Investigation of Short-Term Evolution of Soil Characteristics over the Lake Chad Basin Using GRACE Data

In the Sahelian region, the West African Monsoon (WAM) is an important phenomenon for land water storage evolution, as demonstrated by The Gravity Recovery and Climate Experiment (GRACE) estimations. The Monsoon leads to an annual increase of the water mass. However, GRACE data also displays the existence of a semi-annual cycle whose its origin is still uncertain. This cycle is characterized by a gain of water mass at the beginning of the dry season. In this study, 10-days GRACE data are used to understand the characteristics of this semi-annual cycle. Investigations of the rainfall events, rivers discharge peaks, and the Lake Chad water level variations suggest that they are not at the origin of this cycle. However, MODIS evapotranspiration data display an increase each 6 months, during the rainy season, and at the same time as the semi-annual cycle estimated by GRACE. This increase occurs in regions where the amount of clays at the surface exceeds 30%. The link between both signals and the proportion of clays at the surface leads us to the conclusion that the seasonal variation of the vertical permeability of clays controls the amount of water present in the unsaturated zone

The Role of Space-Based Observations for Groundwater Resource Monitoring over Africa

International audienceAfrica is particularly vulnerable to climate change impacts, which threatens food security, ecosystem protection and restoration initiatives, and fresh water resources availability and quality. Groundwater largely contributes to the mitigation of climate change effects by offering short-to long-term transient water storage. However, groundwater storage remains extremely difficult to monitor. In this paper, we review the strengths and weaknesses of satellite remote sensing techniques for addressing groundwater quantity issues with a focus on GRACE space gravimetry, as well as concepts to combine satellite observations with numerical models and ground observations. One particular focus is the quantification of changes in groundwater resources in the different climatic regions of Africa and the discussion of possible climatic and anthropogenic drivers. We include a thorough literature review on studies that use satellite observations for groundwater research in Africa. Finally, we identify gaps in research and possible future directions for employing satellite remote sensing to groundwater monitoring and management on the African continent. Article Highlights • Overview on the distribution and characteristics of African groundwater resources including future projections • Combination of satellite and in situ observations with numerical models allows us to obtain a synoptic view of groundwater-related processes • Summary of current concepts and achievements of satellite remote sensing-based groundwater monitoring and decision making over Africa Keywords Satellite remote sensing • Groundwater monitoring • Africa • Climate change • Sustainable development • GRAC

The Role of Space-Based Observations for Groundwater Resource Monitoring over Africa

International audienceAbstract Africa is particularly vulnerable to climate change impacts, which threatens food security, ecosystem protection and restoration initiatives, and fresh water resources availability and quality. Groundwater largely contributes to the mitigation of climate change effects by offering short- to long-term transient water storage. However, groundwater storage remains extremely difficult to monitor. In this paper, we review the strengths and weaknesses of satellite remote sensing techniques for addressing groundwater quantity issues with a focus on GRACE space gravimetry, as well as concepts to combine satellite observations with numerical models and ground observations. One particular focus is the quantification of changes in groundwater resources in the different climatic regions of Africa and the discussion of possible climatic and anthropogenic drivers. We include a thorough literature review on studies that use satellite observations for groundwater research in Africa. Finally, we identify gaps in research and possible future directions for employing satellite remote sensing to groundwater monitoring and management on the African continent. Article Highlights Overview on the distribution and characteristics of African groundwater resources including future projections Combination of satellite and in situ observations with numerical models allows us to obtain a synoptic view of groundwater-related processes Summary of current concepts and achievements of satellite remote sensing-based groundwater monitoring and decision making over Afric

Contribution of thermal infrared images on the understanding of the subsurface hydrology.

International audienc

Contribution of thermal infrared images on the understanding of the subsurface hydrology.

International audienc

Global Change in Africa

The main objective of this book is to provide an overview of the benefit of using Earth Observation data to monitor global environmental changes due to natural phenomena and anthropogenic forcing factors over the African continent, and highlight a number of applications of high societal relevance.The main topics presented in the book concern: water resources, floods and droughts, coastal zones changes and exploitation of mineral resources and its impact on the environment

Guest editorial: Relationships between coastal sea level and large-scale ocean circulation

Several hundred million people currently live in low-lying coastal regions, and this number will continue to increase in the coming decades. While some coastal areas are already being inundated by rising sea level, many others will also increasingly suffer from sea level rise and more intense extreme water levels during high tides, winter storms and hurricanes in the near future. Many oceanographic factors associated with both local and large-scale variability can influence coastal sea level, from hours to more than decades. Despite this coastal–open ocean link, differences exist between sea levels observed at the coast and over adjacent shallow and deep ocean regions. Distinct coastal sea level variability can arise, for example, due to coastally trapped waves and shelf currents, localized tidal resonances, bathymetric controls and small-scale features in atmospheric forcing. Identifying important influencing factors is essential for understanding, simulating and ultimately predicting sea level variability at the coast—a key societal concern in the context of our changing climate. In practice, this poses a huge and complex scientific challenge because it is region specific and timescale dependent and involves bringing multi-disciplinary expertise together

International Combination Service for Time-Variable Gravity Fields (COST-G) : Start of Operational Phase and Future Perspectives

The International Combination Service for Time-variable Gravity Fields (COST-G) is a new Product Center of IAG’s International Gravity Field Service (IGFS). COST-G provides consolidated monthly global gravity fields in terms of spherical harmonic coefficients and thereof derived grids of surface mass changes by combining existing solutions or normal equations from COST-G analysis centers (ACs) and partner analysis centers (PCs). The COST-G ACs adopt different analysis methods but apply agreed-upon consistent processing standards to deliver time-variable gravity field models, e.g. from GRACE/GRACE-FO low-low satellite-to-satellite tracking (ll-SST), GPS high-low satellite-to-satellite tracking (hl-SST) and Satellite Laser Ranging (SLR). The organizational structure of COST-G and results from the first release of combined monthly GRACE solutions covering the entire GRACE time period are discussed in this article. It is shown that by combining solutions and normal equations from different sources COST-G is taking advantage of the statistical properties of the various solutions, which results in a reduced noise level compared to the individual input solutions