Modeling the Climatic Impact of Land Cover Changes Using a Regional Model: Sensitivity to Experimental Design and Lateral Boundary Conditions

Abstract:

This paper investigates the potential impact of “ideal but realistic” land cover degradation on the 20^th century Sahel drought using a regional climate model (RCM) driven with lateral boundary conditions (LBCs) from three different sources, including one re-analysis data and two global climate models (GCMs). The impact of land cover degradation is quantified using two different approaches of experimental design: in the 1^st approach, the RCM land cover degradation experiment shares the same LBCs as the corresponding RCM control, which can be derived from either reanalysis data or a GCM; with the 2^nd approach, the LBCs for the RCM control are derived from a GCM control, and the LBCs for the RCM land cover degradation experiment are derived from a corresponding GCM land cover degradation experiment. When the 1^st approach is used, results from the RCM driven with the three different sources of LBCs are generally consistent with each other, indicating robustness of the model response against LBCs; when the 2^nd approach is used, the RCM results show strong sensitivity to the source of LBCs and the response in the RCM is dominated by the response of the driving GCMs. The spatiotemporal pattern of the precipitation response to land cover degradation as simulated by RCM using the 1^st approach closely resembles that of the observed historical changes, while results from the GCMs and the RCM using the 2^nd approach bear less similarity to observations. Compared with the 1^st approach, the 2^nd approach has the advantage of capturing the impact on large scale circulation, but has the disadvantage of being influenced by the GCMs’ internal variability and any potential erroneous response of the driving GCMs to land degradation. The 2^nd approach therefore requires a large ensemble to reduce the uncertainties derived from the driving GCMs.