Prediction of Biome-Specific Potential Evapotranspiration in Mongolia under a Scarcity of Weather Data
2021
Batsukh, Khulan | Zlotnik, Vitaly A. | Suyker, Andrew | Nasta, Paolo
We propose practical guidelines to predict biome-specific potential evapotranspiration (ETₚ) from the knowledge of grass-reference evapotranspiration (ET₀) and a crop coefficient (Kc) in Mongolia. A paucity of land-based weather data hampers use of the Penman–Monteith equation (FAO-56 PM) based on the Food and Agriculture Organization (FAO) guidelines to predict daily ET₀. We found that the application of the Hargreaves equation provides ET₀ estimates very similar to those from the FAO-56 PM approach. The Kc value is tabulated only for crops in the FAO-56 guidelines but is unavailable for steppe grasslands. Therefore, we proposed a new crop coefficient, Kc ₐdⱼ defined by (a) net solar radiation in the Gobi Desert (Kc ₐdⱼD) or (b) leaf area index in the steppe region (Kc ₐdⱼS) in Mongolia. The mean annual ETₚ obtained using our approach was compared to that obtained by FAO-56 guidelines for forages (not steppe) based on tabulated Kc values in 41 locations in Mongolia. We found the differences are acceptable (RMSE of 0.40 mm d⁻¹) in northern Mongolia under high vegetation cover but rather high (RMSE of 1.69 and 2.65 mm d⁻¹) in central and southern Mongolia. The FAO aridity index (AI) is empirically related to the ETₚ/ET₀ ratio. Approximately 80% and 54% reduction of ET₀ was reported in the Gobi Desert and in the steppe locations, respectively. Our proposed Kc ₐdⱼ can be further improved by considering local weather data and plant phenological characteristics.
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