Rainfall and dry spell occurrence in Ghana : trends and seasonal predictions with a dynamical and a statistical model

Improved information on the distribution of seasonal rainfall is important for crop production in Ghana. The predictability of key agro-meteorological indices, namely, seasonal rainfall, maximum dry spell length (MDSL) and dry spell frequency (DSF) was investigated across Ghana (with an interest on the coastal savannah agro-ecological zone). These three variables are relevant for local agricultural water management. A dynamical model (i.e. European Centre for Medium-Range Weather Forecasts (ECMWF) System 4 seasonal forecasts) and a statistical model (i.e. response to sea surface temperatures (SSTs)) were used and analysed using correlation and other discrimination skill metrics. ECMWF-System 4 was bias-corrected and verified with 14 local stations’ observations. Results show that differences in variability and skills of the agro-meteorological indices are small between agro-ecological zones as compared to the differences between stations. The dynamic model System 4 explains up to 31% of the variability of the MDSL and seasonal rainfall indices. Coastal savannah exhibits the highest level of discrimination skills. However, these skills are generally higher for the below and above normal MDSL and seasonal rainfall categories at lead time 0. Similarity in skills for the agro-meteorological indices over the same zones and stations is found both for the dynamical and statistical models. Although System 4 performs slightly better than the statistical model, especially, for dry spell length and seasonal rainfall. For dry spell frequency and longer lead time dry spell length, the statistical model tends to perform better. These results suggest that the agro-meteorological indices derived from System 4′ updated versions, corrected with local observations, together with the response to SST information, can potentially support decision-making of local smallholder farmers in Ghana.</p

Impacts of climate change on European hydrology at 1.5, 2 and 3 degrees mean global warming above preindustrial level

Impacts of climate change at 1.5, 2 and 3 °C mean global warming above preindustrial level are investigated and compared for runoff, discharge and snowpack in Europe. Ensembles of climate projections representing each of the warming levels were assembled to describe the hydro-meteorological climate at 1.5, 2 and 3 °C. These ensembles were then used to force an ensemble of five hydrological models and changes to hydrological indicators were calculated. It is seen that there are clear changes in local impacts on evapotranspiration, mean, low and high runoff and snow water equivalent between a 1.5, 2 and 3 °C degree warmer world. In a warmer world, the hydrological impacts of climate change are more intense and spatially more extensive. Robust increases in runoff affect the Scandinavian mountains at 1.5 °C, but at 3 °C extend over most of Norway, Sweden and northern Poland. At 3 °C, Norway is affected by robust changes in all indicators. Decreases in mean annual runoff are seen only in Portugal at 1.5 °C warming, but at 3 °C warming, decreases to runoff are seen around the entire Iberian coast, the Balkan Coast and parts of the French coast. In affected parts of Europe, there is a distinct increase in the changes to mean, low and high runoff at 2 °C compared to 1.5 °C, strengthening the case for mitigation to lower levels of global warming. Between 2 and 3 °C, the changes in low and high runoff levels continue to increase, but the changes to mean runoff are less clear. Changes to discharge in Europe’s larger rivers are less distinct due to the lack of homogenous and robust changes across larger river catchments, with the exception of Scandinavia where discharges increase with warming level

Limits to management adaptation for the Indus’ irrigated agriculture

Future irrigated agriculture will be strongly affected by climate change and agricultural management. However, the extent that agricultural management adaptation can counterbalance negative climate-change impacts and achieve sustainable agricultural production remains poorly quantified. Such quantification is especially important for the Indus basin, as irrigated agriculture is essential for its food security and will be highly affected by increasing temperatures and changing water availability. Our study quantified these effects for several climate-change mitigation scenarios and agricultural management-adaptation strategies using the state-of-the-art VIC-WOFOST hydrology–crop model. Our results show that by the 2030s, management adaptation through improved nutrient availability and constrained irrigation will be sufficient to achieve sustainable and increased agricultural production. However, by the 2080s agricultural productivity will strongly depend on worldwide climate-change mitigation efforts. Especially under limited climate-change mitigation, management adaptation will be insufficient to compensate the severe production losses due to heat stress. Our study clearly indicates the limits to management adaptation in the Indus basin, and only further adaptation or strong worldwide climate-change mitigation will secure the Indus’ food productivity

Climate-change impacts and adaptation for Pakistan’s irrigated agriculture

Pakistan is one of the most vulnerable counties in terms climate-change impacts on its agricultural productivity. Agriculture is not only the largest sector in Pakistan’s economy, the food security of its over 220 million inhabitants also strongly depends on its production. As Pakistan’s arid croplands are extensively irrigated, agricultural productivity is affected by increasing temperatures (projected to increase up to 6°C between 2000 and 2100 under a limited climate-change mitigation scenario), changes in water availability (i.e. river streamflow and groundwater resources) and atmospheric carbon dioxide concentrations ([CO2]; affecting both crop productivity and water use efficiency). Here we present the impacts of climate change on Pakistan’s primary cereal crops: wheat and rice. Impacts are quantified by combining several climate-change scenarios with a process-based coupled hydrological-crop model, VIC-WOFOST. VIC-WOFOST comprehensively estimates changes in crop growth, water resources and their interactions under climate change. Moreover, the role of elevated [CO2] on agricultural productivity and sustainable water use is specifically assessed. We then explore the possibilities and limitations of agricultural adaptation to enable sustainable food security for Pakistan under various climate-change and population growth scenarios. Our results show that climate-change will severely affect Pakistan’s agriculture, especially due increased temperatures and crop heat stress. However, climate-change adaptation can potentially mitigate some of these effects, especially for wheat production. Moreover, with sufficient agricultural adaptation, climate-change can even be beneficial for Pakistan’s agriculture due to the benefits of elevated [CO2]. While our study is focussed on Pakistan, it indicates pathways for sustainable food production under climate change that may also be important for other regions that strongly depend on irrigated agriculture

Impacts of savanna trees on forage quality for a large African herbivore

Recently, cover of large trees in African savannas has rapidly declined due to elephant pressure, frequent fires and charcoal production. The reduction in large trees could have consequences for large herbivores through a change in forage quality. In Tarangire National Park, in Northern Tanzania, we studied the impact of large savanna trees on forage quality for wildebeest by collecting samples of dominant grass species in open grassland and under and around large Acacia tortilis trees. Grasses growing under trees had a much higher forage quality than grasses from the open field indicated by a more favourable leaf/stem ratio and higher protein and lower fibre concentrations. Analysing the grass leaf data with a linear programming model indicated that large savanna trees could be essential for the survival of wildebeest, the dominant herbivore in Tarangire. Due to the high fibre content and low nutrient and protein concentrations of grasses from the open field, maximum fibre intake is reached before nutrient requirements are satisfied. All requirements can only be satisfied by combining forage from open grassland with either forage from under or around tree canopies. Forage quality was also higher around dead trees than in the open field. So forage quality does not reduce immediately after trees die which explains why negative effects of reduced tree numbers probably go initially unnoticed. In conclusion our results suggest that continued destruction of large trees could affect future numbers of large herbivores in African savannas and better protection of large trees is probably necessary to sustain high animal densities in these ecosystems