基于SPEI法的陇东地区近50 a干旱化时空特征分析

选取陇东地区近50 a平均逐月降水和气温数据,采用Mann-Kendall方法、反距离加权插值（IDW）、功率谱分析、标准化降水蒸散发指数（SPEI）等方法分析了陇东地区近50 a来干旱变化的时空特征。研究显示：近50 a来陇东地区干旱化趋势非常明显,特别是20世纪90年代以来干旱趋势显著。持续干旱事件次数增多,持续干旱累积时间增长,以春夏连旱、伏秋连旱的次数增多为显著特征。发生干旱的周期在不同的时间尺度上表现不一致,随着时间尺度的增长,干旱出现的周期也在变长。干旱发生频率不断加快,尤其是在20世纪90年代以来,极端干旱事件的频率显著上升。近50 a来干旱频率较高的区域在环县西北部和六盘山以西静宁等地,干旱高频区逐步向中南部和东部转移。通过与其他方法对比分析和历史资料比对,证明SPEI在陇东地区有较好的适用性。

Analysis of Drought Spatial-temporal Characteristics Based on SPEI in Eastern Region of Gansu in Recent 50 Years

The eastern region of Gansu Province, typical Loess Plateau was located in the eastern part of Northwest China. The ecological environment in eastern region of Gansu was fragile. Eastern region of Gansu heavily depended on agriculture and regularly suffered from droughts. The characteristics of drought in eastern region of Gansu were studied based on monthly precipitation and temperature data of 15 meteorological stations by means of different scales of Standard Precipitation Evapotranspiration Index,combined with GIS spatial analysis techniques and mathematical statistical methods. The evolution of the spatial and temporal change of drought were quantitatively analyzed by SPEI has been illuminated. The SPEI that was based on a monthly climate water balance (precipitate on minus potential evapotranspiration) was calculated at different time scales. The balances were then converted to standardized units to allow spatial and temporal comparisons. For this purpose the data was fit to a three-parameter log-logistic distribution. Calculation of the index follows a similar approach to that for the standardized precipitation index (SPI) which was a widely accepted drought index due to its multi-scalar characteristic and simplicity of calculation. However, the SPI was based on precipitation only, newly developed SPEI combines the sensitivity of the PDSI to the changes in ET with the simplicity of calculation,but also has the robustness of the multitemporal nature of the SPI. The average temperature and precipitation from 1960 to 2010 in the eastern region of Gansu to each meteorological station were used to calculate the SPEI. The results showed that: over past 50 years, the times of persistent drought events and cumulative duration of persistent droughts has increased, especially spring to summer droughts and summer to fall droughts have significantly increased in eastern region of Gansu. Since 1990s, the duration of drought event has become long. However, it was not obvious in 1980s. It wasn’t inconsistent in drought cycles at different time scales. With the longer time scales, drought cycles were longer appear. Frequency of droughts had been increasing, particularly frequency of extreme drought events increased obviously since 1990s. Over the past 50 years, the higher frequency of droughts were in the northwest of the Huan county and Jingning county that was located in west of Liupan Mountain. On decadal variability, droughts occurred in the high frequency region had transferred to the south-central and eastern study area. Through comparative analysis and historical information confirmed, we suggested that SPEI had good applicability in eastern region of Gansu. In this article, the trends, persistent drought events, the cycles and frequency of drought in eastern region of Gansu was studied based on the SPEI in recent 50 years. The drought trend of eastern region of Gansu was located in the eastern part of Northwest China was obvious compared with general characteristics of drought trend in other regions of the country in recent 50 years. By preliminary analysis, we have come to drought trend in the eastern region of Gansu in recent 50 years was mainly due to obviously increasing in temperature and reduction in precipitation.Although the precipitation and evapotranspiration factors were considered by SPEI, but the drought also was affected by factors of wind, topography, vegetation, and atmospheric circulation. The index didn’t adequately explain the mechanism of drought occurred. In the future, we should study the drought mechanism in-depth and discuss adaptation strategies to droughts in the eastern region of Gansu.