A Framework for Evaluating Irrigation Impact on Water Balance and Crop Yield Under Different Soil Moisture Conditions

Abstract

In agricultural regions, irrigation is a fundamental component of the hydrological cycle that is essential to maintain crop yields but also exerts pressure on water resources. Various irrigation practices and schedules are typically implemented within a watershed, and each may have profound implications for the water balance and plant productivity. However, there is a major paucity of irrigation taking and application data on a fine-grained spatio-temporal scale, which poses challenges for water resource managers to assess the impact of irrigation practices under different moisture conditions. Here, we present a novel framework to evaluate the influence of different irrigation practices on a Lake Erie Basin watershed through a suite of irrigation scheduling models (ISMs) that can be implemented into the Soil and Water Assessment Tool (SWAT) model. We also provide a simple modification to SWAT's AUTOIRR function that bypasses known bugs and enables reliable representation of irrigation. This framework can be easily modified and extrapolated to other watersheds with diverse climates, crop rotations and environmental conditions. We found that a range of ISMs with varying irrigation methods (i.e., drip irrigation vs. sprinkler and surface irrigation), irrigation scheduling (i.e., continuous vs. event-based), irrigation trigger mechanism (i.e., soil moisture threshold vs. no threshold) and water use efficiencies consistently resulted in improved corn and soybean yields, enhanced evapotranspiration and reduced flow discharge. In contrast, the same ISMs result in significant declining trends of evapotranspiration, soil water content, water yield and baseflow when we emulate conditions of prolonged droughts, which suggest that the benefits from irrigation are unsustainable regardless of the water use efficiency. Our study highlights the need for fine-grained monitored irrigation, evapotranspiration and soil moisture content data to more accurately assess the influence of irrigation on watershed hydrology. Importantly, we stress the need to develop adaptive water resource management practices to maintain crop yields and water stores under a changing climate in the Great Lakes Basin and beyond.