Planetary albedo decline over Northwest India contributing to near surface warming

• Published in: The Science of the total environment Vol. 816; p. 151607
• Main Authors: Sai Krishna, S.V.S., Prijith, S.S., Kumar, Raj, Sesha Sai, M.V.R., Ramana, M.V.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10-04-2022
• Subjects: Climate Change; Effective temperature; Heat wave; India; Land cover change; LULC; Planetary albedo; Radiative forcing; Seasons; Warming; India; Warming; LULC; Planetary albedo; Heat wave; Land cover change; Effective temperature; Radiative forcing
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.151607

The increase in frequency and severity of heat waves during the pre-monsoon season (March–May) over Northwest India in recent decades is alarming. This study investigates the causative mechanism for warming through the forcing induced by planetary albedo changes over Northwest India, a hotspot for land-cover change. We use satellite-measured planetary albedo (α) and satellite-derived land-use-land-cover (LULC) data to estimate the impact of LULC changes from 2001 to 2018 on α and the associated radiative forcing. Over Northwest India, significant area under native land-cover, viz., barren, shrub and grass-lands, has been converted to cropland. The associated land-cover-induced changes have perturbed the radiation-budget by modifying the absorption of shortwave radiation, thereby contributing to the pronounced reduction of α as observed over this region. The diurnal-mean α has decreased by 0.016 ± 0.001 from 2001 to 2018 during pre-monsoon season which dominates α-decrease during the annual cycle over this region and contributes to the overall decreasing trend over India. Conversion of barren and shrub-lands to cropland is observed to be the greatest contributor to the α-decrease as compared to other land-cover changes. The radiative forcing due to decline in diurnal-mean α over Northwest India from 2001 to 2018 is highest during pre-monsoon at 5.99 ± 0.34 W/m2. This α-induced forcing averaged over the global land surface (0.02 W/m2) is equivalent to the corresponding direct forcing from rise in atmospheric methane concentrations during this period. We find an enhancement in near-surface heating to be associated with change in α; the decreasing trend in α during pre-monsoon has substantially enhanced near-surface extreme effective temperatures by 3.15 ± 2.61 K thus far and may further lead to more extreme heatwaves in future. Further, our findings highlight a decreasing (warming) and increasing (cooling) trend in clear-sky planetary albedo respectively over Northwest India and coastal regions, suggesting that sudden climate change could occur if one forcing dominates over the other.
[Display omitted]
•Significant decline in planetary albedo observed over Northwest India during 2001–18.•Concomitant changes in land cover observed over Northwest India.•Planetary albedo induced radiative forcing is +5.9 W/m2 in pre-monsoon.•Averaged globally, albedo forcing is equivalent to 30% of direct forcing from CH4.•Trends in near-surface air and effective temperatures indicate regional warming.