VIC–CropSyst-v2: A regional-scale modeling platform to simulate the nexus of climate, hydrology, cropping systems, and human decisions

Abstract

Abstract. Food supply is affected by a complex nexus of land, atmosphere, and human processes, including short- and long-term stressors (e.g., drought and climate change, respectively). A simulation platform that captures these complex elements can be used to inform policy and best management practices to promote sustainable agriculture. We have developed a tightly coupled framework using the macroscale variable infiltration capacity (VIC) hydrologic model and the CropSyst agricultural model. A mechanistic irrigation module was also developed for inclusion in this framework. Because VIC–CropSyst combines two widely used and mechanistic models (for crop phenology, growth, management, and macroscale hydrology), it can provide realistic and hydrologically consistent simulations of water availability, crop water requirements for irrigation, and agricultural productivity for both irrigated and dryland systems. This allows VIC–CropSyst to provide managers and decision makers with reliable information on regional water stresses and their impacts on food production. Additionally, VIC–CropSyst is being used in conjunction with socioeconomic models, river system models, and atmospheric models to simulate feedback processes between regional water availability, agricultural water management decisions, and land–atmosphere interactions. The performance of VIC–CropSyst was evaluated on both regional (over the US Pacific Northwest) and point scales. Point-scale evaluation involved using two flux tower sites located in agricultural fields in the US (Nebraska and Illinois). The agreement between recorded and simulated evapotranspiration (ET), applied irrigation water, soil moisture, leaf area index (LAI), and yield indicated that, although the model is intended to work on regional scales, it also captures field-scale processes in agricultural areas.

Lessons Learned From Modeling Irrigation From Field to Regional Scales

“…However, transferring this work to a data‐scarce region presents challenges, and a strategy for compensating the lack of key data needs to be developed in future work. Future efforts will need to be directed to connecting irrigation water with water resources (e.g., rivers, reservoirs, and groundwater pumping; Leng et al, , , ) and evaporative losses (Malek et al, ) during irrigation in the context of modeling the full components of water cycle. Since the fundamental purpose of irrigation is to increase crop yields, our future work will focus on evaluating the impacts of irrigation modeling on crop growth and yields (Leng et al, ).…”

When Should Irrigators Invest in More Water‐Efficient Technologies as an Adaptation to Climate Change?

“…To investigate the impact of climate change on regional water supply and demand, drought frequency, and investment in more efficient irrigation technologies, we established offline linkages (Figure ) between a hydrologic‐agricultural model (VIC‐CropSyst; Malek et al, ), a river system model (YAK‐RW), and a newly developed investment analysis model. This integrated modeling platform, the Agricultural Spatial Economic Analysis Model Platform (ASEAP), works in a distributed fashion such that it calculates the costs and benefits of an investment in a new irrigation system for each farmer in each grid cell.…”

“…VIC‐CropSyst is coupled to a mechanistic irrigation module (Malek et al, ) that simulates the impact of irrigation management, soil characteristics, and climate on irrigation efficiencies and losses. (Malek et al, ) evaluated VIC‐CropSyst's performance regionally over the Pacific Northwest and locally over three flux‐tower sites in Nebraska and Illinois and found the model capable of simulating crop yield, evapotranspiration, soil moisture, leaf area index, and irrigation demand. Malek et al (2018) also compared VIC‐CropSyst's simulated irrigation demand with the USBR's () demand estimations over the YRB.…”

“…VIC-CropSyst VIC-CropSyst is the component of ASEAP that simulates (1) the Yakima River's flow, which is the main source of irrigation water (USBR, 2002), and (2) the yield responses to changes in climatic conditions (including droughts) and improved water availability as a result of switching to a new irrigation technology. VIC-CropSyst (Malek et al, 2017) is a fully integrated, physically based, large-scale hydrologic-agricultural model. It consists of the Variable Infiltration Capacity (Cherkauer et al, 2003;Liang et al, 1994Liang et al, , 1996 model and a cropping system model (CropSyst; Stockle et al, 1994;Stöckle et al, 2003).…”

“…Because CropSyst requires an accurate vertical distribution of water availability through the RZ, Malek et al (2017) divided the middle layer of the VIC-CropSyst into 15 thin layers. (2) Clay content is included in the soil file; Malek et al (2017) added the capability within VIC-CropSyst to use pedotransfer functions developed by Saxton et al (1986) to internally generate main soil properties (e.g., hydraulic conductivity, field capacity, and bulk density). This requires the inclusion of clay percentage in the soil file.…”