Prediction of Biome-Specific Potential Evapotranspiration in Mongolia under a Scarcity of Weather Data

Khulan Batsukh,Vitaly A Zlotnik,Andrew Suyker,Paolo Nasta

doi:10.3390/w13182470

Khulan Batsukh, Vitaly A Zlotnik + Show 2 more

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https://doi.org/10.3390/w13182470

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Abstract

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.

Highlights

Groundwater represents a vital water resource for ecosystems within an arid continental climate
The relationship between meteorological variables and Food and Agriculture Organization (FAO)-56 PM daily ET0 for weather stations is expressed in terms of Pearson correlation coefficients presented in
Similar RMSE values between FAO-56 PM and the uncalibrated Har equation reported in Mongolia have been observed in southern Italy [50], in south-east Spain [51], in the U.S High Plains [39], and northwest China [52], while lower RMSE values are reported in arid and semi-arid areas in China [53]

Summary

Introduction

Groundwater represents a vital water resource for ecosystems within an arid continental climate. Management of this resource relies on the knowledge of groundwater recharge (GR). The use of hydrological models for simulating the water balance (and GR) within the groundwater–soil–plant–atmosphere continuum represents a valid alternative to direct measurements if the soil hydraulic properties and vegetation characteristics are properly assessed and initial and boundary conditions are well-known [1]. Obtaining a reliable prediction of ETp represents a challenge in countries with limited availability of land-based, full suite weather data. This ETp may be estimated by multiplying a grass-reference crop evapotranspiration (ET0 ) by a time-variant crop coefficient, Kc [2]. The reference grass is defined as a hypothetical crop with a height of 0.12 m, a surface resistance of 70 s m−1 , and an albedo of

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