The trend towards a warmer and wetter climate observed in arid and semi-arid areas of northwest China from 1959 to 2019

Abstract

The observed trend towards a warmer and wetter climate in northwest China is a controversial issue lacking sufficient scientific research. Based on monthly meteorological data from 201 weather stations in northwest China and surrounding regions from 1959 to 2019, we calculated potential evapotranspiration using Penman-Monteith (PM) equation. By analyzing the spatial–temporal variations in temperature and precipitation and by studying changing drought trends, we systematically explored the climate trends in northwest China over the past 60 years. Our findings include: (1) From 1959 to 2019, during the growing season, there was a significant upward trend in temperature across northwest China. The most obvious trend, ranged between 0.4 °C–0.6 °C per decade, was observed in northern Qinghai and northeastern Xinjiang. On a per-month basis, the average temperature increased in all months, with April showing a maximum rate of 0.41 °C per decade. (2) The amount of precipitation in the growing season increased in most regions, especially in western Xinjiang and Qinghai. The areas of reduced precipitation were mainly concentrated in the south of Gansu and Ningxia, the west of Shaanxi and the northeast of Xinjiang. The average precipitation also increased in all months, with June showing a maximum change rate of 1.8 mm per decade. (3) There were obvious spatial differences in the climate trends in northwest China with the warming shifting from areas of bare land to grassland and the trend towards increased rainfall shifting from grassland to bare land. These effects were most obvious in Xinjiang’s Tarim Basin. (4) From 1959 to 2019, the degree of drought in northwest China significantly decreased in most areas. The areas where drought decreased and precipitation increased were fairly consistent, which produced a strong spatial correlation between them.