Predictability of Cardinal Temperatures for Wheat Anthesis at Subseasonal-to-Seasonal Lead Times

Plant growth depends mainly on solar radiation and the availability of soil moisture. In addition, ambient temperature and relative humidity affect the efficacy of the transformation of soil nutrients to biomass through photosynthesis. Optimal ranges of temperature and humidity depend on the species and the development phase of the plant with the reproductive stage being the most sensitive. Cardinal temperatures also vary as a function of availability of soil moisture. Forecasting of the joint probability for departure of these environmental variables from optimal conditions at subseasonal-to-seasonal (S2S) lead times would inform decision making on crop selection, the choice of the sowing timing and also help estimating budgets for irrigation and fertilizing. In this paper we explore the feasibility of such S2S predictions. As a starting point, we focus on one species (wheat), one environmental variable (temperature), one developmental stage (anthesis), and one forecast lead time range (Week-2 and Week-3). We compute the Brier Skill Score for air temperature being within the wheat anthesis cardinal values of 9.5°C and 31°C in the North American Wheat Belt as a function of initialization time. For this we use reforecast data from the NASA GEOS model obtained from the SubX database and data from the ECMWF model obtained from the S2S database.