Assessing Global and Regional Effects of Reconstructed Land Use and Land Cover Change since 1950 on Climate using a Coupled Land-atmosphere-ocean Model

Land use and land cover change (LULCC) is one of the most important forcings affecting climate in the past century. This study evaluates the global and regional LULCC impacts in 1950-2015 by employing an annually updated LULCC map in a coupled land-atmosphere-ocean model. The difference between LULCC and control experiments shows an overall land surface temperature (LST) increase by 0.47 K in the degraded regions and a widespread LST decrease by 0.22 K outside the degraded regions. A decomposed temperature metric is applied to quantify the relative dynamic contribution of surface processes to temperature changes. Furthermore, while precipitation in the degraded areas is reduced in agreement with declined local evaporation, LULCC causes a southward displacement of the intertropical convergence zone (ITCZ) with a narrowing by about 0.5 degrees, leading to a tripole anomalous precipitation pattern over the Paci¦c warm pool and the Indian Ocean.

Decomposition analysis of the energy budget shows that the temperature response to LULCC in degraded regions results from the competing effect between increased albedo (cooling) and reduced evaporation (warming). The magnitude of evaporation contribution decreases with latitude, dominated by the change of surface resistance. The reduced evaporation indicates less atmospheric latent heat release in convective processes and thus a drier and cooler troposphere over the globe, resulting in a reduction in surface cooling outside the degraded regions. The southward shift of the ITCZ implies a northward cross-equatorial energy transport anomaly in response to reduced latent/sensible heat of the atmosphere in the Northern Hemisphere, where LULCC is more intensive. Tropospheric cooling results in the weakening and equatorward shift of the upper-tropospheric westerly jet in both hemispheres, which, in turn, lead to an equatorward narrowing of the Hadley circulation and ITCZ.