Abstract:

The study of the adaptability of meteorological drought indices in alpine grassland is of great significance to improve the accuracy of drought monitoring of natural vegetation on the Qinghai-Xizang Plateau, protect alpine grassland ecosystems, and promote the sustainable socio-economic development of pastoral areas. In this study, the drought monitoring accuracy of indices such as Precipitation Anomaly in Percentage (PA), Standardized Precipitation Index (SPI), Meteorological Drought Composite Index (MCI) and Palmer’s Drought Severity Index (PDSI) in the alpine grassland at the eastern edge of the Qinghai-Xizang Plateau was evaluated by using the day-by-day measured soil moisture data from 2010 to 2022, and combining with the Pearson’s correlation coefficient and the method of drought identification. The PDSI index with higher drought identification accuracy was selected for local calibration, and based on the PDSI_improved obtained from the calibration, the monthly drought conditions of the study area in 2022 were analyzed. The results show that: 1) The drought identification accuracies of the four meteorological drought indices (PA, SPI, MCI and PDSI) in the study area were 48.21%, 38.79%, 37.42% and 59.16%, respectively. Among them, the PDSI responded better to the drought condition of the alpine grassland in the study area, but in the case when the relative soil humidity was less than or equal to 60% and the number of drought days was not consecutive, it was prone to omission or over-measurement. 2) By establishing the correspondence between the relative soil humidity and the PDSI value, and performing the localized calibration of the PDSI and the threshold adjustment of drought level, the improved PDSI can improve the drought identification accuracy by 12.15%, reaching 71.31%. 3) The PDSI_improved was used to monitor the drought situation in the study area in 2022. The results show that the drought mainly occurred in the low-lying areas in the southeast of the study area at an altitude of 3 300-3 700 m, and the drought had obvious seasonal characteristics, which was mainly concentrated in winter and mainly characterized by severe drought and extreme drought.

Key words: PDSI, the Qinghai-Xizang Plateau, alpine grassland, adaptation, calibration

摘要： 研究气象干旱指数在高寒草地上的适应性，对提高青藏高原天然植被干旱监测精度、保护高寒草地生态系统、促进牧区社会经济的可持续发展具有重要意义。利用2010—2022年逐日土壤水分实测数据，结合Pearson相关系数和干旱识别方法，对降水量距平百分率（Precipitation Anomaly in Percentage，PA）、标准化降水指数（Standardized Precipitation Index，SPI）、综合气象干旱指数（Meteorological Drought Composite Index，MCI）和帕默尔干旱指数（Palmer Drought Severity Index，PDSI）在青藏高原东缘高寒草地的干旱监测精度进行评价，选取干旱识别精度较高的PDSI进行本地化校验，并基于校验后得到的PDSI_improved对2022年研究区逐月旱情进行分析。结果表明：1）PA、SPI、MCI和PDSI 4种气象干旱指数在研究区的干旱识别精度分别是48.21%、38.79%、37.42%和59.16%。其中PDSI对研究区高寒草地的旱情监测较好，但在土壤相对湿度小于等于60%且干旱天数不连续的情况下，易出现漏测或者多测情况。2）通过建立土壤相对湿度与PDSI的对应关系，对PDSI进行本地化校验和干旱等级阈值调整，改进后的PDSI_improved干旱识别精度可提高12.15%，达71.31%。3）采用PDSI_improved对2022年研究区进行干旱监测，结果显示旱情主要发生在研究区东南部海拔3 300~3 700 m低地势处，且干旱存在明显的季节特征，主要集中在冬季，以重旱和特旱为主。

关键词: PDSI, 青藏高原, 高寒草地, 适应性, 本地化校验