AbstractsGeography &GIS

Policy makers adopt irrigated agriculture for food security, since irrigation doubles crop production. Therefore, the development of large irrigation systems has a long history in many places worldwide. Although large-scale irrigation schemes play an important role in improving food security, many schemes, especially in Africa, do not yield the expected outcomes. This is related to poor water management, which is generally due to a lack of effective evaluation and monitoring. The objective of this study, therefore, is to propose a new methodology to assess, evaluate and monitor large-scale irrigation systems. Information on irrigation indicators is needed to enable the evaluation of irrigation performance. The evaluation is the first and the most significant step in providing information about how it is performing. After reviewing extensive literature, a list of indicators related to the performance of irrigation, rainwater supply and productivity is suggested. The irrigation efficiency indicators Relative Irrigation Supply (RIS) and Relative Water Supply (RWS) are selected. Potential rainwater supply to crops can be tested based on the Moisture Availability Index (MAI) and the Ratio of Moisture Availability (RMA). Water productivity can be assessed by Crop Yield (Y) and Water Use Efficiency (WUE). However, the central problem facing large-scale irrigation schemes is always the lack of data, which calls for the development of a new method of data acquisition that allows evaluation and monitoring. Remote Sensing (RS) technology makes it possible to retrieve data across large areas. Two different approaches via RS, the Normalized Difference Vegetation Index (NDVI) and Actual Evapotranspiration (ETa), can be utilized for monitoring. The well-known Vegetation Condition Index (VCI), derived from the NDVI, is modified (MVCI) to allow a qualitative spatio-temporal assessment of irrigation efficiency. MVCI takes into account crop response to water availability, while ETa indicates whether water is used as intended. Furthermore, the assessment of the possible hydrological impact of the irrigation system should be considered in the evaluation and monitoring process. The Sudanese Gezira Scheme of 8,000 square kilometers in the Nile Basin, where performance evaluation and monitoring are absent or poorly conducted, is no exception. This research takes the large-scale irrigation of the Gezira Scheme as a case study, as it is the largest scheme, not only in the Nile Basin but also in the world, under single management. The first long-term historical evaluation of the scheme is conducted for the period 1961–2012 rather than only on a short-time scale as is the common practice. An increase in RIS and RWS values from 1.40 and 1.70 to 2.23 and 2.60, respectively, since the 1993/94 season shows decreasing irrigation efficiency. MAI and RMA for summer crops indicate a promising rainfall contribution to irrigation in July and August. The Gezira Scheme achieves low yield and WUE in comparison to many irrigation schemes of the globe. Low… Advisors/Committee Members: Heinrich , Jürgen (referee), Schnider, Karl (referee).