Simulation of Global Water Cycle in Land Using a Crop Calendar Specified by Phenological Analysis of NDVI

Abstract

This study was conducted to propose a global water cycle model on land including irrigation and reservoirs. The proposed model, which comprises a hydrological and land surface model, a runoff model, and a reservoir operation model, simulates water flow on land globally. Cropping calendars for six crops (rice, spring wheat, winter wheat, maize, cotton, and soybean) were specified through phonological analysis of NDVI. A global river channel network is scaled up from a 1 km resolution flow direction map. Those land surface parameters well suit the statistical data. We conducted a global water cycle analysis over ten years. The main findings of results are as follows. Mean annual runoff agreed well with observed data without arid areas. Estimated yearly irrigation water requirements correspond to statistical data in many countries, suggesting that irrigation water requirements are analyzed well using our model. Reservoir operations have a strong impact on river discharge on land compared to withdrawal for irrigation.