AGRICULTURAL DEVELOPMENT UNDER WATER STRESS CONDITIONS, A CASE STUDY IN SOUTHERN PERU

Arid and hyper-arid environments in southern Peru create a challenging environment for agricultural production, which has resulted in the sculpting of mountainous terrain to terraced landscapes. Pre-Columbian cultures established multiple irrigation technologies to introduce agricultural production via terraces, at times channeling water from one basin to another, or across great distances. Ancient irrigation practices are still relied upon today, and they have expanded beyond the modern agricultural frontier in excess of 2000 hectares, or an excess production area of 50% of 20th c. cultivation. The Pasto Grande Irrigation project represents an attempt to extend irrigation area using water from the highlands of southern Peru to the coast, bringing fresh water to these arid landscapes through open channel contour canals. Despite this major engineering development, secondary effects such as salination of downslope agricultural soils and erosion from overland irrigation challenge agrarian expansion. The introduction of new agrarian landscapes also introduces new land tenure regimes that stress land ownership and water rights issues in local communities. In addition, climate change and concomitant water scarcity have complicated the outlook of this mega irrigation project. At the current rate of expansion of the system, water utilization, and crop yield, the projected agrarian expansion is approximately 4.41% per year. Using water loses in the Pasto Grande system that include infiltration and evaporation as well as climate change, a range of possible 10 year outcomes were modeled. Under all scenarios, the Pasto Grande system will result in unstable equilibrium for water consumption within 3 years. After 10 years of the current expansion and projected water consumption rates, loses to the system exceed any storage or recharge capacity of the sources. This research reviews the hydrological and geomorphological challenges presented by agrarian expansion projects in light of changing climatic conditions and utilize pre-Hispanic examples of landscape transformation during periods of environmental stress to contextualize the modern development project in historical perspective.