The following typology of irrigation systems is based primarily on mode of governance. Large-scale public irrigation systems in dry areas, growing staple crops. They include most of the large public schemes of Northern China, the dry part of the Indo-Gangetic Plain, Central Asia, Sudan, the Middle East, the Nepalese Terai, and Mexico. These schemes are mostly run by public management agencies and for the last 10-15 years have been the focus of irrigation management transfer programs. In these schemes water delivery services are typically rather inflexible and inequities between the head and tail ends of the schemes are marked. In response to poor service, farmers typically seek to improve the reliability of supply by stealing water, pumping from drains, or using shallow groundwater in conjunction with canal water. These schemes were built with the purpose of providing large numbers of people with either full or partial irrigation to stabilize and augment staple food production and were usually not expected to pay their own operating expenses. Today, they face the challenge of economic and financial viability, and of the technical and managerial upgrading that would allow them to respond to the new needs of their farmers. Large-scale public paddy irrigation systems in humid areas. These irrigation systems were progressively developed to produce paddy rice and have in most cases gone through a process of accretionary development, leading progressively to increased water control and increased cropping intensity. Typical of this type of systems are the large terrace systems of Southeast Asia or the tank and delta systems of East and South India and Sri Lanka. While they face similar challenges for viability and upgrading as do the dry area systems, they also have unique features and properties related to their high rainfall environment and paddy cultivation. Small-to medium-scale community-managed (and -built) systems. Such systems are found across the world in Afghanistan, Indonesia, Nepal, the Philippines, the Andes Mountains, the Atlas Mountains, Sub-Saharan Africa, and highland areas in general. While this category covers a wide range of situations, it is characterized by the small size of the systems, private or community investment, and management. Public sector involvement focuses on rehabilitation, consolidation, or improvement. These systems form the basis of the economies of their communities and typically show a large variety of cropping patterns. Commercial privately managed systems, producing for local and export markets. These systems do not represent a large share of irrigated areas worldwide but can be important locally. They can be found in Latin America (Argentina, Brazil, Chile, northern Mexico), Morocco, Turkey, and industrialized countries. They are governed by cultivators, employ paid staff, often use advanced technologies, and are responsive to local and international market opportunities. Sugar production is a special case of commercial irrigation, where management of irrigation and cultivation is often combined in a single entity. Farm-scale individually managed systems, producing for local markets, often around cities. These systems develop around cities to take advantage of local markets for high-value

crops like fruits and vegetables. They are highly dynamic and volatile, face land tenure problems as cities grow, and are often characterized by large short-term returns on investment. They rely on groundwater or wastewater and often face environmental and health related problems, for both consumers and field workers.