scholarly journals The Impacts of European and Asian Anthropogenic Sulfur Dioxide Emissions on Sahel Rainfall

2014 ◽  
Vol 27 (18) ◽  
pp. 7000-7017 ◽  
Author(s):  
Buwen Dong ◽  
Rowan T. Sutton ◽  
Ellie Highwood ◽  
Laura Wilcox
Keyword(s):  
Sulfur Dioxide ◽  
Atmospheric Circulation ◽  
North Africa ◽  
Land Surface ◽  
Hydrological Cycle ◽  
Boreal Summer ◽  
Second Phase ◽  
Sulfur Dioxide Emissions ◽  
Sahel Rainfall ◽  
Sahel Precipitation

Abstract In this study, the atmospheric component of a state-of-the-art climate model [the Hadley Centre Global Environment Model, version 2–Earth System (HadGEM2-ES)] has been used to investigate the impacts of regional anthropogenic sulfur dioxide emissions on boreal summer Sahel rainfall. The study focuses on the transient response of the West African monsoon (WAM) to a sudden change in regional anthropogenic sulfur dioxide emissions, including land surface feedbacks but without sea surface temperature (SST) feedbacks. The response occurs in two distinct phases: 1) fast adjustment of the atmosphere on a time scale of days to weeks (up to 3 weeks) through aerosol–radiation and aerosol–cloud interactions with weak hydrological cycle changes and surface feedbacks and 2) adjustment of the atmosphere and land surface with significant local hydrological cycle changes and changes in atmospheric circulation (beyond 3 weeks). European emissions lead to an increase in shortwave (SW) scattering by increased sulfate burden, leading to a decrease in surface downward SW radiation that causes surface cooling over North Africa, a weakening of the Saharan heat low and WAM, and a decrease in Sahel precipitation. In contrast, Asian emissions lead to very little change in sulfate burden over North Africa, but they induce an adjustment of the Walker circulation, which leads again to a weakening of the WAM and a decrease in Sahel precipitation. The responses to European and Asian emissions during the second phase exhibit similar large-scale patterns of anomalous atmospheric circulation and hydrological variables, suggesting a preferred response. The results support the idea that sulfate aerosol emissions contributed to the observed decline in Sahel precipitation in the second half of the twentieth century.

The Late Pleistocene-Holocene African Humid Period as Evident in Lakes

2017 ◽  
Author(s):  
Jonathan Holmes ◽  
Philipp Hoelzmann
Keyword(s):  
Northern Hemisphere ◽  
Ocean Circulation ◽  
North Africa ◽  
Land Surface ◽  
Climate Models ◽  
General Pattern ◽  
Rapid Change ◽  
Boreal Summer ◽  
Summer Insolation ◽  
Humid Period

From the end of the last glacial stage until the mid-Holocene, large areas of arid and semi-arid North Africa were much wetter than present, during the interval that is known as the African Humid Period (AHP). During this time, large areas were characterized by a marked increase in precipitation, an expansion of lakes, river systems, and wetlands, and the spread of grassland, shrub land, and woodland vegetation into areas that are currently much drier. Simulations with climate models indicate that the AHP was the result of orbitally forced increase in northern hemisphere summer insolation, which caused the intensification and northward expansion of the boreal summer monsoon. However, feedbacks from ocean circulation, land-surface cover, and greenhouse gases were probably also important.Lake basins and their sediment archives have provided important information about climate during the AHP, including the overall increases in precipitation and in rates, trajectories, and spatial variations in change at the beginning and the end of the interval. The general pattern is one of apparently synchronous onset of the AHP at the start of the Bølling-Allerød interstadial around 14,700 years ago, although wet conditions were interrupted by aridity during the Younger Dryas stadial. Wetter conditions returned at the start of the Holocene around 11,700 years ago covering much of North Africa and extended into parts of the southern hemisphere, including southeastern Equatorial Africa. During this time, the expansion of lakes and of grassland or shrub land vegetation over the area that is now the Sahara desert, was especially marked. Increasing aridity through the mid-Holocene, associated with a reduction in northern hemisphere summer insolation, brought about the end of the AHP by around 5000–4000 years before present. The degree to which this end was abrupt or gradual and geographically synchronous or time transgressive, remains open to debate. Taken as a whole, the lake sediment records do not support rapid and synchronous declines in precipitation and vegetation across the whole of North Africa, as some model experiments and other palaeoclimate archives have suggested. Lake sediments from basins that desiccated during the mid-Holocene may have been deflated, thus providing a misleading picture of rapid change. Moreover, different proxies of climate or environment may respond in contrasting ways to the same changes in climate. Despite this, there is evidence of rapid (within a few hundred years) termination to the AHP in some regions, with clear signs of a time-transgressive response both north to south and east to west, pointing to complex controls over the mid-Holocene drying of North Africa.

Hydroclimate and atmospheric circulation over North Africa through the last two climatic cycles reconstructed from dust deposited off West Africa

2021 ◽  
Author(s):  
Maxime Leblanc ◽  
Charlotte Skonieczny ◽  
Aloys Bory ◽  
Viviane Bout-Roumazeilles ◽  
Serge Miska ◽  
...  
Keyword(s):  
West Africa ◽  
Atmospheric Circulation ◽  
North Africa ◽  
Hydrological Cycle ◽  
Atmospheric Transport ◽  
Clay Mineralogy ◽  
Saharan Dust ◽  
Tropical Ocean ◽  
Transport Pathways ◽  
Dust Flux

<p>On glacial to interglacial time scales, northern Africa fluctuated between arid to hyperarid states and much wetter conditions called African Humid Periods (AHP). These AHP are characterized by a major transformation of the Saharan hydrological cycle, favoring the development of vast fluvial networks, tropical flora and fauna in a region previously hyperarid. In the present-day context of global warming, it is crucial to understand the environmental mechanisms and responses associated with these dramatic swings between two extreme climatic states in order to improve the climatic projections. Numerous studies have been focused on the last AHP, which occurred at the beginning of the Holocene and corresponds to a period when insolation - governed by precession – and obliquity both reached their maximum almost synchronously, thus complicating the distinction of their respective roles. The study of older AHP corresponding to different orbital configurations is likely to provide some answers. However, finding climatic archives allowing the reconstruction of past changes in the Saharan hydrological cycle on longer timescales remains challenging (e.g., discontinuity of continental archives, preservation of tracers…). In this study, we propose to circumvent this difficulty by studying the Saharan dust deposited in marine sediments of the northeastern Atlantic tropical ocean. In fact, past modifications of Saharan dust deposited off West Africa can provide precious information on changes in environmental conditions in their source areas (aridity, weathering), as well as on changes in the characteristics of their atmospheric transport (pathways and strength). Here, we present a unique high-resolution (1 sample/200yrs) multi-proxy characterization of the dust deposited continuously through the last 240ka - a period punctuated by eight AHP - in the marine core MD03-2705 (18°05N; 21°09W; 3085 mbsl) retrieved from a bathymetric dome, 300 meters above the surrounding seafloor. Considering this particular environmental setting, the terrigenous fraction in this record is assumed to be predominantly of eolian origin. We combine the <sup>230</sup>Th-normalized dust flux<sup>1</sup> together with grain-size distribution, clay mineralogy and geochemical compositions in order to explore changes in the Saharan hydroclimate and atmospheric circulation over North Africa on millennial to orbital timescales, with a particular focus on the mechanisms associated with the recurrence of the AHP.</p><p><sup>1</sup>Skonieczny et al., 2019 – Science Advances 5 (1) - eaav1887</p>

STUDY OF POND STATUS IN INDIA : A REVIEW

2017 ◽  
Vol 23 (1) ◽  
Author(s):  
V.K. YADAV ◽  
SONAM SHARMA ◽  
A.K. SRIVASTAVA ◽  
P.K. KHARE
Keyword(s):  
Fresh Water ◽  
Land Surface ◽  
Human Population ◽  
Climate Changes ◽  
Hydrological Cycle ◽  
Habitat Destruction ◽  
Conservation Strategy ◽  
Goods And Services ◽  
Human Use ◽  
Over Exploitation

Ponds are an important fresh water critical ecosystem for plants and animals providing goods and services including food, fodder, fish, irrigation, hydrological cycle, shelter, medicine, culture, aesthetic and recreation. Ponds cover less than 2 percent of worlds land surface. Ponds are important source of fresh water for human use. These are threatened by urbanization, industrialization, over exploitation, fragmentation, habitat destruction, pollution, illegal capturing of land and climate changes. These above factors have been destroying ponds very rapidly putting them in danger of extinction of a great number of local biodiversity. It is necessary to formulate a correct conservation strategy for pond restoration in order to meet the growing needs of fresh water by increasing the human population. Some measures have been compiled and proposed in the present review.

scholarly journals An LSWI-Based Method for Mapping Irrigated Areas in China Using Moderate-Resolution Satellite Data

2020 ◽  
Vol 12 (24) ◽  
pp. 4181
Author(s):  
Kunlun Xiang ◽  
Wenping Yuan ◽  
Liwen Wang ◽  
Yujiao Deng
Keyword(s):  
Land Surface ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Statistical Data ◽  
Spatial Information ◽  
Hydrological Cycle ◽  
Mainland China ◽  
Mean Annual Precipitation ◽  
Irrigated Area ◽  
Moderate Resolution

Accurate spatial information about irrigation is crucial to a variety of applications, such as water resources management, water exchange between the land surface and atmosphere, climate change, hydrological cycle, food security, and agricultural planning. Our study proposes a new method for extracting cropland irrigation information using statistical data, mean annual precipitation and Moderate Resolution Imaging Spectroradiometer (MODIS) land cover type data and surface reflectance data. The approach is based on comparing the land surface water index (LSWI) of cropland pixels to that of adjacent forest pixels with similar normalized difference vegetation index (NDVI). In our study, we validated the approach over mainland China with 612 reference samples (231 irrigated and 381 non-irrigated) and found the accuracy of 62.09%. Validation with statistical data also showed that our method explained 86.67 and 58.87% of the spatial variation in irrigated area at the provincial and prefecture levels, respectively. We further compared our new map to existing datasets of FAO/UF, IWMI, Zhu and statistical data, and found a good agreement with the irrigated area distribution from Zhu’s dataset. Results show that our method is an effective method apply to mapping irrigated regions and monitoring their yearly changes. Because the method does not depend on training samples, it can be easily repeated to other regions.

scholarly journals Impact of Desert Dust Radiative Forcing on Sahel Precipitation: Relative Importance of Dust Compared to Sea Surface Temperature Variations, Vegetation Changes, and Greenhouse Gas Warming

2007 ◽  
Vol 20 (8) ◽  
pp. 1445-1467 ◽  
Author(s):  
Masaru Yoshioka ◽  
Natalie M. Mahowald ◽  
Andrew J. Conley ◽  
William D. Collins ◽  
David W. Fillmore ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Sea Surface Temperature ◽  
North Africa ◽  
Radiative Forcing ◽  
Sea Surface ◽  
Desert Dust ◽  
Direct Radiative Forcing ◽  
Sahel Region ◽  
Precipitation Reduction ◽  
Sahel Precipitation

Abstract The role of direct radiative forcing of desert dust aerosol in the change from wet to dry climate observed in the African Sahel region in the last half of the twentieth century is investigated using simulations with an atmospheric general circulation model. The model simulations are conducted either forced by the observed sea surface temperature (SST) or coupled with the interactive SST using the Slab Ocean Model (SOM). The simulation model uses dust that is less absorbing in the solar wavelengths and has larger particle sizes than other simulation studies. As a result, simulations show less shortwave absorption within the atmosphere and larger longwave radiative forcing by dust. Simulations using SOM show reduced precipitation over the intertropical convergence zone (ITCZ) including the Sahel region and increased precipitation south of the ITCZ when dust radiative forcing is included. In SST-forced simulations, on the other hand, significant precipitation changes are restricted to over North Africa. These changes are considered to be due to the cooling of global tropical oceans as well as the cooling of the troposphere over North Africa in response to dust radiative forcing. The model simulation of dust cannot capture the magnitude of the observed increase of desert dust when allowing dust to respond to changes in simulated climate, even including changes in vegetation, similar to previous studies. If the model is forced to capture observed changes in desert dust, the direct radiative forcing by the increase of North African dust can explain up to 30% of the observed precipitation reduction in the Sahel between wet and dry periods. A large part of this effect comes through atmospheric forcing of dust, and dust forcing on the Atlantic Ocean SST appears to have a smaller impact. The changes in the North and South Atlantic SSTs may account for up to 50% of the Sahel precipitation reduction. Vegetation loss in the Sahel region may explain about 10% of the observed drying, but this effect is statistically insignificant because of the small number of years in the simulation. Greenhouse gas warming seems to have an impact to increase Sahel precipitation that is opposite to the observed change. Although the estimated values of impacts are likely to be model dependent, analyses suggest the importance of direct radiative forcing of dust and feedbacks in modulating Sahel precipitation.

Control of Sulfur Dioxide Emissions from Coal

Science ◽  
1975 ◽  
Vol 189 (4199) ◽  
pp. 253-253 ◽  
Author(s):  
P. H. Abelson
Keyword(s):  
Sulfur Dioxide ◽  
Sulfur Dioxide Emissions

scholarly journals Multi-source hydrological soil moisture state estimation using data fusion optimisation

2017 ◽  
Vol 21 (7) ◽  
pp. 3267-3285 ◽  
Author(s):  
Lu Zhuo ◽  
Dawei Han
Keyword(s):  
Soil Moisture ◽  
Data Fusion ◽  
Land Surface ◽  
Hydrological Cycle ◽  
Local Linear Regression ◽  
Data Sources ◽  
Superior Performance ◽  
Flood Prediction ◽  
Time To Build ◽  
Moisture State

Abstract. Reliable estimation of hydrological soil moisture state is of critical importance in operational hydrology to improve the flood prediction and hydrological cycle description. Although there have been a number of soil moisture products, they cannot be directly used in hydrological modelling. This paper attempts for the first time to build a soil moisture product directly applicable to hydrology using multiple data sources retrieved from SAC-SMA (soil moisture), MODIS (land surface temperature), and SMOS (multi-angle brightness temperatures in H–V polarisations). The simple yet effective local linear regression model is applied for the data fusion purpose in the Pontiac catchment. Four schemes according to temporal availabilities of the data sources are developed, which are pre-assessed and best selected by using the well-proven feature selection algorithm gamma test. The hydrological accuracy of the produced soil moisture data is evaluated against the Xinanjiang hydrological model's soil moisture deficit simulation. The result shows that a superior performance is obtained from the scheme with the data inputs from all sources (NSE = 0.912, r = 0.960, RMSE = 0.007 m). Additionally, the final daily-available hydrological soil moisture product significantly increases the Nash–Sutcliffe efficiency by almost 50 % in comparison with the two most popular soil moisture products. The proposed method could be easily applied to other catchments and fields with high confidence. The misconception between the hydrological soil moisture state variable and the real-world soil moisture content, and the potential to build a global routine hydrological soil moisture product are discussed.

scholarly journals Validation of a new SAFRAN-based gridded precipitation product for Spain and comparisons to Spain02 and ERA-Interim

2017 ◽  
Vol 21 (4) ◽  
pp. 2187-2201 ◽  
Author(s):  
Pere Quintana-Seguí ◽  
Marco Turco ◽  
Sixto Herrera ◽  
Gonzalo Miguez-Macho
Keyword(s):  
High Resolution ◽  
Land Surface ◽  
Climate Models ◽  
Hydrological Cycle ◽  
Interpolation Method ◽  
Rain Gauge ◽  
Surface Model ◽  
Low Resolution ◽  
Precipitation Events

Abstract. Offline land surface model (LSM) simulations are useful for studying the continental hydrological cycle. Because of the nonlinearities in the models, the results are very sensitive to the quality of the meteorological forcing; thus, high-quality gridded datasets of screen-level meteorological variables are needed. Precipitation datasets are particularly difficult to produce due to the inherent spatial and temporal heterogeneity of that variable. They do, however, have a large impact on the simulations, and it is thus necessary to carefully evaluate their quality in great detail. This paper reports the quality of two high-resolution precipitation datasets for Spain at the daily time scale: the new SAFRAN-based dataset and Spain02. SAFRAN is a meteorological analysis system that was designed to force LSMs and has recently been extended to the entirety of Spain for a long period of time (1979/1980–2013/2014). Spain02 is a daily precipitation dataset for Spain and was created mainly to validate regional climate models. In addition, ERA-Interim is included in the comparison to show the differences between local high-resolution and global low-resolution products. The study compares the different precipitation analyses with rain gauge data and assesses their temporal and spatial similarities to the observations. The validation of SAFRAN with independent data shows that this is a robust product. SAFRAN and Spain02 have very similar scores, although the latter slightly surpasses the former. The scores are robust with altitude and throughout the year, save perhaps in summer when a diminished skill is observed. As expected, SAFRAN and Spain02 perform better than ERA-Interim, which has difficulty capturing the effects of the relief on precipitation due to its low resolution. However, ERA-Interim reproduces spells remarkably well in contrast to the low skill shown by the high-resolution products. The high-resolution gridded products overestimate the number of precipitation days, which is a problem that affects SAFRAN more than Spain02 and is likely caused by the interpolation method. Both SAFRAN and Spain02 underestimate high precipitation events, but SAFRAN does so more than Spain02. The overestimation of low precipitation events and the underestimation of intense episodes will probably have hydrological consequences once the data are used to force a land surface or hydrological model.

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