Drivers of Historical Irrigation Expansion in Peru and its Exposure to Climate Change

Irrigation expansion in Peru represents a complex coupled human-water system where political and economic decisions have reshaped the hydrological landscape. While crucial for food security, this expansion has concentrated water demand in the hyper-arid Pacific coast, creating a path dependency that is increasingly vulnerable to climate variability. This study bridges socio-hydrology and hydro-climatic risk modelling to assess how historically expanded irrigation areas are exposed to future climate change scenarios. We first reconstruct the spatial evolution of irrigated areas from 1950 to 2015, attributing growth to three distinct phases: early global market demands, state-led hydraulic megaprojects (1960–1990), and the recent neoliberal agro-export boom. This historical analysis reveals a strong coastal bias, where infrastructure was developed to conquer the desert for high-value crops. We then assess the future exposure of these established zones using bias-adjusted CMIP6 climate projections (SSP5-8.5) and hydrological simulations from the ISIMIP3b ensemble for the mid-century period (2036–2065). Results reveal a complex seasonal trade-off that heightens the exposure of irrigated systems. While the wet season (NDJFM) is projected to experience increased precipitation and river discharge, particularly in northern regions with increases up to 30%, the dry season (MJJAS) shows a robust drying trend. Of a particular concern, the central and southern coastal valleys, which host the most capital-intensive export agriculture, are identified as "High Drying Exposure" zones, with projected discharge reductions exceeding 20% during peak demand months. This spatial mismatch highlights a severe socio-meteorological risk: the infrastructure built during the historical expansion is now spatially locked into regions facing imminent hydrological scarcity. We conclude that adaptation strategies must urgently pivot from supply-side expansion to demand management to mitigate the collision between anthropogenic water dependency and projected hydro-climatic drying.