Author: Erik HoltslagPublisher:
ISBN:
Category :
Languages : en
Pages : 33
Book Description
Land-atmosphere Interactions and Sahelian Rainfall
Author: Erik HoltslagStatistical and Dynamical Assessment of Land-ocean-atmosphere Interactions Across North Africa
Author: Yan YuPublisher:
ISBN:
Category :
Languages : en
Pages : 272
Book Description
North Africa is highly vulnerable to hydrologic variability and extremes, including impacts of climate change. The current understanding of oceanic versus terrestrial drivers of North African droughts and pluvials is largely model-based, with vast disagreement among models in terms of the simulated oceanic impacts and vegetation feedbacks. Regarding oceanic impacts, the relative importance of the tropical Pacific, tropical Indian, and tropical Atlantic Oceans in regulating the North African rainfall variability, as well as the underlying mechanism, remains debated among different modeling studies. Classic theory of land-atmosphere interactions across the Sahel ecotone, largely based on climate modeling experiments, has promoted positive vegetation-rainfall feedbacks associated with a dominant surface albedo mechanism. However, neither the proposed positive vegetation-rainfall feedback with its underlying albedo mechanism, nor its relative importance compared with oceanic drivers, has been convincingly demonstrated up to now using observational data. Here, the multivariate Generalized Equilibrium Feedback Assessment (GEFA) is applied in order to identify the observed oceanic and terrestrial drivers of North African climate and quantify their impacts. The reliability of the statistical GEFA method is first evaluated against dynamical experiments within the Community Earth System Model (CESM). In order to reduce the sampling error caused by short data records, the traditional GEFA approach is refined through stepwise GEFA, in which unimportant forcings are dropped through stepwise selection. In order to evaluate GEFA's reliability in capturing oceanic impacts, the atmospheric response to a sea-surface temperature (SST) forcing across the tropical Pacific, tropical Indian, and tropical Atlantic Ocean is estimated independently through ensembles of dynamical experiments and compared with GEFA-based assessments. Furthermore, GEFA's performance in capturing terrestrial impacts is evaluated through ensembles of fully coupled CESM dynamical experiments, with modified leaf area index (LAI) and soil moisture across the Sahel or West African Monsoon (WAM) region. The atmospheric responses to oceanic and terrestrial forcings are generally consistent between the dynamical experiments and statistical GEFA, confirming GEFA's capability of isolating the individual impacts of oceanic and terrestrial forcings on North African climate. Furthermore, with the incorporation of stepwise selection, GEFA can now provide reliable estimates of the oceanic and terrestrial impacts on the North African climate with the typical length of observational datasets, thereby enhancing the method's applicability. After the successful validation of GEFA, the key observed oceanic and terrestrial drivers of North African climate are identified through the application of GEFA to gridded observations, remote sensing products, and reanalyses. According to GEFA, oceanic drivers dominate over terrestrial drivers in terms of their observed impacts on North African climate in most seasons. Terrestrial impacts are comparable to, or more important than, oceanic impacts on rainfall during the post-monsoon across the Sahel and WAM region, and after the short rain across the Horn of Africa (HOA). The key ocean basins that regulate North African rainfall are typically located in the tropics. While the observed impacts of SST variability across the tropical Pacific and tropical Atlantic Oceans on the Sahel rainfall are largely consistent with previous model-based findings, minimal impacts from tropical Indian Ocean variability on Sahel rainfall are identified in observations, in contrast to previous modeling studies. The current observational analysis verifies model-hypothesized positive vegetation-rainfall feedback across the Sahel and HOA, which is confined to the post-monsoon and post-short rains season, respectively. However, the observed positive vegetation feedback to rainfall in the semi-arid Sahel and HOA is largely due to moisture recycling, rather than the classic albedo mechanism. Future projections of Sahel rainfall remain highly uncertain in terms of both sign and magnitude within phases three and five of the Coupled Model Intercomparison Project (CMIP3 and CMIP5). The GEFA-based observational analyses will provide a benchmark for evaluating climate models, which will facilitate effective process-based model weighting for more reliable projections of regional climate, as well as model development.
Quantification of Land-atmosphere Coupling and Implications for Drought Persistence in Observations and Model Simulations of 20th Century Climate and 21st Century Climate Change
Author: Erica E. BickfordThe Role of Land-atmosphere-ocean Interactions in Rainfall Variability Over West Africa
Author: Cuiling GongLand, Investment, and Migration
Author: Camilla ToulminPublisher: Oxford University Press
ISBN: 019259429X
Category : Business & Economics
Languages : en
Pages : 272
Book Description
How do people survive and thrive in the uncertain and risk-prone Sahel? Land, Investment, and Migration seeks to answer this question through a long-term study of the people of Dlonguébougou in Central Mali. It uses a combination of infographics, satellite images, interviews, and survey data to present the strategies and fortunes of individuals and their families in this region over 35 years. In the early 1980s Camilla Toulmin spent two years in Dlonguébougou. She has since revisited to explore how climate change, population growth, new technologies, and land-grabs have been affecting the livelihoods and prospects of local people since. Land, Investment, and Migration: Thirty-five Years of Village Life in Mali brings together her findings. A trebling in population, unpredictable rainfall, and the arrival of Chinese investment have forced people into new ways of making ends meet and building up wealth - some doing much better than others. This book presents the search for new cash incomes, the shift of people from village to town, and the erosion of collective solidarity at household and village levels. Land, Investment, and Migration presents a mixed picture of a changing society. It shows the vibrancy of the village economy, rapid uptake of mobile phones and solar panels, and increased migration. It also shows the persistence of large family structures which offer some protection from the risks that many villagers face.
The Impact of Climate Variability and Land Cover Change on Land Surface Conditions in North-eastern Nigeria
Author: Umar Muhammed BibiModeling of Orographic Precipitation with Multilevel Coupling of Land-atmosphere Interactions
Author: Ana Paula BarrosPublisher:
ISBN:
Category : Atmospheric circulation
Languages : en
Pages : 412
Book Description
Land Surface-Atmosphere Interaction
Author: Marika KoukoulaPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
Precipitation-driven hydrometeorological hazards such as floods, droughts, and landslides have significant socioeconomic impacts. Understanding the complex interaction of precipitation with land surface processes and climate characteristics is, therefore, imperative for improving predictability of these extreme events. Soil moisture is an important hydrological state variable playing a crucial role in land-atmosphere interactions as it affects both precipitation and runoff generation. In this work we investigate the impact of soil moisture uncertainty on simulated precipitation from Numerical Weather Prediction models under different climate and meteorological conditions. We then assess the combined effects of soil moisture on precipitation and the antecedent wetness conditions of the basin on the rainfall-to-runoff transformation process driving the catchment flood response under different basin scales and meteorological conditions. The study elucidate the complexity of the relationship between soil moisture and precipitation, suggesting that the control of soil water content on partitioning land surface heat fluxes has significant impacts on both the magnitude and spatial distribution of simulated precipitation. Results indicate different characteristics of the soil moisture-precipitation relationship during the cold and warm periods and under different climate and meteorological conditions. It is also shown that soil moisture affects runoff directly, changing the saturation level of the soil, and indirectly, through the impact on the magnitude and spatial distribution of precipitation. The combination of these two mechanisms results into high sensitivity of runoff generation, in terms of peak flow and runoff volume, on antecedent wetness. It is shown that this relationship between soil moisture and runoff varies under different antecedent wetness conditions, basin scales and soil characteristics.
Natural Climate Variability on Decade-to-Century Time Scales
Author: National Research CouncilPublisher: National Academies Press
ISBN: 0309054494
Category : Science
Languages : en
Pages : 645
Book Description
This volume reflects the current state of scientific knowledge about natural climate variability on decade-to-century time scales. It covers a wide range of relevant subjects, including the characteristics of the atmosphere and ocean environments as well as the methods used to describe and analyze them, such as proxy data and numerical models. They clearly demonstrate the range, persistence, and magnitude of climate variability as represented by many different indicators. Not only do natural climate variations have important socioeconomic effects, but they must be better understood before possible anthropogenic effects (from greenhouse gas emissions, for instance) can be evaluated. A topical essay introduces each of the disciplines represented, providing the nonscientist with a perspective on the field and linking the papers to the larger issues in climate research. In its conclusions section, the book evaluates progress in the different areas and makes recommendations for the direction and conduct of future climate research. This book, while consisting of technical papers, is also accessible to the interested layperson.
Land Surface — Atmosphere Interactions for Climate Modeling
Author: E.F. WoodPublisher: Springer Science & Business Media
ISBN: 9400921551
Category : Science
Languages : en
Pages : 302
Book Description
It is well known that the interactions between land surfaces and the atmosphere, and the resulting exchanges in water and energy have a tremendous affect on climate. The inadequate representation of land-atmosphere interactions is a major weakness in current climate models, and is providing the motivation for the HAPEX and ISLSCP experiments as well as the proposed Global Energy and Water Experiment (GEWEX) and the Earth Observing System (EOS) mission. The inadequate representation reflects the recognition that the well-known phys ical relationships, which are well described at small scales, result in different relationships when represented at the scales used in climate models. Understanding this transition in the mathematical relationships with increased space-time scales appears to be very difficult, and has led to different approaches; at one extreme, the famous "bucket" model where the land-surface is a simple one layer storage without vegetation; the other extreme may be Seller's Simple Biosphere Model (Sib) where one big leaf covers the climate model grid. Given the heterogeneous nature of landforms, soils and vegetation within a climate model grid, the development of new land surface parameterizations, and their verification through large scale experiments is perceived to be a challenging area of research for the hydrology and meteorology communities. This book evolved from a workshop held at Princeton University to explore the status of land surface parameterizations within climate models, and how observa tional data can be used to assess these parameterizations and improve models.