Historical population and cropland exposure to heatwaves in Xinjiang, China

Heatwaves are extended periods of extremely high temperature, which can cause catastrophic impacts on human health, agriculture, and natural system. Hazard and exposure are the key determinants of heatwave risk assessment. The gridded daily maximum temperature datasets were collected 1961-2020, together with the population and cropland datasets during 2001-2020. An absolute threshold was analyzed to determine the historical evolution of heatwaves and exposure of population and cropland in Xinjiang Uygur Autonomous Regio of China. The historical evolution included the number of high-temperature days, the frequency, intensity, duration of heatwaves, and population and cropland, as well as the contribution rate of changes. A heat wave is a period of daily maximum temperature that is higher than 35 °C and duration of more than 3 day.The population and cropland data was resampled to be consistent with the grid resolution of the maximum temperature, then to calculate the average annual heatwave days of each grid and the number of population and cropland, and finally to obtain the population and cropland exposure, as well as the contribution rate of the factors affected the change of exposure. The results indicate that there was an increase in the number of high-temperature days and the frequency, intensity, and duration of heatwaves during the past 60 years. The intensity of heatwaves was highly correlated with the duration, where the duration of the year with the greatest intensity was the longest. There were basically consistent spatial distributions of the frequency, intensity, and duration of high-temperature days and heatwaves. The high-value areas were mainly located in the Turpan Basin and the Lop Nor region. The distribution of heatwaves was closely related to the topography. The frequency of heatwaves gradually decreased with the increase in altitude. The average annual heatwave frequency in some high-altitude areas was less than once per year, e.g. the Altai, Tianshan, and Kunlun Mountains never experienced heatwaves for many years. The first days of heatwaves were spanned from early June to early July, while the last days mostly occurred in August, and the heatwaves of most regions showed an advancing trend in the first days and a delaying trend in the last days. Among them are the areas where heatwaves start early and end late and the areas where heatwaves start late and end early. The high-frequency areas of different levels were located in Turpan, where the higher the level of heatwaves, the smaller the cumulative frequency and impact area. Population and cropland enlarged and was accompanied by the higher intensity during the last two decades. The exposure was mainly caused by climate change, in which the contribution rate declined gradually, whereas, the contribution rates of population, cropland, and combined factors increased gradually.