An acoustic view of ocean mixing

Knowledge of the parameter K (turbulent diffusivity/"mixing intensity") is a key to understand transport processes of matter and energy in the ocean. Especially the almost vertical component of K across the ocean stratification (diapycnal diffusivity) is vital for research on biogeochemical cycles or greenhouse gas budgets. Recent boost in precision of water velocity data that can be obtained from vessel-mounted acoustic instruments (vmADCP) allows identifying ocean regions of elevated diapycnal diffusivity during research cruises - in high horizontal resolution and without extra ship time needed. This contribution relates acoustic data from two cruises in the Tropical North East Atlantic Oxygen Minimum Zone to simultaneous field observations of diapycnal diffusivity: pointwise measurements by a microstructure profiler as well as one integrative value from a large scale Tracer Release Experiment

Economy-wide Impacts of Climate on Agriculture in Sub-Saharan Africa

Two possible adaptation options to climate change for Sub-Saharan Africa are analyzed under the SRES B2 scenario. The first scenario doubles irrigated areas in Sub-Saharan Africa by 2050, compared to the baseline, but keeps total crop area constant. The second scenario increases both rainfed and irrigated crop yields by 25 percent for all Sub-Saharan African countries. The two adaptation scenarios are analyzed with IMPACT, a partial equilibrium agricultural sector model combined with a water simulation model, and with GTAP-W, a general equilibrium model including water resources. The methodology combines advantages of a partial equilibrium approach, considering detailed wateragriculture linkages with a general equilibrium approach, which takes into account linkages between agriculture and non-agricultural sectors and includes a full treatment of factor markets. The efficacy of the two scenarios as adaptation measures to cope with climate change is discussed. Due to the low initial irrigated areas inthe region, an increase in agricultural productivity achieves better outcomes than an expansion of irrigated areas. Even though Sub-Saharan Africa is not a key contributor to global food production or irrigated food production, both scenarios help lower world food prices, stimulating national and international food markets.Computable General Equilibrium, Climate Change, Agriculture, Sub-Saharan Africa, Integrated Assessment Model

Potential impact of climate change on improved and unimproved water supplies in Africa

With significant climate change predicted in Africa over the next century, this chapter explores a key question: how will rural water supplies in Africa be affected? Approximately 550 million people in Africa live in rural communities and are reliant on water resources within walking distance of their community for drinking water. Less than half have access to improved sources (generally large diameter wells, springs, or boreholes equipped with handpumps); the majority rely on unimproved sources, such as open water and shallow wells. Major climate modelling uncertainties, combined with rapid socio-economic change, make predicting the future state of African water resources difficult; an appropriate response to climate change is to assume much greater uncertainty in climate and intensification of past climate variability. Based on this assumption the following should be considered: 1. Those relying on unimproved water sources (300 million in rural Africa) are likely to be most affected by climate change because unimproved sources often use highly vulnerable water resources. 2. Improved rural water supplies in Africa are overwhelmingly dependent on groundwater, due to the unreliability of other sources. 3. Climate change is unlikely to lead to continent-wide failure of improved rural water sources that access deeper groundwater (generally over 20 metres below ground surface) through boreholes or deep wells. This is because groundwater-based domestic supply requires little recharge, and the groundwater resources at depth will generally be of sufficient storage capacity to remain a secure water resource. However, a significant minority of people could be affected if the frequency and length of drought increases – particularly those in areas with limited groundwater storage. 4. In most areas, the key determinants of water security will continue to be driven by access to water rather than absolute water availability. Extending access, and ensuring that targeting and technology decisions are informed by an understanding of groundwater conditions, will become increasingly important. 5. Accelerating groundwater development for irrigation could increase food production, raise farm incomes and reduce overall vulnerability. However, ad hoc development could threaten domestic supplies and, in some areas, lead to groundwater depletion. Although climate change will undoubtedly be important in determining future water security, other drivers (such as population growth and rising food demands) are likely to provide greater pressure on rural water supplies