The AMMA mulid network for aerosol characterization in West Africa

Three ground based portable low power consumption microlidars (MULID) have been built and deployed at three remote sites in Banizoumbou (Niger), Cinzana (Mali) and M'Bour (Senegal) in the framework of the African Monsoon Multidisciplinary Analyses (AMMA) project for the characterization of aerosols optical properties. A description of the instrument and a discussion of the data inversion method, including a careful analysis of measurement uncertainties (systematic and statistical errors) are presented. Some case studies of typical lidar profiles observed over the Banizoumbou site during 2006 are shown and discussed with respect to the AERONET 7-day back-trajectories and the biomass burning emissions from the Combustion Emission database for the AMMA campaign

The effect of vegetation patterns on Aeolian mass flux at regional scale: a wind tunnel study

Although insight on the effect of vegetation pattern on Aeolian mass transport is essential for re-planting degraded land, only limited knowledge on this effect is available. The objective of this research was to understand the effect of vegetation design on the Aeolian mass flux inside a single land unit and at the borders among land units. A simulation of Atriplex halimus shrubs inside a wind tunnel was made, and sand redistribution was measured after the application of 200-230 seconds wind at a speed of 11 ms-1. The study showed that: 1) sediment maximum transport inside a single land unit is related to the neighboring land units and to the vegetation pattern within both the unit itself and the neighboring land units; 2) the effect of neighboring land units includes the protection effect and the ruling of sediment crossing from one land unit to the neighboring land units; 3) for the designing of re-planting of degraded land the ‘streets’ (zones of erosion areas similar to streets) effect need to be considered; and 4) in addition to the general knowledge needed on the effect of vegetation pattern on the erosion and deposition within an area, it is important to have insight on the redistribution of sediment at small scales upon the aim of the project

Tolerable versus actual soil erosion rates in Europe

Erosion is a major threat to soil resources in Europe, and may impair their ability to deliver a range of ecosystem goods and services. This is reflected by the European Commission's Thematic Strategy for Soil Protection, which recommends an indicator-based approach for monitoring soil erosion. Defined baseline and threshold values are essential for the evaluation of soil monitoring data. Therefore, accurate spatial data on both soil loss and soil genesis are required, especially in the light of predicted changes in climate patterns, notably frequency, seasonal distribution and intensity of precipitation. Rates of soil loss are reported that have been measured, modelled or inferred for most types of soil erosion in a variety of landscapes, by studies across the spectrum of the Earth sciences. Natural rates of soil formation can be used as a basis for setting tolerable soil erosion rates, with soil formation consisting of mineral weathering as well as dust deposition. This paper reviews the concept of tolerable soil erosion and summarises current knowledge on rates of soil formation, which are then compared to rates of soil erosion by known erosion types, for assessment of soil erosion monitoring at the European scale

Impact of vegetation and soil moisture seasonal dynamics on dust emissions over the Sahel

International audience[1] To address the challenging issue of estimating mineral dust emissions from the semi-arid Sahel, a modeling approach is developed by combining two specific models: one dedicated to the simulation of the seasonal herbaceous layer in the Sahel (STEP) and the other to the estimation of dust emissions (MB). The area of interest is the Sahelian belt (12 N-20 N, 20 W-35 E) and the simulations were performed at a 0.25 spatial resolution over a 4-year period (2004-2007). The rainfall forcing is provided by a TRMM (Tropical Rainfall Measuring Mission) satellite-derived product; the other meteorological data are ECMWF products. An empirical parameterization is used to estimate the surface roughness and its temporal dynamics according to the characteristics of the simulated vegetation in terms of surface cover and height. Where no vegetation grows, the surface properties are considered as constant in time and are derived from the POLDER-1 satellite measurements. Simulations are constrained step by step by comparisons with observations. Simulated annual dust fluxes emitted from the whole area range from approximately 100 Mt to 400 Mt depending on the year, in good agreement with previous works dealing with Saharan dust emissions. For the fringe where herbaceous vegetation can affect dust emissions, the annual dust emission fluxes range between 0.5 Mt and 20 Mt depending on the year. Inhibition of dust emissions due to the seasonal dynamics of vegetation and surface soil moisture over this fringe varies between 20% and 35%. Citation: Pierre, C., G. Bergametti, B. Marticorena, E. Mougin, C. Bouet, and C. Schmechtig (2012), Impact of vegetation and soil moisture seasonal dynamics on dust emissions over the Sahel

Desertification

IPCC SPECIAL REPORT ON CLIMATE CHANGE AND LAND (SRCCL) Chapter 3: Climate Change and Land: An IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystem

Consequences of Land Use Changes on Hydrological Functioning

International audienc

Integrated biophysical and socio-economic evaluation of water and soil conservation techniques : a case study from Niger

As a result of growing population pressure and limited fertile land availability, Nigerien farmers increasingly rely on marginal lands (Plinthosols) for crop production. These degraded lands, however, generally provide poor millet yields (<100 kg ha-1 yr-1) due to their low soil nutrient content and imbalanced partitioning of water over the root-zone. This dissertation aims to provide scientific verification of the potential of small-scale water and soil conservation (WSC) techniques to tackle these two major crop growth limitations. The overall objective is to evaluate the biophysicail and socio-economic viability of WSC techniques in the Tillaberí region of Niger. In order to monitor WSC techniques, a field experiment was laid on a Plinthosol nearby Sadoré. The treatments include: zaï + manure (Z), demi-lunes + manure (DL), scarification + manure (SCAR), control + manure (CF) and control (C). Grain yields for the conventional practices (C and CF) were extremely low and soil-water storage in the rootzone remained below the critical value for drought stress, even if there was sufficient rainfall. WSC techniques, on the other hand, successfully mitigated drought stress. WSC increased grain yields to 700 kg ha-1 yr-1 for Z and to 250 kg ha-1 yr-1 for DL and SCAR. By applying WSC, soil-water storage increased above the critical value for drought stress. This was mainly a result of significant run-off reduction under WSC (i.e. from approximately 25% for C to 5-10%). WSC techniques were, on the other hand, found to have only little impact on soil evaporation. A design optimization study with a three-dimensional coupled surface-subsurface soil hydrological model showed that rainwater use efficiency of DL could be improved by increasing the density of DL bunds per surface area while decreasing the number of millet plants per DL bund. Soil quality analysis showed that, SOC content increased significantly for the treatments with manure application (CF,SCAR, DL and Z), from ± 2.5 to ± 5 g kg-1. WSC techniques did not improve physical soil quality, but did significantly improve biological soil quality. A socio-economic survey indicated that the adoption of WSC techniques in the region is limited by manure shortage and a lack of specific erosion knowledge