Homogeneity Correction and Long-Term Trend Analysis of Heilongjiang Temperature Data

Using comprehensive metadata, homogeneity test and corrections were conducted on daily mean, maximum, and minimum temperatures at 83 stations in Heilongjiang from 1951 to 2019.The penalized maximal t-test (PMT) and penalized maximal F-test (PMF) methods from the RH test software package developed by Environment Canada were employed. The adjusted series were compared to the CHTM dataset, with a focus on how changes in observation instruments affected data homogeneity over the past decade. From the homogenized daily temperature data spanning from 1951 to 2019, the following climate extreme indices in Heilongjiang were calculated: Cold spell duration index (CSDI), frost days (FD), icing days (ID), and daily temperature range (DTR). The analysis identified 40, 20, and 57 changepoints in daily mean, maximum, and minimum temperatures, respectively. The primary reasons for data discontinuity were station relocations, instrument changes, and automatic observation software upgrades. Spatial consistency improved after corrections were applied. After adjustment, the long-term trends for mean and minimum temperatures increased from 0.27°C/10 a and 0.25°C/10 a to 0.29°C/10 a and 0.27°C/10 a, respectively. The CSDI, FD, and ID indices in Heilongjiang demonstrated a significant downward trend, aligning with the national climate warming pattern. The lowest FD index value occurred in 1998, coinciding with China’s second hottest recorded mean temperature. The warming trend of the annual mean maximum temperature in Heilongjiang was slightly less than that of the annual mean minimum temperature, resulting in a decreasing trend for DTR.