Neue Studien zur Wasserversorgung Äthiopiens: Schwere Dürren sind seltener geworden, höhere Niederschläge für die Zukunft werden erwartet

Gute Aussichten für Äthiopien. Wissenschaftler der Virginia Tech University prognostizieren, dass es im Bereich des Blauen Nil Beckens in Äthiopien im Zuge des Klimawandels zu vermehrten Niederschlägen kommen wird. Hier die Pressemitteilung vom 10. Oktober 2016:

Virginia Tech researchers: Climate change may benefit Ethiopia, increase the country’s access to water
Despite the many disastrous impacts of climate change, there are some regions of the globe that might benefit from hotter temperatures. A team of researchers from Virginia Tech have predicted that water availability in the Blue Nile Basin of Ethiopia may increase in coming decades due to global climate change. It could also lead to increased crop production, spur massive hydroelectric power projects, and foster irrigation development in the region. “For all the catastrophic impacts of climate change, there are some silver linings,” said Zach Easton, associate professor of biological systems engineering. “The sad irony is that climate change may be the catalyst Ethiopia needs to become a food-exporting country.”

The research team used a suite of climate and hydrologic models to predict the impact of climate change on water availability and sediment transport in the Blue Nile. Most previous Nile Basin climate impact studies have only focused on water availability, but the study conducted by the team at Virginia Tech was a first of its kind to to assess sediment transport, a big problem in the basin where some of the highest erosion rates in the world have been measured. The findings of the study were recently published in the journal Climatic Change.

“Ethiopia could experience increased water accessibility making growing seasons longer and potentially allowing for two crops to be grown per year,” said Moges Wagena, from Assosa, Ethiopia. Wagena is first author on the paper and also associated with the Abay Basin Authority, a water resource management entity for one of Ethiopia’s 12 water basins. Wagena is one of Easton’s doctoral candidates in the Department of Biological Systems Engineering, housed in both the College of Agriculture and Life Sciences and the College of Engineering. The team also included Andrew Sommerlot, another of Easton’s doctoral candidates; Daniel Fuka, a post-doctoral student working with Easton; researchers from the University of Maryland; and the International Water Management Institute, Nile Basin Office. The work was funded by the World Bank and the International Water Management Institute.

The team coupled  hydrologic models with bias-corrected and downscaled Intergovernmental Panel on Climate Change, Coupled Model Intercomparison Project 5 models, known as CMIP5, for the project. Previously, studies that looked only at temperature and precipitation from the climate models found an increased rate of water availability of just 10 percent, where Easton and Wagena found potentially 20 to 30 percent more streamflow available in the region in the coming decades.

One potential problem that the analysis identified was increased sediment transport in the rivers due to increased water flow. The increased sediment has the potential to reduce the capacity of reservoirs and dams, making massive hydroelectric projects like Ethiopia’s largest dam currently under construction, the Grand Renascence Dam, less efficient in storing the 65 billion cubic meters of water that could potentially turn its turbines. “Greater water availability is certainly a positive outcome, but this is countered by more sediment. One way to combat that is through installing conservation practices  on farms, for instance using cover crops and low- and no-till planting methods to make the soil healthier, more stable, and reduce erosion,” said Easton. While climate change is and will continue to cause untold problems, nuances in climate-induced weather events could benefit the Blue Nile Basin with increased rainfall in the area. “It’s interesting, because much of the Blue Nile Basin is well above 5,000 feet in elevation, giving it pretty much an ideal climate for agriculture with low humidity, low disease and pest pressure, and potentially great water availability, which could spur development,” said Easton.

Hierzu passt auch das Ergebnis einer Studie von El Kenawy und Kollegen, die im März 2016 in den Cuadernos de Investigación Geográfica erschienen ist. Die Forscher untersuchten die Dürreentwicklung in Äthiopien für die vergangenen 50 Jahre und fanden dass schwere und besonders schwere Dürren über den Zeitraum deutlich abgenommen haben. Hier der Abstract:

Changes in the frequency and severity of hydrological droughts over Ethiopia from 1960 to 2013
Here we present an analysis of drought occurrence and variability in Ethiopia, based on the monthly precipitation data from the Climate Research Unit (CRU-v3.22) over the period from 1960 to 2013. The drought events were characterized by means of the Standardized Precipitation Index (SPI) applied to precipitation data at a temporal scale of 12 months. At the national scale, the results reveal a statistically significant decrease in the severity of droughts over the 54-year period, a pattern that is mostly attributed to a statistically significant decrease in the frequency of high intensity drought episodes (i.e., extreme and very extreme droughts), compared to moderate droughts. To assess the general patterns of drought evolution, a principal component analysis (PCA) was applied to the SPI series. PCA results indicate a high spatial heterogeneity in the SPI variations over the investigated period, with ten different spatially well-defined regions identified. These PCA components accounted for 72.9% of the total variance of drought in the region. These regions also showed considerable differences in the temporal variability of drought, as most of the regions exhibited an increase in wetness conditions in recent decades. In contrast, the regions that receive less than 400 mm of annual precipitation showed a declining  trend, with the largest changes occurring over Afar region. Generally, the highly elevated regions over the central Ethiopian Highlands showed the weakest changes, compared to the lowlands. This study confirms the local character of drought evolution over Ethiopia, providing evidence for policy makers to adopt appropriate local policies to cope with the risks of drought. Over Ethiopia, the detailed spatial assessment of drought evolution is required for a better understanding of the possible impacts of recurrent drought on agriculture, food production, soil degradation, human settlements and migrations, as well as energy production and water resources management across Ethiopia.