Changes in the recent habitat suitability of Euro-Mediterranean Anopheles species due to land-use and climate

Habitat suitability of Anopheles mosquitoes depends on appropriate climate and land-use conditions. Anopheles mosquitoes are the main vectors for malaria transmission in the Euro-Mediterranean region, and there are major concerns that these species will expand and/or shift their range due to the expected changes in climate and land-use. This study aims to identify the main climate and land-use drivers of changes in the habitat suitability for six different Anopheles species between 2000 and 2020 within the Euro-Mediterranean region.

Boosted regression trees were applied to establish the link between climate and land-use predictors and habitat suitability. An ensemble of 16 models, based on different methods of selecting background points and statistical predictors, was applied to each species. The ensemble was evaluated by means of model skill and transferability to identify the best model. Taking contribution, interactions and response range into account, the most important predictors and those responsible for changes were identified.

The model ensembles agreed on the direction of change for four Anopheles species within the study area, with two of these showing an overall increase (An. atroparvus, An. sacharovi) of areas with suitable conditions and two showing a decrease (An. messeae, An. sergentii). Climate change was found to be the main driver of shifts in habitat suitability, with only a few models attributing changes mainly to land-use. The limited influence of land-use changes may be due to the spatial resolution being too coarse. For most species, temperature-related bioclimatic variables (BIO4, BIO5, BIO8) were the most important predictors of changes in habitat suitability. A superior method for either the specific background points or predictor selection did not emerge because the relative ranking of the corresponding models is dependent on the species analyzed.

Between 2000 and 2020, rising temperatures were the main driver of changes in the habitat suitability of Anopheles mosquitoes in the Euro-Mediterranean region, with land-use changes having a relatively minor impact. In particular, regions to the north of the respective distribution area were found to be characterized by an increasing habitat suitability, while regions to the south showed decreasing trends. These trends may also impact the risk of local malaria transmission in these regions.