关键词: 气象干旱, 时空分析, SPEI, 陇东地区

Abstract:

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.

Key words: drought, analysis of spatial-temporal characteristics, standardized precipitation evapotranspiration index(SPEI), the eastern region of Gansu