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Water balance from space: promoting climate resilience in the Blue Nile/Abay Highlands.

While climate models differ significantly in their predictions of the magnitude and trajectory of future climate change, there is little argument that the global climate is changing. Many parts of the world may not see large impacts, but those who will suffer the most are typically those who are least equipped to adapt to the increasing amplitude in climatic swings--toward both the dry and wet ends of the hydrologic spectrum. Rural societies practicing subsistence agriculture often do not have adequate adaptive capacity to see themselves through times of drought or sufficient advanced warning of impending flooding to take proper precautions. When times get rough, environmentally risky decisions are often made (e.g., farming in marginal lands, deforestation).

More advanced information needed

Better decision-making requires better information about climate and. land-surface conditions--spatially distributed and at scales of human influence (the field scale). Our work is aimed at combining meteorological data, satellite remote sensing, hydrologic modeling, and downscaled climate model output to provide data relevant to building more climate-resilient and environmentally and economically sustainable farming and land-use strategies in the Ethiopian Highlands. The Blue Nile/Abay Highlands (BNH), together with the headwaters of the neighboring Atbara and Sobat rivers, is the source of 86 percent of the average Nile River flow at Aswan, Egypt, and is often referred to as one of the primary "water towers of Africa." Despite the apparent abundance of water, agroecosystems in the BNH remain vulnerable to extremes in precipitation. The landscape is characterized by steep, dissected terrain and highly erodible soils. Erosion results in low soil water-holding capacity and reduced soil fertility, which in turn lead to drought-susceptible crop production, low reinvestment capacity, poor farming practices, and ongoing cycles of famine and poverty. Sediment loads reduce dam capacity in downstream nations, necessitating major expenditures for annual dredging, while decreased soil water-holding capacity results in more flashy and unreliable streamflow in the Nile. Problems with land and water management in the BNH therefore also translate across borders.

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Living in flux

Conditions on the ground are changing rapidly in Ethiopia. New irrigation projects are being established around Lake Tana--the headwaters of the Blue Nile--to improve local food production capacity and income. Land-use pressures are increasing due to the growing population and investments in commercialscale agriculture. A new massive Renaissance Dam project is under construction near the Sudan border to supply hydroelectric power to both Ethiopia and Sudan, in support of the Ethiopian mandate to build a Climate Resilient Green Economy (CRGE) with the goal of achieving middle-class status and carbon neutrality by 2025. However, the impacts of these new projects and land-management strategies on the overall hydrology and health of the Abay Basin and downstream nations are not well understood.

This lack of understanding is because the country, in the midst of these changes, is facing an information deficit. Sparse rain-gauge and meteorological station networks are insufficient to provide information at the spatial scales necessary to support decision-making. Where information exists, issues with data sharing, both within Ethiopia and between riparian nations along the River Nile, are further hindering informed decision-making. In contrast, satellites and land-surface modeling systems provide objective and spatially continuous data across contentious borders and can penetrate to the scales at which land management decisions need to be made. The BNH project seeks to integrate and freely distribute the information generated with these data sources. Coupled with climate change and land-use scenarios, the hope is that this information can be used to investigate pending development choices and build more resilient agricultural ecosystems.

Due to the strong physical relationship between land-surface temperature (LST) and evaporative cooling, thermal infrared (TIR) satellite imagery provides useful information about evapotranspiration (ET)--the rate of consumptive water use by agricultural crops and natural vegetation. With the Landsat 30-year archive of TIR data at 60 to 120 m spatial resolution, we can map current and historical water use and availability on a field-by-field basis. Coarser resolution (3 km) but broader coverage TIR data from European Meteosat geostationary satellites can be used to map ET at regional scales, covering the Nile Basin and even the full African continent. These multi-scale remotely sensed maps provide a means for benchmarking the performance of more complex land-surface models that generate a full complement of hydrologic information, including runoff, streamflow, and groundwater recharge. Satellite-derived LST provides particular added value in areas where ET is not tightly coupled to local precipitation rates, such as in the heavily irrigated Nile Delta in northern Egypt and the Sudd Swamps in southern Sudan--a major sink of water along the White Nile course (fig. 1). Water budgets for these regions are difficult to model prognostically without significant a priori knowledge of irrigation practices and groundwater table fluctuations. However, the signature of enhanced ET is clearly revealed in the cooler LST patterns, and it can be effectively exploited by diagnostic energy balance algorithms driven by TIR remote sensing. Temporal anomalies in TIR-derived ET highlight areas of lower than average consumptive water use by crops and natural vegetation that have been affected by evolving drought (fig. 2).

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Tools bring much needed, helpful data

Combined with land-use/land-cover, soils, and digital elevation data, these hydrologic modeling and remote sensing tools can provide valuable data for decision makers at local, regional, and national scales: spatially distributed estimates of high soil erosion potential and sediment load cycles, seasonal water use by various crops and agricultural practices, identification of areas of high and low drought susceptibility, estimates of water diverted for irrigated agriculture, and near-real-time monitors for use in drought and flood early warning systems. Combined with climate model scenarios, downscaled to the county and village scale, these tools are being used to investigate impacts of changing climate conditions and to test the system's capacity to withstand expected shocks. Land-use scenarios may allow identification of optimal farming locations given hillslope, water availability, local microclimate, and soil fertility conditions, as well as proximity to market infrastructure. An economics component builds in market considerations, the most viable entry point for obtaining buy-in at all social levels.

We're on the way

The BNH project involves collaboration between researchers at Ethiopian and U.S. universities and government agencies, working together to develop products and information delivery mechanisms that are tailored to the specific needs of the country. The project is at an early stage, but low-hanging fruit have already been identified that can potentially impact rapidly evolving decision-making processes as Ethiopia moves toward a more climate resilient and green economy

Martha Anderson, research scientist, Hydrology and Remote Sensing Laboratory, USDA Research Service, Beltsville, Md., USA; Martha.Anderson@ars.usda.gov.

Ben Zaitchik, assistant professor, Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Md., USA; zaitchik@jhu.edu.

Belay Simane, associate professor of environment and agricultural development, College of Development Studies, Addis Ababa University, Akaki Campus, Ethiopia; simaneb@yahoo.com, belaysimane@ethionet.et.
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Title Annotation:data and ingenuity for climate change solutions
Author:Anderson, Martha C.; Zaitchik, Benjamin F.; Simane, Belay
Publication:Resource: Engineering & Technology for a Sustainable World
Date:May 1, 2012
Words:1149
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