Climate change and Aedes albopictus risks in China: current impact and future projection
Authors: Liu Hongmei , Huang Xiaodan , Guo Xiuxia , Cheng Peng , Wang Haifang , Liu Lijuan , Zang Chuanhui , Zhang Chongxing , Wang Xuejun , Zhou Guofa , Gong Maoqing 
Published: March 2023

Abstract
Background
Future distribution of dengue risk is usually predicted based on predicted climate changes using general circulation models (GCMs). However, it is difficult to validate the GCM results and assess the uncertainty of the predictions. The observed changes in climate may be very different from the GCM results. We aim to utilize trends in observed climate dynamics to predict future risks of Aedes albopictus in China.

Methods
We collected Ae. albopictus surveillance data and observed climate records from 80 meteorological stations from 1970 to 2021. We analyzed the trends in climate change in China and made predictions on future climate for the years 2050 and 2080 based on trend analyses. We analyzed the relationship between climatic variables and the prevalence of Ae. albopictus in different months/seasons. We built a classification tree model (based on the average of 999 runs of classification and regression tree analyses) to predict the monthly/seasonal Ae. albopictus distribution based on the average climate from 1970 to 2000 and assessed the contributions of different climatic variables to the Ae. albopictus distribution. Using these models, we projected the future distributions of Ae. albopictus for 2050 and 2080.

Results
The study included Ae. albopictus surveillance from 259 sites in China found that winter to early spring (November–February) temperatures were strongly correlated with Ae. albopictus prevalence (prediction accuracy ranges 93.0–98.8%)—the higher the temperature the higher the prevalence, while precipitation in summer (June–September) was important predictor for Ae. albopictus prevalence. The machine learning tree models predicted the current prevalence of Ae. albopictus with high levels of agreement (accuracy > 90% and Kappa agreement > 80% for all 12 months). Overall, winter temperature contributed the most to Ae. albopictus distribution, followed by summer precipitation. An increase in temperature was observed from 1970 to 2021 in most places in China, and annual change rates varied substantially from -0.22 ºC/year to 0.58 ºC/year among sites, with the largest increase in temperature occurring from February to April (an annual increase of 1.4–4.7 ºC in monthly mean, 0.6–4.0 ºC in monthly minimum, and 1.3–4.3 ºC in monthly maximum temperature) and the smallest in November and December. Temperature increases were lower in the tropics/subtropics (1.5–2.3 ºC from February–April) compared to the high-latitude areas (2.6–4.6 ºC from February–April). The projected temperatures in 2050 and 2080 by this study were approximately 1–1.5 °C higher than those projected by GCMs. The estimated current Ae. albopictus risk distribution had a northern boundary of north-central China and the southern edge of northeastern China, with a risk period of June–September. The projected future Ae. albopictus risks in 2050 and 2080 cover nearly all of China, with an expanded risk period of April–October. The current at-risk population was estimated to be 960 million and the future at-risk population was projected to be 1.2 billion.

Conclusions
The magnitude of climate change in China is likely to surpass GCM predictions. Future dengue risks will expand to cover nearly all of China if current climate trends continue.