Southern Ocean albedo, inter-hemispheric energy transports and the double ITCZ: global impacts of biases in a coupled model

Hawcroft, M., Haywood, J., Collins, M., Jones, A., Jones, A. and Stephens, G.

A causal link has been invoked between interhemispheric albedo, cross-equatorial energy transport and the double-Intertropical Convergence Zone (ITCZ) bias in climate models. Southern Ocean cloud biases are a major determinant of inter-hemispheric albedo biases in many models, including HadGEM2-ES, a fully coupled model with a dynamical ocean. In this study, targeted albedo corrections are applied in the Southern Ocean to explore the dynamical response to artificially reducing these biases. The Southern Hemisphere jet increases in strength in response to the increased tropical-extratropical temperature gradient, with increased energy transport into the mid-latitudes in the atmosphere, but no improvement is observed in the double-ITCZ bias or atmospheric cross-equatorial energy transport, a finding which supports other recent work. The majority of the adjustment in energy transport in the tropics is achieved in the ocean, with the response further limited to the Pacific Ocean. As a result, the frequently argued teleconnection between the Southern Ocean and tropical precipitation biases is muted. Further experiments in which tropical longwave biases are also reduced do not yield improvement in the representation of the tropical atmosphere. These results suggest that the dramatic improvements in tropical precipitation that have been shown in previous studies may be a function of the lack of dynamical ocean and/or the simplified hemispheric albedo bias corrections applied in that work. It further suggests that efforts to correct the double ITCZ problem in coupled models that focus on large-scale energetic controls will prove fruitless without improvements in the representation of atmospheric processes.

Framing the decision making process relative to climate-resilient agriculture in Senegal

Emma Visman, Cheikh Tidiane Wade & Birame Faye

The majority of the Senegalese rural population is active in rain-fed agriculture. As a result, household incomes and the national economy are extremely vulnerable to climate risks. Senegal is in the process of developing and revising the main national policies and programs relating to agriculture, offering significant opportunities for an emerging scientific understanding concerning the climate of West Africa, in order to strengthen the resilience of populations. Here we describe the dimensions of decision making related to climate resilient agriculture in Senegal and how the project used this understanding to map the ways in which its results can better support building resilience across levels.

The use of remotely sensed rainfall for managing drought risk: A case study of weather index insurance in Zambia

Emily Black, Elena Tarnavsky, Ross Maidment , Helen Greatrex , Agrotosh Mookerjee, Tristan Quaife and Matthew Brown

Remotely sensed rainfall is increasingly being used to manage climate-related risk in gauge sparse regions. Applications based on such data must make maximal use of the skill of the methodology in order to avoid doing harm by providing misleading information. This is especially challenging in regions, such as Africa, which lack gauge data for validation. In this study, we show how calibrated ensembles of equally likely rainfall can be used to infer uncertainty in remotely sensed rainfall estimates, and subsequently in the assessment of drought. We illustrate the methodology through a case study of weather index insurance (WII) in Zambia. Unlike traditional insurance, which compensates proven agricultural losses, WII pays out in the event that a weather index is breached. As remotely sensed rainfall is used to extend WII schemes to large numbers of farmers, it is crucial to ensure that the indices being insured are skillful representations of local environmental conditions. In our study, we drive a land surface model with rainfall ensembles, in order to demonstrate how aggregation of rainfall estimates in space and time results in a clearer link with soil moisture, and hence a truer representation of agricultural drought. Although our study focuses on agricultural insurance, the methodological principles for application design are widely applicable in Africa and elsewhere.

Climatology of observed rainfall in Southeast France at the regional climate model scales

Stéphanie Froidurot, Gilles Molinié and Arona Diedhiou

In order to provide convenient data to assess rainfall simulated by Regional Climate Models, a spatial database (hereafter called K-REF) has been designed. This database is used to examine climatological features of rainfall in Southeast France, a study region characterised by two mountain ranges of comparable altitude (the Cévennes and the Alps foothill) on both sides of the Rhône valley. Hourly records from 1993 to 2013 have been interpolated to a 0.1◦ Å~ 0.1◦ latitude–longitude regular grid and accumulated over 3-h periods in K-REF. The assessment of K-REF relatively to the SAFRAN daily rainfall reanalysis indicates consistent patterns and magnitudes between the two datasets even though K-REF fields are smoother. A multi-scale analysis of the occurrence and non-zero intensity of rainfall is performed and shows that the maps of the 50th and 95th percentiles of 3- and 24-h rain intensity highlight different patterns. The maxima of the 50th and 95th percentiles are located over plain and mountainous areas respectively. Moreover, the location of these maxima is not the same for the 3- and 24-h intensities. To understand these differences between median and intense rainfall on the one hand and between the 3- and 24-h rainfall on the other hand, we analyze the statistical distributions and the space-time structure of occurrence and intensity of the 3-h rainfall in two classes of days, defined as median and intense. This analysis illustrates the influence of two factors on the triggering and the intensity of rain in the region: the solar cycle and the orography. The orographic forcing appears to be quite different for the two ranges of the domain and is much more pronounced over the Cévennes.

FRACTAL Seminar Understanding Urban Governance: Entrypoints for climate science

Dianne Scott, Gilbert Siame & Tasila Banda

The Future Climate for Africa programme together with the Future Resilience for African Cities and Lands (FRACTAL) research team hosted a critical discussion on approaches for understanding the governance structures that shape medium-term development decisions taken in various African contexts and at various scales (e.g. city region, catchment, and national).

In particular, presentations focused on the application of the concept of urban governance in the Lusaka City Region, from a fragmented spatial configuration of people, institutions and socio-technical infrastructures, towards a more flexible integrated and resilient system of municipal governance which would be better be able to adapt to future climate change. The seminars also focused on Zambia’s preparedness for future climate change and the adaptation measures the country will have to undertake in anticipation of climate change.

On what scale can we predict the agronomic onset of the West African Monsoon?

Rory G. J. Fitzpatrick; Caroline L. Bain; Peter Knippertz; John H. Marsham and Douglas J. Parker

Accurate prediction of the commencement of local rainfall over West Africa can provide vital information for local stakeholders and regional planners. However, in comparison with analysis of the regional onset of the West African monsoon, the spatial variability of the local monsoon onset has not been extensively explored. One of the main reasons behind the lack of local onset forecast analysis is the spatial noisiness of local rainfall. A new method that evaluates the spatial scale at which local onsets are coherent across West Africa is presented. This new method can be thought of as analogous to a regional signal against local noise analysis of onset. This method highlights regions where local onsets exhibit a quantifiable degree of spatial consistency (denoted local onset regions or LORs). It is found that local onsets exhibit a useful amount of spatial agreement, with LORs apparent across the entire studied domain; this is in contrast to previously found results. Identifying local onset regions and understanding their variability can provide important insight into the spatial limit of monsoon predictability. While local onset regions can be found over West Africa, their size is much smaller than the scale found for seasonal rainfall homogeneity. A potential use of local onset regions is presented that shows the link between the annual intertropical front progression and local agronomic onset.

Co-exploratory climate risk workshops: Experiences from urban Africa

A. Steynor, J. Padgham, C. Jack, B. Hewitson, C. Lennard

Co-production is increasingly recognised as integral to appropriate use and uptake of climate information into decision-making. However, the success of co-production is contingent on an innate understanding of the context in which it is being implemented.

Climate knowledge co-production in Africa is unique and requires a nuanced approach because of the immediacy of a myriad of decision challenges on the continent, thereby making it more challenging to engage decision-makers in co-production processes around climate. Given these challenges, the process described here, referred to as “co-exploration”, was designed to complement the multi-stressor decision-making context of various African cities. Users and producers of science work together in an equitable framework to co-explore the urban decision-making space. While the dialogue has potential to inform the development of the science, it is not an explicit expectation of the process.

The paper describes the context for a place-based co-exploratory analysis of climate risks, the elements and steps incorporated in the approach, reflections on the effectiveness of this approach in addressing multi-stressor, place-based decision-making and the challenges that still remain in further refining the approach. The co-exploration approach is complementary to the objectives of the Global Framework for Climate Services and provides lessons for uptake of climate information into urban adaptation planning in Africa.

Read the full article on ScienceDirect.com

Simulation of vegetation feedbacks on local and regional scale precipitation in West Africa

Andrew J. Hartleya, Douglas J. Parker, Luis Garcia-Carreras and Stuart Webster

Planned changes to land use in West Africa have been proposed to both combat desertification and top reserve biodiversity in the region, however, there is an urgent need for tools to assess the effects of these proposed changes on local and regional scale precipitation. We use a high-resolution, convection-permitting numerical weather prediction (NWP) model to study how the initiation and propagation of mesoscale convective systems (MCS) depend on the surface vegetation cover. The simulations covered a 4-day period during the West African monsoon in August 2006. In many aspects of the simulations, there was evidence of vegetation type exerting a significant influence on the location of precipitation where the influence of orography and coastal water was minimal. In this study, vegetation was classified according to the fractional coverage of tree (>30%) and grass (>30%) plant functional types. Tree-grass boundary cover was defined where more than 3 grid cells of both tree and grass occurred in a moving 3 × _3 window, which was further enlarged using a 3 grid cell (∼12 km) buffer. We found that over the whole study region(5N to 17N and 11W to 9E) 33.8% of convective initiations occur over tree-grass boundaries that cover only 28.4% of the land surface. This is significantly more than would be expected by chance (p = 0.0483), providing support to the hypothesis that vegetation gradients provide heat and moisture gradients, of a similar magnitude to that of soil moisture. Additionally, we found that on average, more time under an MCS occurred over boundary cover and orography, followed by tree cover, during the afternoon and evening period, thus supporting the hypothesis that land cover type influences the location of larger propagating systems. Contrasting patterns were found in the quantity of precipitation between small-scale convective cells and larger scale MCS. More small-scale precipitation accumulated, on average, over grass cover during the afternoon period, indicating a tendency for small-scale convection, initiated over boundaries, to prefer the drier and warmer grass side of vegetation boundaries in the afternoon period. However, once these smaller scale convective cells merge together to form larger MCS, a tendency for the most intense precipitation to fall over tree cover was observed. When intense precipitation (>10 mm per hour) occurred simultaneously over tree, boundary and grass cover, we found the highest precipitation rate to be most frequently over tree cover (48.4%), and least frequently over boundary cover (19.9%),indicating a preference of MCS for cooler, more moist forest cover. These results show for the first time that convection-permitting NWP models do exhibit responses to vegetation similar to those observed in the real world, and therefore are useful tools to assess the impacts of proposed future land use changes.

Evolving discourses on water resource management and climate change in the Equatorial Nile Basin

Nina Hissen, Declan Conway, and Marisa C. Goulden

Transboundary water resources management in the Equatorial Nile Basin (EQNB) is a politically contested issue. There is a growing body of literature examining water-related discourses which identifies the ability of powerful actors and institutions to influence policy. Concern about the effects of future climate change has featured strongly in research on the Nile River for several decades. It is therefore timely to consider whether and how these concerns are reflected in regional policy documents and policy discourse. This study analyzes discourse framings of water resources management and climate change in policy documents (27, published between 2001 and 2013) and as elicited in interviews (38) with water managers in the EQNB. Three main discursive framings are identified which are present in the discourses on both subjects: a problem-oriented environmental risk frame and two solution-oriented frames, on governance and infrastructure development. Climate change discourse only emerges as a common topic around 2007. The framings found in the water resources management discourse and the climate change discourse are almost identical, suggesting that discursive framings were adopted from the former for use in the latter. We infer that the climate change discourse may have offered a less politically sensitive route to circumvent political sensitivities around water allocation and distribution between riparian countries in the EQNB. However, the climate change discourse does not offer a lasting solution to the more fundamental political dispute over water allocation. Moreover, in cases where the climate change discourse is subsumed within a water resources management discourse, there are dangers that it will not fully address the needs of effective adaptation.

March 12, 2016
// Water

Modeling haboob dust storms in large-scale weather and climate models

Pantillon, F., Knippertz, P., Marsham, J., Panitz, H. and Bischoff-Gauss, I.

Recent field campaigns have shown that haboob dust storms, formed by convective cold pool outflows, contribute a significant fraction of dust uplift over the Sahara and Sahel in summer. However, in situ observations are sparse and haboobs are frequently concealed by clouds in satellite imagery. Furthermore, most large-scale weather and climate models lack haboobs, because they do not explicitly represent convection. Here a 1 year long model run with explicit representation of convection delivers the first full seasonal cycle of haboobs over northern Africa. Using conservative estimates, the model suggests that haboobs contribute one fifth of the annual dust-generating winds over northern Africa, one fourth between May and October, and one third over the western Sahel during this season. A simple parameterization of haboobs has recently been developed for models with parameterized convection, based on the downdraft mass flux of convection schemes. It is applied here to two model runs with different horizontal resolutions and assessed against the explicit run. The parameterization succeeds in capturing the geographical distribution of haboobs and their seasonal cycle over the Sahara and Sahel. It can be tuned to the different horizontal resolutions, and different formulations are discussed with respect to the frequency of extreme events. The results show that the parameterization is reliable and may solve a major and long-standing issue in simulating dust storms in large-scale weather and climate models.