Annual dynamics of shortwave radiation of bare arable lands on a global scale incorporating their roughness

Abstract

Smoothing soil surfaces, which had previously been deeply plowed, increases their albedo, which results in a lower amount of shortwave radiation being absorbed by their surface layer. Those surfaces emit less long-wave radiation too, leading to a reduction in their surface temperature, which can affect the climate. This paper quantitatively estimates the highest possible amount of shortwave radiation that could be reflected throughout the year from bare soils on arable land in the most extensive agricultural regions, where major crops are cultivated, on six of the Earth's continents. The estimation refers to the highest levels of soil radiation occurring during clear-sky conditions without any clouds when the surfaces that had been conventionally tilled were bare for several days or more after the day of planting and were air-dried in two extreme roughness states: those formed by a plow and a smoothing harrow. The annual dynamics of reflective shortwave radiation of the bare soils were obtained using vectorized and rasterized geostatistical data sets about the areas of the soils and periods when they were bare, as well the spectra of the soil units that occupied the majority of these areas. Adding together all of the diurnal amounts of shortwave radiation reflected from the bare soils for each of the regions in the world, it was found that their radiation peak, appearing on the 140th days of the year, can reach about 22 EJ/day for soils treated by a plow, and a further 3 EJ/day when they are smoothed by a smoothing harrow.

SALBEC – A Python Library and GUI Application to Calculate the Diurnal Variation of the Soil Albedo

“…Similarly, the relationship between the HSD and the slope of the models fitted to the measured data is not ideal. Differences shown in Figure 8 do not exceed the variations of T 3D and HSD shown by Cierniewski et al (2018) in Figures 6 and 8.…”

“…The process of converting the input parameters into a soil albedo model is divided into three steps (A-C), as shown in Figure 2. As observed by Cierniewski et al (2018), the dependency between θ s and a is almost linear if θ s ∈[0°, 75°] and can be approximated linearly by Eq. (3).…”

“…The field of view of the albedometer is larger than the area for which the roughness was estimated. Moreover, the original data collected by Cierniewski et al (2018) show the relationship between soil T 3D and measured α 45 . Similarly, the relationship between the HSD and the slope of the models fitted to the measured data is not ideal.…”

“…The correctness of these equations was expressed by the coefficient of determination and the mean square error that were estimated at 0.91 and 0.03, respectively. Finally, these equations were used to quantify the annual dynamics of shortwave radiation reflected from the air-dried bare arable lands in Israel (Cierniewski et al 2018b), the European Union (Cierniewski et al 2019) and around the world (Cierniewski, Ceglarek 2018).…”

“…Python was selected upon its growing participation in both remote sensing (Bunting et al 2014) and soil science (Boudoire et al 2020). The software follows the concepts described above (Cierniewski et al 2015(Cierniewski et al , 2018(Cierniewski et al , 2019 and is designed to predict the diurnal variation of the clear-sky a based on the soil surface properties: 1. for any soil described by its reflectance spectrum, 2. for any place on Earth, 3. for any daylight time of any day.…”