46(7-8):2353-2370

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Climate change mitigation scenarios and policies and measures: the case of Kazakhstan     

Aiymgul Kerimray  Kanat Baigarin  Rocco De Miglio  Giancarlo Tosato 《Climate Policy》2016,16(3):332-352

This article illustrates the main difficulties encountered in the preparation of GHG emission projections and climate change mitigation policies and measures (P&M) for Kazakhstan. Difficulties in representing the system with an economic model have been overcome by representing the energy system with a technical-economic growth model (MARKAL-TIMES) based on the stock of existing plants, transformation processes, and end-use devices. GHG emission scenarios depend mainly on the pace of transition in Kazakhstan from a planned economy to a market economy. Three scenarios are portrayed: an incomplete transition, a fast and successful one, and even more advanced participation in global climate change mitigation, including participation in some emission trading schemes. If the transition to a market economy is completed by 2020, P&M already adopted may reduce emissions of CO₂ from combustion by about 85 MtCO₂ by 2030 – 17% of the emissions in the baseline (WOM) scenario. One-third of these reductions are likely to be obtained from the demand sectors, and two-thirds from the supply sectors. If every tonne of CO₂ not emitted is valued up to US$10 in 2020 and $20 in 2030, additional P&M may further reduce emissions by 110 MtCO₂ by 2030.  相似文献