Dynamics of surface albedo of a boreal forest and its simulation

Irrigation and warming drive the decreases in surface albedo over High Mountain Asia

Human and climate induced land surface changes resulting from irrigation, snow cover decreases, and greening impact the surface albedo over High Mountain Asia (HMA). Here we use a partial information decomposition approach and remote sensing data to quantify the effects of the changes in leaf area index, soil moisture, and snow cover on the surface albedo in HMA, home to over a billion people, from 2003 to 2020. The study establishes strong evidence of anthropogenic agricultural water use over irrigated lands (e.g., Ganges-Brahmaputra) which causes the highest surface albedo decreases (≤ 1%/year). Greening and decreased snow cover from warming also drive changes in visible and near-infrared surface albedo in different areas of HMA. The significant role of irrigation and greening in influencing albedo suggests the potential of a positive feedback cycle where albedo decreases lead to increased evaporative demand and increased stress on water resources.

Climate impact from agricultural management practices in the Canadian Prairies: Carbon equivalence due to albedo change

It is generally accepted that land use and land management practices impact climate change through sequestration of carbon in soils, but modulation of surface energy budget can also be important. Using Landsat data to characterize cropland albedos in Canada's three prairie soil zones, this study estimates the atmospheric carbon equivalent drawdown of albedo radiative forcing for three management practices: 1) moving from conventional tillage to no-till, 2) eliminating summer fallow in crop rotations, and 3) growing crops with higher albedos. In a 50-year time horizon, conversion from conventional tillage to no-till results in a total equivalent atmospheric CO₂ (CO₂-eq) drawdown of 1.0-1.5 kg m^-2, and conversion from summer fallow to crops results in CO₂-eq drawdown of 1.1-2.4 kg m^-2. Conversion of summer fallow to crops results in different magnitudes of CO₂-eq drawdown depending on specific crops. Lentils, peas, and canola have relatively higher albedo than that of spring wheat and flax; hence, a larger magnitude of CO₂-eq drawdown results when they replace summer fallow in the rotation. For the management changes from 1990 to 2019 for the whole Canadian Prairies, albedo changes induced a CO₂-eq drawdown of about 179.3 ± 20.9 Tg due to increased area of no-till, and 101.6 ± 9.5 Tg due to reduced area under fallow. The study shows that the magnitudes of CO₂-eq drawdown due to albedo change are comparable to that due to soil carbon sequestration. Therefore, it is important to account for cropland albedo changes in assessing the potential of agricultural management practices to mitigate climate change.

Diurnal and seasonal variations of surface albedo in a spring wheat field of arid lands of Northwestern China

Surface albedo greatly affects the radiation energy balance of croplands and is a significant factor in crop growth monitoring and yield estimation. Precise determination of surface albedo is thus important. This study aimed to examine the influence of growth stages (tillering, jointing, heading, filling and maturity) on albedo and its diurnal asymmetry by measuring diurnal albedo variations. Results indicated that the daily mean surface albedo generally exhibited an increased tendency during tillering to heading but decreased after heading. Surface albedos were much higher in the morning than the corresponding values of the same solar elevation angles in the afternoon when the solar elevation angle was less than 40°, indicating a diurnal asymmetry in surface albedo. However, less difference was found in surface albedos between forenoon and afternoon when the solar elevation angle was greater than 40°. Dew droplets on the leaf surface in the morning were assumed to be the main factor resulting in the diurnal asymmetry in albedo of spring wheat.